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UNCLASSIFIED
AD 405.137
DEFENSE DOCUMENTATION CENTERFOR
SCIENTIFIC AND TECHNICAL INFORMATION
CAMERON STATION, ALEXANDRIA. VIRGINIA
UNCLASSIFIED
NOTICE: 'When government or other drawings, speci-fications or other data are used for any purposeother than in connection with a definitely relatedgovernment procurement operation, the U. S.Government thereby incurs no responsibility, nor anyobligation whatsoever; and the fact that the Govern-ment may have fornulated, furnished, or in any waysupplied the said drawings, specifications, or otherdata is not to be regarded by implication or other-wise as in any manner licensing the holder or anyother person or corporation, or conveying any rightsor permission to manufacture, use or sell anypatented invention that may in any way be relatedthereto.
r405" 131
T&MINAL FCREST P M!kaNCE ~FILE
-iDC
TISIA Q~
-TERMINAL FORECAST REFERENCE FILE
, DOVER AIR FORCE BASE
,DELAWARE
,PREPARED BY DETACHMENT 5, 15TH WEATHER SQDN
-8TH WEATHER GROUP
,AIR WEATHER SERVICE, (MATS)
TABLE OF CONTENTS
PageSECTION I. LOCATION AND TOPOGRAPHY OF DOVER AFB, DEAWARE
1, COORDINATES AND ELEVA ................................ l-I2. GEOGRAPHICAL LOCATION OF THE STATION....1-1........... .....-
3. AIR POLUTION SOURCES ... ,. .... 00 . .00.00000Goo*.0.. .. . . * .. 1-2
h. PHYSICAL LOCATION OF THE WEATHER STATION .................. 1-2
SECTION II. WEATHER CONTROLS
1. INTRODUCTION ........... . ..... 00.......0... .... ...... 2-1
2. SU14ARY OF SEASONAL WEATHER CONDITIONS ............. ...... 2-2
3. MAJOR SYNOPTIC FEATURES . . ........................... 2-6
SECTION III. CLIMATIC AIDS
CLIMATIC AIDS ....... ............. . ................... ..
DIAGRAMS AND CHARTS .. .............. ....... o.......... .3-2
SECTION IV. LOCAL kORECAST STUDIES
A. INTRODUCTIONo...... .... o..o........0 .. 0.. ....... .........0 -
B. CLIMATIC SUMMARY OF SEVERE WEATHER ADVISORIES ATDOVER AFB AS PREPARED BY THE USAF CLIMATIC CENTER ......... 4-2
C. OBJECTIVE METHODS
a. THUNDERSTORM FORECAST. ... **............••............... ..h-hb. SNOW FORECASTING ALONG THE EAST COASTo .............. o.4-9
D. SPECIAL SYNOPTIC STUDIES... o ............... ........... 4-31
E. EMPIRICAL RULES ............................ h-45
SECTION I. LOCATION AND TOPOGRAPHY OF DOVER AFB, DELAWARE
1. COORDINAES AND ELEVATION ........................ -1
2. GEOGRAPHICAL LOCATION OF THE STATION ........ ..... ..1-1
3. AIR POLUTION SOURCES . ......... 6 ........ ............ 1-2
4. PHYSICAL LOCATION OF THE WEATHER STATION .......... 1-2
LOCATION AND TOPOGRAPHY
OF
DOVER AIR FORCE BASE, DELAWARE
1. Coordinates arKn Elevation
Latitude )9 081" North, Longitude 750 281" West. Elevation - 28 feetabove sea level.
2. Geographic Location of the Station
Dover Air Force Base is located near the center of the State of Delaware,about three miles west of the Delaware Bay, thirty-five miles east of theChesapeake Bay, and near the northwest end of the Delmarva (Eastern Shore)Peninsula. It is open to tie Atlantic Ocean, about 2, miles southeast,dcxwn the Delavare Bay.
A "fall-line" runs from near Richmond, Virginia, to near Washington,Baltimore, Philadelphia and on to New York City, east of which elevationsdo not exceed 400 feet above mean-sea-level. Dover is situated some 40Miles east of the falJ.-line on the flat, frequently marshy, coastal plain.'he entire Delmarva Peninsula is under intensive cultivation, the farmsbeing interspersed Uzth salt ma.rshes and saall patches of woods, mostlyscrub pine. The communities are small and agricultural, rather than indus-trial.
Locally, salt vater marshes exist between the Delaware Bay and the Basefrom a point north of the Bare through east to the immediate south; anarrow river flows south- southeas tward from the city of Dover, four ndlesnorthwest, into the rarsh to the south passing the Base about a mile to thewest. This is a tidal river and it is bounded by salt water marshes. Drygrounds exist to the north-northwest only. See Figures 1-1 and 1-2.
The local terrain is so flat that there is no up nor down-slopemotion. However, on a micro-scale, the Base is situated on the southernend of a vwry slight ridge (i.a., the Base elevation is 28 feet and issurrounded, except to the north-northwest, by tidal water salt marshes)from which there is some cold air drainage at night under no-gradientconditions. This cold air drainage is sufficient, frequently, to keep theBase free of grou;nd fog while the surrounding marshes are covered withthick radiation fog. This is especailly true over the marsh to the south,over which aircraft must pass at a hundred feet or so on final GCAapproach to runway O1.
l-1
3. Air Polution Sources
Basically, the Delmarva Peninsula is populated with truck ard dairyfarms and small communities which exist on an agricultural rather thanan industrial econon•r. The nearest industrial smoke pollution areasare forty miles to the north near Wilmington, and sixty miles to the west,in the Baltimore area. These have no appreciable effect on localvisibility.
Locally, Dover, four miles to the northwest and Ml ord, fifteen milesto the south, do not have industriAl plants sufficient to create a smokeproblem. However, about 1/2 mile south-test of the main entrance, there is asmall dump which is newly opened; this dump, up to now (1arch 1962) has notproven to be a problem from the visibility or pollution standpoint.
4. Fhysicrtl Location of Weather Stotion
The physical location of the Weather Station is actually in twoseparate sections.
a. The station proper is locoted in the IIATS Terminal Building (T-501).ThKis is the adriinistrativc and forccasting section, along with the observerswho directly support the forecasters. The instruments and equipment utilizedare the teletypes, facsimile machines, the AN/APQ-13A radar set and the1L-2 Barortmeter.
b. The second location, the representative observing site, is locatedbetween runways 010 and 310 in Building T-1307. ihe actual room is a glassenclosed tow:er, iwhich houses thc recording units of the AN/GIQ-2A ceilometer(an AIN-GC:Q-!O tr)nsnissomcter, -md the AN/GIIQ-U Wind Recorder. The ML-3Barograph, 1.1-102D anaroid barometer, the SAME teletype and the Electro-itriter, are also in the toy-er. The observing umits for the ceilometer,transmi.;someter and wind gaugc along with the instrument shelter, whichhouses a 11,-24 psycrometer, and the I1-17 rain guage, are in representativelocations outside of the building. The representativcness of our observa-tions is very good; however, the visibility is hampered to the southeastbecause of a hanfar and because of hangar and apron lights at night.
c. Surface observations are representative of the immediate runwaV complex,however, they may not be representative of conditions in or about the runwayapproachs. This is especially true of ai;proachi:s on rurnay 19 and 31 whichare partially over water area of the Delaware Bay. Whenever low and raggedceilings exist, ceilings are generally lower on the arproaches to 19 and 31,than arc mcasured near the center of the field. All other parameters arerepresentative.
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SMCTIOV II, WCATUR CONTRLS
* 2o SUN(AR! OF MABONAL VIATHER (KUDITIOIS...2-2
* 3. MAJOR SYNOPTIC AUI..........-
( tSIKHBR 0ONTROL8
1. I •1i Oulf Stream with its attendant wars water turns to the
northeast off the DelsArva Peninsula. Between the Oulf Stream and the coast
there is considerable upwolling of cold water. The position of the ul Strewm
and the amount of upvelling vary with the direction and intensity of the surface
air flow over the local coastal area. With an established westerly.or offshore
flows the Gulf Stream wres somehat to the east of its normal position and
becomes lightly cooler and theroe is more upwalling along the coastal area;
with a several hundred mile onshore air fetch the Oulf Stream is much closer
to the coast and considerable of the upwslling disappears. In addition, the
water of Delaware Bay is colder than the coastal water seven to eight months
of the year. The Bay will freez, over about once in twenty years.
From the above, it can be inferred that easteraly o southeasterly overwater
trajectories originating over or to the east of the Gulf Stream flow over in-
creasingly colder water to the coast and for the greater part of the year on up
the Bay to the Basel and as a result there will be cooling and condensation of
the moisture laden air as it moves to the coast and the Base. This is true
between October and May and with a weak southeasterly gradient, fog will occur.
on the coast and inland to well beyond Dover. With a stronger flow - in excese
of about eight knots, sors turbulent muiung occurs and a stratus ceiling of a
hundred feet or so will exist, slightly higther during diurnal beating and
oommonly going to dense fog at night during nocturnal cooling.
During the sumner months, fog is essentially non-existent up the Bay from
the coast as a result of this cause; however, stzatus ceilings of several
hundred feet are common at night burning off two to tlhee hours after sumrise.
(This is dependent upon the sky condition above the stratus, with an upper
or middle overoast, the stratus can hold in all day.) The typical year round
synoptic situation for this fog-stratus condition is for the east-west axis
( of the Bermuda High to be found to the north of Delaware with a five
hundred mile or more over-water trajectory from the east or soutbaoto SeB
Figures #2-1 and 2-2 for sea-surface water temperatureo off the coast. Refer-
ing to these figures, it is obvious that an air trajectory fram the north-
northeast to northeast is parallel to the isotherms and no cool0ng wifl occur
while a trajectory from the southeast gives uaximm cooling with a resultant
"no fog" or nfog" forecast.
Due largely to the influences of the Gulf Stream and the Delaware Bay,
mild winters and relatively cool sunmrs are usually observed at Dover Air
Force Base,
2. SUMMARY OF SKASONAL WA'IR CONDITIONS
WIN.%R Cold fronts pass the station on the average of once every five
days. During periods of strong zonal flow, fronts will mve through the Dover
terminal on the average of once each three days. Cold front weather will eel
seldom produce ceilings below 2000 feet and visibilities less than 3 miles in
showers. The warm front, on the other hand, generally produces low ceilings,
poor visibilities and steady rain or snow. The warm front is difficult to
forecast due to the fact that the Appalachian barrier is conductive to the
stagnation of a cold pool or air over the coastal plains. Because of this,
the warm front remains quasi-stationary along the Appalachians and low ceilings
and poor visibilities may prevail for an extended period. As a rule, the
arrival of a Pacific occlusion will result in clearing conditions. This
situation is not limited to the winter season, but is also applicable to Spring
and Sumner. A case study of this type of situation is discussed in Section IV
under Special Synoptic Studies.
The Hatteras Low affects Dover Air. Force Base much the sams as a warm
front, resulting in low ceilings, poor visibilities, steady
2-2
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( type precipitation and gusty surface winds. Gusts up to 50 knots
are not uncommon with a strong low pressure area. Low pressure
areas which move northward across the coastal plains generally pro-
duce the strongest surface winds at Dover with wind directions east
to east-northeast. Gusts over 35 knots are likely with this type.
If the low is off the coast, generally northeasterly surface winds
of less than 35 knots are the rule. With this type, however, the
possibility of snow rather than rain is greater. Clearing conditions
occur as the low moves north of Dover, however, gusty surface winds
up to 35 knots may continue for another 24 hours.
SPRING: During this season, the surface pressure gradients are
weak and fronts diffuse and often difficult to locate with any degree
of certainity. Thunderstorm activity increases considerably during
the latter part of spring. A slight increase in frequency of early
morning fog also occurs during this season. The major forecasting
problem lies in predicting the location of the surface front relative
to Dover and the attending low level flow pattern. Low ceilings and
poor visibilities are the rule with easterly flow. Good visibilities
prevail with southwesterly through northerly flow except Mhen wind
velocities are under 10 knots following a weak cold front passage.
SUIM: Thunderstorm activity reaches its peak during this
season. A high frequency of evening thunderstorms occur with maxi-
mum frequency in rmid-July near 1900L. Frontal activity occurs on the
average of once every seven days. Cold fronts are usually of the
Facific type resulting in thunderstorm activity and pre-frontal
squall lines. Occasionally, a cold front will pass Dover from the
north ("Back Door Cold Front") resulting in below average temperatures
2-5
for this time of year. (It is this type of front that most often
breaks a persistent heat wave over the northeastern seaboard.)
FALL: During this season, cold fronts pass the station on the
average of once every seven days. As in the other seasons, these
cold fronts do not produce prolonged or significant weather conditions.
Precipitation is in the form ofrain showers with conditions seldom
less than 2000 feet and 3 miles. Thunderstorm activity decreases
rapidlj reaching minimum frequency by the end of the season.
Late sunmer and early fall is the hurricane season. On the
average, one hurricane p r season will pass close enough to the Dover
Terminal to produce gusty surface winds up to 35 knots. Statisticallyj
winds of hurricane force or higher can be expected once each eighteen
years.
3. MAJOR SYNOPTIC FEATURES
The following pages contain illustrations and discussions of. the
major synoptic features which control the local terminal weather. No
attempt has been made to type these situaticns other than to indicate
the season in which the feature occurs.
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FALL THROUGH LATE SPRIWI: This pattern represents a typical warm
front eituation which occurs during the period fall through late
spring. The warm front often takes on an odd configuration, but
generally a shallow dome of cold air persists over the Virginia -
Carolina area causing the warm front to be quasi-stationary along
the eastern slopes of the Appalachians. Minor waves often form
in the vicinity of Cape Hatteras. This situation produces wide-
spread fog, drizzle and stratus over Carolina, Virginia and east
of the Appalachian range as far north as New York State. Freezing
drizzle or rain will occur if surface temperatures are near or
below freezing. Ceilings along the coast (and at Dover) will vary
from 400 to 800 feet with visibilities 1 - 3 miles in fog and
drizzle. Ceilings further inland will be lower. The forecaster
must examine this situation very carefully, less he forecasts the
warm front to pass the Dover area. Generally, conditions do not
improve wntil the major front from the west occludes and passes
the Dover terminal.
(9
2-9o
( rPigurs 2-4
tAT! VaNTM - WRING: A persistant high located over Hudson Bay
with a secondary high located over the Great Lakes and surface
lows forming over Texas move erratically acrose 'the northern half
of thie Gulf Coast states passing off the coast near Hatteras
without intensification. With west to northwest flow at the
500 * level, clouds and precipitation will be confined to the
immediate vicinity of the surface low. As a rule, precipita-
tion will not reach Dover. The only cloud cover over Dover will
be broken to overcast middle and high clouds, and in some cases
only high clouds depending on position of the 500 mb jet. The
heavy middle and high clouds are found to the south of the 500 ab
jet and north of the surface low. If a confluent zone exists to
the north of the surface low, clouds and precipitation will extend
ahead of the surface low to the approximate center of the confluent
sone at the 500 mb level.
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IA& FAIL - RSAL! WINKMs A meridonal jet stream with major tmou&
in the Great Lakese region and a quasi-stationary low centered in
the Gulf of Alaska from 4dah lowe are fed, These lows taaok
northeast across tabrador to a deep upper low centered near the
tip of Greenland. Frontal passages over the Delaware region are
weak or the fronts remain to the north blocked by the RP hiJ*o
There is no weather of consequence in the Dover area. The east
coast "Indian Sumnr* is related to thi pattern. Generallyj
fair weather prevails at Dover with gusty southwest smrface winds
in advance of the weak frontal systems.
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The mjor trough is in the mid-west with the 500 ob jet generally
south of Delaware. The trough is usually shallow and therefore
wave formation in the southern plains or Gulf area is rare.
Frontal qstems move at moderate speeds and pass Dover at inter-
vals of 3-5 days. Weather lies in a narrow band along the front
with ceilings of 2000-4000 feet in rain showers occurring with
frontal passage at Dover. In-flight visibility wil generally be
on the order of 1-3 miles in showers. In advance of the front,
ceilings of 800-1000 feet and visibilities of 3-5 miles in base
may occur during the early morning hours depending on available
moisture and surface wind direction. Generally, southeasterly
flow is favorable for early mor•ing.stratus.
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(I Frigure 2-7
W I The mean 500 mb trough lies over the Misusisippi or
Ohio Valley region with southwesterly flow over. the eastern
seaboard. A high pressure center is quasi-stationary over
the Maritime Provinces or the Newfoundland region. Surface
wavesadevelop in the Gulf or along the Georgia-Carolina coast
and move northeastward and deepen. Dover receives most of
the winter's snowfall from this type low. Gusty northeasterly
winds also occur with this situation and therefore, the fore-
caster must give serious consideration to the affects of snow
mnd blowing snow on surface visibility. As surface waves pass:
Dover, clearing generally occurs, but gusty surface winds may
prevail for as long as 36 hours depending on the speed and
direction of movement of the storm center.
2-16
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The muor trough is over or just east of Dover. Lowe fota north-
west of Hudson Day and genemally move around the periphery af the
upper dlosed low. A trailing cold front followed by se or A air,
sweeps southward to the Gulf Coast with the high centers •asing
to the south of Dover. Waves without major development form on
the trailing cold front# and can result in a weak snowfall in the
Delaware area. Usually a Sc overcast of 1000-1500 feet and light
snow flurries are the only related phenomensm at Dover*. 8ow showers
from off the Great Iakes may cross the Appalachians during this
regime in the cold outbreaks, hovever, there instability type
snow flurries seldom reach to Dover.
0 0l
(I Vig" 2-9
A split. jet results in northern lows, trailing cold fronts
%hich remain in Canda, and southern lows whioh ato eastward
across the Oulf Coast states. If the high axis is north of
Dovers low cloudes fogs drissle exist; if the axis is to the
south, the weather is oharacterised by the warm cleaw days of MP.
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Weak muridonal flow of the jet stream and a relatively intense
Bermuda high will commonly produce frontal thunderstorms along
a cold front from a surface low moving Just north of the jet*
Severity of thunderstorm activity in Dover area A4ll dqepnd on
strength of 500 ob jet. Generally speakingj severe thunder-
storms occur at Dover when 500 ab flow pattern is WSW to NW and
wind velocit~y is approximately 50 knots or more., A 500 ab
maximum isotack of this speed, moving towards Dovers results
in an ideal situation for severe thunderstorms. Past experience
has indicated that thunderstorms which form over the Delaware
Peninsula are more likely to produce sewore weather as compared
to those which form west of the Chesapeake Bay. It is believed
that the thunderstorm weaken in passing across the Bay*
2-22
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The fbaokdoor5 frontal passage. With a strong Bermuia High
extending westward to the Mississippi Valq, persistent high
pressure over Northern Quebec and the Icelandic Low displaced
well to the south. Lows will form north of Quebec and move 8t into
the Mid-Atlantic Low with a trailing cold front passing over
Dover to become stationary in Virginia or the Carolinas. While
the front is south of Dover, we have low stratus and fog (it
will go below 200' and 1/2 mile during April or May, or while
the front is passing Dover from south to north.) With the
front north of Dover, MT air prevails in the area and late
afternoon and evening thumdershowers are likely to occur.
2-24
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Waves from a low in the vicinity of British Columbia are fed
across the Great Plains then northeastward to Iabroador. with
the trailing cold front moving as far south as Cub&* Wresasly
cold CP and A air follow the cold fronts acoompaned by the
winter's coldest weather along the east coast. In the regomp
the major trough is near Dover and advances or retrogresses
Aom 15 degrees to parallel the cold fronts as they sweep off
the east coast. During this time, the Bermuda High is displaced
eastward. The warm frontal weather is the major feature of this
type of system. Ceilings Aill vary from 50041000 feet with 1-3
miles in rain and fog. Light shower, will generally accoapar7
the cold front, although often times no weather is associated
with cold front. This is especially true if it is the second.
or third cold frontal passage of a series. Clear skies and
gusty surface winds of 25-35 knots are the rule following
cold frontal passage.
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AP46 VIA(
19
PAIO 4 W90 I I ' I *I0 $910 0 438 6 63 630 6 0
Iwo 6"oil 1 6% 61
6300 Wo 441 634 1911 ke 64P 0 6 III's 6
0 54 no as%.
st sft,) 1410 sit $16
solo s4s 514 silo .1, 11 49
459 5/4 Is 5210 # $1 4%
mo st0 441 4amis 440 4560 4 rAw- -
4500 'mo 4110 4m 4120 42 41so
44JO dis ISO 414080 43J 0 42 4 t4o 'tSO
0 imp "00 0 4410 4130 412 Sol
SAO 4ft . . 307
JSJO 1"0 - $92
3410 JpsO 3270 2260 3060 Its
3*0 14 3010
-0'8 '0 7igo 0 1100?00
219 ?I.\
v4 0 2110 2 M Io'560 two 0
8490 -1460 is 0 liso P200 ISO 0 207
.1440 All240
7Vo 114
0211
PooIII
0710
Iwo 000
PSWC 6 LecxEup
0 K%
Figure 2-13
WINMT
This situation is somewhat similar to Fig.2-13 except major trough over
Mississippi Valley is deeper. This is usually the situation acompanring
the first major cold outbreak into central U.S. The major low pressure
centers track across the Great Lakes. The initial cold front passage at
Dover results in rain showers with ceilings 1000-2000 feet and visibilities
1-3 miles. The weather is brief and confined to the immediate frontal zone.
This type situation is ideal for formation of Gulf lows on the trailing cold
front. These waves deepen rapidly as they move northward along the eastern
seaboard producing widespread low ceiling, poor visibilities, and strong
surface winds. Conditions at Dover remain above GCA minimums, but gusty
surface winds of the order of 30-40 knots are not uncommon. This is not
an ideal situation for snowfall at Dower depending on temperatures and
depth of cold air over Dover. As a rule, if surface winds are from the
ENS through south, rain will occur. If surface winds are north to north-
easterly, snow is likely. The rain vs snow forecast study in Section IV
will assist the forecaster in determining if precipitation will be rain or
snow.
In some cases, the Gulf wave may develop into the main storm center thus
setting the stage for the initial invasion of Artic air ihto the Eastern
U.S. This development generally culminates in a low index situation over
U.S. and fair, but windy and very cold temperatures are likely to persist
for several days.
SECTION III. CLIMATIC AIS
CLIMATIC AIDS...................... 3-1
DIAGRAMS AND CHARTS.... ............. 3-2
SECTION III
CLIMATIC AIDS
The following Diagrams and Graphs were made from data gatheredover a ten-year period and include information for the followingt(both monthly and annually)
1. Temperatures
2. Precipitation
3. Sky Cover
4. Ceilings
5. Thunderstorms
6. Visibilities
7. Fog
8. Surface Winds
9. Hurricanes
10. Summry
3-1
C DOVER AFB CLIMATIC DATA FOR ALL M OCTHSCEILINGS
___60 500O FfO rTF'A
23 24-0-T 02 23 24 01 0 23 24 01 0
21~~2 0421040205 20523 003
I9 19 ~ - ' '>06 19 -.. 06
0
6
16 09
1 60 9 I6 0 9 (p
I51 1 101 1014 13 12 1114 1- 2 1114 13 12 1
l et II B I I l -
L ALESIHN3L3M2L LESS THAN ?Ml 1 3M°
23 24 1 02 202 2324 Of0 22320
2122 03 02122 - - 03 02122 03 0
20 05 20> 0500
19 ->Ž- 06 19 ~-~x&~ 06 19 06
Is - 07 I8s J/ij- 07 is 0?
NN
1T 08 17 08 I1 0616 09 16 09 16 09
15 10 I5 10 15 1014 1i A if 14 r
CALM ( 8.5%) LESS THAN 11K __6S_3
NLEGEND:FIGURES IN OUTER CIRCLE SHOW
AVERAGE NUMBER OF DAYS THEW ED SPECIFIED ELEMENT MAY BE
EXPECTED.
WESE TIMES ARE LOCAL STANDARD,
SSW-'"'' SSE
IlK TO 2iK(Z 3 9 °o SURFACE WINDS MRE THAN 21K 1 Z.O ,N N
NNWNNENNW -- a -NNE
NNE NW NE
W SWNE SCALE o W NW \ EN
E SW E
-2 SEEWSW ESE SS 0 W
3-2
DOVER AFB CLIMATIC DATA FOR JRNUFRY(C AVERAGE NUMBER OF DAYS WITH
DAILY TEMPERATURES SPECIFIED PRECIPITATION* AMOUNTS10
MAXIMUM K.Y 9. .
D LOWEST HIGHEST. OeSSERVED OBSERVED -
6
MINIMUM 10%1 0% I0o 4 .
AVG PRFCIPITATION !..-V IM I ... 1.
...... .... AVG SNOWFALL A IN 0
-40-30-20 I 010 0 0 203040 50 60 ?0 00 90 I01to 120 - - 1.01-.
TOTAL SKY COVER INCHES , LIQUID • OIVALIrNT
CLEAR _;AT TERM BROKEN
2 0 2 01 232 01 o 2324 ol 02
22 1203 22 0~)Oz 010 Z0 22 o0ý 0 03
21 '.l \l-7-" 4 21.• 0OZ 4 21 0 04
,s \ /..;?2,• / ..w o ,oaS:-. 9._L•, ,s -0 o 105 20o 005 20 c4 05
190 106 190 0 • ~ 6 I ~ ~ 006
is 04 0 y18 07 $ d- 07 Is 08
I? 0 17 11 08 70 '09
is 0~ of,P 09 163 .4 0 0916 ~ g
4 2 10 14 1312 II1S 4~ 13 121 13 12,
OVERCAST
23 002
22 .. /fAt, LEGEN
21 0i , 04 LEGEND
20 -" , - 05 FIGURES IN OUTER CIRCLE SHOW
19 12 __ '< 14 06 AVERAGE NUMBER OF DAYS THE
18 / \\"--- . 07 SPECIFIED ELEMENT MAY BE
1I 1? 1, 3 08 EXFECTED.
I --. 141 09 TIMES ARE LOCAL STANDARD.
I5S 1014 13 12 II
PRECIPITATION THUNDERSTORMS FOG (vsBY< IMI)
23 2402 2302 2 o02 224 o0 0222 03 22 03 22 1.7I.1.7
.o 03*% 04
21 41. ~ 04 21 04 10
20 , q05 20 05 20 05z
19 4-z 06199 0_1..- ..- 06 19 1.. IS 06
C16-f~ 0 '7 I*,-> -. 07 18 17 1. 0?
08o IT 08 g1.2 ~ 08
09 161 09 16 II09. I715 1 4 13 10
14 13 12 1114 13 11 3- 14 13 12 11
( DOVER AFB CLIMATIC DATA FOR JRn(uRy
CEILINGS
BELOW 500 FT _BELOW _,000 FT BELOW 10,000 FT
23 24 01 02 23 24_-o 02 23 0222 iy1.3-1.5 t 03 22 -d~ j01 03 22 ,*. 11' " u-1 03
/1 04 21 I 04 21 0412.1 , 1. 1.
20 05 20 3 N., 05 20 24 05
19 o, 06 1-9 X06 19 11 2.10
is .0 L U 07 187 07 £2 07
1711 15,08 17 3. 8 70
160 09 16 ,j0 1- 09
1510 15 ~'s 10~ .o1 ~y 014 13 12 II 14 13 1211 14 13 12 11
LMMI VI I IT0 %._._ LESS THAN IMK 1, 3%MlWN.ST•.NANUMLEIOML 24 01
23 24 0102 232f023 02 23 02
w.5 0221 ýl 04 21 04 21 qp.5 04
20Z. 17 05 20 3 70 5 201.0 0
19Z 17-- 706 I9 717 4-.~QL - .0 06 19 qj f__
"i -> - EX PE C T E D
I s "1 -- ,/SETIME07 RE 9C .NR07
17 0r A.6 5.7/ 08 17~ 9.7Tv0.2 2.7 0I 17, A
16 ,~ 2.(, 09 16 09 16 r. 09
15 1.1 2.11. 10 15 1-04,0 )J 10 15 q1
*f 10
14 13 12 it14 13 12 1114 13 12 11
CALM( K 01 %) LESS THAN I1K (1..7%)
NNW NNNENWE
NLEGENDFIGURES IN OUTER CIRCLE SHOW
WNW/ ENE AVERAGE NUMBER OF DAYS THE
W E SPECIFIED ELEMENT MAY BE
EXPECTED.
STIMES ARE LOCAL STANDARD.
IIK TO 21-K / SURFACE WINDS MORE THAN 21 K S%)
NWNENNW N NNE
NW . NENWE
WNW / .ENE SCALE WN N
9 0e
«'SE
sww3-4 SS SSE 3
DOVER AFB CLIMATIC DATA FOR FEB•RUARY'AVERAGE NUMBER OF DAYS WITH
DAILY TEMPERATURES SPECIFIED PRECIPITATION*AMOUNTSMAX I MUM,.0
-Y
> cKWD OBSERIVED £
E!. . . ---.-------------------
110%, o0. .0%1Y_ .0
AVG PRECIPITATION 2.IN -I-
T1-- AVG SNOWFALL .. IiN 0 - 1.-
-40-30-20 -10 0 10 20 30 40 50 60 ?0 0 00110 120 51 . 51 JI,
TOTAL SKY COVER INCHEt * LIQUID E0UIALENT
CLEAR CATTERD BROKEN
23 -24 02 240' 02 232401 02
21 22 2I 2l 30 04 21 220 04 21 220 04
20 12 05 20 16 05 20 3 4f 09
19 7 ~-. - 10 06 196 y06 19'1I 06
15 8071 18 7 6.o 1Ti86b
17' f 608 17~ 7 08 2I209 09 16 o09
~ .5~ I10 6 16 7 D10~4 13 1
1 4 1 3 1 2 1 5 i4 1 3 1 2 I I 1 1 4 1 3 1 2 I 1
OVERCAST
23 24 01 02
21 22 04 0 o 0-0 LEGEND
20 o ? 05 FIGURES IN OUTER CIRCLE SHOW
19 _o 9 06 AVERAGE NUMBER OF DAYS THE
is 9 q r07 SPECIFIED ELEMENT MAY BE
171 1N0 08 EXPECTED,16 10 1 09 TIMES ARE LOCAL STANDARD.
15 1014 13 12
PRECIPITATION THUNDERSTORMS FOG (VSBYc iMi)
23 01 02 23 40102 23'402
22 2.f T 03 22 03 22 ,03
21 A0 71 04 21 0104 21 0 1 1. 04
20 .005 20 0., 0
19714 47. 06 1 9 06 19 A1.0 1 1i. 0is .7 07 Is - 07 is 1 0?
IT08 17 08 1I? .06
.16 709 16 09 1 . 0
5 7 '~ .L~ 15 10 15 .*7 10
14 13 12. 3-54 1 1 14 i3 12 II
DOVER AFB CLIMATIC DATA FOR Frmunny
( BELOW 500 FT BELOW I.000 FT
2324 01 02 23 24 01 02 2 o22 161.11.1 1.. 03 22 2. 25 03 92 ... 7 03
I 1.
215 40 04 21 1 04 21 04
22 ' 05 202 . 05 20 05
19 1.0 -- 1.106 192.1 "Z. 2.06 19 S06I.07 1Z. 20 70
Is~ ~ 7 is 7i -- o Gm
08 I0 Os IT 031 6d 09 09 s 0
is .4(2.4 2 10
15 uIt 0 15 10 1
14 13 12 I 14 13 12 14 13 12
C L ESSTVIIBILITIE LESS THAN IMI P3'
23223 02 23 04 222 1.1 1. 0 SE I ELEEN 03 22 MA 7 03
21 .111111004 21 2. .h7 421 ljC
20 .7 .z05 20 25 11 5 20 Az .0 0
19 10 __. . . Iz 06 19 2.3 1. 06 19 0.0 of
181. .7 07 180 Ilor I 18.2 1. 1
57 .SS Z. SSE.7 O I 716 1K "%09 16 W.NDS09 16 0 9
14 13 121 14 13 12 1114 1312
CALM(12 %) LESS THAN IlK
NNW NNNENW E
NW NELEGEND:
WNW ENEFIGURES IN OUTER CIRCLE SHOW
AVERAGE NUMBER OF DAYS THE
WSPECIFIED ELEMENT MAY BEEXPECTED.
WSW ESETIMES ARE LOCAL STANDARD.
SW SE
SSW SSE
DOVER AFB CLIMATIC DATA FOR MRRCHAVERAGE NUMBER OF DAYS WITH
DAILY TEMPERATURES SPECIFIED PRECIPITATION*AMOUNTS- -• "-- T VT--- .. .........
MAXIMUM KEY 9LW-ST "MK1S?-sBN4 _. OS S- - .-
AVG PRECIPITATIONI - - -I
AG SNOWFALL 2.1 IN I
-4040.M0-100 1 0 203040 50 607?06 0 90olo 100I -K 1 1-I5.5,1-10 = S .
TOTAL SKY COVER INCHES * LIOQUI WNVLNTCLEAR SCATRED BROKEN
2324 02 2324 0102 2324 010222~ ~ 132330 2 D 03 22 420
21 221 3 121 304 21 22 + 3 304 21 223 4- 2 2 0-5- 052 5 0420 q 12 05 20 50_2 05.,
19L q o6 9•III 06 197 306
I7. 977o . RE , OUT. 06CL SOis•_ 0• 18/L 07 SPIsIE ELMN MAB
08 EXPECT.016 16 5 5-/O9 09 16 A O YA0R
•+ 00', 152 o7 70 10i ol ol
15 & 10 15 5 7 in 15 3 7 ý12514 13 12 15 14 13 12- 1 14 137 1 0
OVERCAST
22401 0222 12/2 03
21 22 2 03 04 LEGEND0 o4
20 , 05 FIGURES IN OUTER CIRCLE S00W
19 3 06 AVERAGE N9MBER OF DAYS THE
is 11' 07 SPECIFIED ELEMENT MAY BE17 12 13 08 EXPECTED.16 133 09 TIMES ARE LOCAL STANDARD.
14 13 12 11
PREC IP ITATI ON THUNDERSTORMS FOG~vsoY< imI
23 201 02 2401 02 2324002220 22 1,2. 032231. 0
21 22. 47- 3 304 21 222 .2 0.9 304 21 22 .0304'
20 4o05 20 0.1 0520 -Z0
I9 3.6 v.06 19 _ __ _06 19 1.3 1 .3 06
~'>- '~oi 18 -j$~ZZ - .1 01 181 7 . 1.50
1(37 . 08 170 0. 08 ITL 0 *16 ' 09 116 09 16 7 y 09
15 5s.1 411 10 15 10 IS 15 .4 .7 $5 1014 13 12. 11 14 13 12 11 3-7 14 13 12 11
(i DOVER AFB CLIMATIC DATA FOR, MURCHL
BELOW 500 FT SELOW 1,000 FT BILLOW IO3O00 Ft
2324 01 02 23 24 02 i3s 40 of
22 1.L 0 22 2 ) 2 03 22 0. .1 03
21 ?J. 04 21 I I 04 21 4 04
20 g05 20 .0520 05 O
19 1 21 0 19U ___ 7 06 19 1 0
IS 17 Z 07Is .7 .007 16 1. /2
is 15 ,o1- , 1009 16 1o 00 .2.Io 09 16 1, \ 10 09
,, j•j/ ' ' lo 14 rg\ 12
03(ZJ 01 1 31 lI. I014 1 f 143 32 12 214 013 2
JAL. i*P. LU LESS THAN lIt 1, 3 M
202 23 0223201022 1,.5 l If 03 22 7 322 It%~ 9., O
04 2.2 x Z0 4 10
21 041 212 23
20J .R05 20N 2UTER 20 C SNOW
914 1106 192. __ 06 19 7 3 *06
iS .7 or 182.2 07 oris I Orr
7 10872. INQ I? - £
16 7. 09 Is 09 q 009510 15 A/ 3 0 15 1331 c 10
14 13 1 14 13 12 1 4 1 21
CALMt 4.2%) LESS THAN IlK(5
NW NELEGEND:FIGURES IN OUTER CIRCLE SHOW
WNW ENEAVERAGE NUMBER OF DAYS THE
W O E SPECIFIED ELEMENT MAY BE
EXPECTED.
WSW ESE TIMES ARE LOCAL STANDARD.
SSW S S SE
33K TO 21K 1( 4.7%) SURFACE WINDS MORE THAN 21KNoNN W N NNE NNW N NNE
NWh NE NW NE
WESE W
S E SW E
S WSE :8SSW S SEE
SSW S S S S
( DOVER AFB CLIMATIC DATA FOR Alm
tWERAGE NUMBER OF DAYS WITHDAILY TEMPERATURES SPECIFIED PRECIPITATION* AMOUNTS
w- --- -----
----- - -LOWEST -.- ,
~~09IE9 ... O6M• OIIVlOIt •
MINIMUM7
ITtv. - --- I II- J --- A- -
= n-L-- - -a
,i AO PRECIPITATIONIICIN I - , - .-AVG SNOWFALL 111 I 0
.40-30-I0-00 0 10 20 3040 l0640o T000100110110 0 o- - Loot , .ui •. fU
TOTAL SKY COVER INCEI * LIOUIOD .OVLIENTCLEAR A BROKEN32401 2324 01 02 23 02
2 2 ql ' 321 030 22 021 22 0o 04 21 2? 'if 440 04 21 2 r J 3034
20 ,05 20 05 20 -1 0519 s06 I9 1 -l 06 19 0O
Is 3 r 07 Is &.- o 07 Is &?
, s. • -o ,6 Oa o,,,8116 r09 1609 le091 0I10 114
32 I 014 13 12 15 14 1 2 I
OVERCAST
23 24 01 0222 ~" IL03
21 22 i 1 0 04 LGN20 it 05 FIGURES IN OUTER CIRCLE SHOW
19 IL I~. t. 06 AVERAGE NUMBER OF DAYS THE18is •' 07 SPECIFIED ELEMENT MAY BE
17 u 08 EXPECTED.16 t 09 TIMES ARE LOCAL STANDARD.
14 13 12 II
PRECIPITATION THUNDERSTORMS FOG (vseY< INI)23o24 02 23 2402 2324O 02
21 22 431 0 04 21 20304 21 22010 0420/,.05 20 05 20 0 601
191- 6 19 06 1906,j 06,. 07 Is 07 Is 061 07
8 IT 08 1701 06
14 13 1 , 14 13 12 11 39 14 13 It"
( DOVER AFB CLIMATIC DATA FOR,,11RSIL
BELOW 500 FT BELOW -,OOFT BELOW 10.000 Ft2324 01 02 2324 01 02 2324 of 2
22,I .22 2 lk& 03 22 O321 04 21 04 21 0420 14 /
105 2 r05 20019 4~-2. k6 *,9 06 19 006 19~. L 9.06Is'. -. *07 98 4 1 07 is" .107
1?087%. '8 17' ~ 0 016 ~ 09 16 ,09 16~ 095 (0 10 g15 -. l it,.s to 15 ri 1014 2 114 .13 2 91 13 -12 11 14 13 12 11
VISIBILITIESLESS THAN TAN IiLESS THAN 7MI - 3MI23 0 23 02 23 02
1 029 2' 04
22 . 14 1. 14 0317 12116 09 90 6 19 9 196 0OB
CALMI •_ %) LESS THAN IlK (
•-. " NW NE NELEGEND:
AVERAGE NUMBER OF DAYS THE
SPECIFIED ELEMENT MAY BE
",%*, EXPECTED.
Il TO 2IK( 3•=_ % SURFACE WINDS MORE THAN 29K I 2.,jg•
N E NW N
sssw s SSE
DOVER AFB CLIMATIC DATA FOR ... yAVERAGE NUMBER OF DAYS WITH
" DAILY TEMPERATURES SPECIFIED PRECIPITATION*AMOUNTS
MAXIMUM K .. .. ... . .. .-_ LOWEST MNiTU
MINIMUM 0, % I -•---
--- 5. t I - t . 3,,"[email protected] " it 41, ",, o ,i .0
.40.0-0-0 40 0 0 to S10 40 50S L0 TO so0 =Ito ItoTOTAL SKY COVER I.NCHES L=, It~uw
SqLEAR SCTTRE IROENH23 24 0102 2:3 24 Of 02 232 O 02
21 2 1 04 21 4 ' 04 2 1 0 04
20At c05 20 11 i05 20~ to05
16 3 09S I 0916 ,h ,4 09 ,6 tIS to 11t is 105154 13 12 11514 13 12-115 4 13 12 1
OVERCAST
23 24 01 0222 1) 03
"21 1 0 LEGEND
20 111% 05 FIGURES IN OUTER CIRCLE SHOW
19 %,- it 06 AVERAGE NUMBER OF DAYS THE
IS a It. 1) 07 SPECIFIED ELEMENT MAY BE
17 i 08 EXPECTED.
16 I if 09 TIMES ARE LOCAL STANDARD
15 1014 13 12 II
PREC I P ITATION THUNDERSTORMS FOG (vsSYc IM I)
23 24 Of 02 23 401 02 22 24 01 02
22 ' • 03 22 0 - 03 27 03
21 04 21 1,1 04 21 'g U 04'
20~ 05 20, 1 05 20,a ~ 05
19 I.- a.06 19 6.1 b - 6 19. j. 06
Ia SOl is A -07 Is 4 0e?
I7 08 17 08 17 20.
16 09 Is 1510. 09 1 1 p A 0
I5 jl~ 10 15 'b* 10 I pO~ 1014 13 12, 11 14 13 12 311 14 13 12 1
DOVER AFB CLIMATIC DATA FOR-JI1./
BELOW 500 FT BELOW 1O00 FT BELOW I0,000 Ot2324 o02 2324 01 02 23 24 lo
22 03 22 Za 03 22 0321 0 I 04 21 1 04 21 04
20~ 0 20 kv 05 20. 061994 06 19O1._ .406 19 a 061B 4 JK~. 07 I1 a L 07 Is ' 07
16 0.6 OT 16 09 I6Is 10 15 1 1.% a 10 15 10
14 13,121" 14 13 1213 I3 !
LESS 1HAI IMI LS LTHAN 3 I LESS THAN TIl b S3MI24 :!4 ul24 0123 24C02 23 4OI02 23 02
22 23 IL 03 22 23 ,& 03 22 30321 o4,04 21 4* 04 21 04
21.4 05 201.5 05 20 1 105I9~ .. ~ -%06 19 1 __ 3.1 06 19 C. ,06
ie4 eO Is'I~-,b07I ~'107is , ,'I 7 is 11 ,0 Is -0
161909 16 1. 09 1I5 10 I15~ 10 I5 10
14 13 1II 14 13 II 14 13
CALMi(GjwI LESS THAN Ilk 4-6.7NNW N NNE
NWE LEGEND:
FIGURES IN OUTER CIRCLE SHOWWNW EAVERAGE NUMBER OF DAYS THE
W ESPECIFIED ELEMENT MAY BE
EXPECTED.
WESE TIMES ARE LOCAL STANDARD.
SSW S SSE
IlK TO 21K( ?', i% SURFACE WINDS MORE THAN PIK
NNW N NNE NNW N NNENN• NE NW NIE
W E 'ewi
WWESE L,0 WSW
ssw EE - ssw s ,SEE
DOVER AFB CLIMATIC DATA FOR JUNiiE . L
AVERAGE NUMBER OP DAYS WITHDAILY TEMPERATURES SPECIFIED PRECIPITATION*AMOUNTS
- . . . . -- - - - - -• . . . .
MAXIMUM C - - -
-.- . ... - - - LOWEST "OMIT
asHS SY......................MINIMUM gvqj 40 10 4 3
AVG MCIPITATION IIIN I -. __ ~~V _JL_ JLLWI•SOWFALL -r" IN 0- .'--40-30-20-10 0 10 20 30405060 09001 0 11 m rum~lOl 5 0 Z I: -• I-I4L I.Ef % £ 19.0
4 00TOTAL SKY COVER INCH .WAom INCLEAR SCTEE BROKEN
23 4 01 02 24 02 01 02
020,9 SŽ3 -- 06 19 1?$ 9_¶6 90
20 3 5 FIGRE 05 OUTE CIL SHOW
19 .'• • • • ••_06 AVEA9 06 BE 19 DaY T6H0
1- -,4o007 SPECIF DIs 10 M. b?
17 08 1XPECT .0616 2 0916 99 7 09 is 09q
TIME 9R qOA STANDAR1.
15 15 1I14 13 12 II14 13 12 II 14 1 12 11
OVERCAST
224 01 02
2122 7 77 04 LEGEND
20 o 05 FIGURES IN OUTER CIRCLE SHOW
19 '110J 06 AVERAGE NUMBER OF DAYS THE
is a ,07 SPECIFIED ELEMENT MAY BE
17 008 EXPECTED.16 297 1 09 TIMES ARE LOCAL STANDARD.
15 7 1014 13 12 14
PREC I PITATION THUNDERSTORMS FOG i vsay-, I ml)23 24f 02 2401 02 23240102
22 2.ý2 103 22 jo f1 03 22 0321 IS2 04 21 00 0 2I1 04
20 2.t 2.5 - 05 20g A0405 1920.0
19Z 06. A9 . 06 19-L
ieZý-----. 07 I8 IZ .~ U-1. 07 Is .2. 0?
17 4 ~ 08 17 0'~8 IT 0 l0116671 .0 o
16 1 09 16 a.09 1 0 015 1201.7. 10 15 . 10 15 O.~0.6.0 10
14 13 12. II14 13 12 11 3-1 14 13 12 1
DOVER AFB CLIMATIC DATA FOR JUI•E
CEILINGSBJELOW 500 FT BELOW 0_00 FT_ BELOW IO0.00 FT
23 24 _0 02 23 24 01 02 24 0222 01 a 03 22 1.3 I..03 22 71 03., 3 -1, .7 ,,.1 0321 >004 21 0'4 21 £04
2 0 05 20 05 20 05
190.3 1.\>L~ 3 06 19 1.3 K.- .206 19 f3_-.,J06IS is I. .K .. 07 .81 . 07 Is 1 '07
0T. V/0 1. 0e 17~ 06.7 . .,2 '
16 03 ~ 09' 16 j2. 09 16 oAf 0915 010 0 -7 10 15 '1.2f.1, 10 1 014 10
14 13 12 1 14 1312 14 13 12il•SIBIL ITIES
24SI 0ILTES - LESS THAN 7MI 3,3 MI
23 24 01 02 23- 29 02 23 0222 - 03 22 1,30322 1(1f 0
22 .7 04 21 2421 T .0 1 ., 03
14 04 2119 . ~ ~ '-~ 06 19 g - 0 19 7,4 018.?O 20j4 07 is0 207#2.07
17 0817 08 1 2 028
2309 16 09 16 0915 .1 10 15 1.1.3 105 is 717. '
14 13 12 14 13 12 14 13 12 1
CALM ( 8 1 % LESS THAN IlK (7Z.8%)NNW N NNE
NW NLEGEND:FIGURES IN OUTER CIRCLE SHOW
WNW ENEAVERAGE NUMBER OF DAYS THE
W E SPECIFIED ELEMENT MAY BE
EXPECTED.
WSW SE TIMES ARE LOCAL STANDARD.
SSW S- SSE
I1K TO 21K( 'a.1 o/.) SURFACE WINDS MORE THAN 21K % ]NNW N NNE NNW IN NE
NW E NW NE
" E W E-14
WSW ESE .2 WSW SE
SSW *--S- -SSE 3-1.4 SSW s SSE
DOVER AFB CLIMATIC DATA FOR ,uL,( AVERAGE NUMBER OF DAYS WITH
DAILY TEMPERATURES SPECIFIED PRECIPITATION*AMOUNTS
MAXIMUM • yo. , -
- - LOWEST "MmeSt.-CSSHVED ommKEVED
MINIMUM 1010% 0
-AVGo PRECIPITATION .W IN - - -,
-.... JAG SNOWFALL .0 IN-40-30.90-100 1020 o30 40 so So ro so so goo10o rlo 0l - I1-•( .- I 1004• 5 E.O-
TOTAL SKY COVER INCHES * LIOUWo WAVAL.N?CLEAR SCATTERED BROKEN
23 24 01 02 01 02 01 0222 5u111103 22 ~7 7 03 22 515F5S5 03
21o 12 , 04 21 o 04 21 7 5 04
SIi 3 II . 3
20 3 7 05 20 11 905 20 8 6 05
I 9 11, 0 f 6 19 it 9 06 19 8a 7 018 3 5 07r i I/ a, 07 is to 7 b?17 2 0817 006 08 07 180
1626 05 6I q 09 i6 It 78010 2 09 0610 It #1 8 0 9t15 10 15 I 15i 114 13 12 14 03 12 1114 13 12 I
OVERCAST
23 24 01 02~22 5 6e 03
-121 7 7804 LEGEND20 l/ s8 05 FIGURES IN OUTER CIRCLE SHOW
19. 6 - 7 06 AVERAGE NUMBER OF DAYS THE
Is 7 8 07 SPECIFIED ELEMENT MAY BE17' 08 EXPECTED.
16 17 09 TIMES ARE LOCAL STANDARD.
14 13 12 II
PRECIPITATION THUNDERSTORMS FOG (vseBy i)23 24 0 02 23201 02 2324O 02
22 ' 03 22 - . o. 03 22 0321 ~ ~ 04 21 0.0' 04 21 04L
20 1..1* 05 20 0. 05 20 .1 2 0
19 7.L I... a. 06 19 I.7 0-3 06 19 .1 3. 060- + 07' is I -0' i0 .1 Z.907
ct 1.,- 1 1 1.008'~16 081 0.,08 16 ,z0
16 3 09 16 09 1 0
1 4 13 02. II 04 03 02 11 3-15 14 03 12 1
( DOVER AFB CLIMATIC DATA FOR J"u"L
_ .IL NG•SBELOW 500 FT BELOW O!_O 00 FT BELOW 10.000 Ft
23 24 0102 2324 I2240222 •3 • - q,,- 03 22 1.. -9 . , , 03 22 7 .,.o 03• I \ \ 1/ 2.- 6 o so..• 021 0401 04 21 u2..04
20 Ii05 20 o. .05 20 9 05O
19 09 1706 19 0. / 06 198 01061 1/ 107 II 1 - "-7 1874 Ma 07
VISIBILITIES ,
17 ,..,_E S / HA IMI 90 _90.8 THAN. MUIM 22
AA 3I J A MjJIj. LESS THAN 7MI 3MI2401 _ 24 O/01 240 O1
23 2 0102 23 24- 02 23 0 0222 *j.1 .I.1 03 22 p..I,, 03 22 1. Of.7~ 03
S• , . ,• ,o ,,&. Ir. ,219 3 04 21, '. 04 21,. all.0
190 05 20 1.2 5.1 05 20 o. 0
CA M ( /• % LE__S HA l 97, 13,%)
3. 06XPE1.Ct ED 1 . 3 I
IS .3 1 7is 07 Iq y
9 09 16 09 is 09
15 *Z . 10 15 1¾51.3 97 0 15 1 ~j 0. '
1 13 12 11 14 93 12 114 13 1 .2
CALMi K TO' L E SS T H A N 111( ( 7 3.16
NNW N NNE
NW NELEGEND
WNW FIGURES IN OUTER CIRCLE SHOWWNW\'ENE AVERAGE NUMBER OF DAYS THE
W E SPECIFIED ELEMENT MAY BEEXPECTED.
WSW ESE TIMES ARE LOCAL STANDARD.
SS SE
SSW S SSE.
IlK TO 2 1K L j_ 1 *6 SURFACE WINDS MORE THAN 21K .3%
NNW NNNENW NE
NW NENWE
WNW ENE SCALE WNN
W E W2 EE
SW W
DOVER AFB CLIMATIC DATA FOR r~u6uST -AVERAGE NUMBER OF DAYS WITH
DAILY TEMPERATURES SPECIFIED PRECIPITATION* AMOUNTS- F-[ -T ... IO - --
MAXIMUM 9 -- - -; - **--- -
LOWEST HMIGHESOSEWO OSSINVOIS--- - - - - - - -
M~INIMFUMI 10%~ 00% '10% 1 4 -
£3.8 .' .. _4
AVG PRECIPITATION ±.-2-N I "- -
000 SNOWFALL - 0 IN 0 - • 1 13 ,;
-40-30-O-I0 - 0 1020 30 40 50 SO T 0 90 100110 IMs0i -
TOTAL SKY COVER INCHES * LIGUIC 10VAL.NTCLEAR SCiATTEREDBROKE
23 2401 02 0102 23 24 OI002
2122 la 2 ) yI yI7,0304 21 22 7 7 677 703 04 21 22 5 S'u 4- 4 03
28 It q 7 17 0
20 3 q05 20~ 9' 705 20 8 I0
194 it-' '06 19 to 16 06 t9o '06
220 03
92
,02270
ae,,O I0 1811 X- 807 o:59 08--•.o 9 9:_0
17 08 17 08 1792 0909 0
16 Z 2 is 016 if 16 1,
is._ 2 10 1q 1 9 10 1514112 iz t13 12 1413 12 I .1 2
OVERCAST
23 2 01 0222 7 77 03
"--72 7 4 LEGEND
20 7 a 05 FIGURES IN OUTER CIRCLE SHOW
19 6 8 06 AVERAGE NUMBER OF DAYS THE
18 a 1 07 SPECIFIED ELEMENT MAY BE
I 7 7 9 0 08 EXPECTED.
IS 09 TIMES ARE LOCAL STANDARD.
14 13 12 II
PRECIPITATION THUNDERSTORMS F'OGivsSy< IMi),
23 0102 234 02 23 01 02
2122 2- 2 is 2. 2-2 03 02122 - 10 ORa a 03 04212? LT. 03 02 &I. ~ Z 04 21 .. 0.. 190
20 L Z. 0 20 1.0 d0. 20 .0.2z05
19 21 .- 2.5 06 19 0..__ ., 06 19 .0 7.0116
0 80
18 # • 07 is 0. 07 Is .0 L 0?
I 8 I 08 1I? - 1 o
16 ZiI 09 16 0. 09 16 ,,-0 0I 09
Is0s 15 0 3 .Q~ 10 15 10
141 2 114 1312 11 3-17 14 13 12 1
"DOVER AFB CLIMATIC DATA FOR 7rwuu'rC CEILINGS
BELOW 500 FT BELOW 1,OO0 FT BELOW 10000 Ft
2324 01 02 23 24 OI 02 234 o
22 23 0. 0.30. 03 22 .00. 1 .Z1 03 22 7 .1..2 0321, 07 o'.• \ / z.a 04o
21 0.o 04 21 04 21o0420 05 2 012 1. 05 20 .105
19. __o 2 1.0 06 19. > 3.a 06 19 ~.1 . ~ 0
i8s. Z-*P07 is' '.10 Is8?
* 17 ~ .1 08 170.r 08 I? 09
16 .0. 1 10 09 15 -- 1. .8 1 09 16 5 .0 09
14 1 .1 2 1 1 4 1 -3 1 2 1 11 3 2 1
' VISIBILITIES LESS THAN 7MB 3MlL-. ESS T HA N IM I E S T.A ? ý,-,M, 0,s1T. .. . .,P n•4"- ]--'--'--- •24 01
23 01.02 23 a 02 23 0222 NeI.. 03 22 ,4.2 7 03 22 z" .03
21 04 21 2604 211 04Z.7 t.
20 05 20 1.o 05 20 5o 0•j0
*19 _ -3.5 06 19 1.71 -> <_8306 19g0ol1 '06
8 -0? I8'' 07 is'. 1807'
16 09 16 . .109 '1 0. 3. 3. 0 915 1i~ 10 S 21-I-3 -9 10 15 eI D ~ 114 13 12 14 13 12 14 13 12 11
CALM (117 %) LESS THAN IlK (7•4%)NNW N NNE
NW NE LEGEND:FIGURES IN OUTER CIRCLE SHOW
"WNW" ENE AVERAGE NUMBER OF DAYS THE
W SPECIFIED ELEMENT MAY BE
EXPECTED.
WSW yESE TIMES ARE LOCAL STANDARD.
SW S
SSW S SSE
IlK TO 21K (13.4 0/2) SURFACE WINDS MORE THAN 21K ( "
NNW N NNE NNWN• NE NW N
WN ENE SCAE WNW SENE
W~ E
SSW S;SE 3-18 'SSW S SE
DOVER AFB CLIMATIC DATA FOR SEPTEMBERAWERAGE NUMBER OF DAYS WITH
( DAILY TEMPERATURES SPECIFIED PRECIPITATION* AMOUNTS-.... .. vi- -T-r ....... --- - -
MAXIMUM I(EY i,LOOM? lOMS
1 [, O PAECIPITATION• •IN I ---•. M WO OMrALL .0 IN 0 -Z .
-40-40-40 40 0 10 20 30 40 50607060 6009 01 10.4
TOTAL SKY COVER INCHES LIUIu UAVALINTCLEAR S BROKEN
23 2401l02 232 002 232 002
21 22 isIS5 0o3 0 21 22 7 L 7. Y 0 21 22 740 . 03 0, It 7 L 04,20o05 20 05 20 1,019 7 06 19 _ 806 19 6 506I sy f
60 7 18 10
a 807is B
2'"01
4 '0y470 16 197081 51413 ,2 0 15 1 7s 10 09151414 13 12 14 13 12
OVERCAST
23 24 01 02
22 4 LEGEND
2 1 7
8 0
43
20 If9 05 FIGURES IN OUTER CIRCLE SHOW19 7 - 0 9 06 AVERAGE NUMBER OF DAYS THE
1I e7 10 07 SPECIFIED ELEMENT MAY BEI 08 EXPECTED.
0 q ~10 160 S0TIMES ARE LOCAL STANDARD.
I15 8I 1014 13 12 II
PREC I P ITATION THUNDERSTORMS FOG (vsBy< I Mo
23 24 01,02 23201 02 23 010222 0*~~ ~ 3 22 0o. #.IV 03 22 ~I.7. 03
21 0 04 21 Z 04'
20 2. 0O5 20~ 4'0. 05 20 0191.! " - . 06 _9 . 0.0 06 19 2. 06I •. 2" 0 7 ke.0O IB. s 0?
'08 .• o08 ,o 1."0o
It ii09 I0s 4 .15 2.1 2. 10 I5 0.9 62 to 15 o.2 ,o0
"14 13 12. " 14 13 12 i 3-19 14 13 12
DOVER AFB CLIMATIC DATA FOR.SEPTENHOR
CEILINGSBELOW 500 FT BELOW I000 FT BELOW 10,000 Ft
23 24 O 02 23240102 23 24 0o22 *a I . 03 22 1 .2 lz 1 03 22 7. 03 ~iO21 .3 04 21 1. 0. 2 4 21 .04
2O0 L 0 5 20. 14 305 209 08__# 06 19 .06 9I
Is ~ I 0?, lB a 1-- i07 I: 17o
Sy08 17 J 08 1,7 '0
6 OjO09 1' 109 1o 09Iso10 is 1 o 15 -, 10
14 13 12 I 14 1 12 14 13 12 1
LESS tHAN IMI L AVISIB LITI LESS THAN ?MI 33Ml
23 04 Of 02 23 02 23 0222 .7.7- 0304 212 2 03 22 1
21C LE THAN 04 21.0.
FIUR.,NOTE IRCE SO
20 .405 20 45. 0 20g0.1 1.OG
19.. NZ.y06 19 AVERA1E 19BE ODYTis ~ ~ ~(~0?15 .0'~7=to. 07 I9 70 0?
ZG' 07 Is -. 0 7 Is Iy 0op10 07 I7 .0 1 16 3..
16 7' 09 16 09Ds 0I5 Z .,1 10 I5S1 1 1141. 10 1 5 . ffd to
14 13 12 1114 13 12 1I 14 13 12 1
W -ESPECIFIED ELEMENT MAY BE
EXPECTED.MTIMES
ARE LOCAL STANDARD.
IlKTO 21K,( jq.g%| SURFACE WINDS MORE THAN 21K LlI..o %!NNW N NNE
NW NOENWE
NWS E LEGEND: SS
SW SEE
DOVER AFB CLIMATIC DATA FOR oc, o..AVERAGE NUM9tR OF DAYS WITH
( DAILY TEMPERATURES SPECIFIED PRECIPITATiON*AMOUNi
MAXIMUM K ---- -- --r
', '".t,,- - - - - - - - - -Jill -,-,,------' + ,o----MINIMUM
anS S FALL -'" Im O lo o
*40-30-10-10 0 10 20 30 40 50 W0 TO0 TOTAL SK1OE NlS LW UL~TOTAL SKY COVER ,.wms LIGUI smoumJ.CLEAR TR BKN
23 24 01 02 23 24 O0 02 23 02
21 2 11It 03042 22 4 y 30 21 22 3 'd3 03 020 j1 20 ' 05 20 06
199 12 06 19f 06 19011
18 7 7 18C i 0 7 ISq i7 17
7 L 9 '0 15 I q 1 771514 13 12 1413 12' 1 14 13 12
OVERCAST
2324 01 0222 03
21 2 1 04 LEGEND
20 9 05 FIGURES IN OUTER CIRCLE SHOW
19 q 06 AVERAGE NUMBER OF DAYS THE
07 SPECIFIED ELEMENT MAY BEI? 06 EXPECTED.
7 q TIMES ARE LOCAL STANDARD.15 I0
14 13 52 11
PRECIPITATION THUNDERSTORMS FOGtvnvc Ito-23 240 02 23 01 02 23 o fl
122 2 0 1 030 212 034 21 . '
20** 1. 05 20 03 05 .20' 0S
19 Z3 06 1903 •_ 0J6 19 060?r Is - 07 Is. .70
172. 1 08 17 )8 17 I 400
6 I1 09 , o0. 15 10 14 30 I 510 15 14
14 13 12, II 13 5 I 3-2,1 13 It
DOVER AFB GLIMATIG DATA FOR OC'TO, ER
- BELOW 500 FT BELOW _1O00 FT O ELOW long)p23 24 01 02 23 24 Ol 02 3.. 24 0
23 02 z2 =o2 o O 03 LlA1JIZ 03 22 03O
21 0 •04 21 04 21 04
90 J 05 20 *05 20 0
19 0j -- 06 190 Of 21 206 19W.0
I i 1 is) 2707 is @
17 06 I 7 la08 1.7
1 d 09' 1 1 09 I6 g0
15 1 O IS 15 i O 15ImI 014 3 12 14 13 12 14 I3 1 II
VIIILTIESLESS IM_ L LESS THAN -, MLESS THAN IMI "SMI
7424 0123 02 23 2 93
22 1. L7 035 222 222 0022122-21 04 2). 04 21
20A 200 05
19 -06 1 zs 6 199.706is A 0 is•o 11 -.. ,o ,-s 0, •
e 2 09 is 09 IS
15 zS Io 1514 13 12 I 2 14 ,i
CALM (8.41%) LESS THAN IIK _____
•NNW N NNE
NW NE LEGEND:FIGURES IN OUTER CIRCLE SHOW
AVERAGE NUMBER OF DAYS THE
) E SPECIFIED ELEMENT MAY BE
EXPECTED.
WSW ESE TIMES ARE LOCAL STANDARD.
SSW S SE
IIK TO 21K z.17-1 - SURFACE WINDS MORE THAN 21K .
INNW N NNE NNW N
NW NE NW NE
wsvW :SE
Ew ":
S ,E SW EZ'
WS ES, s E 0' W SW w s m
DOVER AFB CLIMATIC DATA FOR biovfMB'RAVERAGE NUM1ER OF DAYS WITH
DAILY TEMPERATURES SPECIFIED PRECIPITATION*AMOUNTS( .........------------MAXIMUM
OI~tinO O- -l - • - -- . - 1- f "
/rI -
MINIMUM % 40. -.-
- -. - - - r - -
AVO M*CIPIATMo A2fIN I 0 --- - - - - --... - 0AVG NOWFALL LLi._ O - '" /k /. 1.0
40os30 -100o so 0 o a1 , o so 0 o 00o so 90 n i Dl 0 In-k o-a .1 tETOTAL SKY COVER INC=t * LMIG umOu wT
CLEAR -SCATEQ.U02iE23 24 02 2324 o0 02 23 24 01 02
22 it 14 1 03 21277 6 03 29 4 03I 13 4 217 7 0 21 '5
20to 305 207 405 go yO(9 _ j4 06 19 4 06 19 ,os
is 80D? le o 9 07 4S- bIT7 10 08 17 8 8 a06 j6 ~ 7 o
"16 • , 09 16 1,5"709 q 8 0.1 14 13 12 I5I46G, 10 10
-OVERCAST
23 24 01 02
22 q 77 03
21h. q" L• Ig
9 70420 9l 8 05 FIGURES IN OUTER CIRCLE SNOW19 I0 - ' 06 AVERAGE NUMBER OF DAYS THEIs It 8 071 SPECIFIED ELEMENT MAY BE
08 EXPECTED.615 1 t 0 01 09 TIMES ARE LOCAL STANDARD.
14 13 12 11
PRECIPITATION THUNDERSTORMS- FO2G ivss~c Ihi).232403 of02 232 of 02 of~ 002
22 ~ '03 22 03 22 J y 0321 ~. 3. 04 21 04 29 2.I 04'3,10
.9 2 --13
20 T!.05 20 05 Z2g .04D19 2. 1- 908 19 __0 06 19 .6 23. Ol182, 2. 0-f Is 07 is Ak oil?
16 2 Z. 09 Is 09 IS9O15 .0 (0 15 10 IS ,..4 101413 12. 14 13 12 It 3-23 14 13 It 1
DOVER AFB CLIMATIC DATA FOR --NOVEMOU
CEILINGS(BELOW 500 FT BELOW 1000 _FT BELOW I0,000 pt
23 24 01 02 23 24 102 23 24 0122 1 22 ZZ 22 03 "212.2 .1 0/,0304 212 \1 /• 04 21 04
20o 05 20 i 2o.2.05 20 .0
19 1,406 191. 2. o 06 19. 6o-1.7 07 Ia Z.0 2I07 Is% 07
23 24 O 08 172 . 08 1 27 06
15 .51 7 1 15 fog ,.1. "16 o.09 16;.2I ,7,09 16 i0
15~I 0f d. .41 1014 1312 11 14 13 12 11 14 13 12"
VISIBILITCAELSLESLSSATHANK
LESSTHA IM _L THN 3MixIGUE MN OTRCRLES THANMW,3M
23 2Of02 23 02-o 23 00222 1, 2,O 03 22 7 .2 .Z 03 22 72) 7~ 1 r 03
21 04 21 i 4 2•lr. ' Z.5.5 W4S20 1.0 2.5 05 204 05 20 .1 0519 .9 1. - ~ 06 19~ _1 --- ' 06 19 74- 06is .4 -- -- 4707 is. 7K g 07 IS 71 - a?
I 08 17 '(0 17 6 016 9 2209 16 09 16 D9
1 3 1 2 II1 14 13 12 114 13 12 1
CALM (16.4I%) LESS THAN I1K 001t.7%
SW NE -LEGENDEFIGURES IN OUTER CIRCLE SHOW
WNW ENEAVERAGE NUMBER OF DAYS THESPECIFIED ELEMENT MAY BE
EXPECTED.
WSW ESETIMES ARE LOCAL STANDARD.
11K TO 2KL?5-3 -/) SURFACE WINDS MOET~f 1
NNW NNENNW NN
3-4
DOVER AFB CLIMATIC DATA FOR DEC.EMI3ERAVERAGE NUMBER OF DAYS WITH,
DAILY TEMPERATURES SPECIFIED PRECIPITATION*AMOUNTS
(I - " " " ---OlIIPW - ----- - - -
MINIMUM 00%. 1ob 0%
AVG PRECIPITATI UL. IN II - - ! -
I -__ON0 ALL- .? IN o -.I*40.-30-.. -1 01 30 40 50 a o io 00 T 0 00 I -e;0 4 4 , ýS
TOTAL SKY COVER INCHES * LIQUID EQUI•ALENCLEAR S.CA i BROKEN
22 24201OI 0 23 24OI02 0202 0102
2I 24 03 04 21 2 03 04 21 22 OI 04201, 05 20, 405 20q. 0519 ¶ . ~--j06 19~ .Ž 5--- 506 9
S 1 07 18 d 7 07 IS
04 1714 q- 0 8 7 0I o16 100 16 77 10o09 16 7 4 7 1io0
14 13 12 II14 13 12 1114 13 12 1
OVERCST
232 01 02
'21 22 J0 101/ 30 LEGEND20 05 FIGURES IN OUTER CIRCLE SHOW
19 Il _.-- it 06 AVERAGE NUMBER OF DAYS THEIs It 11 , 0 SPECIFIED ELEMENT MAY BE
I? 12 0Z EXPECTED.IS 09 TIMES ARE LOCAL STANDARD.
IS ~J~ J' ~ 1014 13 12 11
PREC IPITATION THUNDERSTORMS F)G (vsBY' imI)
23240102 232401 02 2401 0222 35 03 22 03 22 03
21 .1 1.04 21 04 21 1 04
2Oij. 3 05 20 05 20 05
I9. 3,~ -406 19 -~06 19. 06
181I is--~ 018 -- 7 - 07I.407
17'~O 17 08 1? . 0
IS,. q 09 16 09 11 -7 0915 1073Z 15 I 10 IS415 -- D 10
14 13 12. 11 14 13 12 11I -2 14 13 12 11
DOVER AFB CLIMATIC DATA FOR DLCiMU
(I WLOW 500 Ft BELOQW IfiO FT . Oe M r08 032 4 02 2 2 03 0
t '04 9I 04 SI 04to .05 90 05 20
19~~
' 06 1*O
Io
18 .0 7 gl i 0 7' I I 01'
I9 309 19 0) 1 9 as
i0 Is 0? 0 o Is
Is 10 15 *g 1014 13 1 go 1413 12 11 1 13 it1S14 14 I I
VISIBILITIES LtS THAN TMI 31Of 1ý71 i 24 01
23 02 23 Olt 23 022 03 22 03 a2 0.1i 04 21 -O4 1 04
20 .. O5 203 1 as to19 o .19 1 . 0s19 .l
is )h97 07 Is ofI? '0D 17 am I7 Do
Is 09 I6 09 16
I 1 10 1 I70 IQ15 Z 1014 II 14 131111
CALM(f%. L ESS THAN IiIMIKNNW N NNE
SNW LEQEND:FIGURES IN OUTER CIRCLE SHOWAVERME NMUENR OF PAYS THE
EXPECTED.
WSW ESE TIMES ARE LOCAL- STAKOARAX
Sw E
SSW ,S SSE
11K To 21KL=.tL SURFACE WINDS .IM01.TJON L .11•"--t7 !
NNW N NNE''" :
3-2 85 WWSW, ES"62WSW
SE
SW ;E $W SE'
ss•qq _ WS -),a Os w ee
~~ OU%O%@V
"[3 m vjcp~rolw~m I II..I
jar 0 0
H '
Novo 40
3d!3-27
SECTION IV. LOCAL FORECAST STUDIES
A. INTRODUCTION. ......... .. . o .................... ooj-
B. CLIMATIC SUMMARf OF SEVRE WFATHLR ADVIS.OCIES ATDOV•R AFB AS PREPARED BY THE USAF CLIMATIQ CYTA...o 4-2
C. OBJECTIVE METHODS
a, THUNDERSTORM FORECAST. . ................. . .......
b. SNOW FORECASTING ALONG THE EAST COAST ............- 9
b. SPECIAL SYNOPTIC STUDIES .......................... ...- 31
E. EMPIRICAL RULES* .................................... h-
(.
C SECTION IVA. INTRODUCTIONs
LCLFORECAST 6TDE
1. The operational weather requirements of the base are$
a. To predict, two hours in advance, ceiling and visibility ofless than 200 feet and/or 1 mile visibility.
b. To predict, at least 2 hours in advance, occurrence of thunder-storm activity and severe weather associated with thunderstorm, to in-clude hail and surface winds in excess of 35 knots.
c. To predict, six hours in advance, snowfalls of 1 inch or morewithin the next 24-hour period.
d. To predict, at least 2 hours in advance, gusty surface windsin excess of 35 knots and direction of surface winds to within 10 degrees.
e. To predict, at least 2 hours in advance, the occurrence of freezingprecipitation, heavy frost and/or freezing temperatures, following awet snowfall.
2. Of the above, items a, b, c are-the most important and perhaps themost difficult to forecast.
3. To assist the forecaster in meeting the above operational require-ments, we have developed the following reference aids%
a. Objective methods.
b. Special synoptic studies.
c. Empirical rules.
4. It should be noted that the objective techniques were recentlydeveloped. It will require several years of verification before theirtrue value can hb determined.
4-i
B. CLIMATIC SUMMARY OF SLVLU WAIAH ADVISORL&S AT D(7ER IJAkt F oN BASS
AS PREPARED BY THE USAF CLIMATIC CITkR:
CLIMATIC CFlTER, USAFAIR WEATHER-SEVICE UJATS)Annex 2,, 225 D Street# 8.1..
Washington 25,. D..C.
C=CA 4M2 l2 ji16Q
Sev Weather Advisoies at Dover AID
9WWS
1. Raference letter 9MWSO, 18 thy 61, Request for 8urfaTe Data.
2. We have ex=m4ned the wBAuo from Dover AIP, Andreve AIB, andOlmsted AYE. These forms includ all the dates betueen March 1955and September 1960 when Severe Weather Advisories vex* Lsued.Tabulaticns have been ondo of mxlwu winds., peak gusts, and tbmfer-store occurrences at each base. These tabulatins were then ec 'Ato detenine whether Dover AFB received fewer "hits" than the othetbases.
3. Results of the caarisons are as follovw:
a. laxl-i gusts reported (% of time) when valid advisor-esexist
Dover APB - 47% of time had the mxiudm gustsAndrews As - 35% of tima had the maximss gntoO3=Ste AB - 18% of time bad the mszxim gusts
b. Mam steady wind reported as in a above.
Dover AFB - 41% of time had the maximu steadr vWadAndrews AFB - 384 of time had the maximiu steaA windOlmsted AIB -21% of time had the =xi=ma st•Way vS
a. Thunwdrstozms reported
Dover APB - 33% of time SWT was in effectAndrews Ar-D - 33 of time SW as in effectOlmsted APB - 22% of time MN was in effect
4. A further analysis of the froquency of winds (iallY Peak V.ust)over 35 knots was sad, Durina the period stated there wen 0 "when Severe Woathor Advisorics were Isoued; of theae, there Von T dapduring which Dover experienced gusts higher than 3" knots . & frequnqodaO;. Hoever, cny One of the gusts was under 0 akotsaNA thehisghest was 115 knots.
4-2
' o. Onolucs rM the anly.oes. indicate tbat the 3alk of "hits inearly 2.961. van not In line vith pa~st histwey While Abe effet, otfChesapeae an the Dover veathor =W bay* sm bm*vjg than Is "little to go on bon considering the previm. yes. Anof the standard sumxros for Dover and Anroev has mosled that €XYduring My and Boptaber does Andrevs have wore thwmd rstomz than doesDover. One factor, howeVmr, my indicate a possible Chesupeasa bInfluanooj that is, Dover bad more nocturnol-typ thandsa'stomu Uhe did -
Andrew. Those data frtom the atozidaz4 amp~aries are for the no" garbfrom an identoal nmxaor of oborvntsions,
6. Your statemont that the stndard sumnrles indicate critical vidAspeeds over 35 knots occur rroly is quite right. Hwever, thesetabulation are based on stoeay-stato (1-minute averwsed) vinds and donot include Cucts, Using a gust factor of about 1.3-1.5 vill e•ive a stotstate vind of 25 knots, a probable gust of 35 knots. Therefore, todetermne the froquancy of wind speeds In the > 35-knot catec.oryl- yMshould use the 25 knot cateGory in the standard smarle. We feelthisis Justified becauue the peak gust will verify a vind-warning forecast.
7, From a.l these analysos and statomonto casn the final conaludingadvice s the meot likoly climtoloaical wind f•recasti, Am Dover Is InasSevere Weather Area, Is stcady-state wind of 25 omots vith gusts to 3 bmet*#vith a 1 risk of guoto to 45 knots. Ouast above 15 kots shouAl beconsidared only vhen the buse cauawndr vwnts a "no risk" foecast• Mo I"no rink" wind spoed Is essentiaWly the peak gut stated In th. eVereWeather Mdvinorys.
R. . F,Doepu Director
4-3
C, OBJECTIVE METHODS.
a. THUNDbhRSTORM FORECAST
*OBJECTIVE THUNDERSTORM FCRECAST FOR DOVER APB, DEL.
Authors I/Lt George Le Schofield, Jr.
Date Completed: 5 September 1961
*Based on "Objective Thunderstorm Forecast for EasternVirginia"'9 as published in the 1961 February issue of theAWS Bulletin.
Projeoti Objeotive Forooet Studys To evaluate n objeogtive thwldwgtomprediotion toolmiquo bas4 on a stuAy piupw.d tor Zatznm VirgiiaaaMi described in the Fbruary 1961 teau of tho Ats3 Dwietin.
Progress Repore Perioi 8 June to 5 otobor 1961.
1. The 1200Z 1aeh.tngton eounltn- (fnA) was usud to detsmins twoSaramtore wioh w•re extractod from a nomogrm in a ye or no toMAttaoskut 1& 2)
go The follwAng is a swwnry of the verifioation of thig mehds
:came Foreost .Observed P.U.Mrksrest ~10 Yea: 110 ______________
17 x , X Stion, incl.oof,
10 x I _ _x
SI2 1 x ,_... .. _.. . . ._ _
x x
Mono;ýrar in-41io7t yes arl no.Tw8 X X X oanes or yra on ".,:'C "Tn sP"Me
vwrifiod as Tmn. Six oases didnot wrifyo
Findlingst sI Thi. objective t oohntque is vory rooi for foreoasting thuier-Paton.s in tho Dovur a.ua durinj the puriod June through Sopterm-bor. The initial vorifioition of 25 caoes during the period8 Juno to 9 Auwust was PO pt:roont. Tho overall varoicntionthrovn-h 5 Ootobir 1961 was only 66 percent. The reduced vwii-fiontion is dcnu to thu larger nuwb.r of "busts" In Soptade.Therefore# w bolieve tho atuly n"oul bo anfineA to theevn, tor months of June through Scpt.nf'*r.
Fitylir~s 2N A yes anA no fooest did not verify. Thoiioro9 wthen a yesaryl no arnwr is In W ctudv tao f orucast shoul I be no Ath thefollowin' oexceptions A yes on graph one .4Ith otrong CyV3oniocurvature atth surfaces foreo•o•t yos
4-
* Graph 1, SWWC STABILIT INDEX
IM
'I'-
ýIiw
if 5. 0 P1~~*I I0I
20P
ICAt
C+ ;u
0 b0
:1
0 4-6
00 00 -
ITI
.1 H Ili LI.
4 - 11
L. L
"froject: Objective Forecast Study: To evaluate an objective thunderstormprediction technique based on a study prepared for Sastern
Virginia and described in the February 1961 issue of the AMSBulletin.
Progress Report; Period 27 April through 31 August 1962.
1. The following is a sumnary of the verification over theabove period:
Nr of Forecast Observed RemarksCases
Yes No Yes No
32 X X Thunderstorms within 20 miles of stationI included
9 X X
71 X X
4 X X
3 -X l iomogram indicated yes and no.
Findings: Verification 86A. Zvcn if we excluded the 71 cases of "No"
Forecast - "No" Observed (assuning that we wouldn't haveforecast thunderstorms cven without the objective technique)verification is 66 rercent.
4h-8
C. OBJECTIVE METHODSt (Continued)
{C b. SNOW FORECASTING ALONG THE ,PAST COAST
"Snow Forecasting Along the East Coast with Technique
for Predicting Snowfall at Dover Air Force Base"
Authors l/Lt Joseph A. Ships, Jr.
Date Completed: 28 November 1961
( 14-9
SNOW FORECASTING ALONO TME EAST GCST
C Prepared By
Lt Joseph A. Shipe, 28 Mov 61
I think the following quote from J. J# George aptly describes the problem."Ranking next to togp heavy snowfall (snowstorms) cause the greatest amountof operational difficulties to aviation, both military ard commeroial. Tothe general public, they are without doubt the worst oommon manifeutationaof the weather; to the forecaster, they seem to be the "ultimate expressionsof the weather elements, because of the complexity and number of factors in-volved in their formation and prediction."
It has been found that mosnajor snowstorms are closely associated with strongtroughs of the main jet stream approaching the boundaries of sharply contrast-ing air masses, and the resulting major surface cyclone. However, because ofthe infrequency of major snowstorms at any one location in the U.S., localforecasters have very little experience to call on for what We be their mostimportant assignment. It is the purpose of this seminar to join togetherthe latest research results of cyclone intensification with those of precipi-tation quantities and t•rpes for a general heavy snowstorm-forecasting guideover the northeastern U.S. To accomplish this' two forecast mettlode and alist of rules of thumb will be discussed. The first method is a general fore-cast guide for snows of 10" or more and the second is a method developed forWashington, D.C., that can be adapted for use here. The Washington method isfor snows of 5 inches or more.
The heavy snow forecast study was prepared by R. E. Bailey and is reproducedin George's text, "Weather Forecasting for Aeronautics".
The forecasting data were chosen so that the heavy snow generally fell duringthe second half of a 24-hour forecast period. With the causes of the heavysnow determined in this period, forecasting parameters defining a heavy snow-storm can be anticipated by an experienced forecaster an addition 12 hoursahead, making a 24-36 hour forecast quite feasible. The southern geographicallimit of heavy snowstorms coincides quite well with the annual ten inch snow-fall line. They are, however, extremely rare south of the 20 inch annual lineshown and should be forecast south of this line only under the most favorableconditions.
The forecasting of cyclone deepening is closely associated with trough move-ments and vorticity advection at upper levels, cold air advection at lowierlevels and the presence of sufficient moisture in close proximity to a deepcold air mass.
Over a ?eriod of eight iinters, November 1949 through April 1957, some 1332 syn-optic situations were investigated which gave moderate-to-heavy snow from lowcenters. Hundreds of smaller cyclones, or low moisture situations, were elimi-nated even if they produced 6 to 8 inches of snow. In like manners all of theGreat Lakes' air mass snowstorms of late autumn and edrly winter were eliminated.
( Some 56 major snowstorms were included; a sufficient number to establish a setof minimum synoptic conditions to guide the forecaster and to enable him toavoid over-forecasting to a dangerous degree. These conditions, starting aloft,were as follows*
1. 500 i,: At least a 70-knot observed isotaoh meadon blowing tbrouh thetrough. Including at least a 1000 isotherm ribbon of not rare than 30 milswidth and the trough moving eastward with a speed of at least 20 knots.
2. 850 rbs Cold air advection in the southwest quadrant of the surface lowand not more than 1000 miles away.
3. Surfacer All the major storms reach at least a 20 count. The term countis used to define cyclone intensity. This is the sum of the gradient in mbpmeasured 600 miles in each cardinal direction from the low center, divided by 4.
Now let us amplify these conditions at each level ano find out what informationis needed. At the 500 nb level, the isotach max an!sotherm ribbon were usuallylocated west or southwest of the surface low to be deependd, at an average dis-tance of about 500 miles. Another important factor in predicting these severesnowstorms is the concept of diffluent contours measured at 500 nbe. Such diffluentcontours over the surface low are present in a good majority of the heavy snow-storms.
TIwu [,ra•ton or Diffl.ueiAi. Oontour5 at 1300 mb level
In the above illustration, the downstream contour space count is about 3.5. Theupstream count is about 5.5. The ratio-of the upstream count to the downstreamcount is called the "diffluence ratio", and here amounts to about 1.6. When the ratioreaches 1.5, the surface low begins to "slip out of gear' with the steering flo~wTaloft, slowm down, curves to the heft into colder air, and causes heavy snow.When the ratio reaches 2.0, these-effects become pronounced and often lead tocapturing of the surface low.
A special feature to notice is the occasional appearance of a concentrated isotachmax far up the west side of a 500 mb trough. It usually shows 100-knot windsand a 300 mile wide isotherm ribbon of 1500 or more, bordering tempe, well below-3000 in the trough. These features are the reflection of an intense isotachmax, possibly as large at 20_01ts in the overlying jet-stream core, which willrace through the trough within 24 hours and often creates a major storm in 30to 36 hoursal
4-11
Moving down to the 850 mb levels it was found that the rsceuar7 coldadvection for all major cyclones can best be measured here. The coldadvection center is determined from open contours going through the trough.
Locos;ion of ao n R0-a-b or 700-mbCold Advection CenLer, marked "A.."
this center, Ac in the illustration, should alWs be in the southwest quad-rant of the surface low, and not more than 1000 miles awy. The wind throughAc must be at least 20 knots and the isotherm field A-C at least 1O°C. Theproduct of the 2 parameters obtained should not drop below 250. In the caseof a cold advection center at the extreme range of 800-1000 miles, a productof at least 400 to 450 is needed.
Lastly, we come to the surface conditions. In nearly all potential heavy snowsituations, a low is already present under southwest flow aloft. For heavysnow, a low of initial count less than 20 mb should intensify by at least 10 abin the succeeding 24 hours to a minimum count of 20j, unless the center is initi-ally 17-19 count and deepens to a 20- plus storm. All snow producing stormdeepening to a 30 count are heavy and of the bliszard type. A mininmn surfacedewpoint of 40OF must be observed within 300 miles of the low in the warm secatrat forecast time. If a low is already captured, that is, within 250 miles ofa 500 ob cold low center, the heavy snow stage is usually over. However, ifthe system remains stationary, a light to moderate rate of snow may accumulatelarge amounts over a 24 to 48 hour period. It should be stressed that if adeepening low is expected to go into the capturing proceses it will usuallyproduce a heavy snowstorm while being captured.
The heavy sncw area is usually located in the northwest madrant of the low#with its western boundary near the 700 mrb trough line. This rule applies toall lows starting under diffluent contours at 500 nob, but for storms movingunder straight contours aloft, the snow will fall in a 100-200 mile strip tothe left of the predicted track, taking place in thenorth quadrant of thelow.
4-12
The following cyclone deepening graph combines the important v•rtoitir adVecthiand cold advection factors in one simple diagram that requires only a fewmlnutes for the computation of cyclone inteneity 24 hours in advance. Ths gaphclearly defines the great storms that deepen beyond a 25 count, along with the
1200
~~1000
2C)
H
t 800 a
S600
)!100
20060 70 80 90 100 110 1?0 130 140 150
JET STREAM FACTOR
A 211 hr Cycl'•ne-Intensity Prediction Grapheast ooast cyclongenesis of explosive proportions which reach a 20 count within18 hours*
The attached worksheet should be used to list the minimum conditions at eachlevel.
4-/
Wi=14iT 30
( HEAVY MOTWS1Q3IS
The method of forecasting heavy unowstortm is by a pocees of ombinint qnoptUGfactors *ich met a series of experimentally deterodned mlninms, as discussedin the body of the text.
1. Ainixuia Requiremnts at 500 m
a. Trough located 300 to 700 miles west of surface low center.....
b. Stop here if trough is filling, or maxim= winds east of troughare generally twice as strong as those west of trough.
e. Isotach maximum of 70 knots or more with a 10OC isotherm ribbon(300 miles wide) in trough W or SW of surface lows Divide mx-imum wind by 10 and square this figure...................*.....__________
d. Trough movement 20 knots or more during past 12 hr, or forecastacceleration rate if indicated. Add to answer from step NC" andenter Cyclone Deepening Graph (Fig. 15.6) with m 0m. *...........____0#_*
e. Diffluence ratioa of Contours over surface low center of at least1.5 to 1 is frequent but notneceseary. • ........ • • • . .___
f. Special Cases 100-knot isotach maximum with 150C isotherm ribbonon west side of trough should be used for trough measurements asit catches up to lain trough.
2. Minim=w iequirements at 850 ob and 700 ab
a. Location of probable snow area by location of 850-rob OoC isothem,usually associated with blocking surtace high in immediate futurepath of cyclone precipitation pattern.
b. Cold advection center, As, showing at least 20-knot flow of atleast 1OoC over 600-aile range. Product minimum 250. As locatedwithin 1000 miles (usually loes than 800 miles) of surface lowin SW quadrant. Enter product on Cyclone Deepening Graph.....___ ..
c. Cold advection factor at 700 mb over Rocky Mountains if 850 mbdoes not apply. using same measurements as step "b".. ......... _______
d. Locate maximum dewpoint at 850 mb within 300 miles of surface
low center. Should be at least -4oc..........................
3. Minimum Surface Requirements
a. Use Cyclone Deepening Graph for forecast cyclone intensity(within 24 hr.
(1) Initial low count. Should be less than 20 ub, using 600-mileradius for LaPlacian measurement ......... • •.• • • .. .....•
[-14
(2) Twenty-four-hr forecast of cyclone intensity from graphshould show at least 10-eb deepening from pervious stepsexcept lows already 17-19-rob ot...........
(3) Final count in 24 hr should be 20 ob or more,.
(4) Add 5-ob deepening to Step (2) for lowe starting along,East Coast ovroean........................e........,
(5) Forecast track, Should be north of 600. meptions A25 or more count forecast under parallel 60-70# 500-,bcontours with surface and 850-rb dewpoint mjnjm. 45°Fand 50C, respectivelys, Within 300 miles of low center...
(6) All lows under diffluent contours at 500 ab will tract3600 to 500
(7) All forecast 30-rb-count cyclones with zinimum moisturerequirements at 850 Ab and surface.
b. Locate dewpoint ma•Jimu within 300 miles of low center. Shouldbe at least 4O°F. ..... ....... .. •... . ..............
a. Surface low should not be captured (within 250 miles of 500-roblow), unless forecast to remain nearly stationary, therebycausing long duration of a Light-to-moderate snow rate in onelocation.
4-15
The second method conbines semi-objective methods of prediction for na~or snow-atorms in Nkshingtons D. C. with a deep sample of experience of such storm. asrepresented by some 59 occasions when heavy snow occurred. In this study, avajor storm is defined as one which produces an accumulation of 5 inches ormore of snow#
Although each situation has features not comon to the others, a generalsynoptic pattern does evolve and the outstanding features of this generalsynoptic picture are as followes
SURFACE MAPS:
The general developmenLf "Snowstorms" along the northeast coast are the resultof the following sequences, listed in the order of their frequencVs
1. Cyclogenesis along the east coast with the storm center deepeing and movingnortheast off-chore between Hatteras, N.C. end Nantucket, Mass.
2. Cyclones in the Gulf States or in the Gulf of Mexico which deepen and movenortheast and track along the coast line from Hatteras, N.C. and Nantucket, Mass.
3. Cyclones moving eastward through the Ohio Valley and crossing the coastlinebetween Hatteras, N.C. and New York Cit1y.
The surface pressure patterns which favor snow over rain in the northeast coastalarea, display a strong anticyclone over or just north of the Great Lakes area andlow pressure over the Nova Scotia area.
850 MIL1 BARSt
In order to prevent the air at this level over the northeast from being warmedabove the freezing point, the zero degree isotherm should be well south of thestations along the coastline. This is particularly true when southerly flow isestablished over the stations for some time before the start of precipitation.If the zero degree isotherm is close to the stations involved, snow will notoccur unless it sccurs simultaneously with the passage of the ridge line to theeast of the station. In many of these cases, the ridge line is situated acrossPennsylvania 12 hours before the onset of snow, with the northern boundary ofthe snow area marked by the 850 rnb ridge line. The strongest warming in the areaunder study, occurs when the zero isotherm is oriented NW-SE across the OhioValley rith west-couthwest winds across it indicating warm advoction.
In order to accurately predict snowstorms for a given locale, the following
meteorological items must be determined:
1. Will the precipitation occur in the form of snow?
2. The intensity of the snowfall.
3. The onset and cessation of snowfall.
This study deals principally with items one and two, although A solution isC presented to determine the duration of moderate and heavy snow.
4-l6
t *type of precipitation is determined throua graphic uwtiple eC ttonbased on objective parametoers The oolutios ae for period of 24 &Az 12 hoursfrom data tim to the onset of precipitation. The parameters all taken f ta thesurface and 850 ab charts nearest to 24 and 12 hours before the start of theprecipitation.
The teperature of the lower atmsphiere determines the *pe of precipitationreaching the ground. Essmatially, a corroot forecast of'the tipn at the str-face and at the 850 nb levels will predict precip types. The mtihod used hereis an indirect temp forecast for these levels with the final solution expressedin term of precip. types. George, in 1947, developed a pattern method todetermdne the tupe of precipitation likely to occur at Now York City, associatedwith Atlantic secondary storms. This method is satisfactocr wh'en the patnsaxe well defined, but presents difficulties in more obscure situations. -to"obetion to the pattern method can be overcome by numerically indweig thepatterns with objective measurements of surface pressure,. The usual surfacepressure pattern associated with snow in the norther coastal area of the US.displays high pressure to the north of the Great takes with low pressure overthe Nova Scotia and Now Foundlnnd areas. This arangement of pressure systemspvides general northerly flow through eastern Canada and the easter Great
as area with westerly or northwesterly flow throeSh New England. As ameasure of this circulation pattern,- the surface pressure difference betweenGreen Bay, Wisconsin and Portland, Maine, (Pgrb-Ppmn, is used to evaluatethe flow through eastern Canada end the eastern Gkeat Lakes area. The flowindex so obtained is plotted against the sum of the surface temp and dewpointin the first stage of multiple correlation. The sum of the temp and dempointis used as a. quick approximation proportional to the wet bulb temp.
The second phase of the multiple correlation involves the 850 mb level. Themajor factor at 850 is warming. Therefore, it becomes necessary to measurethe zonal advection at 850 over a large area. Advection of warmer air Intothe northeast coastal area for the layer between the surface and 850 isassociated with the breakdown of high pressure and the increase in low levelthickness through eastern Canada and the eastern Great Lakes area. However,strong warming at 850 just prior to precipitation is quite rare. The maxdwuwarming ur the 24 hour period preceding precip at Washington is 0 C, Toesbelow -70C will indicate snow if precip is to occur within 24 hours. If theair mass is extrmely cold, the current 850 tamp is a ver7 good forecastparameter, however, in the range from near zero to .. 0,, it become quite obscwe.The advection at 850 plotted against the present tamp, is the second step ofthe nmltiple correlation.
The method of determining the advection is based on a series of seasuremitsof the flow and temp fields at 850. The net moral component of the flow througha large portion of eastern Canada and the eastern U.S. is obtained by masuringthe difference in height in tens of feet, between Greensboro, N.C. and Y IOsen#,
Ont., (6S3% o- MOa,54•e. Positive values will indiate a net west wind withnegative values indicating a net east wind. The east-west temp gradient atapproximately the mid-point of the line used to determine the moral flow indexis measured by determin the temp difference between Albar#, We and Flintp
i ( F, wJ. The product 9f the ,oral flowwest temp, index is ueto obtain units of sonmZ. advection, (G50o?. M 0 s
(1 (Lberso - .~rV0 Positive values indicate cold &&GOc On.
[4-17
The net meridional flow across the Oreat LAkes to the northeast oca stp i swed( the diffqrence in height between Green Bar, Wis. and Portland, Me.easO) . Positive values will indicate a north wind and negative a seuth
wind. %be north-oouth tamp gradient across this line at approximdtel" the mid-point is determined by measurin the difference in'temp between Pitt sburgh ar4Maniwake, Quebec, (P/ 7-,. - M The product of the ridionil fow .index and the north-south tamp indeoo$ No 9 P w4a.)(lTj,%S. - M ,is used to obtain wnits of meridional advection. Positive values indicate oodadvection and negative warm advection.
The total adveotion is the sum of the zonal and meridional advection withpositive vause indicating net cold on no tive indiat net •mr .
The final solution is obtained in stage 3, in which the value of the stage I, orsurface data, is plotted against the value of stage 2 or the 850 ab. data. Theparameters are obtained in identical fashion for both 24 and 12 hours. Followingare the charts for 12 and 24 hours, with a map and worksheets
(4
Il-ia
The Stage One Graph is based on surface data. The flow index
is obtained by subtracting the pressure at Portland, Maine
from the pressure at Greenbay, Wisconsin. (PG RB a ppP )
The Stage Two Graph is based on 85OMb data. The advection
factor is obtained through the following computation;
(GSOz 4-Oz) ( BT-NTT) 4 (GRBZ-PWz) (PIT T4WT)
The Z values are expressed in tens of feet.
The T values are expressed in degrees centigrade.
The final sum is expressed in hundreds of units.
In The Third Graph the plotted letters have the following
significance:
R - Rain E- Sleet RS - Rain & Snow
S - Snow ZR - Freezing rain ER - Sleet & Snow
The arrows connecting two letters indicate a change from one
form of hydrometeor to the type indicated by the point of the
arrow. Points falling in the lower right'zone of the graph
indicate snow as the proper forecast, whereas puints falling
in the upper left zone indicate rain as the proper forecast.
The central portion of the praph bounded by the two heavy
curves represents the transition zone from rain to snow.
Since this constitutes an area of uncertainty, the proper
forecast in this zone should be a combination of rain and
snow.
WO-K SHET FOR 3NOMITSTOR1,1 AT DOV.Z, IOL.
C This work sheet shmnld he "scd after tle staiting itimeo of precipitation hasbeen predicted. The computations are ri,.de from the surface and R0 mb chartsnearest to 24 and 12 hour,, before 0h', :;tort of precipi-itfL on at Dover, Del.
TIME VALUS3 CAII rhe TL;•T•) 14j 4ITVfkR T116 24 OR 12 HOUR Cl!i\A.TS, DEFWPENT ONTHE TIM INTSRVAL D0ITIW4; Tli& aURiLVST CIIA•frS A]D TIE I"FOICAST TI11-9 OF FPI -CIPITATION..
1. Subtract the rurface pressure at Fortland, Il. from the jur-face pressure at Greenhay, -'is# (Pq.%?p) ......
2. Iote the sun of thc Curfqce temp. and dewpoint at Dover, Del.
3. Enter the values from rteps (1) and (2) in stage one of theforecasting :raphs and record the valuu "jxn'-ca+t, by theweight lines.
4. Note the temp. at Dovr, Del. on the 35O rib chart.
5. At 1'O mlb subtract Vhe hoifht at M1oonsonee, Ont. from theheight at Greensboro, N!.C. ond record in ten's of feet.GS)z 8 o'CYV).-..Lo6. At 850 mb :-'ftract tVw tmr. at Flint, .. i.c-h. from the temp.
3t• .lbany, .*. (ALVTI Y.. i'i ITO)
7.. "'hultipll- t.e valwi'r itnilly" in rtmr- M and(
3. At 950 rib cubtract the Y3e-,-t at, fortl•,7n, Au. from thoheight at r'reenboy, !7is. and i'.aoo'd in iii'~ or" feiut.
9. At 850 mib subtract the temp. at Manawa-i., CQuo. from the temp.at littshuri;h, a a. ( I or,^C
10. Miltiplv the values obi~aint:c Ln stops (3) and (9).
11. Add thri values olbtainjJ in ;t•rps (7) and (10).(Entered in" l0' s of units)
12. Tnteur the volues from M1epn (0) al0 (ii) in the stale twographs and record the value indicated by the weight lines.
13. Enter the values from itcps (3) and (1?) in the final graphfor the forecast of prc,31l.,itation i[,)pe
1I4. To dotermiru o hP cuilin- andl vij.i)lit.y forecart, enter thepronostic porlitlnns of the iy,"'&!c c r.'ine on the snow zonecha.rt
4-20
00
00
730 Is
33Of 3S 0 ~ t ~ --- , I ~O I ~0 0Iv O 4~ v, 40 0so
64- *D33~ 7371
CL 0 42
-03 0* 4 6" -w X?/
iSiI 0, Gow 63
0~ 062
b 0 2 f 1 0 6
' + • +' '•,"+ , ' .. . +'
~a l- 4 .i*~,l4rt ,14 '.~~n ",' , ', .'- , , ,+ ."-
16 lb - 1. 14 l+ 11 II 1 0' , 9 6 I
. 0 /0 -00S. .// /
,.-! . . ...- - -
-; .... . . . . . . . ..,.....- - - - -
E 1.M '.IRF ACc EFMPP •, , J R AN E V JINT AG I/N.' : tl
WASHINGTON 24 HOuit GRAPH
42I,, ...
k; 4-4
A Fl/ C I ON f-AC ,10i
WASHINGTON 24~ HOURt GRAPH
R
HR R
RR
Ps
I__s-- 6.M---- I-
WASHINGTON 24& HOUR GRAPH
.4 12 &0~C' 7
6
+1 4
I0SOtM OF SZJRFACE.TEMPERATURE AND DE WPOINT AT WASHINTON 9
WA8HINOTON 12 HOUJR GaAM
4-2
IIPY
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4' +
WAIM '2 -H G '-
446
f, N -SfA
161
'>17: RRS.4 F
R-
-R-
4S- R- R -S
-~~s -s. Ut 2-
bT AGE C- N E
WASHINOM(~ 12 HOUR OHMP
4-2
Cktven a situation in vhich snow will occuws the next step is to pmeit theintensit of the snowfall. The sppoach used to determi. this featut W.asbased on the duration of low ceilings and visibi.tieus. - I= values ofceilings and visibilities wer assigned to heavy moderate and 10t snow inthe follo•idng fashions
1. Heavy snow - ceilings less than 200 feet or visibilit~y loss than 1/2 mile.
2e Moderate snow - cei s 200 lest through 400 feet Vitibility 1/2 mile upto, but not including 1 mile.
3. Light snw - ceilings 500 feet or higher; visbilitu 1 mile o' better.The qnoptio situations which produce heavy or moderate saw fbr periods of mthan a few hours duration are associated with the passage of a surface 00loneto the south and east of the station involved. The most favorable situationfor heavy snow is associated with deep or deepening cyclons. he histo•y ofthe storm situation falls into the 3 categories mentioned earlier. ThW mer
the Gulf States low wving northeast along the Atlantic oSt, &pa ccloneoalong the coast and moving northeast and a low from the Ohio ValQ" mving eastinto the Atlantic crossing the coast north of Hatteras.
For all such cyclones producing snow at Washington, the ceiling and visibilitieswere plotted at te position of the low center at six hour intervals as thelow moved northward. From these plots was obtained the following chartp whichshows that a sonse exists in which the ceilings and visibilities indicate heavymow as defined earlier and a larger area which indicates moderate snow. Thischart should be used in conjunction with the prognostic •jýs:ition• of the surfacecyclone. The ceilings and visibilities should be forecast in accordance withthe positions' of the cyclone, relative to the moderate and heavy snow sensssThe duration of low ceilings can be predicted from the tim of entry to the timeof exit from the low ceiling sono. The prediction of moderate snow sones is basedon the predicted time that the surface cyclone will enter and leave the moderatesnow zone. The same holds for heavy snow. A suggested value for ceiliog andvisibility when the low is in the moderate zones is 3001 and 3/4 mile. In theheavy zone, 100' an" 1/4 mile, is a suggested value for ceiling and visibilitq.
Rules of Thu* for snow
850 mb Temp
-200 or less at the start of the PreOip-.70 or less 24 hours before precip is to occur
700 nib TegM
.700 or less at the start of the precip
Temp above 900 ab below freezing;C,• •Wet-bulb temp below 900 nob, below freezin.
4-28
WV
GAV
o 731.Y3/ ML
age ac 17 WOV
opw om0 Oft
64 Am at llýNo (AV6. an ow 0 1"0 4" *0 121 s"4U w 63 623 Sit, 7w
aspAl0* vp sitA S31
aw 4 Own .04"
AMOR or
S24 AO0 AV 18 0 0
'K $12ADC 0 M A80 $1 x0 sit 0
C P" - -. 4
0 oux
I V') WA0mawl 40F
437 0421 on X
4171^
LIN 0 00 . 425 a"
422 0
"F04124 0 401 P y4St
0 KO 00,
TYS10
0 300 t"I ram"3QfAT ý0
AW 312 3 cm 3ý a W6
0 -89t t treLclc
,?,An r.jjtfij-ýj
' _ f oroc Underof tlhq amhot contoiirs Oft w"'
821? Produce no 'Sn 0 ye ýhtWAB n too on
Snow at, Dover#
SVXI 4.12 and 4-16)
0A66
Mai-IV.0m
%V 4-29
17900 or greater 10-90 Snow17800 24-76 017700 41-5917400-17600 50-50"17300 86-14"17200 or loes 95-05 "
Another iuportant factor is atmospherio o•oling by melting snow in lowerinthe freesing level to the grounds Determine the average a ArT above flengon the Skew-T Log-P Diagram. "Inn to determine the mount of liqui pieipneeded to lower the freezing level to the surface, use the felledg equtiea
Awomt. of Snow
1. Determine the difference of uixing ratio in gm/Ag between the basr andtop of the moist layer. 0.C0 in/hi of liquid precip will oocur fr eachgm&g of misture precipitated by cooling. Determine V•e produot.
2. Multiply this value by the number of hrs that precip is forecasted*This gives you the total liquid precip.
3. Multiply this result by 10 to obtain the snow depth.
References:Mdeather Forecasting for Aeronautics" by J. J. George"An Analogue ?4ethod for Forecasting Heavy Snows at Washington,, New Yorkand Bostori" by A.11. Stakely and Lt.". I,.TitinZ
14-30
1). EG&IA SflI0JTIG SEMDIU
A a," study of a ttack-door" cold front followed by an extsoded pgoM oflow ceilin~gs and visibilities#
1o. Snoptic Situations At 1200Z on 29 April 3.62 a wek s•iata n1 htmWas oriented laste-West from the oemtral Rew nUnd states tieeeel a b t-ward as a warn front through Illinois, N•i-so-., into a tw ja'*est.in Kansas. An occluded front extended northrd ram 'this low 6• to.The 5004 chart was characterised by southwesterly flow ~0er 04 at thl Its*with a mjor trough over the Rookies. The mjor ridge was located jsC eftthe east coast of the U.S.
By 120M 30 April 1962, the occluded front had pr ed to 4m1e1Wisooumin and Iowa, -while the stationary front over ew ftland bi d,seouthftrd as a cold front to a line along eastern ?sqaW1v&.alWa s amttNew Jersey. This was duo to the building of the uper ridge amee e*abU.S. with a corresponding increase in the intensity of the sutface rji4dge rthe Newfoundland area. This so-called "back-door" cold front ooatiatud t6
move southward along the eastern seaboard in response to the persistent aorth-erly flow aloft at the 500-I level.
By 1200Z 2 May 1962. the cold front was oriented along a line from Norfolk
to Gordonsville to ,4artinsburg. It remained quasi-stationary in thie appre-imate position until near 0600Z on 3 May 1962, at which time the occuded frontfrom the west moved through the area and off the coast.
Figures 1 through 9 show the composite surface and 500-41 patterm durugthis period., Surface observations for a nunber of stations along the wastalarea are depicted in Figures 10 and 11. The passage of the cold front isreadily apparent at all stations. Figure 12 illustrates the daily savomnof the cold front through the period 0600Z on 1 May 1962.
2. Surface Weather Patterns An extended period of low ceilings and poorvisibilities prevailed at all stations following the passage of the o*ldfront. Ceilings varied from zero to 800 feet with visibilities 1/]8 to 4miles. At Dover, ceilings below 800 feet prevailed for som 80 bhos.
3. Conclusions: This pattern is a typical one for the eastern seaboad and
Dover Air Force Base. The basic pattern may evolve in two e s is
described here. The other evolves from a normal cold fmont ishih Patee the
Dover area and after becoming quasi-stationary over the central Gdlf 60"tstates, returns as a warm front and becomes imbedded in the AppalackhlaMountains with a north-south orientation. A cold do=. of air Oesist. 04
the Piedmont plains and coastal area thus blocking the warm frost and causig
it to remain stationary in the mountains.
In either case, the results are the sam a extensive lxw eeliWg and r
visibilities prevail at most stations located within the cold air xsse. iforecaster must guard against prematuro3y predicting the passage. of the we
front. He must be guided by the existing and predicted V0M pet, .0s!*.The presistence of the ridge aloft over the eastern seaboard, as .tmi'stAeR0eby northerly winds over or Just off the east coast., is the)W *aowihbyalerts the forecaster to the fact that the surface hipnirn r"Au * q• ,stationary and dominate the coastal area. (Note that in Fgure 9# We 4 0
t
ridge has also blocked the occluded front resulting in a bent-back occlusion.)An occluded front from the west will eventually push its way to the coastresulting in clearing conditions at Dover. In all cases, this occluded frontis a Pacific front (warm front type occlusion) and results in warmer temperatures.
4S4~-32
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ulo 1, Do tot for st a minima tempeture below 140 it theft
in no snow cover on the ground.
Rule 2. Minimum Temp'- Mx IM (at M of UM Tee)- 122
Rule 3. If temperature at 700 vb in -60C or colder forecast snow; itf lessthan -7cC, forecast reain; if' -70C, rain and snow mixed.(Use as first approximation only - Temps not be foreewst)
Rule 4*. If 1000-500 ob thickness is 17,600 feet or less, forecast sneowabove 17600 feet, forecast rain.
Rule 5. If strong gusty surface winds (25K+) are expected in advance ofa deepening low along the coast, forecast rain. If sow do"ebegin, forecast one inch or less with saow changing to rain.E~2nep:J If surface winds are N-NI, forecast snow. Amount
l depend on speed of movement of storm center.
Rule 6. Do not forecast post-frontal snow showers unless 700-& Troughis west of Dover. (Very reliable)
Rule 7. Light Sw Flow and clear skies - ver7 favorable for fog in Falland Winter. (First approxiuatior)
Rule 8.. (a) SS winds with Dew point temperature below (ocean) watertekperature, Fog unlikely (all seasomn)
(b) S winds with Dew point temperature above water teemPsratMrFog likely (all seasons)
Rule 9. With clear skies, high dew point temperatures and light south-westerly surface winds, forecast ground fog at about sunrise.(Visibilities below 1/2 Nile possible# but will last for lesthen 1 hour.)
Rule 10. Below ]CA conditions prevail (less than 200 feet and/or 1/2 mile
visibility) and winds are calm or light from south or easterly
directions Forecast above GCA conditions 1 - 2 hours after wind
shifts to southwest or westerly dirsection. (Very reliable forshort range period.)
Rule 11. Fall, Winter and Spring$ If scattered clouds form below 2000 feetnear sunrise, forecast a ceiling by 0900L. (Ceiling will immin
-broken and persist tinl noon.)
Rule 12. Behind slow moving "back door" cold front, forecast reduced vii-C bilities in Hase.
S4-45
" Empirical Rules (Continued)
Rule 13. If cloud cover and light precipitation prevail during daylighthours (or if considerable precipitation hasi fallen during thepast 2 hours) in advance of a slow moving cold front which isexpectedvpassOA Dover near sunset, resulting In cleating, thenforecast heavy ground fog for a period of 1-3 hours afterclearing occurs.
Rule 14. With a weak surface low over Virginia at 1500 EST "n southý-westerly flow aloft, forecast thunderstorms over Delaware in
the late evening. (Summer season)Rule 15. Thunderstorms which form over the Delmarva peninsula., build
rapidly and are generally stronger when passing over Dover
than thunderstorms which form west of the Chesapeake Bay.
44
h-h6
