Best

Available Copy

TERM ItSJAL FOREOA0

REFERENCE FIL.E

OFFUTT AFB

■‘Of

X

. 'v^

SEPTEMBER 19/1

' UNCLASSIFIEDSecurity Classincetion

DOCUMENT CONTROL DATA ■ R & D(Smcurlty cJm99itlcmtion ot f/ll*, body ot abstract and indexing ^notmtion mu*f be entered when the overall report is cJassiUed)

1. ORIGINATING ACTIVITY (Cofpofte muthot)

Hq 3d Weather Wing (MAC)2a. REPORT SECURI TV CLASSIFICATION

UnclassifiedAerospace Sciences Division Offutt AFB. NE 68113

26. GROUP

N/AS RrPORT TIT 1 t

TERMINAL FORECAST REFERENCE FILE, OFFUTT AFB

4. ucscRiPTt vC nor^9 (Type ot repaet end Inelueive detem)

N/AS- AUTHORISE fFtrsf name, middle initiml, teet nmme)

Base Weather Division, 3WWg<■ REPORT DATE

Sep 19717a. TOTAL NO. OP

103■ PAGES 76. NO. OF REFS

24•a. CONTRACT OR GRANT NO

N/Ab. PROJECT NO

•a. ORIGINATOR*! REPORT NUMBERlS)

N/A

C.

d.

9b. OTHER REPORT NO(SI (Any other numbere that may be meel0ted thte report)

None1 ■ DISTRIBUTION STATEMENT

Approved for public release; distribution unlimitedII SUPPLEMENTARY NOTES

None

12. SPONSORING MILITARY ACTIVITY

Hq 3d Weather Wing Offutt AFB, NE 68113

l»7 ABSTRACT

Thi^ publication discusses the location and topography, climatology, and weather regimes affecting Offutt AFB. It also provides a section for forecast studies to objectively aid one in forecasting for Offutt AFB.

Details of Illustrations In^-, thi$ document may be bettei!

V studied on microfiche

FORM 1473 UNCLASSIFIED

n^.tASSIFlED Stcurity ClBatificBtton

KEv wonoi

Terminal Forecast Reference File

Climatology

Forecast Studies

Precipitation Type

Offutt Air Force Base

NOLI WT

TTNCLASSIFIED Security Classification

Tj^tUtüL ifUKjiUAi»'!' dj^iätmia Vila.

PAia* I

Luaxiuu

KJiiU'iU.lfl'S

UJüTHliWüHTATlUM

PAUK

X-A-1

i-B-1

I-C-1

I-D-1

l-K-l

r-^ Details of illustrations in^ , -^ this document may be better If:

I]] "■■^ ÜO (3?/

siuoisd on microfiche

'^L uihi .J

■TAUM^Sl —~ r ,„r public rdedflOS \ Approved lot pu';1 .. ,, \

DiDtribuilon I)

as; \

i, J

1-1

SKCTtON A lOCVnON

Offutt AFB Is located In east central Nebraska at geo-

graphical coordinates bl' O?' N and 95° 55' « and Is on Central

Standard Time (GWr-6). The runway direction is northwest (300°)

southeast (120°) and is situated approximately one and one-half

miles west of the Missouri "iver and three miles north of the

r-latte "Uer. The two rivers Join about four miles south of

the southeast end of the runway.

Omaha, population 390,000, lies ten miles north and the

city of Bellevue, population 25,000, adjoins the base to the

northeast. See Chart 1 (I«cal Area).

I-A-l

CRIBNCR P924 1 /1 . W f ) C% Ml

NE( LA101 T^.Tf

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N—IN X

ct«MM*A 104^; - t\ -' ^fS«2' / «OLl \'o«o -1A . .

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CarttoM ^ s ■. M—

A-"-J

Sftott Mtm YT

3orSf tmt M>m 1^1 1 I I I

^11 "TS

SiCTIUN h TütüliKAPHY

Tba baaa la lacatad on ralativaly low land batwaan tba

Miasouri ülvar and tba Bapillion Craalc. Tba runway alepaa

up fxoa 970 feat soutbaast to 10^0 faat noxtbwaat whara it la

bigber than tba ioiMdlata terrain.

Tba Miasouri ttiver Valley slopes up generally fron tbe

soutbeast to nortbwest vitb elevations at at Joaapb, Ha of

b25 feet) umaha, Heb ^0 feeti Sioux City, la 1000 feet) and

Huron, U> 12^0 feet. Tbere is a ridge between Üuran and

Hinneapolia, Minn witb ■axiaua beigbts to 1600 feet wbiob

lowers to 1600 feet between Uaaba and Sea Meines and to 1000

feet in tbe Lamoni, la - Kansas City, Ho area. To tba west

the terrain starts to rise just west of tbe ilatta Mivor

reaching an elevation of 1800 faat 80 allaa west of Uffutt.

A ridge runs soutbeaatward fro« just aouth of North Platte,

Heb towards Kansas City witb elevations to IBOO feet south-

west of uffutt.

▲s tbe topographic nap shows, 120o-160° is upslopo

while winds fro« 330o-3600 are neutral or ali^itly dowoslopa.

Winds fro« 160o-3300 and 36üo-1200 are downslope.

I-B-1

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CiiAitT 3 TiiiHiUIN PHOTUGBAPU i-a-3

Pollution by anokc is at tinMS a oontributin« factor to

reduced viaibility but rarely the major cause of visibility

below three miles. Unataa is the major source of smoke over

the general area, ideally, the Allied Chemical Plant located

one mile south of Uffutt is the major source (iaee Uiart4).

The OPPD power plant which is one mile northeast of the base

is another source but usually involves relatively high level

aaoto or contributes to the formation of river fog. The Allied

Chemical Plant contributes to the fog intensity with weak

southerly or southwesterly flow. On on« rare ocoasien, smoke

reduced the visibility to less than one half mile, 'ihis was

over a snow cover with a strong surface inversion, surface

temperature near zero, and calm surface winds, amoks collect-

ed in the low areas after sunset and reduced the visibility

to 1/16 mile between 2}00 and 0100 UW. By 0200 U>T the visi-

bility was above one mile and no further decrease in visibility

was noted.

I-U-1

äfiCXIOH 1) IltbThUtUiMXAIIUll

TYPÜ rfJADUUT ÄüJOütb

WIM!) ÜMkll Du»l Ob alte Base Wea Control Twr ua KAIUJJ»

bensor at bK and in slight hollow, ben- sor at M end partly aheltered by building«

CLüU) HüJHiha' U'^IJ Dual üb bite Max height 3900'

ViälblUn Udiil 0 Dual Ob bit« ü'WI KVü

MUMIÜlTi IMHll üb üit«

i>K4bäbKK MI412 111.102 »üi563

Ob Site

PtuHim'A- TlüJi

ML17 Ob Sit«

S'äJKM UAIMH FRi77 Baa« WM

mii üaa« WM

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äJsmuN £ UbüftKVlMU UMITATIÜM

The zapreaantetive observation sit« is located near tbe

center of the runway in a alight hollow. The building is con-

structed three fast off the ground auoh that a standing observer

has his aya level at about nine feat. Local terrain and con-

struction limits his field of view in several aeators and liaits

his visibility check points, läse Chart b)

I-Jsi-I

HORIZON VISIBILITY OBSTRUCTIONS FROM

SURFACE 03SERVATIÜN SITE

CHART 6 OBSERVING LIMITATIONS

SECTION A

SECTION B

SECTION C

SECTION D

SECTION E

SECTION F

SECTION G

TERMINAL FORECAST REFERENCE FILE

PART II

CLIMATOLOGY

REFERENCES

CLIMATIC BRIEF

THUNDERSTORMS

WINDS

FLYING WEATHER

EQUIVALENT CHILL

MEAN STATION PRESSURE

PAGE

1I-A-1

II-B-1

II-C-1

II-D-1

II-E-1

II-F-1

II-G-1

II-1

Tb« following ilat of refarencas ia pxovidad to indloata

«hat la iuadlately availabla in the my of oliaatio aida in tha

weather station. Moat of the inforaation la too bulky to repro-

duce in this papar and auaaariiation la not aaaningful. A brief

review of all Hated aids by each foreoaatar ia suggested fox

overall understanding of their content.

1. UlUUUAi. UJOl'm UbtfVJtt Location« Top shelf of forecasters cabinet Description« Hourly heating and cooling by celling, wind

direction, and wind spaed

2. WIMI) aTJUTlFlJO) PUUiilbTlNUti müJAiULm Location« fop shelf of forecasters cabinet Descriptioni Ceiling-visibility pereiatence probability

by month. Initial tiM, and wind direction

3. WIND fUt&lii'i.'diUU miBABlLm Locationt Top shelf of fozeoaatara cabinet Description« 3-6-12-24 hour persistence probability for

i'Ak1 tiaes by categorlea of wind apaad and diraction

4. CJükWU-VIäibiUn ÜAl'BBÜia FlUÄiüiiJICX Location« Top shelf of foraoaatara cabinet Description« Percent frequency of observed ceillng-viai-

bllity categoriaa by hour and wind direction

5. DBrüHiüKA'i'lüM Pil^ilü'i'KNCb PKUBAÜIUTY Location« Top shelf of forecasters cabinet Description« 1 through 24 hour probability of a lower

final category

6. UhäbT-DlJtüii'iuN TAoLbSi Location« Top ahelf of forecasters cabinet Description« Oeiling-vlsibility category duration by

month and onset time

7. OUU'UMH aUriUUt UK ttoWl^bUMDU OüüJ!iUVATlUlft> vocation« Top drawer of forecasters files Deeoription« contains winds aloft data, height sunmary,

temperature-hufflidity sumnary

ii-a-1

8. HttVISJä) UMirUHM bUMMIOtY Ulf UUMKAUit Wi^THÜb UttbJiKVATIüNb Location I Top drawer of foraoMtara fiiaa Deaoriptioni Contains frequency dato for weattier phenomena

including category dato for surface winds, ceil- ings and visibility

9. HüLiTÜD UjaUUU-VIälBlUTY UtibliKVAIlUNä Rlh OiYOTT, UACOÜt, AMD LITl'Lki tiüCk

Locationi Surface records storage cabinet Description! Me la tea above paianaters by month and hour

10. UWOTI mu>im uat^HVATio«!» Locationi üurface records storage cabinet Descriptiom statistics relating to pressure altitude, sta-

tion pressure, and sea level pressure by month and hour

11. UFfUTT ÜtUtUii DAYS Location« Surface records storage cabinet Description! Data based on 6S0F threshhold by nonth

12. JAMiAiQ W1KD CUXLL Location! Surface records storage cabinet Description! Category probability by hour

1 i» 24 MUUtt PiUCIPITATlUN AMOUHITS Location! Surface records storage cabinet Description! Frequency distributions for categories by

year and aonth

14« FKb^UjiNCY DibTHlJJUTlOJl UK P£*K UUSTS Location! üurface records storage cabinet Description! Deterained for specific categories by year and

month

15. DALLY MU-HIN TiMPÜHATÜtüi tmdJUUCUS Location! Surface records storage cabinet Description! Occurrence for max (Jun-Sep) and min (Deo-

Keb) by year

16. 12002 SNOW Dtm Location! üurface records storage cabinet Description! Occurrence by year and month

17« 24 UOUM SNOWFALL Location! Surface records storage cabinet Description! Occurrence by year and month

10. DAILY Mtt-MIM OF tmU'SUVt. nbMlDlTY Location! Surface records storage cabinet Description! Occurrence by year and month

ll-A-2

19. }WWM 1U^-fa Location i üurt'aoe records »tone» cabliMt Oascrlptlom Monthly ollMtologloal wind factors for ••iactcd

great drei« routes

2Ü. WLATEttt i&Ui>)UTUU> VUK FUi ÜUUDITIUMä Location! üurfacs records storeys cabinet Descriptioni Frequency at 18üOI< of tesperature, dew point,

tenperature-dew point spread, wind direction and wind speed

21. MUirfhU TAkfet OKF ANS ÜLIMB DATA Location» Under plexiglass at forecasters work table Descriptioni Provides monthly mean temperature, pressure

altitude, climb winds, climb deviation, and 3000 ft temperatures

22. t-HüBAdlLlTY üF GKIUBÜ-VlüLblUTK FüM ÜIVKN WakThiH UOUDXTIUNü Locationi Posted above forecasters work table Description i (iives probability of categories A-B for given

weather conditions

iI-A-5

i'h« following AMü Cliafttic Brief for offutt Ufa tea bean

•xtnioted fron AWSP 10^-4 Vol II for easy rafaxenca.

il-ü-1

WSCUMATIC BRIEFPr«aofd bv ETAC ( niy. l97ol

TEMPCRATURE^F)

FEBMARAPRMAYJUNJUL

II5II

72 P8 92 98"

[L05

i|iS|M ci

7k62 a74.! 53 82^

AUGL02

NOV 80

106 I 61

QFnJTT Ayp/C-AllA. MEBRitaKA PERIOD 1948-67

N fy? U Q

PRECIPITATION (in)

-20-16

-1517

”281

51

-11-13

1.2Z.2

1.61.8

3.12.5 l.ii 1

J.?! 4.3 4.81 4.94.J4.13.41.41.3

31.2

3.5

hIIx5

5^0If

iVsl 25

5.3 32 -4

18 1 18

1911

4

400

WIND (KT)

fiNWNUNWSSESS5

SSE

'sSE

'iwNVi‘

“nw

52 43 60 48 62

8 60'

MEAN

5!;:mHi

5880

80

6765615153

5<r

~5i5:

ha

Ui 0>

m> tt. jtt-

131.08 1700 .11 L750 .14 [1850.22 flilOO

58 4C

.35

.52

.62"

.58

•42.27.16Vu.25

jWBAN 4P 14949 -jwMO # 72554

ELEVATION: 1057 ftlSTN lTRS K0>"MEAN NUMBER OF DAYS

1650

1550"

1400

1400'

1^

1600

1750'

1750"

1700

^ ITEMPERATURECF)! S• 5 I ®

“ i I -d j

M I2 gi'7r

11

- I2 ; 1 10

i Ig /. 70 ‘ 8 ‘ 6

■ 0 jio ! 50-^9 t- 6

(- - !— 1 tw* MAXIMUM , MINIMUM 1> ! > 1 V

I

VI

i 90 80 32 ' 0 I! 0 0 ; 30, 6 T' o' 0 : 25 - 3"

g ■ 22ri“ '6

■ 3 6"0 1 t'iA 10 ' /!»' o'i ■ 20 ■ 0 0“i 'si

; n' 26 ■■ o’ 0“‘'5"8"' 9 24!' Oi O'

3rnT'#i O' -f-4I "At 0-

7'r'o‘ 51 ■; f 0* 'TrT28' 3~

30 981133:1318^ 181 18,18

(RECORDS UPDATED THRU' DEC 1970.HJSSUO PORj Hrly Oba: Jan 43 - Aug 67

Dally Oba: Jan 48 - Jun 65, Aug-Dec 65

NOTE; "-DATA NOT AVAILABLE. »LESS THAN O.S DAY. 0.5 OR 0.05 INCH, OR O.S PERCENT C43 AS APPLICAOLE.FLYING WEATHER (%FRE0) HOUF.S (LST) I JAN

CIOleaa than 3000 feat and/or

VSBIlaaa than

3 Bdlea

t- OD - 02 ' 2403-05 j >-6 06 - 08 2909 - 11

_18 ^_20._.,21.^23 _

tAU, HOURS

FEB

27-t-

MAR”23"

2731

APR”15'

1823

30. 24

f6-22:_'i3:

26 18

MAY

Ihs

-&10

_1014

JUN8

101215

JUL AUG

9! 912 1 12 1711 12! 17

1014

OCT NOV.DEC ANN EYR

'I 17 I 22 1511 : 17 ‘ 25 • 18 16 j 10' 26’ 21 161' 21; 27 21

-1

13_._9.^_i0 !'14, . 13_r 17 23; 1-367-11

4■'sT

1089

13 i U 17 IT4’'“21'

■ 23 ■

15131317

CIOleaa than 1500 feet and/or

VSBYleaa than

3 mllea

.18 [ 20 20 ; 22

00 - 02

1:114

■-S,i6j_i6 r:i6]

_9

5 4 5

?21-23 j 16 15, JL3.I _7

■» '

__3 _4

ALL HOURS : 17 ! IS' 161 10 : 7

-r-I

4

'7'’

I-'io^

67t

32

it-If-.,

10! L4'i2r-i7‘'

II ^-13; "19; '91' lA^'^lS

'27'7,

.Ihl8; 7

1C' 14'

-g—13' 'ic‘ '15

CIOless tha.T 1000 feot and/or VSBY

less than 2 mllaa

00 - 02 12 h 11!_ 9:

09-11 : 171 14'

-6t"

a2_-_i4._.,_i2. 11-Ol

-Si;„21._- 23_ p^l.ll]_.8j_

ALL HOURS ri3 I 12 I U-

2' 2

It-iBr-IF'ht-ir

4' 3'

4:1:4'4t

■M::F:.Ft

- 6t -9' 7I 10I

-ipir

#r -2i

65c'

ICIO

lass than 200 feet and/or VSBY

leas than ^ Bile

-t- 3'-1, - 3

--5;3

00 - 0203 - 05

Ji5_^J7_,FX-F i _21..^.ZL_._2!_ 2

2

if-

AU HOURS i

-it-11

tt-it

g

I0

■#

0 #1'If ■ //

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-f—O'

-{g

Ifi:o^-or"■Jr Jt

1:--t-FiF

!

TABLE 1 U-B-2 CLIMATIC BRIEF

TAF TIPS

Explanation of Data Tables

FLYING WEATHER

Frequency of occurrence of each of 5 categories is given. The sum of 5 category values for each month is 100, since observations which meet criteria of two categories are considered only in category with more-restricted limits. Values were computed from RUSSWO, Part D, and are compatible |

with values obtained from PP tables, though some differences occur because of different periods of record. ' i

Caused by: Relative importance of the1 3 components contributing to the "CIG a/o VSBY" values in categories D, C, B and A were computed froiji R.USSWO, Part D, tables. ' ' •

Peak Occur: Time of peak occurrence determined from PP tables and recorded as the center hour of 3 hour period (see LST & HRS'Code).;

i ' ■ i

Percy: Normal persistence was determined from PP tables by counting humber of consecutive hours LST (t HRS Code that initial category is the most likely or the equally likely category on each of the 8 monthly pages. Values were ordered and two values , at each end of distribution deleted. An "x" indicates there was no occurrence of category on at least 3 of 18 i , pages, i.e., x-x-x- l-l -3-5-6, appears as x-3. In this case. Max Percy is 6 (hrs) and time Max Percy is determined from page of PP table producing this 6 hour persistence.

i

VISIBILITY AND WEATHER CONDITIONS , —.^^^—^-——^—————^ ^—— ^

Caused by: Relative importance of weather factors contributing to conditions noted immediately above. Their sum may exceed 100, since parameters hiay occur simultaneously. ,

00-02 01 03-05 04 06-08 07 09-11 10 12-14 13 15-17 16 18-20 19 21-23 22 ■

- Dash indicates consecutive, equally likely periods.

/ A slant indicates non-consecutive, equally likely period». ,

x'Indicates no occurrence. ,

SURFACE WIND DATA

Prevailing Directiop: "total 4 kts and ovefr'

Prevailing direction was determined by inspection of column of Surface Wind pages of RÜSSWO. Part C;

ll-B-3

direction recorded is that of middle class of 3 ^acentf ^""»P"^"«

largest frequency of occurrence. Percent frequency of speed criterion is the sum for the 3 classes used in determination of prevailing direction.

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II-B-7

Th« following Tables and aasoolated graphs ars pxovidsd to ac-

quaint tbs foraoastar with pxafarrsd tines and Months of tbundaxston

ooeurrsnos and their duration. Two additional graphs are provided re-

lative to Tornado occurrence«

A quick review of the infornation will show that June is tbs pre-

ferred month for thunderstorm and tornado activity with the oaximm

per month and the longest duration. Additionally, it is evident that

the evening hours (19001. to OäOOL) show maxlaua activity.

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A...MUST B...MOST

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(AU TIMBS LOCAL)

MONTH

JAMUAKY

FUbüUAKY

MAHÜM

APhlL

MAY

JUNS

JULY

AUGUST

bEpraiBjäH

ÜCTÜBKH

NUVdHriiäi

5 JAN I955 24 JAM 1967 24 JAM I967

2a fsa 1951 19 FIS> 1954

18 MAH 1963

8 APK 1965

28 KAY 1962 22 MAY 1965

24 JUN 196}

K) JUL I956

22 AUS I934

2 ä£P I96I

20 ÜC'i" 1934

1 NOV 1964 13 i*>V 1964 1» MOV I965

02 05 1i2

03-05 12-14

11-14

OI-09

08-21 00-10

04-13

00-08

16-00

17-00

00-05

00-01 03-04 04-05 17-18 23-00

24 JA4 1967 2Hr8

28 Jf'Jää 1931 19 PüU 1954

28 APH I963 8 APH 1963

Jure 3Hr8

18 MAH 1963 4hX8

9Uz« 9Un

Dkcmmu. 26 vmu 1939 ie

28 MAY 1962 13Ura 22 MAY 1963 14Hr8

9 JUN 1967 14Hn

26 JUL 1967 lliMrs

22 AUO I934 9Un

2 SüP I96I 8UXB

20 UCT I934 3Un

11 MOV 1963 6UX8

26 Dl&i 1939 ihr

TAüLjä ö I'ÜM KÜUOWö II-C-18 PERIOD OF RECORD: 1951-1967

NEBRASKA

AVG NO OF TORNADOES

1916^1963

F M A M J J A S O N D

ChAHT 11 TumADü' ettoi n-ü-19

NEBRASKA

DIURNAL OCCURRENCE OF

TORNADOES 1916-1958

15

6 I? HOUR LST

ühAHT 12 DIUMMÄL TUKMASU

SECTION D WINDS

The following set of histograms depicts a freouency distri-

bution of wind "elocity and direction by month. Throughout the

year two maxima exist: NW being dominant from October through

April with 3R dominant for the remainder of the year. The NW winds

normally result from cold frontal passes and continue while the

ad-ancin? surface high remains north. Wind velocities are highest

in all categories during the winter and spring. SE winds occur in

the flow to tho rear of eastward moving highs and in developing

lows or ".he leF-side trough of the Rockies. June shows the highest

frequency of occurrence of winds from S-SE and also the highest

frenuency of occurrence of winds above 10 knots from these direc-

tions.

Il-D-1

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IX-D-9

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lN30H3d CHAKT 24 SiüC WIMDS

U-D-13

OFFUTTAFB, NE

00 10 20 PEAK WIND GUST in Knots

30 40

Nomogram relating average wind speed to peak wind gust in knots.

WG = Weighted mean gust, MG = Minimum gust, 99 = 99% of p eak wind gusts will be less than that indicated by the regression line.

WG = 1.2 (Mean Wind Speed) +10. 5

MG = (Mean Wind Speed) +7

99% of gusts will be less than: 1.2 (Mean Wind Speed) +21

Period of Record: 1 January 1952 through 30 April 1967

II-D-14

ÖMJTIUB üi flXIMIi WätXhläi

•Sb» aoeoBpaqying chart depict» tba orazMll flying wathax

obaarvad at üffutt AF£. 'fha oxdinata ia in paxeant fraquancy of

ocouxxanoa and tha abaoiaaa ia } hourly tiaa blooka by aonth. 'üha

araa enoloaad by tha uppar lina io ttw paroant of tiaa tha hourly

obaarvation ia lass than 1500 faat and/or } ailaa whila tbt iowar

lina rapraaanta 200 faat waä/or £ aila. far a nora datailad

auaaaxy rafar to fart S of tha Kaviaad bnifora Suaaaxy of Surfaoa

Weathar Obaarvationa for Uffutt AM.

XI-E-1

.

< tu

Ü Z

z <

ü H A u 1

2 5

F L 1t I U (J

A

During ttaa winter «Mson th* ooabiiMd «ffacts of wind mp—A

UA fzva air tmpaxatur« ramlt in an affaotiva senaibla ta^aim-

tura whieh ia conaidaimbly lowar tiian that racozdad on tha Uffutt

obaarvationa. Cartain pxotacUva aauuraa an takan by baa« agan-

Oiaa whan tha Squivalant Chili Tanpexatura exoeada oartain oritioal

valuaa. Xhraa cbarta axa providad to acquaint tha navly auaigaad

foraoaatar with tfaoaa parioda «ban baaa a«aaaiaa will ba intaraatad

in fiquivalant Chili laapazatux« and thay arai (1) Chart uaad to

obtain tha nuaarioal valua for liquivalant Chili Tanpaxaturat (2)

tha nonthly «varaga ooeuxranoa for balow -20°? and -40°?! and (3)

tha diurnal variation for thaaa two aalaetad valuaa during tha

«orat aonth of January.

1I-F-1

WIND SPEED

C»LM

3-6

7-10

11.15

It-I«

JO ■ 23

M-31

39-33

31-31

UPH

' "COOLING POWER OF W'ND EXPRESSED AS "EQUIVALENT CHILL TEMPERATURE"

TEMPERATURE (»F)

-10

EQUIVALENT CHIIL TEMPERATURE

WINDS ABOVE 40 HAVE LITTLE ADDITIONAL FfFECT.

UTTLE DANGER

.30

• IS

■60

-60

-65

INCREASING DANGER (plcsh may frcet« within 1 min.)

-75

-7!

-75

-80

-80

-85

•30

•50

-75

-TO

-05

-9<

-80

-5C

-95

-MC

-1C<

-BO

-95

-100

-105

-no

-75

-05

-95

-10?

-110

-U5

-115

-SO

-ICO

■no

-115

.120

-125

-co

.100 -105

-no

-120

-125

-130

-90 •55

-110

-IP

-135

-130 -140 -V.

GREAT DAliCER (Plesh may fraeis within 30 «oconda)

70

.120

•135

-140

-145

-150

DANGER OF FREEZING EXPOSED FLESH FOft PROPERLY CLOTHED PERSONS J INSTRUCTIONS

„»SURE LOCAL ,E«PE»TURE ->NP .,N0 SPEtO lf POSMBLE, IP NOT, ^ATE. ENTEB TABLE AT CLOSEST >'f'"\\*^\ZV* W ""' ^^R0Pf„ATE „NDSPEEOALONCLEPTSIOE. .NTERSECT.ON 0,VES APPROBATE EOU.V.LENT CH.LL TEMPERATE. THAT ,S. THE

TE«PEBATURE THAT «OULD CAUSE THE SAME RATE OF COOLINO UNDER CALM CONDITIONS.

NOTES

W|N0 , ,„,s TABLE «AS CONSTRUCTED USING M.LES PER HOUR (MPH). HO.EVER, A SCALE OlViNO THE EQUIVALENT RANOE IN

KNOTS HAS BEEN INCLUDED ON THE CHART TO FACILITATE ITS USE WITH EITHER UNIT.

2 mm MAY BE CAL« BUT FREEZING DANGER GREAT IF PERSON ,s EXPOSED IN MOVING VEH.CLE, UNDER HELICOPTER

ROTORS IN PROPEL1.0R BLAST. ETC. IT IS THE RATE OF RELATE AIR MOVEMENT THAT COUNTS AND THE COOLING

EFFECT IS THE SAME WHETHER YOU ARE MOVING THROUGH THE AIR OK IT IS BLOMNG PAST YOU,

J. EFFECT OF «IND .ILL BE LESS IF PERSON HAS EVEN SLIGHT PROTECTION FOR EXPOSED PARTS - IIGHT GLOVES ON

HANDS, PARKA HOOD SHIELDING FACE, ETC.

ACTIVITY DANGER IS LESS IF SUBJECT IS ACTIVE. A MAN PRODUCES ABOUT 100 «ATTS (341 BTU.l OF HEAT STANDING STILL BUT

UP TO 1000 »ATTS 1341) BTU.l IN VIGOROUS ACTIVITY LIKE CR0SS.rOUNTRY SKIING.

PROPER USE OF CLOTHING ond ADEQUATE DIET ore both imporlon"

COMMON SENSE THERE IS NO SUBSTITUTE FOR IT. THE TABLE SERVES ONLY AS A GUIDE TO THE COOLING EFFECT OF THE »INO ON

BARE FLESH .HEN THE PERSON IS FIRST EXPOSED. GENERAL BODY COOLING AND MANY OiHER FACTORS AFFECT THE

RISK OF FREEZING INJURY.

. Im» aJavlrJ !""•' til1 ll-l-l-ll

AWS HAY 68 TABLK 9 KktblVALisitT CHILL II-F-2

ATCH 1 lo AWSR 10S-»

MACS AFB, 111 et-MM

EQUIVALENT CHILL TEMPERATURE AVERAGE NUMBER OF OBS

LESS THAN -20 F AND -40 F

|ui O

u O i

at a. <

O o

mmmmmZ

S S §8 o

Sflo AinnoH JO »gswnN CUArfT 26 BHIIVALENT UHIU.

II-F-3

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II-F-4

MEAN STATION PRESSURE AND DEPARTURE FROM MEAN TABLES AND GRAPHS

The tables and graphs for mean station pressure and departure from the mean for Offutt AFB, NE, were compiled from hourly data from 1 January 1951 through 31 December 1958 and from three hourly date from 1 January 1959 through 30 April 1967.

To make all hours compatable, an average value was determined for each hour for the first period of data; then an average was determined for each three hourly for the entire period. An average of the difference between these two figures for three hourly data was used for linear inter- polation of the intermediate hourly values between the three hourly data.

Due to a different period of record than that used in the RUSSWO, the mean monthly pressure values in these tables in general are less. The largest difference is 0.02 in. Hg. for the month of February.

The mean station pressure curve, the previous 24-hour pressure curve and prognostic chart pressure values may be used to forecast pressure and altimeter values for the station.

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TAPT ITT

WKATHE"? RRC5IMRS

SECTION \ WTMTEP 1

«SETTIOK T> WING

-FTTTON n. s^l^^I!:', 1

SETTTON D FALL

TTT-A-1

iri-B-l

TTI-C-1

ITT-D-1

! I

TII-1

•"iVm"1'' A '.-ilHTF"

'oi.r ani \ITMC air ma?scs dominate over "ebras^a during

winter. Flylnf; weither deteriorates in low clouds, snow and fog

"s cyclonic sr.orms and cold frontal weather move through the area

normally alLernatlnp, with generally fair, cold hlßhn. Approxl-

iiitely 2^t of the winter L-e'lin^s and visibilities fall below

WOO > I with 12? below 1000 ', ?.

;old fronts move south or southe-ast with the cold air

bound.-irv whilf remaining nearly stationary from tbr; Nebraska

panhandle northwest into Idaho. The cold front usually brings

s narrow east-wor» band of clouds with stfoni» north or northwest

wire!:; An* eood /isibility except in occasional smwshowers.

Now syntfTis which bring the worst weather are of two types.

''h'i '.'irr;:, rievoloD? In the lee of the "ockios and moves south-

east, "be 'nrond, and often the more severe, develops and tracks

east 'v'vii Colorado. Fast raovinp stormr. and those which move

north of ncfutt normally do not cause very poor weather, while

slower moving system"- pa^sini» to the south can nroduce freezing

pree'r-itation and heavy ;snows as Gulf moisture bocoraes available.

■>« Pipure I.

The severity of both storms is hiphly dependent upon the

location and duration of the high pressure cell over the southeast

V\\ vrhioh advents moisture-laden air frnni the Tulf up the

virssouri, r'lver valley, ^he associated ly.^vr lovel trsuph con-

',-'J uter to tho storm's intensify wlioti it "d'^s" southwar-i and

III-V-l

mover! «lowly eartward over the surface low and, with moisture

present, develops a thick nimbastratus with heavy snowfalls just

east of the trough.

Occasionally, the N'ebraslca area will experience snow under

a contlnental high either from low l^vel stratocuimlus or from

vjosterly flow over-running the cold dome. In the latter, cloud

baser: are usually above 3000ft, Stratocumulus with bases of one

to three thousand feet often forms In the northwest flow behind

cold fronts when winds in excess of twenty knovr create sufficient

turbulent mixinij. The stratocuraulus also tends to form one to

three hours after sunriso and dissipate shortlv after sunset.

Most lilrely, heating or its cessation effects the stability of

the boundary layer and hence, mixing,

«Inter fogs are usually of a radiation tyno, forminR in the

early morning near sunrise, in the calm or llpht southeant flow

•jf a hiftfi which has Just moved eart of Offutt, Those foi»s, being

local in extent or confined to the river areas, normally last only

a few hours aftar sunrise. Less frequent, but morn widespread and

persistent fogp, develop when a stationary north-south oriented

front to thn west traps saturated southerly flou. After Initial

cooling on.i "oniatlon, the heavy fop and •U.ral.i-- may last for a

vjot'c -ir more ir.d usually requires the front to pass to the east,

of tho rtation to relieve the situation,

TTT-A-2

Moan Winter "y-loiV! tracks .affecting tho Offtitt ;.rea (after Bovrie and '..'eiKh tman)

l/clone; it. -as*-; 1 normally develop under an upper level short wave

moviiip! ^lontä t,h> jtatior. cf \rclir. front In the lee ■.'■' the ',t)c'<ies.

lycloKenesis in '.asr ? Umifüly ooourr undnr a strong raatward iioviriR trough.

Ft gum 1

IIT-4-3

HOl RtpR00 VJCIB^

In this transition period, the mean position of the polar

front begins to move northward yielding more frequently to the

tropical Gulf air. As the season progresses, maritime polar a3r

begins to cross the Rockies, replacing the drier continental air.

Cyclonic storms are still significant with flying weather Improv-

ing steadily. Sarly spring's visibilities and ceilings are as

poor as winter values decreasing to 6' and Itf below 1000 k 2 for

April and May respectively.

\s warmer Gulf air becomes available, rain and freezing pre-

cipitation increase and are often mixed with snow. The wanner air

also lowers stability values and thunderstorms increase from ono day

In March to four in April and oight in May. Thesfi storms, which

may be frontal or over-running, contribute to higher precipita-

tion totals for spring and summer.

For. is not widespread during this season ■.Ithough it may

Torrn in moist air that has had restricted heating the day before.

Tloar skies and licht gradients aid this fog situation and are

not uncommon. \ low stratus may form In light southerly now

whore cooling is not sufficient and winds are too strong for foe-

III-

fiETTTOM 0 ^JMMER

"ho summer months art: doinia'»ted by maritim«! tropical air from

l,hfl Oulf of MPXICO. This air is displaced two or three times a

month by maritime polar air which bar moved across the Itockies and

then eastward behind a weak cold front. At irregular intervals,

continental polar air pushes south into the are*, but as a rule,

fjuickTy retreats northwari.

The only prolonged perio'ls of U ( weather occur with lows

which form to the southwest nlong an east-west stationary polar

front. As the low moves into the Oklahoma, Kansas area, low stratus

ceilings, reduced visibilities in pre-warm frontal fog, and light

continuous precipitation will persist as the low moves from the pan-

har.dls to eastern Missouri.

Thunderstorms, reachinp a peak frequency of ten days per month In

June, brinp perhaps the most hazardous weather of any season. U-

mast ill thun<terstorm9 are frontal with air mar«! storms being rare.

Thunderstorm«: nauicd by over-runninr usually display little organi-

iMon mJ jfton develop over Inrpp. areas Tn l^iis than an hour,

la.-.tlnp for periods yf six hours or more. In ■ontrast, cold frontal

or squall linp stormr can usually be tracked by ra.-iar at a distance

a:: they lovelnp to th.1 we-it. They novmally nov» through the Offutt

vicinity in ono or tv."> hours. ?h9"o storms te.irt to Intensify just

ea.'t of ''fluti, where mols'urc vnlues increase in the southerly flow

fr^n hhe 'lulf.

NOT REPRODUCIBLE

MOTIOJ! D K/ar,

I'uiiner rrnopLic patterns continue over Hi?bras!ca during

"cptemhrsr .inH Uie 'aj-ly p-irt of October vlth .uirltime tropical

alt- truiRt's racking slowly southward, rtirin^ October, relatively

(i"7 a-id r-tnb'.o tnarltLne polar hißhn move Into "'obraska folloiri.nr

vieak troagh« with axc^llent flying woathrr continuing for sevrsral

days. Tlio first, siüniiicant incursions of continental polar air

occur In fJovombor wit1 frontal struct.nre«! boeomi-nc more defined

and assotiitii; ^OKS regularity of mo'/ctnent.

The -nain c-mse or unfivornble Hying wnatbor in the fall ir-

IDV; prosiTure pystr^s pissing to the nouth of th«> station. Oncurr-incea

of rain are most prevalent with rain changing 'o snow or rain and

snow nixed becoming predominant during the latter part of the season.

Another cause of poor flying weather is radiation fog, becoming

•nore frequent In October and November. Vt/pionl case of radiation fog

occurs as the return circulation around a high brings light southeast

winds up the ^tissouri 'Uver valley. Another case is a weakening mard-

tine front moving in from the northwest with a iubstantlal rain pattern

and either riding? aloft over Offutt or wafMng n\it In the local area. ^oth

situations are precedori by restrictive daylight nesting, increasing

dew points, and very light winds after sunset. Precipitation may or

mry not preeed.-1 the for* formation, but clearing at '.unset Is nornal

before fo«; rormition.

III-D-1

HOT RtPR00l

TERMINAL FORECAST REFERENCE FILE

PART IV

LOCAL AREA AND TERMINAL FORECAST STUDIES

PAGE

SECTION A FORECAST STUDIES . IV-A-1

D D O

Approved lor p!.u;;;c: rjl-jnao; Kstrlbulion Unlimited

IV-1

AN OBJECTIVE TECHNIQUE FOR

PREDICTING PRECIPITATION TYPE

AT OFFUTT AIR FORCE BASE

by

DAVID L. NELSON. Capt, USAF

JULY 1971

BASE WEATHER DIVISION

OFFUTT AFB, NEBRASKA

IV-A-1

I. Acknowledgement

The author wishes to gratefully acknowledge Lt Col Dale Rogers. Chief, Climatology Branch. Aerospace Sciences Division, 3d Weather Wing, for his continual support and encouragement in this project. He performed all of the data processing: pro­

viding the author with the completed product. Without his suggestions and programming support, this paper would not have been possible.

II. General

The forecasting of precipitation type at Offutt Air Force Base has been a long standing problem. Several forecast aids have been provided by scientific services personnel which re­

late probability of frozen/liquid forms of precipitation to various thickness/temperature values from soundings or prog charts. The two used previously at this station were Hilworth (1) and Wagner (2). Both studies were prepared for precipita­

tion type over a large geographical area and not specifically designed for this airfield. The acquisition of a RAOB history tape for (knaha, Nebraska offered a unique opportunity to make a detailed analysis on various parameters from a local sound­

ing and relate these values to precipitation type at Offutt.

111. Nuta

Two data sources were necessary to relate upper air and huifacc parameters. The RAOB tape for Omaha, Nebraska was used ior upper level thicknesses and temperatures and the sur­

face data tape for Offutt AFB was used for determining precipi­

tation type and surface temperature at RAOB release time, ilie Omaha PAOB station is seventeen miles north of the airfield and is considej-eJ reprc.'-entative of the air mass affecting Offutt. The period of Tecord used was October to April only from 1957 through ly^“.

IV, i. (jccdurcs

It ? ;t; ici la’i'.n ;r this study was the "perfect fore­

cast" assMPi I ! :n. I'-recipitation type near the sounding time was related to KAGB parameters. Specifically, OOZ and 12Z sound­

ings were available and surface observations within three hours of the Ri'OB time were used to categorize precipitation type.The types considered were: hail, snow, sleet, freezing precipi­

tation, rain, rain and snow mixed, and snow showers. Rain and snow mixed was also counted as a rain occurrence and a snow occuirence, and snow showers were also counted as a snow occur­

rence .

IV-A-2

Several schemes were tried relating various parameters in order to get the best discrimination in the data. Surface temp- erature and the 950MB temperature were both related to five thickness values (1000-500, 1000-700, 1000-850, 850-500, and 850-700MBs). Two other schemes were attempted relating 1000- SSOMB thickness to the 850-700MB thickness and the 900MB temp- erature versus the 85O-950MB temperature difference. Each scatter diagram was analyzed for data discrimination with the goal being to isolate the most cases with 98 percent reliability.

V. Results

The scatter diagram which produced the best shred was the 1000-700MB thickness versus surface temperature. To repeat, the best shred was defined to mean the scatter diagram which isolated the most number of cases with 98 percent reliability. The re- sults are shown in figure 1. Raw data figures are provided for information to assist the user in making value judgments on the reliability of each area. Due to the relatively small number of freezing precipitation occurrences, 98 percent reliability was not possible in this area. However, due to the operational significance of this area, the area was delineated such that it included the most occurrences of freezing precipitation possible without diluting the reliability. This area forecasts 50 percent of all freezing precipitation occurrences with 74 per- cent reliability. Again, the raw data figures will assist the user.

The investigator was now faced with the central area where data types overlapped and no one type of precipitation was clearly dominant. The data points which fell in this area were processed by all the remaiiing schemes which were used for the original data with few emouraging results. So few data points were isolated by any one scheme that further study was discon- tinued. Based on several years experience as a Chief Forecaster, it was also determined that the scheme would get more utiliza- tion it it was kept simple and easy to use. The overlap area was then analyzed by a most probable or best forecast scheme with the results shown in figure 2. As shown, a rain and snow mixed area was delineated as a "best forecast". This phenomena did not dominate the area, but 80 percent of the occurrences of ram and snow mixed did fall in this area and there is almost equal probability of rain or snow. As a reminder, the SO cases of wlxed "o ip'J ids-5 as a rain and a snow occurrence such that realisitc nambers are: snow 73, rain 112, and mixed SO. The fore- cast of mixed will then verify about 20 percent of the time, but in this investigator's opinion, it is the "most reasonable" forecast.

IV-A-3

PRECIPITATION TYPE AS A FUNCTION OF 1000-700MB THICKNESS AND SURFACE

TEMPERATURE

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IV-A-4

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H(;UKF. 2, JV-A-5'

The remaining area was delineated by a "best fo'f «* technique. Care must be taken in this area because of the high frequency of occurrence of all Phe"«ens:. R'* ?"aii| ures are provided to assist the user. Since the entire area is at or below freezing on the surface, occurrences of tain were included as freezing precipitation. Freezing P««i|Atm- tion versus rain will then be a function of t«»P«««" ^nd

(i.e. is the temperature going above or below *™zing with time?). This judgment can be made at the time of th« forecast. One will notice that the "best forecast" is not the "»ost pro- bable" in the case of freezing precipitation, freezing preci- pitation, however, has a much greater OP«^1»^ »i80"1"11" ?han snow, and even though this is a technical P»P«r' " ^ " be an "operational forecast aid". The two freezing P"«1?^- tion areas (figures 1 and 2) forecast 85 percent of all occur- rences of this hazardous phenomenon and is considered Justified because the forecaster will be correct almost 50 percent of the time. In the case of freezing precipitation, a high pre- figurance was deemed more important than post agreement.

VI Statistics

Using figures I and 2. the following table can be construct- ed using the dependent data in the study:

FORECAS1

S Z E R M T

s 1245 142 0 5 73 1465

z 21 162 0 2 3 188

OBSERVED E 9 24 0 3 7 43

R 2 5 0 979 112 1098

M 3 0 0 6 50 59

T 1280 333 0 995 245 2853

NOTE: For the above table, rain/snow mixed was deleted From rain and snow occurrences such that data are not reflected twice.

\s ran bo seen, this table produces an 85 percent correct forecast using the proposed scheme. The Skill Score which re- sults ls 0.77 explaining 59 percent of the variance. It must le remembered, however, that a high Skill Score was not the „nl, goal as was explained in the freezing precipitation an

figure 2. The goal was also to pre- as explained in the freeiing precipitation and

■:.:-7V >, . ; < I ,r<,a., in figure 2. The goal was also to p™ dict'hjruious weather und make the most reasonable opera- tional forecasl

IV-A-ft

VII Verification

This study was tested on an independent data sample from October 1968 through April 1969. The frequency of occurrence of precipitation types was similar to the dependent data sam- ple and the results should then be representative. The test rules were exactly the same as were for the original study. The following table depicts the results:

FORECAST S Z E R M T

s 133 21 0 2 20 176 z 2 33 0 0 0 35

OBSERVED E 1 4 0 1 1 7 R 2 1 0 136 24 163 M 2 0 0 1 6 9 T 140 59 0 140 53 392

Percent Correct = 308/392=78.6 Skill Score=(308-128)/(392-128)=0.68

These results may appear disappointing and they tempted this investigator to search for a "better" independent sample. There are, however, some encouraging facts in the table. First, the verification was lowered for two reasons: the relatively high occurrence of snow in the forecast freezing precipitation column and the high occurrence of rain or snow in the rain/snow mixed column. The first cause can be easily rationalized by noting that this study may overforecast freezing precipita- tion but it did forecast 94 percent of all freezing precipi- tation occurrences. If you'll recall, that was ray intention. The second cause can also be rationalized; 67 percenc of the mixed occurrences were correctly forecast and the frequency of occurrence of pure rain or pure snow is almost equal. The second interesting feature is the accuracy of pure rain/pure snow forecasts. A forecast of rain verified 97 percent and a forecast of snow verified 95 percent.

VIII Conclusion

The high percent of freezing precipitation observations which were correctly forecast and the high rain/snow forecast verification rate makes this study informative and useful. It should be incorporated into the forecast routine for the deter- mination of forecast precipitation type.

IX References

(J) Schafer, R.J., et al: "Further Studies in the Develop- ment of Short Range Weather Prediction Techniques", Scientific Report No. 1, Eastern Air Lines, Inc., Contract No. AP19(604)~ 2073, April 1958, pp.IKS-169.

IV-A-7

(2) Wagner, A. James: "Mean Temperature from 1000MB to SOOMB as a Predictor of Precipitation Type", AFCRC-TN-57-288. May 1957.

IV- A-8