5 March 2003National Weather Service State College PA Mid-Atlantic Severe Weather Climatological Aspects by Kevin S. Lipton Richard H. Grumm and John LaCorte

5 March 2003 National Weather Service State College PA

Mid-Atlantic Severe WeatherClimatological Aspects

byKevin S. Lipton

Richard H. Grummand

John LaCorte


Introduction

• Creating a Severe Weather Database

• Climatic Issues– Location, type, and – Time if severe weather events– Local Pennsylvania problems/considerations

• Improving the forecasting of severe weather events

• An example


Methods and Data

• NCDC Storm Data– Has some use issues– Tornado gets counted by every county it impacts– Inflates some numbers

• SPC Severe Plot Data– Lowers tornado probabilities– A cleaner data set– Loaded into mySQL and MS-Access

• NCEP-NCDC Reanalysis Data– Plot anomalies and show how case looked– Apply to model forecasts for forecasting (GrADS)


Creating a Severe Weather Database

• Prototype with Storm data to get top 20 events in eastern US– Case examples to follow

• Severe Plot used for a parallel study– Timing of events– Location of events– Seasonality of events

• The Severe Plot data was found to be more reliable


Climatic Issues

• Pennsylvania problems/considerations– Terrain may enhance bow echo climatology

• Focus on Pennsylvania Severe Weather– Location,– type (Severe and tornadic)– Seasonality– Diurnal trends


Enhanced Bow echoesterrain influence


13 August 1999 Tuscarora valley SLBE

SRM saw this bow before REF


SeasonalitySummary of Severe Events by Season

127

2042

5142

1019

0

1000

2000

3000

4000

5000

6000

Winter Spring Summer Fall

# o

f E

ven

ts


Monthly Occurrences

Sumary of All Severe Events by Month

0

500

1000

1500

2000

2500

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

# o

f E

ven

ts


Diurnal Trend in PennsylvaniaStatistical Analysis of Severe Weather Occurrance Times

15:00

16:05

15:44

16:05

15:00

15:44

14:24 14:38 14:52 15:07 15:21 15:36 15:50 16:04 16:19

Median of the Times

Mode of the Times

Average of the Times

Times (Local)

Severe Weather Excluding Tornadoes

Severe Weather Including Tornadoes


Number of Events (Thunderstorm Wind/Hail) by Hour

101

55 4531 32 21 21 28

49

96

142

190

420

668

936

1020 1013

916

712

520

347

197

117

73

0

200

400

600

800

1000

1200

MID

NIG

HT

to

1A

M

1A

M t

o 2

AM

2A

M t

o 3

AM

3A

M t

o 4

AM

4A

M t

o 5

AM

5A

M t

o 6

AM

6A

M t

o 7

AM

7A

M t

o 8

AM

8A

M t

o 9

AM

9A

M t

o 1

0A

M

10

AM

to

11

AM

11

AM

to

12

PM

12

PM

to

1P

M

1P

M t

o 2

PM

2P

M t

o 3

PM

3P

M t

o 4

PM

4P

M t

o 5

PM

5P

M t

o 6

PM

6P

M t

o 7

PM

7P

M t

o 8

PM

8P

M t

o 9

PM

9P

M t

o 1

0P

M

10

PM

to

11

PM

11

PM

to

12

AM

Nu

mb

er

of

Se

ve

re

68% of all Severe Weather occurs between 1PM and 7PM

50% occurs between 2PM and 6PM


Big Events

341

182

129

98

66

53

33

21

0 50 100 150 200 250 300 350 400

> 5 Reports

> 10 Reports

> 15 Reports

> 20 Reports

> 25 Reports

> 30 Reports

> 40 Reports

> 50 Reports

Number of Days

# of events in each category


Data Normalized For Number of Occurrences

0.000

0.200

0.400

0.600

0.800

1.000

1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 69 73 77 81 85 89 93 97 101 105 109 113 117

Number of Reports in an Event

Pe

rce

nt

of

the

Tim

e T

ha

t a

Giv

en

Nu

mb

er

of

Re

po

rts

Oc

cu

rre

d

Example: Only 5% of the events had 25 or more reports of severe weather

Example: Approximately 61% of all events were comprised of 2 or more reports of severe weather

Example: Less than 2% of all events had 50 or more reports of severe weather

Severe Thunderstorms including Tornadoes

1370 Seperate Events


Climatic Examples

• Test Climatic Anomalies– Top severe events– Compare to severe weather occurrences

• Wind Anomalies– Appear to have some forecast potential– Relate to helicity

• Precipitable water• Shear climatology

– This was only recently developed (Sep 2002)– Has many potential forecast Applications– Relates to helicity


Events with most reportsEastern US

• 1/21/1999-1/22/1999: 129 Tornadoes, 14 other severe; MS, LA, AR• 11/21/1992-11/23/1992: 84 Tornadoes, unknown severe; GA, AL, MS, LA• 11/23/2001-11/24/2001: 76 Tornadoes, 31 Severe; AL, MS, LA, AR• 5/31/1985: 60 Tornadoes, 30 Severe; OH, NY, PA• 4/16/1998: 48 Tornadoes, 72 Severe; TN, KY, AR, AL• 5/30/1998-5/31/1998: 43 Tornadoes, 300 Severe; NH, MA, NJ, NY, PA, VT,

MI, MN• 11/15/1989-11/16/1989: 32 Tornadoes, 3 Severe; NY, NJ, PA, GA, AL• 7/12/1992: 30 Tornadoes, Unknown Severe; OH• 4/14/1999 - 4/15/1999: 25 Tornadoes, 30 Severe; NC, SC, GA, AL, MS• 5/18/2002: 22 Tornadoes, 80 Severe; IL• 5/15/1998: 21 Tornadoes, 184 Severe; IA, MN• 7/19/1996: 20 Tornadoes, Unknown Severe; MD, PA• 4/28/2002: 22 Tornadoes, 137 Severe; KY, TN, MD• 5/16/1999: 14 Tornadoes, 104 Severe; IA• 5/10/2001: 13 Tornadoes, 104 Severe; IA• 4/20/2000: 13 Tornadoes, 101 Severe; IL, KY, TN


Shear Values 10m to Value

850 hPaAverage Shear

0.0135

700 hPaAverage Shear

0.009

850 hPa Average Positive-Anomaly

+2.16

850 hPa AveragePositive-Anomaly

+1.71


Strong Shear EventsEvent Date 10m-850

hPa10m-700 hPa

31 May 1985 +4.5 +3.2

12 July 1999 -- +2.9

20 April 2000 +3.5 +2.3

28 April 2002 +3.5 +2.0

31 May 1998 +3.6 --


Integrating Data setsGrADS-reanalysis-Severe plot (SPC)


Shear ExamplesEastern US tornado Outbreak May 1985


Shear ExamplesPA-NY tornado Outbreak May 1998


Forecast Applications

• Use of ensembles• Climatic anomalies• Shear climatology verse model

forecasts• To anticipate a potentially large severe

weather outbreak• Example: 10-11 November 2002

– Large shear anomalies– High CAPE for November– Largest severe weather outbreak of 2002


The two big events of 2002

• 28 April Eastern US Severe outbreak– LaPlata Tornado

• 10-11 November 2002 Severe outbreak– F2 in Pennsylvania…rare in November


28 April 2002severe reports

Figure 1. Storm Prediction Center (SPC) plots of severe weather over the eastern United States on a) 27 April and b) 28 April 2002.


Strong Shear Case LaPlata Tornado 28 April 2002


28 April 2002anomalous low and southwest winds

Figure 2 Eta forecast initialized at 0000 UTC 28 April valid at 2100 UTC 28 April 2002. Upper panel shows 700 hPa heights (m) and anomalies (Standard deviations from normal) and lower panel MSLP (hPa).

Figure 3. As in Figure 2 except forecasts of 850 hPa winds (U and V) and departures from normal.


28 April 2002SREF CAPE

Probabilities and spaghetti

Figure 5 NCEP SREF forecasts of CAPE (Jkg-1). Upper panel shows spaghetti plots and dispersion about the mean. Eta members are black and RSM members are red. Lower panel shows the probability of the CAPE greater than or equal to 1200 Jkg-1 and the position of the consensus 1200 and 2400 contours.


28 April 2002SREF CAPE

Probabilities and spaghetti

Figure 6. As in Figure 5 except valid at 2100 UTC.


LaPlataSupercell

complete with hook and TV

Figure 13. Reflectivity and SRM data from KLWX radar around 2357 UTC 28 April 2002.


Columbia County

Tornado cSplit in line depicts

the F1 tornado location

Figure 12. As in Fig 11 except at 2202 UTC.


Lebanon County

Tornado cOh no..its a tornado near RT-22 in Ono!

Figure 1. Reflectivity and SRM valid at 2207 UTC showing the structure of the thunderstorm which produced a tornado in Lebanon County. The A denotes initial thunderstorm and the arrows refer to points noted in the text.

A


10-11 November 2002 Severe outbreak

• Big in Mississippi Valley and east• Strong southerly low-level flow• High CAPE for November

– Not uncommon as some big November events like 4 November 1950

• Strong shear• Rare strong tornado in western

Pennsylvania in November


Figure Storm Prediction center storm reports. Color coded by type. Upper panel is 10 November and lower panel is 11 November 2002


Shear Forecasts with AnomaliesEta Model

Figure . Eta shear forecasts initialzed at 1200 UTC 10 November valid from left to right a) 2100 and b) 0000 UTC 10 November and c) 0300 UTC 11 November 2002. Upper panels show the shear and anomalies from the surface to 850 hPa lower panels show the shear anomalies from the surface to 700 hPa. Eta surface based CAPE is plotted on the upper panels and layer CAPE on lower panels.


Conclusions

• Built a regional Severe Weather Database

• Addressed many Climatic Issues– Location, type, and – Time if severe weather events– Local Pennsylvania problems/considerations

• Climatic Anomalies show great forecast potential when applied to model and ensemble forecasts

• New tools to integrate Data sets

Documents

5 March 2003National Weather Service State College PA Mid-Atlantic Severe Weather Climatological Aspects by Kevin S. Lipton Richard H. Grumm and John LaCorte