5 March 2003 National Weather Service State College PA
Mid-Atlantic Severe WeatherClimatological Aspects
byKevin S. Lipton
Richard H. Grummand
John LaCorte
5 March 2003 National Weather Service State College PA
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
5 March 2003 National Weather Service State College PA
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)
5 March 2003 National Weather Service State College PA
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
5 March 2003 National Weather Service State College PA
Climatic Issues
• Pennsylvania problems/considerations– Terrain may enhance bow echo climatology
• Focus on Pennsylvania Severe Weather– Location,– type (Severe and tornadic)– Seasonality– Diurnal trends
5 March 2003 National Weather Service State College PA
Enhanced Bow echoesterrain influence
5 March 2003 National Weather Service State College PA
13 August 1999 Tuscarora valley SLBE
SRM saw this bow before REF
5 March 2003 National Weather Service State College PA
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
5 March 2003 National Weather Service State College PA
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
5 March 2003 National Weather Service State College PA
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
5 March 2003 National Weather Service State College PA
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
5 March 2003 National Weather Service State College PA
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
5 March 2003 National Weather Service State College PA
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
5 March 2003 National Weather Service State College PA
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
5 March 2003 National Weather Service State College PA
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
5 March 2003 National Weather Service State College PA
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
5 March 2003 National Weather Service State College PA
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 --
5 March 2003 National Weather Service State College PA
Integrating Data setsGrADS-reanalysis-Severe plot (SPC)
5 March 2003 National Weather Service State College PA
Shear ExamplesEastern US tornado Outbreak May 1985
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Shear ExamplesPA-NY tornado Outbreak May 1998
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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
5 March 2003 National Weather Service State College PA
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
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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.
5 March 2003 National Weather Service State College PA
Strong Shear Case LaPlata Tornado 28 April 2002
5 March 2003 National Weather Service State College PA
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.
5 March 2003 National Weather Service State College PA
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.
5 March 2003 National Weather Service State College PA
28 April 2002SREF CAPE
Probabilities and spaghetti
Figure 6. As in Figure 5 except valid at 2100 UTC.
5 March 2003 National Weather Service State College PA
LaPlataSupercell
complete with hook and TV
Figure 13. Reflectivity and SRM data from KLWX radar around 2357 UTC 28 April 2002.
5 March 2003 National Weather Service State College PA
Columbia County
Tornado cSplit in line depicts
the F1 tornado location
Figure 12. As in Fig 11 except at 2202 UTC.
5 March 2003 National Weather Service State College PA
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
5 March 2003 National Weather Service State College PA
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
5 March 2003 National Weather Service State College PA
Figure Storm Prediction center storm reports. Color coded by type. Upper panel is 10 November and lower panel is 11 November 2002
5 March 2003 National Weather Service State College PA
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.
5 March 2003 National Weather Service State College PA
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