Severe Thunderstorm Watch 21

Issued

Feb 11, 2009, 8:19 PM EST (01:19 UTC)

Expired

Feb 11, 2009, 10:53 PM EST

In force

3 hr

Issued by

the Storm Prediction Center

Largest hail expected

0.5 in

Strongest gust expected

70 kt

The Sterling radar (KLWX), 76 km from the middle of the area, began a volume at 01:22 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

Two or more tornadoes

5%

One or more EF2 to EF5 tornadoes

5%

Ten or more severe wind reports

95%

One or more gusts of 65 knots or more

50%

Ten or more severe hail reports

5%

One or more hailstones of 2 inches or more

5%

Six or more combined severe hail and wind reports

95%

• Mesoscale Discussion 104Feb 11, 5:32 PM EST
• Mesoscale Discussion 106Feb 11, 8:00 PM EST
• Mesoscale Discussion 107Feb 11, 10:14 PM EST

672 
WWUS20 KWNS 120121
SEL1  
SPC WW 120121
DCZ000-MDZ000-NYZ000-PAZ000-VAZ000-WVZ000-CWZ000-120600-

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 21
NWS STORM PREDICTION CENTER NORMAN OK
820 PM EST WED FEB 11 2009

THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF 

       DISTRICT OF COLUMBIA
       MARYLAND
       SOUTHWEST NEW YORK
       CENTRAL PENNSYLVANIA
       NORTHERN AND CENTRAL VIRGINIA
       FAR EASTERN PANHANDLE OF WEST VIRGINIA
       COASTAL WATERS

EFFECTIVE THIS WEDNESDAY NIGHT AND THURSDAY MORNING FROM 820 PM
UNTIL 100 AM EST.

HAIL TO 0.5 INCH IN DIAMETER...THUNDERSTORM WIND GUSTS TO 80
MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 70
STATUTE MILES EAST AND WEST OF A LINE FROM 15 MILES EAST OF
RICHMOND VIRGINIA TO 60 MILES NORTHEAST OF JAMESTOWN NEW YORK. 
FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH
OUTLINE UPDATE (WOUS64 KWNS WOU1).

REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
DO PRODUCE TORNADOES.

OTHER WATCH INFORMATION...CONTINUE...WW 18...WW 19...WW 20...

DISCUSSION...LEADING EDGE OF INTENSE VERTICAL MOTION ALONG FAST
MOVING COLD FRONT/SQUALL LINE CONTINUES TO PRODUCE SEVERE WINDS WITH
MEASURED GUSTS IN EXCESS OF 50 KT OVER MUCH OF THE CENTRAL
APPALACHIANS.  AS MAIN UPPER SYSTEM AND ASSOCIATED JET MAXIMA ROTATE
ENEWD...EXPECT THREAT OF DAMAGING WINDS WILL BE MAINTAINED ALONG
NARROW LINE OF MOIST CONVECTION WITH OR WITHOUT OCCASIONAL LIGHTNING
STRIKES.  WIND DAMAGE THREAT MAY BE WIDESPREAD WITH THE MORE INTENSE
LINE SEGMENTS.

AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 0.5 INCH. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 70
KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 350. MEAN STORM
MOTION VECTOR 26050.


...EVANS

Severe Thunderstorm Watches in Virginia, 2009Severe Thunderstorm Watches in Pennsylvania, 2009Severe Thunderstorm Watches in Maryland, 2009Every severe thunderstorm watch in 2009

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.