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URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 227
NWS STORM PREDICTION CENTER NORMAN OK
125 PM EDT THU MAY 27 2010
THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF
DISTRICT OF COLUMBIA
NORTHERN DELAWARE
CENTRAL AND EASTERN MARYLAND
MOST OF NEW JERSEY
SOUTH CENTRAL AND SOUTHEAST NEW YORK
CENTRAL AND EASTERN PENNSYLVANIA
NORTHERN VIRGINIA
THE EASTERN PANHANDLE OF WEST VIRGINIA
COASTAL WATERS
EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 125 PM UNTIL
900 PM EDT.
HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70
MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.
THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 65
STATUTE MILES EAST AND WEST OF A LINE FROM 65 MILES NORTHEAST OF
BINGHAMTON NEW YORK TO 40 MILES WEST OF PATUXENT RIVER MARYLAND.
FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH
OUTLINE UPDATE (WOUS64 KWNS WOU7).
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.
DISCUSSION...THUNDERSTORM DEVELOPMENT IS EXPECTED IN THE NEXT 1-2
HOURS ALONG A SLOW-MOVING SURFACE FRONT FROM ERN NY SWD TO NEAR THE
NJ/PA BORDER. THE BOUNDARY LAYER CONTINUES TO WARM TO THE W OF THE
FRONT...WITH MODERATE INSTABILITY NOW PRESENT WITH WEAKENING
CONVECTIVE INHIBITION. ADDITIONALLY...A WEAK MIDLEVEL VORTICITY
CENTER IS MOVING SSEWD FROM ONTARIO TOWARD CENTRAL NY...AND THIS
FEATURE MAY ALSO AID IN CONDITIONING THE ENVIRONMENT TO SUPPORT
THUNDERSTORM DEVELOPMENT. STEEP LAPSE RATE PROFILES AND
MODERATE-STRONG INSTABILITY THIS AFTERNOON...AS WELL AS 25-40 KT
NNWLY MIDLEVEL FLOW...WILL FAVOR SWD MOVING MULTICELL CLUSTERS
CAPABLE OF PRODUCING DAMAGING WINDS AND LARGE HAIL. SOME EMBEDDED
SUPERCELL STRUCTURES MAY OCCUR ALONG THE FRONT WHERE VERTICAL SHEAR
WILL BE SOMEWHAT STRONGER...AND THIS MAY LOCALLY ENHANCE THE
POTENTIAL FOR LARGE HAIL.
AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60
KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM
MOTION VECTOR 36025.
...THOMPSON
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TornadoesProbability of 2 or more tornadoes
Low (10%)
Probability of 1 or more strong (F2-F5) tornadoes
Low (5%)
WindProbability of 10 or more severe wind events
Mod (60%)
Probability of 1 or more wind events > 65 knots
Mod (30%)
HailProbability of 10 or more severe hail events
Mod (50%)
Probability of 1 or more hailstones > 2 inches
Mod (30%)
Combined Severe Hail/WindProbability of 6 or more combined severe hail/wind events
High (90%)