Monday, July 25, 2011
THE NATIONAL WEATHER SERVICE IN WAKEFIELD HAS ISSUED A * TORNADO WARNING FOR... SOUTHEASTERN CITY OF NEWPORT NEWS IN VIRGINIA... NORTHWESTERN CITY OF NORFOLK IN SOUTHEAST VIRGINIA... NORTHWESTERN CITY OF PORTSMOUTH IN SOUTHEAST VIRGINIA... * UNTIL 900 PM EDT * AT 821 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A SEVERE THUNDERSTORM CAPABLE OF PRODUCING A TORNADO. THIS DANGEROUS STORM WAS LOCATED 5 MILES WEST OF NORFOLK NAVAL AIR STATION...AND MOVING EAST AT 15 MPH. * THIS DANGEROUS STORM WILL BE NEAR... NORFOLK NAVAL AIR STATION AND WILLOUGHBY SPIT AROUND 840 PM EDT. WARDS CORNER AND OCEAN VIEW AROUND 850 PM EDT. PRECAUTIONARY/PREPAREDNESS ACTIONS... TAKE COVER NOW. MOVE TO AN INTERIOR ROOM ON THE LOWEST FLOOR OF A STURDY BUILDING. AVOID WINDOWS. IF IN A MOBILE HOME...A VEHICLE... OR OUTDOORS...MOVE TO THE CLOSEST SUBSTANTIAL SHELTER AND PROTECT YOURSELF FROM FLYING DEBRIS. HEAVY RAINFALL MAY OBSCURE THIS TORNADO. DO NOT WAIT TO SEE OR HEAR THE TORNADO. TAKE COVER NOW. TORNADOES ARE DIFFICULT TO SEE AND CONFIRM AT NIGHT. TAKE COVER NOW.
AREAS FROM NERN OH ACROSS WRN NY AND NY SRN TIER TO THE MOHAWK VALLEY...AS WELL AS NWRN PA...WILL BE INCLUDED IN A SLGT RISK AREA WITH THE ISSUANCE OF THE NEXT SPC DAY 1 OTLK BY 1630 UTC/1230 EDT. FURTHERMORE...A WATCH MAY BE NEEDED ACROSS SOME OF THIS AREA BEFORE NOON EDT. VSBL SATL IMAGERY DEPICTS AN AXIS OF RELATIVELY CLEAR SKIES FROM OH ENEWD ACROSS THE SRN TIER OF NY. EXPECT THAT SURFACE HEATING ACROSS THIS CORRIDOR...ALONG WITH INCREASINGLY FAVORABLE LARGE SCALE ASCENT ASSOCIATED WITH AN APPROACHING UPPER TROUGH...WILL SUPPORT THE CONTINUED DEVELOPMENT OF SEVERE TSTMS INTO THE AFTERNOON. COINCIDENT WITH THE INCREASE IN INSTABILITY WITHIN THE VERY MOIST AND WARMING AIRMASS...DEEP LAYER SHEAR WILL BECOME INCREASINGLY STRONG AS 40-50KT MID-LEVEL SPEED MAX SPREADS EAST FROM THE UPPER GREAT LAKES. THIS WILL PROMOTE LONGER-LIVED/ORGANIZED UPDRAFTS LIKELY TAKING THE FORM OF LINE/BOWING SEGMENTS CAPABLE OF PRODUCING DAMAGING WINDS AS WELL AS SOME HAIL. IF LATEST TRENDS WITH THE BROKEN PRE-FRONTAL LINE OF STORMS NOW MOVING INTO WRN NY CONTINUE...A SVR TSTM WATCH WILL ALSO BE COORDINATED SHORTLY FOR PARTS OF THE REGION.
Discussion... Observation of 11z HRRR short-range model indicates a strong bowing severe thunderstorm cluster will develop on the eastern fringes of Wyoming and move into South Dakota. Originally in Wyoming, the storms will start out possibly supercellular before congealing into the bowing line. That said, there will be a more elevated threat of tornadoes in NE Wyoming, then a skyrocketing high wind threat into South Dakota.
11z HRRR doesn't indicate any severe weather for Montana, but does introduce moderate showers and thunderstorms in ragged clusters. Unfortunately, 12z RR and 13z RUC are both updating at this time, so we cannot get their inputs.
In summary, South Dakota has a good threat for severe weather for today.