SPC AC 211608
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1108 AM CDT FRI AUG 21 2009
VALID 211630Z - 221200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE MID ATLANTIC STATES
NEWD INTO NEW ENGLAND...
...NORTHEAST STATES...
LARGE UPPER LOW/TROUGH OVER THE GREAT LAKES/OH VALLEY REGION WILL
ROTATE NEWD ACROSS THE NERN STATES THIS AFTERNOON....WITH STRONG
SHORTWAVE TROUGH/SPEED MAX SHIFTING NEWD THROUGH WRN PA/NY INTO THE
EVENING HOURS. STORMS HAVE ALREADY DEVELOPED AHEAD OF THE UPPER
TROUGH ACROSS PORTIONS OF ERN PA/SRN NY...REFERENCE WW/S 726 AND
727...AND AS FORCING SPREADS ACROSS THE REGION...WIDESPREAD STRONG
TO SEVERE THUNDERSTORMS ARE ANTICIPATED.
THE VERY MOIST AIR MASS IN PLACE...DEWPOINTS 68 TO 75...COMBINED
WITH PW VALUES AROUND 2 INCHES AND ADDITIONAL HEATING SHOULD RESULT
IN MLCAPES TO RANGE FROM 3000 J/KG IN AREAS THAT RECEIVE STRONG
WARMING...TO 1500 J/KG WHERE CLOUDS ARE MORE PERSISTENT. A 50-60 KT
MID LEVEL SPEED MAX WILL RESULT IN SUFFICIENT SHEAR FOR SUPERCELLS
AND LINE SEGMENTS/BOW ECHOES THROUGHOUT THE AFTERNOON/EARLY EVENING
HOURS. UNIDIRECTIONAL SWLY WINDS THAT INCREASE WITH HEIGHT ABOVE THE
BOUNDARY LAYER WILL BE MOSTLY FAVORABLE FOR DAMAGING WINDS.
HOWEVER...THE PRESENCE OF A VERY MOIST BOUNDARY LAYER AND VEERING
WINDS WITHIN THE BOUNDARY LAYER MAY SUPPORT A TORNADO OR TWO.
...CENTRAL/ERN TX ENEWD INTO THE CAROLINAS...
STRONG TO OCCASIONALLY SEVERE ELEVATED STORMS WERE ONGOING ACROSS
PORTIONS OF NRN TX THIS MORNING WITHIN AREA OF MODERATE INSTABILITY
AND EFFECTIVE SHEAR AROUND 30 KT. THESE STORMS SHOULD DIMINISH AS
WEAK MID LEVEL WARM ADVECTION SUBSIDES. HOWEVER...DESPITE WEAK
DYNAMICAL FORCING...CONVERGENCE ALONG OUTFLOW BOUNDARIES/EDGE OF
THICKER CLOUDS AND WHERE STRONGER HEATING/DESTABILIZATION
OCCURS...WILL FAVOR SCATTERED STRONG STORMS DURING THE
AFTERNOON/EVENING HOURS. SINCE THE SHEAR WILL NOT BE PARTICULARLY
STRONG AND THE THREAT FOR SEVERE STORMS APPEARS LOCALIZED...ONLY LOW
SEVERE PROBABILITIES ARE FORECAST.
...NRN CONTINENTAL DIVIDE AREA...
SOUTHERN TAIL OF UPPER TROUGH IN BC WILL MOVE EWD ACROSS THE NRN
ROCKIES LATER TODAY. CONVECTION HAS OCCURRED IN FAR NWRN MT THIS
MORNING IN ASSOCIATION WITH A SHORTWAVE TROUGH LIFTING NEWD INTO
ALBERTA. MORE STORMS SHOULD DEVELOP LATER TODAY AS LARGE SCALE
FORCING SPREADS IN FROM THE WEST. DEEP LAYER SHEAR AT 30 TO 40
KT...MUCAPES NEAR 2000 J/KG AND STEEP LOW-MID LEVEL LAPSE RATES
SHOULD SUPPORT A FEW STORMS WITH STRONG AND GUSTY WINDS.
..IMY/GARNER.. 08/21/2009
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 2000Z
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