SPC AC 211233
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0733 AM CDT FRI AUG 21 2009
VALID 211300Z - 221200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS MUCH OF THE NORTHEASTERN
UNITED STATES...
...NORTHEAST STATES...
A LARGE UPPER TROUGH WILL CONTINUE TO ROTATE EASTWARD ACROSS THE
GREAT LAKES AND OHIO VALLEY TODAY...WITH THE MAIN SURFACE COLD FRONT
MOVING ACROSS THE APPALACHIANS INTO THE NORTHEAST STATES. AHEAD OF
THE FRONT...VERY MOIST AIR IS IN PLACE WITH DEWPOINTS IN THE 70S AND
MORNING RAOBS SHOWING PW VALUES WELL ABOVE 2 INCHES. EARLY VISIBLE
SATELLITE IMAGERY SUGGESTS THAT WIDESPREAD CLOUDS WILL LIMIT HEATING
AND DESTABILIZATION IN MOST AREAS. HOWEVER...SUFFICIENTLY STEEP MID
LEVEL LAPSE RATES WILL RESULT IN MODERATE AFTERNOON INSTABILITY AND
POSE A RISK OF SCATTERED THUNDERSTORMS OVER A LARGE AREA OF NEW
ENGLAND/NY/PA AND ADJACENT REGIONS.
SHOWERS AND THUNDERSTORMS ARE ONGOING THIS MORNING AHEAD OF THE
FRONT FROM NY INTO EASTERN KY. THIS ACTIVITY WILL PROGRESS EASTWARD
THROUGH THE DAY AND WILL LIKELY INTENSIFY...POSING A RISK OF
ISOLATED SEVERE WEATHER BY EARLY AFTERNOON FROM EASTERN NY/PA INTO
WESTERN NEW ENGLAND. OTHER BANDS OF STRONG CONVECTION ARE LIKELY TO
DEVELOP THROUGH THE AFTERNOON IN REGIONS WHERE HEATING CAN OCCUR.
FORECAST SOUNDINGS SHOW SUFFICIENT EFFECTIVE SHEAR FOR ORGANIZED
UPDRAFTS AND SUPERCELLS...ALONG WITH BOW/LEWP STRUCTURES IN LARGER
CONVECTIVE CLUSTERS. DAMAGING WINDS APPEAR TO BE THE MAIN THREAT
DUE TO WATER LOADING AND DOWNWARD TRANSFER OF MOMENTUM. HOWEVER...
VERY MOIST LOW LEVELS AND SUFFICIENT LOW LEVEL SHEAR MAY ALSO POSE A
RISK FOR ISOLATED TORNADOES.
...ELSEWHERE...
SCATTERED THUNDERSTORMS ARE EXPECTED AHEAD OF THE TRAILING BOUNDARY
ACROSS THE TN VALLEY AND GULF COAST STATES. A FEW OF THESE STORMS
MAY PRODUCE LOCALLY GUSTY/DAMAGING WINDS...BUT ORGANIZED SEVERE
WEATHER IS NOT ANTICIPATED. A FEW STRONG STORMS CAPABLE OF DAMAGING
WINDS WILL ALSO BE POSSIBLE THIS EVENING OVER SOUTHERN AZ AS
EASTERLY MID LEVEL WINDS INCREASE THE THREAT OF THUNDERSTORM
ACTIVITY AFFECTING THE LOWER DESERTS.
..HART/GRAMS.. 08/21/2009
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z
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