SWODY1
SPC AC 151240
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0740 AM CDT THU SEP 15 2011
VALID 151300Z - 161200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
A PRONOUNCED MIDLEVEL SHORTWAVE TROUGH OVER THE GREAT LAKES WILL
ROTATE EWD OVER NEW ENGLAND THROUGH TONIGHT...WHILE AN ASSOCIATED
SURFACE COLD FRONT MOVES SEWD OFF THE SE NEW ENGLAND AND MID
ATLANTIC COASTS LATER THIS AFTERNOON/EVENING. THE COLD FRONT WILL
ALSO CONTINUE SWD TO THE SE ATLANTIC AND GULF COASTS BY THE END OF
THE PERIOD. FARTHER W...THE PERSISTENT UPPER TROUGH OVER AZ WILL
CONTINUE TO WEAKEN SLOWLY WHILE PROGRESSING EWD TOWARD NM. A
POST-FRONTAL UPSLOPE REGIME WILL REMAIN ACROSS THE SRN HIGH
PLAINS...TRANSITIONING MORE TO A WAA REGIME TONIGHT AS A SLY LLJ
DEVELOPS FROM TX INTO OK. OTHERWISE...A SEPARATE NRN STREAM TROUGH
WILL MOVE INLAND OVER THE PAC NW...WITH A RISK FOR THUNDERSTORMS
ALONG AN ASSOCIATED COLD FRONT FROM SE ORE ACROSS ID TO SW MT THIS
AFTERNOON/EVENING.
...DELMARVA TO SE NEW ENGLAND THROUGH THIS AFTERNOON...
THE COLD FRONT IS EXPECTED TO MOVE SLOWLY SEWD TO AN AXIS FROM
CENTRAL VA TO THE SE NEW ENGLAND COAST BY MID-LATE AFTERNOON.
ASCENT ALONG THE FRONT AND SURFACE HEATING E OF THE FRONT/THICK
CLOUD BAND SHOULD PROMOTE ADDITIONAL THUNDERSTORM DEVELOPMENT THIS
AFTERNOON. A NARROW ZONE OF OVERLAP IN THE PRE-FRONTAL INSTABILITY
/MLCAPE OF 500-1000 J PER KG/ AND THE SERN FRINGE OF THE STRONGER
MIDLEVEL FLOW COULD SUPPORT A FEW ORGANIZED MULTICELLS/MARGINAL
SUPERCELL STRUCTURES THIS AFTERNOON...WITH AN ATTENDANT RISK FOR
ISOLATED DAMAGING WINDS AND MARGINALLY SEVERE HAIL. RATHER MODEST
INSTABILITY SUGGESTS THAT THE SEVERE STORM RISK WILL REMAIN TOO
MARGINAL FOR A CATEGORICAL SLIGHT RISK AREA.
...SE AZ/SRN NM/FAR W TX THIS AFTERNOON INTO EARLY TONIGHT...
THE MIDLEVEL TROUGH OVER AZ WILL ONLY DRIFT EWD...BUT A BELT OF 30+
KT SWLY MIDLEVEL FLOW WILL BE MAINTAINED OVER SE AZ/NM/W
TX...ROUGHLY COINCIDENT WITH THE MIDLEVEL DRY SLOT. SURFACE HEATING
AND WEAK ASCENT WITH THE MID-UPPER TROUGH WILL SUPPORT SCATTERED
TSTMS ACROSS SE AZ/SW NM. THE THICKER CLOUDS WILL LIMIT SURFACE
HEATING ACROSS W TX...BUT WAA ABOVE THE SHALLOW COOL AIR MASS AND
UPSLOPE LOW-LEVEL FLOW WILL PROMOTE THUNDERSTORM DEVELOPMENT.
MEANWHILE...DEEP-LAYER VERTICAL SHEAR WILL BE MORE FAVORABLE FOR
SUPERCELLS ACROSS W TX COMPARED TO SE AZ...AND INSTABILITY WILL BE
RATHER MODEST IN BOTH AREAS. COMBINING THESE FACTORS...IT APPEARS
THAT THE STORM ENVIRONMENT COULD SUPPORT A LOW-END RISK OF
HAIL/DAMAGING WINDS THIS AFTERNOON ACROSS SE AZ/SW NM...AND THIS
RISK COULD PERSIST INTO EARLY TONIGHT ACROSS FAR W/SW TX IN THE
DEVELOPING WAA REGIME.
..THOMPSON/HURLBUT.. 09/15/2011
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