DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 281950
SWODY1
SPC AC 281948

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0248 PM CDT FRI SEP 28 2012

VALID 282000Z - 291200Z

...NO SVR TSTM AREAS FORECAST...

THE ONLY CHANGE TO THE OUTLOOK AT 20Z IS TO EXTEND THE 5 PERCENT
WIND DAMAGE PROBABILITY FURTHER TO THE NORTH ACROSS SOUTH FL.
MESOANALYSIS SUGGESTS SUBSTANTIAL INSTABILITY EXISTS ALONG A
CORRIDOR FROM LAKE OKEECHOBEE SWD TO THE ERN FL KEYS ALONG WHICH
SEVERAL STRONG THUNDERSTORMS ARE ONGOING. ELSEWHERE ACROSS THE
CONUS...THE OUTLOOK APPEARS TO BE ON TRACK.

..BROYLES.. 09/28/2012

.PREV DISCUSSION... /ISSUED 1122 AM CDT FRI SEP 28 2012/

A BROAD UPPER TROUGH IS PRESENT TODAY OVER THE NORTHEAST UNITED
STATES...WHILE RELATIVELY WEAK FLOW ALOFT PERSISTS OVER THE
REMAINDER OF THE NATION. WATER VAPOR IMAGERY SHOWS A SERIES OF WEAK
SHORTWAVE TROUGHS TRACKING EAST-NORTHEASTWARD ALONG AN AXIS FROM THE
UPPER OH VALLEY AND MID ATLANTIC REGION INTO SOUTHERN NEW ENGLAND.
PORTIONS OF THIS AREA WILL SEE A LOW RISK OF STRONG/SEVERE STORMS
LATER TODAY.

...EASTERN PA/SOUTHEAST NY/SOUTHERN NEW ENGLAND...
A SURFACE LOW IS ANALYZED AT 16Z OVER EASTERN PA. THE ASSOCIATED
WARM FRONT EXTENDS EASTWARD FROM THE LOW ACROSS LONG ISLAND AND OUT
TO SEA. THE LOW IS FORECAST TO TRACK NORTHEASTWARD INTO NEW ENGLAND
LATER TODAY VERY NEAR THE COAST OF NY/CT/RI/MA. DESPITE THE LIMITED
NORTHWARD MOVEMENT OF THE WARM SECTOR TODAY...SOME RISK OF
STRONG/SEVERE STORMS WILL IN VICINITY OF THE BOUNDARY. MODIFIED
FORECAST SOUNDINGS IN THE WARM/MOIST AIR MASS SHOW MLCAPE VALUES OF
500-800 J/KG AND EFFECTIVE SHEAR VALUES OF 25-35 KNOTS. THESE
VALUES...COUPLED WITH ENHANCED LOW LEVEL SHEAR NEAR THE SURFACE
LOW/FRONT WOULD SUPPORT A RISK OF WEAKLY ORGANIZED SUPERCELL
STRUCTURES CAPABLE OF GUSTY/DAMAGING WINDS OR A BRIEF TORNADO.
GIVEN THE VERY SMALL AREA OF CONCERN AND THE MARGINAL
ENVIRONMENT...WILL MAINTAIN ONLY LOW SEVERE PROBABILITIES IN THIS
REGION.

...SOUTHERN PA/WV/VA/NORTHERN NC...
FARTHER SOUTHWEST...THE TRAILING COLD FRONT WILL SAG SOUTHWARD INTO
PARTS OF PA/WV/VA LATER TODAY. BROKEN CLOUDINESS OVER THIS REGION
WILL ALLOW SOME DAYTIME HEATING WITH AFTERNOON TEMPERATURES LIKELY
TO REACH THE 80S. MOST MODEL SOLUTIONS SHOW INCREASING CONVECTIVE
DEVELOPMENT LATER THIS AFTERNOON AHEAD OF THE FRONT ACROSS THIS
REGION. MODERATE CAPE VALUES WILL COMBINE WITH RELATIVELY STRONG
WESTERLY FLOW ALOFT TO PROMOTE A RISK OF GUSTY WINDS IN THE
STRONGEST STORMS. AT THIS TIME...ORGANIZED SEVERE WEATHER IS NOT
ANTICIPATED TODAY.

...SOUTH FL...
THE 12Z MFL RAOB SHOWED CONSIDERABLE LOW LEVEL MOISTURE AND AMPLE
CAPE. FORCING IS WEAK AND SUBTLE OVER THIS AREA...SUGGESTING THAT
COVERAGE OF AFTERNOON THUNDERSTORMS WILL BE QUITE SPARSE.
HOWEVER...POTENTIAL EXISTS FOR LOCALIZED DOWNBURSTS IN THE STRONGER
STORMS. HIGHEST THREAT APPEARS TO BE ALONG THE IMMEDIATE COAST
WHERE SEA-BREEZE INTERACTIONS WILL INCREASE THE RISK OF INITIATION.

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