SWODY1
SPC AC 271243
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0743 AM CDT TUE SEP 27 2011
VALID 271300Z - 281200Z
...NO SVR TSTM AREAS FORECAST...
...LOWER GREAT LAKES INTO CAROLINAS...
LITTLE NET MOTION OF MIDWESTERN UPPER LOW IS FORECAST THROUGH THE D1
PERIOD. HOWEVER...A NUMBER OF VORTICITY MAXIMA WILL CONTINUE TO
PIVOT AROUND PARENT CIRCULATION...ONE OF WHICH WILL LIFT NWD FROM
THE CNTRL APPALACHIANS THROUGH THE UPPER OH VALLEY THIS MORNING. AS
THIS OCCURS...THE NEXT VORTICITY LOBE OVER THE LOWER MS VALLEY WILL
TRANSLATE INTO THE CNTRL APPALACHIANS BY AFTERNOON AND EVENTUALLY
THROUGH THE UPPER OH VALLEY BY TONIGHT. IN THE LOW LEVELS...SOME
OSCILLATION OF SYNOPTIC FRONT WILL OCCUR THROUGH THE PERIOD WITH
BOUNDARY EXTENDING GENERALLY FROM WRN OR CNTRL PARTS OF NY/PA SWD
INTO THE CAROLINA PIEDMONT.
CLUSTERS OF TSTMS ONGOING OVER PORTIONS OF CNTRL PA AND ALONG THE
VA/NC BORDER ARE LIKELY BEING FORCED BY THE GLANCING INFLUENCE OF
LEAD IMPULSE LIFTING NWD. 12Z SOUNDINGS SHOW THE PRESENCE OF A
MOIST AND WEAKLY CAPPED AIR MASS...SUGGESTING THAT THESE STORMS MAY
PERSIST THROUGH THE MORNING WITH SOME RISK FOR GUSTY WINDS. TSTMS
ARE EXPECTED TO INCREASE IN COVERAGE AND INTENSITY BY AFTERNOON AS
AIR MASS DESTABILIZES AND LARGE-SCALE FORCING FOR ASCENT ONCE AGAIN
INCREASES AHEAD OF UPSTREAM VORTICITY MAXIMUM. THOUGH LAPSE RATES
WILL REMAIN RATHER WEAK...DAYTIME HEATING COUPLED WITH A MOIST
BOUNDARY LAYER WILL BOOST MLCAPE VALUES TO AROUND 1000 J/KG LOCALLY.
WHILE ISOLATED DAMAGING WIND GUSTS WILL BE POSSIBLE...THE
DISPLACEMENT OF THE STRONGER VERTICAL SHEAR TO THE WEST OF THE WARM
SECTOR WILL LIMIT THE POTENTIAL FOR A MORE ORGANIZED SEVERE WEATHER
THREAT.
...CNTRL TX EWD ACROSS THE GULF COAST STATES...
SEWD-MOVING TSTM COMPLEX OVER MS/WRN AL MAY POSE AN ISOLATED
WIND/HAIL THREAT THIS MORNING BEFORE WEAKENING WITH THE CESSATION OF
THE NOCTURNAL LLJ. IN ITS WAKE...12Z WARM-SECTOR SOUNDINGS INDICATE
THE PRESENCE OF A MOIST BOUNDARY LAYER BENEATH STEEP MIDLEVEL LAPSE
RATES WHICH WILL YIELD A STRONGLY UNSTABLE AIR MASS BY AFTERNOON
WITH MLCAPE APPROACHING 3000 J/KG. OUTFLOW BOUNDARY REMNANT FROM
NOCTURNAL MCS AND STALLED SYNOPTIC FRONT WILL SERVE AS THE FOCI FOR
WIDELY SCATTERED TSTM DEVELOPMENT LATER TODAY AS CAP IS ERODED
THROUGH HEATING AND CONVERGENCE IN THE BOUNDARY LAYER. THOUGH WARM
SECTOR WILL REMAIN DISPLACED TO THE S OF STRONGER MIDLEVEL FLOW
ATTENDANT TO DEEP-LAYER CYCLONE OVER THE MIDWEST...THE STEEP LAPSE
RATES AND STRONG CONVECTIVE INSTABILITY WILL SUPPORT INTENSE
UPDRAFTS CAPABLE OF SEVERE HAIL AND LOCALLY DAMAGING WIND GUSTS.
..MEAD/ROGERS.. 09/27/2011
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