SWOMCD
SPC MCD 091235
RIZ000-CTZ000-NYZ000-MAZ000-NJZ000-PAZ000-DEZ000-MDZ000-VAZ000-DCZ000-091430-
MESOSCALE DISCUSSION 2236
NWS STORM PREDICTION CENTER NORMAN OK
0735 AM CDT TUE SEP 09 2008
AREAS AFFECTED...NJ...DE...CT...DC...PORTIONS ERN PA...SRN MA...SERN
NY...RI...MD...NRN/ERN VA.
CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE
VALID 091235Z - 091430Z
INITIALLY ELEVATED CONVECTION HAS BECOME BETTER ORGANIZED IN BAND
FROM VT SWWD ACROSS ERN PA TO N-CENTRAL MD...AS OF 12Z. ACTIVITY
MAY BACKBUILD INTO FAVORABLY UNSTABLE AIR MASS IN NRN VA. SVR
POTENTIAL MAY INCREASE THROUGH MID-LATE MORNING AS THIS ACTIVITY
MOVES INTO PROGRESSIVELY MORE MOIST/UNSTABLE INFLOW
AIR...PARTICULARLY S OF WARM FRONT DESCRIBED BELOW. MAIN THREAT
WILL BE DAMAGING WIND. HOWEVER...FCST AMBIENT SHEAR PROFILES
SUGGEST ANY RELATIVELY DISCRETE CONVECTION ALONG/S OF WARM FRONT MAY
BECOME SUPERCELLULAR WITH LARGE HAIL AND SLGT TORNADO
POTENTIAL...GIVEN LARGER THAN USUAL LAPSE RATES AND BUOYANCY FOR
THIS REGION AND TIME OF YEAR.
SFC MESOANALYSIS AHEAD OF CONVECTIVE BAND SHOWS WARM FRONT FROM SERN
PA VICINITY RDG...ENEWD OVER NYC AREA AND CT COAST THEN SEWD OVER
ATLANTIC. THIS FRONT SHOULD LIFT NWD ACROSS SRN NEW ENGLAND THROUGH
18Z. COLD FRONT IS ANALYZED BEHIND CONVECTIVE BAND...FROM ERN KY
NEWD ACROSS WRN PA...THROUGH WEAK/ELONGATED SFC LOW OVER NERN NY.
THIS LOW IS FCST TO DEEPEN THROUGH 18Z AS UPPER GREAT LAKES
MID-UPPER SHORTWAVE TROUGH APCHS. THIS WILL RESULT IN SLGT
ENHANCEMENT TO LOW LEVEL ISALLOBARIC/ISALLOHYPSIC FIELDS AND
RESULTING STRENGTHENING OF LOW LEVEL SHEAR. DEEP-LAYER SHEAR ALSO
SHOULD STRENGTHEN JUST AHEAD OF CONVECTION AS TROUGH ALOFT
APCHS...IN SUPPORT OF ORGANIZED SVR POTENTIAL...WITH 40-50 KT
EFFECTIVE SHEAR MAGNITUDES BEING COMMON. MAIN CONCERN IS
THERMODYNAMIC....WITH THICKENING CLOUD COVER AHEAD OF ACTIVITY WILL
MUTE BUT NOT ELIMINATE DIABATIC HEATING. AS FOREGOING AIR MASS
GRADUALLY DESTABILIZES DURING NEXT FEW HOURS...FROM COMBINATION OF
THAT HEATING AND WAA...PARCELS WILL BECOME SFC BASED. MODIFIED 12Z
IAD/APG RAOBS AND MODEL SOUNDINGS SUGGEST PRE-STORM MLCAPES
1500-2000 J/KG ARE POSSIBLE S OF WARM FRONT...GIVEN MID-60S TO
LOW-70S F SFC DEW POINTS...BENEATH 7-7.5 DEG C/KM 700-500 MB LAPSE
RATES.
..EDWARDS.. 09/09/2008
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...BOX...OKX...ALY...PHI...BGM...AKQ...CTP...LWX...
39477719 40847573 41567415 42127289 41927172 41197159
41077184 40637317 40567374 40577393 39717408 39377440
39127468 38957480 38937498 38777508 38397503 38067523
37777551 37097587 38157843 39317731
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