MESO: Mesoscale Discussion 1998

ACUS11 KWNS 271918
SWOMCD
SPC MCD 271918
MDZ000-PAZ000-DCZ000-VAZ000-WVZ000-272115-

MESOSCALE DISCUSSION 1998
NWS STORM PREDICTION CENTER NORMAN OK
0218 PM CDT THU SEP 27 2012

AREAS AFFECTED...NRN VA THROUGH NRN MD AND EXTREME SRN PA

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY

VALID 271918Z - 272115Z

PROBABILITY OF WATCH ISSUANCE...20 PERCENT

SUMMARY...STORMS ARE EXPECTED TO INCREASE IN COVERAGE FROM NRN VA
THROUGH NRN MD AND EXTREME SRN PA THIS AFTERNOON. A FEW MULTICELLS
MIGHT BECOME CAPABLE OF ISOLATED STRONG TO DAMAGING WIND GUSTS...BUT
AT THIS TIME OVERALL THREAT DOES NOT APPEAR SUFFICIENT TO WARRANT A
WW.

DISCUSSION...THIS AFTERNOON A QUASI-STATIONARY FRONT STRETCHES FROM
SRN NJ WWD TO NRN MD...CNTRL OH AND BEYOND. SOUTH OF THIS FRONT AND
EAST OF THE CNTRL APPALACHIANS...DIABATIC WARMING OF THE BOUNDARY
LAYER HAS BOOSTED MLCAPE TO BETWEEN 1000-1500 J/KG. MAGNITUDE OF
INSTABILITY WILL LIKELY REMAIN AOB 1500 J/KG DUE TO RELATIVELY WEAK
MID LEVEL LAPSE RATES. COMBINATION OF OROGRAPHIC FORCING AND DEEPER
ASCENT DOWNSTREAM FROM VORT MAX ADVANCING EWD THROUGH THE OH VALLEY
WILL CONTINUE TO PROMOTE STORMS DEVELOPING OVER THE HIGHER TERRAIN
OF NWRN VA. ACTIVITY WILL SUBSEQUENTLY MOVE THROUGH NRN PORTIONS OF
THE WARM SECTOR...POSSIBLY INTERACTING WITH THE STATIONARY FRONT.
THIS REGION IS EMBEDDED WITHIN WEAK LOW LEVEL WINDS...BUT MODEST 30
KT WLY FLOW ALOFT AND EFFECTIVE SHEAR AOB 35 KT. SHEAR/INSTABILITY
PARAMETER SPACE MAY PROMOTE A FEW SUSTAINED MULTICELL STORMS THAT
MIGHT BECOME CAPABLE OF PRODUCING LOCALLY STRONG TO DAMAGING GUSTS
AS LOW LEVEL LAPSE RATES STEEPEN.

..DIAL/MEAD.. 09/27/2012

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...CTP...LWX...

LAT...LON 39727788 39927695 39667637 38897670 38367750 38287838
38637861 39727788

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