spc.noaa.gov/products/md/mcd1753.gif MESOSCALE DISCUSSION 1753 NWS STORM PREDICTION CENTER NORMAN OK 0103 PM CDT THU AUG 22 2013 AREAS AFFECTED...PORTIONS OF PA...NY...VT...WRN NH...WRN MA CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY PROBABILITY OF WATCH ISSUANCE...20 PERCENT SUMMARY...A BROAD AREA OF ISOLATED...MARGINAL SEVERE THUNDERSTORM POTENTIAL WILL EXIST THROUGH THIS AFTERNOON. WHILE TRENDS WILL CONTINUE TO BE MONITORED...THE ISSUANCE OF A WW IS CURRENTLY UNLIKELY. DISCUSSION...VISIBLE SATELLITE LOOPS INDICATE THE CU FIELD BECOMING INCREASINGLY AGITATED ACROSS A BROAD AREA AHEAD OF A FRONT CROSSING SRN ONTARIO/QUEBEC. AREAS OF INSOLATION ARE SUPPORTING DIABATIC SFC HEATING AMIDST FAIRLY RICH BOUNDARY-LAYER MOISTURE CHARACTERIZED BY SFC DEWPOINTS IN THE LOWER/MIDDLE 60S. DESPITE WEAK MID-LEVEL LAPSE RATES...SFC TEMPERATURES HAVE CLIMBED INTO THE MIDDLE 70S TO LOWER 80S ALLOWING FOR MLCINH TO BE SUFFICIENTLY REDUCED TO SUPPORT ISOLATED THUNDERSTORM DEVELOPMENT PER RECENT MOSAIC RADAR/LIGHTNING DATA. WITH MLCAPE VALUES FORECAST TO HOLD AROUND 500-1500 J/KG THROUGH THE AFTERNOON OUTSIDE OF AREAS OF CONVECTIVE OVERTURNING...A FEW INTENSE UPDRAFTS/DOWNDRAFTS WILL LIKELY ENSUE AS CONVECTION INCREASES IN COVERAGE/INTENSITY OWING TO DIURNALLY DEEPENING PBL AND OROGRAPHIC CIRCULATIONS. ADDITIONAL ASCENT WILL EMANATE FROM ASCENDING BRANCHES OF LAKE BREEZE CIRCULATIONS E OF LAKES ONTARIO AND ERIE...AND AROUND DIFFERENTIAL-HEATING INDUCED BAROCLINICITY ALONG FRINGES OF MULTI-LAYERED CLOUD DECKS FROM NRN NY INTO NRN VT/NH. ISOLATED MARGINALLY SVR WIND/HAIL CANNOT BE RULED OUT WITH THE MOST INTENSE CONVECTION THAT COULD LOCALLY/OCCASIONALLY ORGANIZE INTO SMALL CLUSTERS/LEWP SEGMENTS. HOWEVER...WATER VAPOR LOOPS SUGGEST THAT MORE PROMINENT MID-LEVEL PERTURBATIONS AND ACCOMPANYING STRONGER DEEP ASCENT WILL REMAIN DISPLACED TO THE N OF THE DISCUSSION AREA THROUGH THE AFTERNOON/PEAK OF DIURNAL HEATING...WITH EFFECTIVE BULK SHEAR MAGNITUDES EXPECTED TO REMAIN GENERALLY 25 KT OR LESS. THE LACK OF OVERLAP OF THE AFOREMENTIONED BUOYANCY WITH STRONGER VERTICAL SHEAR NEAR THE FRONTAL ZONE SHOULD PREVENT A MORE ORGANIZED/WIDESPREAD SVR THREAT FROM EVOLVING. HOWEVER...THERE IS SOME CONCERN THAT STRENGTHENING LOWER/MIDDLE TROPOSPHERIC FLOW MAY OCCUR ACROSS NRN NY INTO NRN VT/NH LATER THIS AFTERNOON AS THE FRONT ENTERS THE AREA FROM THE N. WHILE TRENDS WILL BE MONITORED...IT CURRENTLY APPEARS THAT STABILIZATION OWING TO PRE-FRONTAL CLOUDS/PRECIPITATION MAY PROVE DELETERIOUS IN MAINTAINING A MORE ROBUST CONVECTIVE THREAT IN ASSOCIATION WITH THE SFC FRONT LATER TODAY.
Posted on: Thu, 22 Aug 2013 18:10:18 +0000
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