MESOSCALE DISCUSSION 1239 NWS STORM PREDICTION CENTER NORMAN OK 1118 AM CDT FRI JUN 22 2012 AREAS AFFECTED...PORTIONS NRN/ERN VA...CENTRAL/ERN PA...SWRN NEW ENGLAND...SRN NY...DE...MD...NJ...DC. CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE VALID 221618Z - 221845Z PROBABILITY OF WATCH ISSUANCE...60 PERCENT SUMMARY...SVR THREAT FCST TO INCREASE FROM MULTICELLULAR CONVECTION...OF DISCRETE...CLUSTERED AND QUASI-LINEAR CHARACTER...DEVELOPING THROUGH MID-AFTERNOON AND MOVING OVER THIS AREA. MAIN CONCERN IS DAMAGING GUSTS. DISCUSSION...TSTMS ARE FCST TO DEVELOP IN AT LEAST TWO PRIMARY SWATHS OR BANDS... 1. NEAR AND E OF DIFFERENTIAL HEATING ZONE...ASSOCIATED WITH LOW-MIDDLE LEVEL CLOUD BAND NOW EVIDENT ON VIS IMAGERY FROM ERN PA SWWD ACROSS VA/WV BORDER REGION. ANY SUCH TSTMS WILL POSE EARLIEST SVR RISK FROM TIDEWATER AREA NEWD OVER COASTAL MID-ATLC AND SRN NEW ENGLAND. 2. ALONG/AHEAD OF SFC COLD FRONT...INITIALLY OVER HIGHER TERRAIN OF CENTRAL PA INTO NRN WV. FRONT PRECEDES POSITIVELY TILTED MID-UPPER TROUGH BY ABOUT 100-150 NM USING MOISTURE CHANNEL IMAGERY...BUT WITH SOME LARGE-SCALE ASCENT EVIDENT OVER FRONTAL ZONE. THESE FEATURES WILL SHIFT EWD OVER MID-ATLC REGION THIS AFTERNOON. 16Z SFC ANALYSIS SHOWED COLD FRONT FROM NRN NY SWWD ACROSS CENTRAL/SWRN PA AND WRN WV. SFC TROUGH WITH WEAK EMBEDDED LOWS WAS EVIDENT PARALLEL TO COLD FRONT AND FARTHER E...EXTENDING FROM SERN VA NNEWD OVER SRN CHESAPEAKE BAY AND ERN NJ TO RI AND ERN MA...INTERSECTING WARM FRONT JUST OFFSHORE NH. WARM FRONT EXTENDED NNEWD FROM THERE OVER MAINE. TROUGH APPEARS COLLOCATED WITH SEA BREEZE BOUNDARY OVER ERN NJ...AND A COUPLE OF TSTMS ALREADY HAVE DEVELOPED THERE. MODIFIED IAD/APG/WAL/OKX RAOBS SUGGEST PREFRONTAL BOUNDARY LAYER SHOULD MIX VIGOROUSLY ACROSS MUCH OF NEAR-COASTAL CORRIDOR IN RESPONSE TO CONTINUED STG SFC DIABATIC HEATING. SIMILAR PROCESS SHOULD OCCUR BEHIND AFOREMENTIONED PREFRONTAL CLOUD BAND. RESULT WOULD BE POCKETS OF REDUCED SFC DEW POINTS...AT BASE OF INVERTED-V THERMODYNAMIC PROFILE FEATURING NEARLY DRY-ADIABATIC LOW-LEVEL LAPSE RATES. YET MOISTURE WILL REMAIN SUFFICIENT EVEN IN THOSE RELATIVELY DRY AREAS TO OFFSET MODEST MIDLEVEL LAPSE RATES AND KEEP AT LEAST MRGL BUOYANCY OVER REGION. GIVEN HORIZONTALLY INHOMOGENEOUS NATURE OF EXPECTED MIXING/MOISTURE FIELDS...MLCAPE WILL VARY GREATLY WITH VALUES RANGING FROM 500-2500 J/KG...TRENDING INVERSELY WITH STRENGTH OF VERTICAL MIXING. 30-35 KT EFFECTIVE SHEAR MAGNITUDES SUPPORT SOME ORGANIZATION TO MULTICELL MODES...AND POTENTIAL FOR SMALL BOWS WITH LOCALLY ENHANCED COLD-POOL FORCING. ..EDWARDS/WEISS.. 06/22/2012 ATTN...WFO...BOX...OKX...ALY...PHI...BGM...AKQ...CTP...LWX... LAT...LON 40577881 43297415 41777296 41317279 40647311 40567396 40587407 40487425 40417399 39797408 39447430 39217462 38977484 38947498 38737510 38347509 37947531 37837545 37537632 37627736 38077913 40577881
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