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Mesoscale Discussion 1240
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   MESOSCALE DISCUSSION 1240
   NWS STORM PREDICTION CENTER NORMAN OK
   1131 AM CDT TUE JUN 30 2015

   AREAS AFFECTED...PORTIONS OF ERN PA...WRN NJ...SERN NY...MD...NRN
   DE...NRN VA...AND WASHINGTON DC

   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

   VALID 301631Z - 301900Z

   PROBABILITY OF WATCH ISSUANCE...40 PERCENT

   SUMMARY...TSTMS WILL INCREASE IN NUMBER AND INTENSITY THROUGH THE
   AFTERNOON AND POSE AN INCREASING RISK FOR DMGG WIND GUSTS AND
   POSSIBLY A COUPLE OF TORNADOES. WW ISSUANCE WILL BE POSSIBLE.

   DISCUSSION...VISIBLE SATELLITE IMAGERY DEPICTS AREAS OF INSOLATION
   FROM THE NRN VA PIEDMONT TO S-CNTRL PA AMIDST A BROAD...MERIDIONALLY
   ORIENTED WARM/MOIST CONVEYOR ON THE PERIPHERY OF AN ERN-CONUS
   TROUGH. STEEPENING LAPSE RATES IN THOSE AREAS HAVE CONTRIBUTED TO AN
   UPTICK IN CONVECTION ACROSS PARTS OF S-CNTRL/SERN PA PER RECENT 7-KM
   CAPPI RADAR DATA. AS LOW-LEVEL STRATUS CONTINUES TO ERODE ACROSS
   PARTS OF E-CNTRL/NERN PA AND POINTS FARTHER N/E...THE ENTIRE AREA
   WILL BE SUBJECTED TO CONTINUED DIURNAL DESTABILIZATION AMIDST RICH
   PBL MOISTURE CHARACTERIZED BY DEWPOINTS FROM THE MIDDLE 60S TO THE
   LOWER 70S. THIS WILL FOSTER A CONTINUED INCREASE IN THE
   COVERAGE/INTENSITY OF CONVECTION INTO THE AFTERNOON IN THE
   LOW-MLCINH ENVIRONMENT... ESPECIALLY AS A LOW-AMPLITUDE MID-LEVEL
   PERTURBATION ACROSS PA GRAZES THE AREA.

   THE PRESENCE OF 30-40 KT OF EFFECTIVE BULK SHEAR WILL SUPPORT SOME
   POTENTIAL FOR ORGANIZED/SUSTAINED CONVECTION AND POSSIBLE
   SUPERCELLS...WITH ISOLATED TO WIDELY SCATTERED DMGG WIND GUSTS AND
   PERHAPS MARGINALLY SVR HAIL. WHERE SFC WINDS REMAIN BACKED --
   ESPECIALLY IN AREAS WHERE VERTICAL MIXING IS MORE SUPPRESSED --
   LOW-LEVEL DIRECTIONAL SHEAR WILL CONTRIBUTE TO SOME RISK FOR A
   COUPLE OF TORNADOES. THIS WOULD PARTICULARLY BE THE CASE IN ERN PA
   AND VICINITY WHERE INTERPOLATION BETWEEN REGIONAL VWPS IMPLY THE
   STRONGEST FLOW WITH THE LLJ. THE MODEST NATURE OF MID-LEVEL LAPSE
   RATES AND UNCERTAINTY IN ANTECEDENT CLOUD/BUOYANCY EVOLUTION YIELD
   SOME LIMITATIONS TO EXACT CONVECTIVE INTENSITY CONFIDENCE...THOUGH
   THE AREA WILL CONTINUE TO BE MONITORED FOR POSSIBLE WW ISSUANCE.

   ..COHEN/HART.. 06/30/2015


   ATTN...WFO...OKX...PHI...BGM...CTP...LWX...

   LAT...LON   39647785 41167731 41667687 42007625 42057503 41367424
               39987489 39007609 38737739 39647785 

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Page last modified: June 30, 2015
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