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Mesoscale Discussion 1724
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   MESOSCALE DISCUSSION 1724
   NWS STORM PREDICTION CENTER NORMAN OK
   1049 AM CDT THU AUG 20 2015

   AREAS AFFECTED...PORTIONS OF SRN/WRN NY...PA...NRN WV...MD...NRN VA

   CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 

   VALID 201549Z - 201815Z

   PROBABILITY OF WATCH ISSUANCE...5 PERCENT

   SUMMARY...CONVECTION WILL CONTINUE TO INCREASE IN INTENSITY THROUGH
   MID-DAY/THE AFTERNOON...AND POTENTIALLY POSE A RISK FOR LOCALIZED
   WIND DAMAGE. WW ISSUANCE IS NOT ANTICIPATED.

   DISCUSSION...VISIBLE SATELLITE IMAGERY AND MOSAIC RADAR LOOPS IMPLY
   DEEPENING CONVECTION PRINCIPALLY WITHIN TWO REGIMES:
   /1/ A BAND OF FRONTAL ASCENT STRETCHING FROM NEAR ERIE PA TO
   CHARLESTON WV...
   /2/ PRE-FRONTAL CONFLUENCE FARTHER E FROM NEAR ROCHESTER NY TO
   ELMIRA NY TO STATE COLLEGE PA TO HAGERSTOWN MD.
   CG LIGHTNING HAS RECENTLY BEEN NOTED WITH ACTIVITY EVOLVING IN THE
   LATTER REGIME AND WAA EVEN FARTHER E. FURTHER UPTICK IN TSTM
   ACTIVITY IS ANTICIPATED INTO THE AFTERNOON HOURS ACROSS THE MCD
   AREA...IN RESPONSE TO MODEST DIURNAL HEATING /DESPITE WIDESPREAD
   CLOUDS/ OF A MOIST PBL CHARACTERIZED BY SFC DEWPOINTS IN THE UPPER
   60S/LOWER 70S AMIDST NEAR-NIL CAPPING.

   ALL OF THIS ACTIVITY WILL GRADUALLY SPREAD EWD INTO THE AFTERNOON
   HOURS...WITHIN THE WARM CONVEYOR OF THE DEEP EXTRATROPICAL CYCLONE
   CENTERED OVER THE UPPER GREAT LAKES REGION PER WATER-VAPOR IMAGERY.
   VWP DATA SUGGEST THAT SSWLY DEEP-FLOW FIELDS RELATED TO THIS CYCLONE
   ARE SUPPORTING AROUND 20-30 KT OF 0-6-KM BULK SHEAR -- AIDED BY
   SLIGHT VEERING OF THE FLOW WITH HEIGHT IN THE LOWER TROPOSPHERE.
   THIS MAY SUPPORT A FEW SUSTAINED...POSSIBLY BOWING QUASI-LINEAR
   SEGMENTS...WITH CONVECTIVE MOMENTUM TRANSPORT ASSISTING IN LOCALLY
   STRONG WIND GUSTS.

   HOWEVER...NEARLY MOIST-NEUTRAL THERMODYNAMIC PROFILES IN THE MID
   LEVELS SAMPLED BY THE 12Z PIT AND IAD RAOBS SUGGEST THAT CONVECTIVE
   ACCELERATIONS WILL BE WEAK...IN ASSOCIATION WITH NARROW CAPE
   PROFILES. NEVERTHELESS...MESO-GAMMA-SCALE CIRCULATIONS EMBEDDED IN
   BOWING/LEWP CONVECTIVE STRUCTURES MAY ENHANCE THE RISK FOR LOCALIZED
   TREE/POWER-LINE DAMAGE -- AIDED BY WATER LOADING RELATED TO PW
   VALUES AROUND 1.75-2.00 INCHES PER GPS DATA. HOWEVER...SEVERE WIND
   GUSTS WILL BE UNLIKELY WITHOUT STRONGER BUOYANCY/BACKGROUND
   FLOW...AND GIVEN DEEP WIND FIELDS LARGELY ORIENTED PARALLEL TO
   LOW-LEVEL ASCENT/EVOLVING CONVECTIVE BANDS.

   ..COHEN/KERR.. 08/20/2015


   ATTN...WFO...PHI...BGM...BUF...CTP...LWX...PBZ...

   LAT...LON   40367585 39517641 39037732 39017904 39527993 41017980
               42557894 42987847 43297742 42917600 41537560 40367585 

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Page last modified: August 20, 2015
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