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Mesoscale Discussion 1341
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   MESOSCALE DISCUSSION 1341
   NWS STORM PREDICTION CENTER NORMAN OK
   0209 PM CDT THU JUL 09 2015

   AREAS AFFECTED...PA/MD/NORTHERN WV TO NORTHERN VA AND DE/NJ

   CONCERNING...TORNADO WATCH 397...

   VALID 091909Z - 092045Z

   THE SEVERE WEATHER THREAT FOR TORNADO WATCH 397 CONTINUES.

   SUMMARY...DAMAGING WIND/ISOLATED TORNADO POTENTIAL IS EXPECTED TO
   INCREASE/SPREAD EASTWARD THROUGH LATE AFTERNOON ACROSS PARTS OF PA
   AND NEARBY NORTHERN WV/MD. TORNADO WATCH 397 CONTINUES UNTIL 01Z. AN
   ADDITIONAL WATCH IS LIKELY BY LATE AFTERNOON /APPROX 20-21Z/
   ESPECIALLY FOR PORTIONS OF EASTERN PA AND NJ/DE/NORTHEAST MD.

   DISCUSSION...18Z SUBJECTIVE SURFACE ANALYSIS FEATURES AN
   EASTWARD-MOVING SURFACE LOW ACROSS FAR WESTERN NY/NORTHWEST
   PA...WITH PRECEDING 2-3 MB TWO-HOURLY PRESSURE FALLS ACROSS
   SOUTH-CENTRAL NY/NORTH-CENTRAL PA. A WAVY/NORTHWARD-SHIFTING WARM
   FRONT EXTENDS EAST-SOUTHWARD FROM THE SURFACE LOW ACROSS ACROSS
   NORTH-CENTRAL/EASTERN PA INTO NJ.

   AS OF 19Z/3PM EDT...A NARROW/BOWING CONVECTIVE LINE CONTINUES TO
   GRADUALLY GROW UPSCALE AND MOVE EASTWARD ACROSS SOUTHWEST PA/FAR
   WESTERN MD...WHILE FARTHER NORTH...WITH OTHER LOWER-TOPPED
   SEMI-DISCRETE STORMS INCLUDING A COUPLE OF SUPERCELLS CONTINUE TO
   FLUCTUATE INTENSITY-WISE ACROSS WEST-CENTRAL PA. AHEAD OF THIS
   ACTIVITY...VISIBLE SATELLITE IMAGERY SUGGESTS THAT THE CUMULUS FIELD
   CONTINUES TO BECOME INCREASING AGITATED/DEEPEN WITHIN THE WARM
   SECTOR PARTICULARLY ACROSS PA/NJ WHERE MLCAPE IS ESTIMATED TO BE AT
   LEAST 500-1000 J/KG COINCIDENT WITH UPPER 60S/LOWER 70S F SURFACE
   DEWPOINTS. 

   SIMILAR TO PREVIOUSLY DESCRIBED CONVECTIVE TRENDS...LATEST THINKING
   IS THAT THE EASTWARD-MOVING BAND OF STORMS WILL CONTINUE TO GROW
   UPSCALE/ACCELERATE EASTWARD ACROSS EASTERN/NORTHERN WV AND
   MD/SOUTHERN PA...WITH OTHER SEMI-DISCRETE STORMS/SUPERCELLS
   REMAINING A DISTINCT POSSIBILITY FARTHER NORTH /AND POSSIBLY EAST
   AHEAD OF THE LINE/ ACROSS ADDITIONAL PORTIONS OF PA/NJ AND DELMARVA
   VICINITY. WHILE DAMAGING WINDS ARE LIKELY TO BE THE MOST PREVALENT
   RISK...TORNADO POTENTIAL WILL EXIST...PARTICULARLY WITH ANY
   SUPERCELLS INTERACTING WITH THE WARM FRONT ACROSS PA/NJ. LATEST
   WSR-88D VWP DATA FROM STATE COLLEGE IS SAMPLING 0-1 KM SRH OF
   APPROXIMATELY 200 M2/S2...WITH LOCALLY HIGHER VALUES WHERE LOW-LEVEL
   WINDS ARE BACKED TO MORE SOUTHEASTERLY /SUCH AS THE THE WILLIAMSPORT
   VICINITY AS OF 18Z-19Z/.

   ..GUYER.. 07/09/2015


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

   LAT...LON   40977926 41477889 41857748 41747597 41247498 40597431
               39337483 38847584 38797686 39147828 39137948 39308016
               40977926 

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Page last modified: July 09, 2015
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