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Mesoscale Discussion 408
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   MESOSCALE DISCUSSION 0408
   NWS STORM PREDICTION CENTER NORMAN OK
   0817 PM CDT MON APR 20 2015

   AREAS AFFECTED...PORTIONS OF CNTRL/ERN PA...SWRN NJ...CNTRL/ERN
   MD...DE

   CONCERNING...TORNADO WATCH 90...

   VALID 210117Z - 210245Z

   THE SEVERE WEATHER THREAT FOR TORNADO WATCH 90 CONTINUES.

   SUMMARY...THE SVR RISK CONTINUES ACROSS REMAINING VALID PORTIONS OF
   WW 90. LOCAL TEMPORAL EXTENSION OF THE WW WILL BE NEEDED.

   DISCUSSION...ONGOING SCATTERED CONVECTION IS CONGEALING INTO
   SEMI-ORGANIZED CONVECTIVE CLUSTERS SPREADING EWD/NEWD ACROSS PARTS
   OF CNTRL/ERN PA...AND ACROSS PORTIONS OF ERN MD W OF CHESAPEAKE BAY.
   ALL OF THIS ACTIVITY WILL CONTINUE TRACKING EWD/NEWD...WITH THE SVR
   RISK CONTINUING ACROSS PARTS OF ERN PA AND PERHAPS SWRN NJ BEYOND
   THE SCHEDULED 02Z WW EXPIRATION TIME OWING TO RELATIVELY STRONGER
   MID-LEVEL ASCENT AMIDST STRONG DEEP SHEAR. THIS WILL WARRANT LOCAL
   TEMPORAL OF THE WW. HOWEVER...WITH NOCTURNAL STABILIZATION AMIDST
   RELATIVELY MODEST TROPOSPHERIC MOISTURE /REF. IAD 00Z RAOB THAT
   SAMPLED PW AROUND 0.9 INCH/ AND LACKING DCVA...THE SVR RISK SHOULD
   GRADUALLY WANE LATER INTO THE OVERNIGHT HOURS...AND PRESENT
   INDICATIONS ARE THAT A NEW WW WILL NOT BE NEEDED ATTM.

   ..COHEN.. 04/21/2015


   ATTN...WFO...PHI...BGM...AKQ...CTP...LWX...

   LAT...LON   38467717 39147664 39667764 40417769 41137720 41447662
               40257528 39397507 38507575 38467717 

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Page last modified: April 21, 2015
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