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Mesoscale Discussion 110
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   Mesoscale Discussion 0110
   NWS Storm Prediction Center Norman OK
   0747 AM CST Wed Mar 07 2018

   Areas affected...eastern PA...central and northern NJ

   Concerning...Heavy snow 

   Valid 071347Z - 071745Z

   SUMMARY...Heavy hourly snowfall rates of 1-2 inches per hour are
   likely to develop later this morning.  Locally higher rates (2+
   inches/hour) are possible primarily after noon local time within the
   frontal snow band and/or convectively augmented bursts.

   DISCUSSION...13Z surface analysis places a sub 1000mb developing low
   60 mi ESE of WAL.  Temperatures are in the 32-34 degrees F range
   from the northern part of Chesapeake Bay to NYC.      

   The 12Z IAD RAOB from Dulles, VA showed a temperature profile
   subfreezing except immediately near the surface.  The 500mb
   temperature was -25.5 C.  Looping water-vapor imagery indicates the
   mid-level trough was located over the central Appalachians as of
   13-14Z.  As this disturbance approaches the region, strong mid-level
   ascent associated with the trough (leading to significant columnar
   cooling in the mid-levels) coupled with the northern periphery of a
   plume of steep 700-500mb lapse rates (7-8 degrees C per km) will
   combine and result in pockets of weak buoyancy and upright
   convection.  Convection will increase in coverage from northern DE
   northeast towards the NYC area during the late morning into the
   early afternoon.  Models indicate the development of strong
   frontogenetic forcing will begin primarily around or after 17Z.  As
   the deep-layer large-scale ascent strengthens and becomes vertically
   juxtaposed with the intensifying frontogenesis, hourly precipitation
   rates will markedly increase from around 0.10 inch to 0.10-0.25

   Marginal surface temperatures will effectively result in a
   significant concern/limiting factor for the spatial coverage of 1+
   inch/hour rates farther southeast across portions of NJ as a sharp
   rain/snow precipitation-type gradient becomes established.  Eastern
   PA into northern NJ will likely maintain snow as the precipitation
   type and heavy snowfall rates will focus in a narrow corridor from
   the north part of PHL north-northeast into northern NJ.  Higher
   elevations will likely attain the coldest temperatures (due to the
   low-level thermal profile cooling as elevation increases from sea
   level to 1-2 kft) and the most intense accumulation/hourly rates.

   ..Smith.. 03/07/2018

   ...Please see for graphic product...


   LAT...LON   40197573 41297505 41527459 41407422 41187402 40637420
               40077524 40047555 40197573 

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