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Mesoscale Discussion 13
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   Mesoscale Discussion 0013
   NWS Storm Prediction Center Norman OK
   0325 AM CST Wed Jan 09 2019

   Areas affected...portions of VT...NH and western ME.

   Concerning...Heavy snow 

   Valid 090925Z - 091530Z

   SUMMARY...A belt of increasingly heavy snow, with rates commonly 1-2
   inches/hour and locally/briefly higher, should pivot across this
   corridor from southwest to northeast through mid/late morning local
   time.  Brief mixed precipitation, including light freezing rain, is
   possible around the south and east edges.

   DISCUSSION...A low/middle-level cyclone, manifest on the 9Z surface
   chart by a binary low with diffuse pressure minima near PSF and SLK,
   is expected to deepen and consolidate as it crosses southern VT/NH
   through dawn, reaching the ME coastline near PWM around 12Z, then
   moving slowly up the coast thereafter with continued deepening.  As
   the low-level cyclone intensifies, mass response will likewise
   strengthen, including the combination of elevated forcings in the
   conveyor occupying its proximal northern semicircle.

   Meanwhile, large-scale lift forced from higher aloft -- contributed
   by both DCVA immediately preceding the mid/upper trough/low and
   left-exit region of a cyclonically curved/eastward-shifting jet
   streak south of southern New England, will contribute to deep
   columnar cooling.  As evident in time series of forecast soundings,
   this process will freeze layers above the surface (near 850 mb) that
   initially are warmer than 0 deg C, effecting transition of sporadic
   freezing rain on the eastern rim of the advancing precip area to
   snow.  As deep-layer lift from multiple sources strengthens in the
   dendritic-growth zone, snowfall rates should increase beneath the
   laterally expanding and vertically deepening area of ice-phase
   precip production.  Steep midlevel lapse rates within a column that
   is saturated (or very nearly so) also may support development of
   transient lenses of weak MUCAPE, supporting embedded convective
   elements and locally contributing to short-lived bursts of snow
   rates topping 2 inches/hour, especially at higher ground elevations.

   ..Edwards.. 01/09/2019

   ...Please see for graphic product...


   LAT...LON   43907285 44307248 44757187 44927171 45147153 45277128
               45237085 44827013 44347010 43907047 43217150 43247297
               43477323 43907285 

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