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Mesoscale Discussion 15
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   Mesoscale Discussion 0015
   NWS Storm Prediction Center Norman OK
   0200 PM CST Fri Jan 11 2019

   Areas affected...East-central Missouri...far west-central Illinois

   Concerning...Heavy snow 

   Valid 112000Z - 120200Z

   SUMMARY...Heavy snow is expected over the next several hours, with
   up to 1 in/hr rates likely in some spots, especially along the I-70
   corridor, including the St. Louis metropolitan area.

   DISCUSSION...As a mid-level trough continues to progress across the
   Central Plains during the afternoon, the northward advection of a
   deep, moist airmass will continue across the region along with
   increasing large-scale ascent. Recent Mesoanalysis has indicated
   700-500 mb frontogenesis is underway across the area, where an
   800-1000 m deep, near-saturated to saturated dendritic layer is
   present, fostering the potential for efficient snowfall production.
   Latest KEAX and KLSX dual-polarimetric data suggest a transition to
   all snow north of a west-east oriented line approximately through
   Cass County to Jefferson County in Missouri.

   While several locations are above freezing at the surface, 10+F T/Td
   spreads and a sub-saturated sfc-850 mb layer suggest that
   evaporative cooling with the onset of the initial precipitation will
   cool and saturate the lower-level troposphere to foster occasionally
   heavy snow, with up to 1 in/hr rates possible in some areas. Latest
   high resolution ensemble guidance continues to suggest that the
   greatest threat for heavy snow will remain confined in a narrow
   corridor across portions of central/eastern Missouri through the
   evening hours.

   ..Squitieri.. 01/11/2019

   ...Please see for graphic product...


   LAT...LON   38608991 38299021 38249085 38789260 39229373 39589353
               39549207 39499078 39148997 38868989 38608991 

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