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Mesoscale Discussion 12
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   Mesoscale Discussion 0012
   NWS Storm Prediction Center Norman OK
   0616 PM CST Sun Jan 07 2018

   Areas affected...Portions of eastern IL...IN...and western OH

   Concerning...Freezing rain 

   Valid 080016Z - 080615Z

   SUMMARY...Freezing rain rates around 0.05 inch per 3 hours should
   occur this evening.

   DISCUSSION...A shortwave trough over the central/southern Plains at
   00Z will dig southeastward to the lower/mid MS Valley by late this
   evening. A low-level warm air advection regime and large-scale
   ascent associated with this shortwave trough has encouraged a broad
   area of light to moderate precipitation to develop from the Ozarks
   northeastward into IL. This precipitation shield is forecast to
   shift eastward in tandem with the shortwave trough, and
   strengthening of a southwesterly low-level jet appears likely across
   eastern IL, IN, and western OH through 06Z.

   Surface temperatures across much of IL/IN are above freezing as of
   00Z, with the exception of northeastern IL (Chicago metro area),
   where light freezing rain is ongoing per multiple surface
   observations. A residual dry low-level airmass over IN and western
   OH will likely experience substantial wet bulb cooling this evening
   as the precipitation shield over MO/IL overspreads this region.
   Latest RAP Mesoanalysis suggests the 32F wet bulb temperature is
   at/below freezing across nearly all of eastern IL, IN, and western
   OH. Warm air advection centered around the 900-850 mb layer will
   likely melt frozen hydrometeors aloft, allowing for re-freezing at
   the surface through wet bulb cooling processes. Freezing rain rates
   around 0.05 inch per 3 hours should occur given the light to locally
   moderate radar reflectivities noted thus far. A transition to snow
   may occur on the western extent of the precipitation shield as
   low/mid-level temperatures cool with the shortwave trough passage.

   ..Gleason.. 01/08/2018

   ...Please see for graphic product...


   LAT...LON   39268814 40428868 41968883 42158864 42178777 41978738
               41718690 41748555 41658432 40798421 39408470 38918519
               38658657 38778743 39268814 

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