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Mesoscale Discussion 39
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   Mesoscale Discussion 0039
   NWS Storm Prediction Center Norman OK
   1028 AM CST Fri Jan 13 2017

   Areas affected...Portions of southwest IN...southern
   IL...southern/central MO...southeast KS...OK

   Concerning...Freezing rain 

   Valid 131628Z - 132230Z

   SUMMARY...An extensive corridor of freezing-rain potential will
   continue through the day from portions of OK to parts of the lower
   OH Valley.

   DISCUSSION...A persistent plume of elevated warm advection and
   moisture transport will continue to foster an extensive corridor of
   precipitation potential through the day -- from portions of OK to
   parts of the lower OH Valley. With the 12Z Norman OK, Springfield
   MO, and Lamont OK soundings sampling maximum elevated warm-layer
   temperatures around 9C-12C, complete melting of descending
   hydrometeors will occur prior to their contact with the subfreezing
   surface layer. Meanwhile, subfreezing surface temperatures from
   parts of southwest OK to southwest IN will be reinforced by
   continued cold advection within the surface layer -- reflected by
   modest pressure rises on the order of 0.5-2.0 mb per 2 hours. As a
   result, the risk for freezing rain will continue through the day,
   with freezing-rain rates around 0.02-0.08 in/hour -- locally higher.

   The greatest coverage and intensity of freezing rain should remain
   concentrated within a corridor from far northeast OK and southeast
   KS east-northeastward through parts of south-central MO and into
   southwest IL. This is where (1) isentropic ascent aloft should
   remain strongest, and (2) generating convective elements from the
   southwest will likely reach maturation stages while congealing.
   Furthermore, marginal (though non-zero) elevated buoyancy -- rooted
   within the elevated warm layer -- was sampled by the aforementioned
   soundings. This will offer some convective enhancement to
   freezing-rain rates, along with continued lightning potential
   accompanying the heaviest freezing rain. Slight northward spread of
   this precipitation shield may occur through the day, in tandem with
   the motion of the warm-advection zone.

   Eastward from the greatest coverage/intensity corridor into
   southwest IN, weaker ascent should tend to mitigate overall
   freezing-rain intensity to some extent. However, the influx of
   precipitation generated upstream, atop sub-freezing wet-bulb surface
   temperatures, suggests light freezing rain will be possible.

   Areas well southwestward into parts of north-central, central, and
   southwest OK will be a region of development of convective elements
   (as indicated by recent mosaic radar loops). Ascent -- albeit
   relatively more modest -- should be sufficient for widely scattered
   coverage of freezing rain showers through the day. The influx of
   moderate midlevel lapse rates (sampled by upstream AMA/MAF
   soundings) suggests that some convective enhancement will accompany
   this activity. This should yield brief instances of light to
   occasionally moderate freezing rain through the day.

   ..Cohen.. 01/13/2017


   LAT...LON   36799477 35009797 34749918 35129952 36029900 37599563
               38759218 39178820 38878692 38258709 37628885 36799477 

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