Mesoscale Discussion 1891
   NWS Storm Prediction Center Norman OK
   0815 PM CST Wed Dec 30 2020

   Areas affected...Texas Big Bend into the Trans-Pecos

   Concerning...Heavy snow 

   Valid 310215Z - 310815Z

   SUMMARY...A prolonged period of 1+ inch per hour snow rates is
   expected to begin within the next few hours. Heavy snow will be
   possible through tomorrow morning, when the heaviest rates are
   forecast to occur.

   DISCUSSION...IR satellite imagery shows a closed upper low
   developing west of the Mexican Plateau. Increasing mid-level ascent
   is also evident within the Big Bend region and points southward.
   Earlier this evening, a period of heavy snow was already observed at
   Marfa where temperatures have remained below 30F. This upper low is
   expected to slowly push eastward this evening and overnight before
   pivoting to the northeast tomorrow morning. This will create a setup
   where portions of the Big Bend region into the Trans-Pecos will be
   situated within a favorable zone of mid-level ascent for a prolonged
   period. This evening's sounding out of Midland shows a saturated
   profile within the dendritic growth layer. Even with weak surface
   warm advection occurring, diabatic cooling from precipitation should
   keep temperatures at or just below freezing. Snowfall rates of 1
   inch per hour are possible for several hours through the overnight.
   The heaviest snow is expected to occur towards Thursday morning as
   the trough pivots and takes on more of a negative tilt.

   ..Wendt.. 12/31/2020

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...SJT...MAF...

   LAT...LON   29820430 30530428 31330339 31600294 31660244 31520194
               30980172 30270213 29580303 29390330 29360362 29820430