Mesoscale Discussion 1850
   NWS Storm Prediction Center Norman OK
   1001 AM CST Tue Dec 15 2020

   Areas affected...Northwest Oklahoma and the far northeast Texas
   Panhandle

   Concerning...Heavy snow 

   Valid 151601Z - 152000Z

   SUMMARY...Areas of moderate, to potentially heavy, snowfall are
   expected across northwest Oklahoma and the far northeastern Texas
   Panhandle mid-day today. Snowfall rates around one inch per hour are
   possible and may approach two inches per hour for brief periods.

   DISCUSSION...Mid-morning regional radar imagery shows reflectivity
   coverage increasing across western OK, the northern TX Panhandle,
   and western KS. Snowfall across western KS is being primarily driven
   by weak to moderate mid-level warm advection at around 700 mb as
   well as mid-level confluence within a deformation zone over the
   region. This will lead to transient banding in the near term that
   could support periods of moderate snowfall rates, but the continued
   east/southeastern progression of the synoptic wave should limit the
   duration and coverage of more intense snowfall rates. 

   Further south closer to the synoptic low, stronger isentropic ascent
   is noted between 850-700 mb ahead of the low over the eastern TX
   Panhandle and western OK, and is likely responsible for the recent
   uptick in reflectivity coverage. A few locations are already
   observing moderate to heavy snow with visibility down to one-half to
   one-quarter mile near the TX/OK border with lighter snowfall
   reported further east (where full column saturation is likely still
   ongoing). With the main mid-level confluence axis displaced to the
   northwest, the potential for deformation snow banding appears
   limited. This idea is supported by morning guidance, but a broad
   swath of deep warm advection, coupled with ascent within the
   left-exit region of the upper-level jet to the south, should support
   at least 2-4 hours of persistent snowfall over northwest OK though
   the early afternoon hours. Recent RAP forecast soundings suggest
   that lift within the dentritic growth zone should help support
   moderate snowfall rates near one inch per hour over this region.  

   Additionally, steep mid-level lapse rates noted in the 12 UTC
   Amarillo, TX sounding are supporting weak upright instability (~100
   mb MUCAPE rooted at around 600 mb) across southwest OK, which should
   allow for convective elements to advect to the north/northwest
   within the southerly flow regime. These convective elements will
   further augment snowfall rates, leading to periods of heavy snow
   with snowfall rates between 1-2 inches per hour for some locations.
   This activity should persist into the early afternoon hours before
   gradually abating with the weakening of the low and the departure of
   forcing for ascent to the east.

   ..Moore.. 12/15/2020

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

   ATTN...WFO...OUN...AMA...

   LAT...LON   36120051 36660018 36939964 36899867 36439801 35849772
               35519781 35379827 35329880 35259965 35350012 35570039
               36120051