Storm Prediction Center Mesoscale Discussion 171

   Mesoscale Discussion 0171
   NWS Storm Prediction Center Norman OK
   0815 PM CST Sat Mar 13 2021

   Areas affected...Eastern Colorado into Wyoming and western Nebraska

   Concerning...Heavy snow 

   Valid 140215Z - 140815Z

   SUMMARY...Heavy snow with rates around 1 in/hr will continue
   periodically through the next several hours. Widespread heavy snow
   with rates of 1 to 2 in/hour in the Plains, and 3+ in/hr in the
   foothills/mountains will likely expand in coverage late this evening
   and overnight.

   DISCUSSION...Evening water vapor imagery showed a deep upper-level
   low atop the Four Corners with a 100 kt 500 mb speed max rotating
   around the low across the High Plains. Surface low pressure across
   the Texas Panhandle will gradually intensify and shift northwestward
   across Kansas through this evening and overnight. A TROWAL signature
   was also noted to the northeast of the center of the low in response
   to strong mid-level warm advection occurring to the east. 

   00Z operational RAOBS and university/research soundings show a deep
   layer of saturated east northeasterly upslope flow stretching from
   southeastern Wyoming into northeastern Colorado. This deep
   orographic lift is supporting moderate to heavy stratiform
   precipitation along the I-25 corridor. Snowfall rates of 1 in/hour
   are likely within the heavier bands of precipitation through the
   next several hours. The most likely location for the heaviest
   snowfall rates will be along the eastern slopes of the northern
   Front Range, southern Laramie Range, and the Cheyenne Ridge where
   orthographic enhancement will be maximized. Expansion of the
   snowfall deeper into the Nebraska panhandle is also expected this
   evening as nocturnal/dynamic cooling of the column promotes a
   changeover to all snow this evening.

   More widespread heavy snow will likely develop after 04z this
   evening and overnight as the main forcing for ascent from the upper
   low spreads eastward across Colorado. The TROWAL will move
   east/southeast centered across northern Colorado and southern
   Wyoming supporting intense lift and precipitation through the
   overnight hours. Localized blizzard conditions may develop across
   portions of northern Colorado and southern Wyoming in response to
   increasing surface pressure falls from the strengthening lee low
   across western Kansas. Snowfall rates of 1 to 2 in/hr will be
   possible across the Plains with very heavy rates of 3+ in/hr
   possible in the foothills and mountains northwest of Denver.

   ..Lyons.. 03/14/2021

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

   ATTN...WFO...PUB...BOU...CYS...RIW...

   LAT...LON   42960627 42590650 42260610 41580580 41250575 40840579
               40220586 39840601 39570606 39290605 38930600 38720591
               38510567 38390542 38360508 38340446 38410401 38410388
               38510383 38760373 39020362 40120334 40730326 41270314
               41730314 42430326 42790363 42990420 43060514 43060590
               42960627