Mesoscale Discussion 2033
   NWS Storm Prediction Center Norman OK
   0908 AM CDT Sat Sep 28 2019

   Areas affected...Rocky Mountain Front and adjacent High Plains of
   north-central MT

   Concerning...Heavy snow 

   Valid 281408Z - 281815Z

   SUMMARY...Heavy snowfall rates around 1 inch/hour are expected
   through midday near and along the I-25 corridor from immediately
   northwest of Great Falls to the east side of Glacier National Park.

   DISCUSSION...Radar mosaic shows a moderate to heavy precipitation
   shield with the southern edge currently in between Helena and Great
   Falls.  Surface temperatures are near freezing (32 degrees F) at
   Great Falls according to the 8am MDT observation.  Colder
   temperatures are observed farther north (Cut Bank 26 degrees F).  

   A slow-moving mid- to upper-level low over the Pacific Northwest
   will favor prolonged deep ascent across north-central and northwest
   MT.  Low-level northeasterlies are maintaining a fetch of adequately
   cool air and when combined with the heavier precipitation rates,
   surface temperatures are generally expected to remain at or below
   freezing.  The 12z Great Falls raob showed a saturated column from
   the surface through 600mb and a very shallow layer above freezing
   near the surface.  The shallow above-freezing layer has since cooled
   to around 32 degrees F.  Steep lapse rates were observed by the raob
   in the 600-450mb layer and around 160 J/kg MUCAPE was noted.  

   The strong orographic forcing (due to the gradual eastern rise to
   the higher terrain) and large-scale ascent will favor 0.5-1.0 inch
   per hour snowfall rates through the day.  The marginal buoyancy
   noted in the Great Falls raob suggests locally higher rates (perhaps
   exceeding 1 inch per hour) are possible for several hours this
   morning with weak convective elements contributing to an enhancement
   of snowfall rates.

   ..Smith.. 09/28/2019

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

   ATTN...WFO...TFX...MSO...

   LAT...LON   49011383 47301279 47551175 48401099 49001120 49011383