Mesoscale Discussion 1839
   NWS Storm Prediction Center Norman OK
   0119 AM CST Sat Dec 12 2020

   Areas affected...portions of central and eastern Iowa

   Concerning...Heavy snow 

   Valid 120719Z - 121315Z

   SUMMARY...An area of heavy snowfall is forecast to evolve over the
   next 2-3 hours, with snowfall rates around 1" per hour expected --
   likely peaking during a 3-5 hour period from roughly 08-09Z through
   12-14Z.

   DISCUSSION...Latest radar loop shows a zone of light to moderate
   snowfall occurring from eastern Nebraska eastward to eastern Iowa,
   with the current rain/snow line extending roughly from KLWD (Lamoni
   IA) to roughly KCWI (Clinton IA).  This zone of snowfall is
   occurring within a zone of deformation north of a well-defined vort
   max -- evident in current WV imagery over the Ozark Plateau of
   southern Missouri -- which will continue moving east-northeastward
   with time and reaching central Illinois around sunrise.

   Favorable large-scale ascent will continue within the deformation
   zone as the surface low -- now over northeastern Missouri --
   continues to gradually deepen as it shifts east-northeastward with
   time, in tandem with translation of the upper feature, and
   strengthening of the cold conveyor belt.  With moist/saturated
   thermal profiles -- including within the favored dendritic growth
   zone -- an increase in snowfall rates within the deformation zone is
   expected, possibly aided by some weak convective enhancement given
   steep lapse rates and even some minimal CAPE hinted at within model
   forecast soundings.

   Snowfall should increase over the next 2-3 hours, and continue at
   around 1" per hour rates within the MD area for several hours,
   before tapering gradually from west to east through mid morning.

   ..Goss.. 12/12/2020

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

   ATTN...WFO...DVN...ARX...DMX...

   LAT...LON   41359369 42049372 42419298 42719181 42719091 42219068
               41759143 41239217 41359369