ZCZC SPCSWOMCD ALL
ACUS11 KWNS 251032 
SPC MCD 251032 
SDZ000-NEZ000-MTZ000-WYZ000-251630-

Mesoscale Discussion 1903
NWS Storm Prediction Center Norman OK
0432 AM CST Sun Dec 25 2016

Areas affected...Eastern WY...western SD...extreme western NEB
Panhandle

Concerning...Heavy snow 

Valid 251032Z - 251630Z

SUMMARY...Freezing rain/sleet will develop and spread northward
12-15z and then transition to heavy snow 15-18z.  Snowfall rates of
1-2 inches per hour will be possible with embedded
convection/thunder from late morning into this afternoon.

DISCUSSION...A surface cyclone is deepening across northeast CO and
will develop northeastward to western NEB Panhandle by this
afternoon in advance of a strong shortwave trough ejecting
northeastward from CO/NM.  Strong large-scale forcing for ascent, in
the form of low-level warm advection/frontogenesis and differential
cyclonic vorticity advection, will contribute deepening of the
cyclone and an increase in precipitation through midday across the
northern High Plains.  The strong ascent plume is evidenced by the
band of thunderstorms developing north-northeastward across eastern
CO early this morning.  Thermodynamic profiles will initially favor
freezing rain and some sleet given a warm nose in 800-700 mb layer
in observed and forecast soundings, though cooling of profiles aloft
with time will allow a transition to snow by late morning into the
afternoon, especially across eastern WY and northwest SD.  Steep
midlevel lapse rates and strong forcing for ascent will support
embedded convection with the possibility of thunder, which could
boost snowfall rates into the 1-2 inches per hour range by midday
and continue into the afternoon.

..Thompson.. 12/25/2016

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

ATTN...WFO...UNR...CYS...BYZ...

LAT...LON   44940453 45370384 45390319 45230265 44880230 44470230
            43950261 43310298 42720326 41030349 41020467 41570491
            42590503 44040496 44940453 

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