Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
354 PM EDT Wed Apr 24 2019

Valid 00Z Thu Apr 25 2019 - 00Z Sun Apr 28 2019


...Northern Plains/Upper Midwest...

A shortwave trough sliding across the Pacific Northwest on Friday
is expected to amplify as it moves east of the Rockies into the
northern Plains Friday night into Saturday.  Models are split on
the timing and amplitude of the system, lowering forecast
confidence.  In typical fashion, the NAM is along the slower and
more amplified side of the guidance - drawing more cold air down
on the backside of the system, resulting in heavier snow
accumulations than the GFS.  However, the NAM does have the
support of recent runs of the ECMWF - suggesting the GFS is too
warm and too fast with this system.  Even the GFS with its faster
and less amplified solution does indicate good low to mid level
frontogenesis, which along with upper jet forcing could support
heavier precipitation rates and the potential for rain changing to
accumulating snow on the backside of the system across southern
North Dakota and northern South Dakota Saturday morning.  Farther
east, significant evaporative cooling, with plenty of low to mid
level dry air in the wake of a downstream system moving into the
Northeast, may support snow or rain changing to snow across
central and southern Minnesota and central Wisconsin on Saturday. 
Once again, strong low to mid level frontogenesis with upper jet
forcing may support heavier precipitation rates, fostering the
transition from rain to snow.

Pereira