Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
356 AM EDT Sat Apr 10 2021

Valid 12Z Sat Apr 10 2021 - 12Z Tue Apr 13 2021


...Pacific Northwest to the Northern Plains...
Days 1-3...
An amplifying upper level shortwave trough and its associated
frontal band will move progressively east from the Pacific
Northwest to the northern Rockies on Saturday.  This fast-moving
system is expected to bring windy conditions and periods of snow
to the region.  While snows may be briefly intense, accumulations
are expected to be generally light.  For Day 1 (ending 12Z
Sunday), WPC PWPF high probabilities for accumulations of 4-inches
or more are largely confined to portions of the northern Cascades,
the northern Idaho and northwestern Montana ranges.

As the system moves into the northern Plains on Sunday it is
expected to assume a negative tilt.  A rain-snow mix is expected
across western to central North Dakota on Sunday, changing over to
mostly snow Sunday night.  While widespread heavy accumulations
are not expected, still monitoring the potential for at least an
inch or two, with some potential for heavier accumulations,
setting up along an axis of strong forcing supported by an
elongated low-to-mid level low centered over western North Dakota.

On Monday, this system is expected to phase with a low centered
farther east over the Upper Great Lakes.  Cold air advection on
the northwest side of the consolidating low will support light to
moderate snows spreading across northwestern Minnesota and North
Dakota on Monday.  WPC PWPF shows some 10-40 percent probabilities
for accumulations of 4-inches or more centered over north-central
to northeastern North Dakota on Day 3 (ending 12Z Tuesday).

For Days 1-3, the probability of significant icing (0.25-inch or
more) is less than 10 percent.

Pereira