Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
509 PM EDT Mon Apr 12 2021

Valid 00Z Tue Apr 13 2021 - 00Z Fri Apr 16 2021


...Northern Plains...
Day 1...

Snow is expected tonight into Tuesday across northern North Dakota
and northwest Minnesota as low level cold advection supports all
snow, with the precip uncertainty confined to northeast Minnesota
where temps are initially too warm for snow. The combination of
deep moisture and low level lift overlaps in eastern North Dakota
to adjacent northwest Minnesota, where locally several inches of
snow are expected.

Snow accumulations of 4 inches or more are likely across much of
northern North Dakota into northwestern Minnesota, with isolated
maxima to 8 inches. The event winds down as the upper trough
weakens and moves east, with ascent decaying Tuesday
afternoon/evening, with snow coverage/intensity declining as a
result.

...Great Basin to the Central Rockies...
Days 1-3...

Tonight, developing low level southerly flow at 700 mb  advects
moisture north with pooling moisture along the front range of CO
combining with 700 mb convergence maxima to produce lift and light
snow developing.
Tomorrow night, the models show a developing 700 mb closed low in
northern NV that drifts east northeast across northern Utah Wed
and then WY Thu. Downstream from the low, continuing bands of 700
mb convergence support continuing snow showers in the ranges of
CO, with several more inches likely on Day 2 into early Day 3.

Enhanced moisture convergence along the 700 mb low tracks combines
with upper divergence maxima to support locally heavy snow, so
locally heavy snow maxima are expected in higher elevations of
northern NV to northern UT, southeast ID, and WY. These areas
include the Uinta mountains in northern Utah, the Wind River Range
and Bighorns of Wyoming, and the Medicine Bow Mountains and Front
Range in southeastern Wyoming to central Colorado.  WPC PWPF shows
moderate probabilities for snowfall accumulations of 8 inches
across those areas. 

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

Petersen