Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
431 AM EDT Fri Apr 10 2020

Valid 12Z Fri Apr 10 2020 - 12Z Mon Apr 13 2020


...Northern Rockies to the Central Plains...
Days 1-2 (12Z Fri-12Z Sun)...
A strong cold front associated with an upper level shortwave
dropping south from western Canada will support areas of heavy
snow moving south and east through the northern Rockies and High
Plains Saturday into Sunday.  Areas impacted are expected to
include the western and central Montana Ranges, as well as the
Absaroka Range, Bighorn Mountains and Black Hills.  In addition to
strong large-scale ascent, upslope flow is likely to bolster
totals, with WPC PWPF continuing to indicate that localized totals
of a foot or more are likely across these areas by early Sunday. 
Meanwhile, favorable upper jet forcing along with low-to-mid level
frontogenesis is expected to extend a swath of lighter amounts
farther east into the central Plains Saturday night into Sunday
morning.  WPC PWPF shows high probabilities for accumulations of
4-inches or more across much of southwestern to south-central
South Dakota, as well as the Nebraska Panhandle into central
Nebraska.

...Central Plains to the Upper Great Lakes...
Day 3 (12Z Sun-12Z Monday)...
An ejecting shortwave associated with a weakening upper low
emanating from the Southwest is expected to lift from the Southern
Plains into the Ohio valley ahead of a northern stream trough
amplifying over the northern Plains.  As the southern stream wave
begins to assume a negative tilt, a rapidly deepening surface low
is forecast to track from the mid Mississippi valley to the Great
Lakes late Sunday to early Monday.  Northwest of the developing
low, strong upper jet forcing in combination with low-to-mid level
frontogenesis is expected to support a stripe of impactful snows
from the central Plains to the upper Great Lakes.  WPC PWPF shows
higher probabilities for snow accumulations of 4-inches or more
extending from northeastern Nebraska to the U.P. of Michigan,
however notable spread shown by the overnight models with respect
to placement and magnitude of heavier amounts suggests significant
changes may be forthcoming in future runs.   

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

Pereira