Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
432 AM EDT Sat Apr 11 2020

Valid 12Z Sat Apr 11 2020 - 12Z Tue Apr 14 2020


...Northern Rockies to the Central Plains...
Day 1 (12Z Sat-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 western to south-central South
Dakota, as well as the northern Nebraska Panhandle into central
Nebraska.

...Central Plains to the Upper Great Lakes...
Days 2-3 (12Z Sun-12Z Tue)...
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 lower Ohio valley to the Great Lakes
Sunday night 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, with the
heaviest amounts over northern Wisconsin and the U.P. of Michigan
- where lake enhancement in the wake of the departing system is
likely to bolster totals late Monday into Tuesday.    WPC PWPF
continues to show high probabilities for snow accumulations of
4-inches or greater from northeastern Nebraska and southeastern
South Dakota to the western U.P. of Michigan.  High probabilities
for accumulations of a foot or more are shown across portions of
northern Wisconsin and the western U.P. of Michigan.  Forecast
certainty was limited by continued model spread.  Overnight models
fell roughly into two camps - with the NAM, SREF Mean, ECMWF and
EC Ensemble Mean indicating an axis of heavier amounts well to the
northwest of the GFS, GEFS Mean and UKMET.  WPC continued to
prefer a compromise solution, but with more weight given to the
northwest camp.

...Southwest to the Southern High Plains...
Days 2-3 (12Z Sun-12Z Tue)...
Models show a longwave trough covering much of the contiguous U.S.
early next week.  Mid level energy moving into the base of the
trough along with a developing upper jet couplet is expected to
support a stripe of organized precipitation, including high
elevation snows, across northern Arizona and New Mexico Sunday and
Monday.  Cold air in place over the High Plains is forecast to
support accumulating snows over eastern New Mexico into the Texas
Panhandle Monday night into Tuesday morning.

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

Pereira