Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
424 AM EDT Fri Apr 14 2023

Valid 12Z Fri Apr 14 2023 - 12Z Mon Apr 17 2023


...Northern and Central Rockies...
Day 1...
A broad-scale trough centered over the western U.S. is expected to
amplify and shift east as a series of shortwaves move southeast
into the base of the larger scale feature.  Ongoing snows over the
central Rockies will continue to spread east across the western to
central Colorado, southern Wyoming, and northern New Mexico ranges
today.  WPC probabilities continue to show accumulations of 4-8
inches likely in the higher terrain, with locally heavier amounts
possible.  Guidance continues to suggest that post-frontal upslope
flow will help accentuate totals along the Colorado Front Range,
where WPC guidance is showing higher probabilities for
accumulations of 8 inches or more.  Meanwhile, snow showers are
expected to develop farther to the north along the northern
Rockies, with mostly light accumulations expected.

...Upper Midwest...
Days 2-3...
The previously discussed trough moving across the Rockies today is
forecast to continue to translate east, amplifying further as it
moves across the Plains on Saturday.  Most models show the trough
beginning to assume a negative-tilt, with an upper center
developing over the mid Mississippi Valley on Sunday.  This will
likely support the transition from rain to snow along the western
edge of the associated precipitation shield.  While the high sun
angle will likely hamper the threat, some models do suggest that
rates will be sufficient for accumulating snow.  Models still
present plenty of uncertainty however, with WPC guidance showing
only low probabilities for any significant accumulations through
late Sunday.  However, by Sunday night with the models showing the
system continuing to amplify as it tracks north into the Great
Lakes, confidence is increasing on the potential for significant
snow accumulations impacting portions of the upper Great Lakes
region.  While confidence in the details is low, it appears likely
that strong forcing attributed to a coupled-upper jet and
low-to-mid level frontogenesis will contribute to at least light
accumulations, with a significant late-season storm possible
across the region.  Probabilities for at least an inch of snow
have increased across much of central to northern Wisconsin with
the latest run.  Higher probabilities for heavier amounts remain
centered over the western U.P. of Michigan, where northwest flow
on the backside of the system is likely to support some
lake-enhanced totals Sunday night into early Monday.

...Pacific Northwest...
Day 3...
Shortwave ridging centered over the region Days 1 and 2 will give
way to a trough moving out ahead of a low dropping southeast from
the Gulf Alaska.  This will bring a well-defined cold front and
the return of wet weather into the region on Sunday.  High snow
levels are expected to confine any heavy accumulations to the
higher elevations of the Olympics and the Cascades during the day.
 However, snow levels are forecast to fall with the frontal
passage, bringing accumulating snows into the Cascade passes
Sunday night.

The probability for icing over 0.1" is less than 5 percent Days
1-3.

Pereira