Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
350 PM EDT Wed Oct 25 2023

Valid 00Z Thu Oct 26 2023 - 00Z Sun Oct 29 2023

...Northern Rockies through the Northern Plains...
Days 1-3...
A long-duration winter storm, producing periods of moderate to
heavy snowfall, will continue to impact portions of the northern
Rockies and the northern Plains through Thursday.

An ongoing swath of light to moderate snow currently centered over
eastern Montana and North Dakota will continue to shift
east-northeast along with its supporting mid-to-upper forcing. 
Mid level energy and favorable upper jet forcing ahead of deep low
centered over the Pacific Northwest, overlapping a well-defined
low to mid level baroclinic zone, are expected to produce light to
moderate snow across northeastern North Dakota and northwestern
Minnesota, with at least a few inches of accumulation expected
during the evening and overnight hours.

Meanwhile, moderate to heavy snow is forecast to develop back to
the west as Pacific moisture is drawn into a region of enhanced
ascent ahead of the upper low.  Heaviest amounts are still
expected to center across the western Wyoming ranges, with WPC
guidance continuing to show high probabilities (greater than 70
percent) for accumulations of 6 inches or more, across much of the
Absaroka, Teton, and Wind River ranges beginning this evening and
continuing through the day on Thursday.  Locally heavy amounts of
a foot or more can be expected across the higher terrain.  Snow is
expected to diminish across the region Thursday night as the upper
low transitions to an open wave and ejects east into the northern
Plains.

Following a brief lull, snow is expected to develop east of the
northern Rockies tonight and intensify tomorrow across portions of
the northern Plains.  A coupled upper jet and increasing moisture
along a low-to-mid level baroclinic zone will support moderate to
heavy snowfall spreading east-northeast from southeastern Montana
to northwestern Minnesota beginning tonight and continuing into
late Thursday.  HREF guidance continues to show snowfall rates
intensifying to over an inch/hour at times, beginning across
southeastern Montana into southwestern North Dakota and
northwestern South Dakota early Thursday, before shifting
northeast across North Dakota into northwestern Minnesota during
the day into the evening hours.  Snows are expected to diminish
from west to east as the upper wave lifts into western Ontario on
Friday.  The heaviest additional totals across the northern Plains
are expected to center from southwestern to northeastern North
Dakota.  WPC probabilities have increased, now showing a high
chance (greater than 70 percent) for accumulations greater than 8
inches along this axis.

...Central Rockies into the Plains...
Day 3...
Deep southwesterly flow and increasing ascent ahead of a
positively-tilted upper trough settling across the West will
support precipitation developing across the central Rockies, with
locally heavy snows possible across the higher peaks of the
north-central Colorado Rockies.  Lighter snow is forecast to
spread east along a mid level baroclinic zone centered over
Nebraska and southern South Dakota into Iowa and southern
Minnesota.   


***Key Messages for the Northern Rockies through the Northern
Plains Winter Storm***

-- A long duration winter storm will continue from the Northern
Rockies to the Northern Plains. Another round of snow is expected
on Thursday before ending on Friday.

-- Periods of heavy snow may exceed 1"/hr in the Northern Rockies
and High Plains through Friday morning. Travel may be difficult
due to snow-covered or icy roads and poor visibility in areas of
blowing snow.

-- There is a high chance (>70%) of an additional 8 inches of
snowfall over northwest Wyoming and much of southwestern to
northeastern North Dakota.

-- Temperatures will be well below normal by 20-30 degrees across
the Northern High Plains and Northern Plains through the weekend.
Low temperatures in the teens and single digits will be common
over much of Montana into the Northern Plains. Wind chills may dip
below zero at times.

Pereira