Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
401 PM EDT Thu Oct 26 2023

Valid 00Z Fri Oct 27 2023 - 00Z Mon Oct 30 2023

...Northern Plains...
Day 1...
A mid-to-upper level shortwave associated with the ongoing snow
across North Dakota will eject east-northeast from the northern
Rockies/High Plains this evening, and move progressively across
the Dakotas and northwestern Minnesota before lifting into western
Ontario early tomorrow.  Favorable upper jet forcing along with
low-to-mid level frontogenesis will support moderate to heavy snow
northwest of the surface low.  HREF guidance continues to show
snowfall rates of over 1 in/hr at times shifting east across
northeastern North Dakota into northwestern Minnesota this evening
and overnight.  Snow is expected to diminish as the system moves
into southern Canada tomorrow morning.  WPC probabilities show
that an additional 4 inches or more is likely (greater than 70
percent chance) across northeastern North Dakota and northwestern
Minnesota during the evening and overnight hours.

...Central Rockies & Central High Plains...
Days 2-3...
A positively tilted upper trough will dig south across the western
U.S., with the axis dropping into the Great Basin by late Saturday
and the Four Corners region on Sunday.  Increasing moisture and
ascent along with deepening cold air in the wake of a front
settling south of the central Rockies and Plains will raise the
threat for impactful mountain snows beginning Saturday and
continuing into Sunday across the north-central Colorado ranges. 
WPC probabilities show widespread high probabilities (greater than
70 percent chance) for accumulations of 8 inches, with localized
high probabilities for greater than a foot across some of the
higher terrain.  While the heaviest amounts are expected to remain
west of the I-25 corridor, accumulating snows are likely, with WPC
guidance showing high probabilities for accumulations of 2 inches
or more extending out across southwestern Wyoming and northeastern
Colorado, including the Cheyenne and Denver metros.

Models continue to show a signal for at least light to moderate
amounts setting up along a mid level baroclinic zone extending
across Nebraska and southern South Dakota.  There is some signal
for locally heavy amounts developing along this band, with the GFS
being one of the more bullish members.  However, models are far
from agreement on an axis or amounts at this point.  Even with the
uncertainty, the probability for accumulations greater than 4
inches has increased with the latest run, now showing a moderate
chance (greater than 40 percent) extending from the southern
Nebraska Panhandle into central Nebraska.

Farther south, a wintry mix is expected, with accumulating ice
possible across portions of Kansas on Saturday before spreading
south into the Panhandle Region Saturday night along the
northwestern edge of the precipitation shield.     


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

--Additional rounds of heavy snow are forecast to persist tonight
before ending on Friday.

--Periods of heavy snow near 1"/hr are likely (60-90% chance) in
the Northern 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 medium chance (30-60%) of an additional 6 inches of
snowfall over central and northeastern North Dakota through Friday
morning.

--Temperatures will be 20-30 degrees below normal 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.

--Dress in layers and wrap up well before going outside to protect
yourself from hypothermia.


Pereira