Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
323 AM EST Sun Jan 30 2022

Valid 12Z Sun Jan 30 2022 - 12Z Wed Feb 02 2022

...Pacific Northwest to the Northern Rockies...
Days 1-3...
An upper low centered over the Gulf of Alaska this morning is
expected to transition to an open wave as it moves into northern
British Columbia later today.  Energy digging south of the low is
forecast to phase with a more southerly wave over the eastern
Pacific and move inland across the Pacific Northwest this evening.
 Ample moisture along the associated cold front is expected to
bring organized, moderate to locally heavy precipitation,
including mountain snows, into western Washington and Oregon this
evening.  Snow accumulations will he heaviest in the northern
Washington Cascades, where accumulations of a foot or more are
likely by early Monday.  With snow levels quickly falling behind
the front, significant accumulations are possible down into the
passes, with WPC probabilities indicating accumulations of 4
inches or more likely at both Stevens and Snoqualmie passes by
early Monday.  The frontal band is expected to progress steadily
east Sunday night, bringing locally heavy snows into portions of
the northern Rockies, notably the Bitterroot Range in northern
Idaho and the Rocky Mountain Front in northwestern Montana.

Continued onshore flow, along with a well-defined shortwave
associated with the previously noted upper low, will support
unsettled weather and the potential for additional heavy
accumulations across portions of the Olympics, northern Cascades
and the northern Rockies through Monday into early Tuesday.

...Central and Southern Rockies...
Day 3...
The leading shortwave moving into the Northwest on Sunday is
expected to swing across the northern Plains late Monday-early
Tuesday before lifting north of the upper Great Lakes Tuesday
evening.  At the surface, a trailing cold front will plunge south
through the High Plains and Rockies.  Post-frontal easterly flow,
along with increasing synoptic scale ascent ahead of large scale
trough amplifying over the West, is expected to support widespread
mountain snows across the Colorado and northern New Mexico ranges.
 Locally heavy accumulations are most likely along the Sangre de
Cristo Mountains, where WPC probabilities indicate the greatest
threat for accumulations of 8 inches or more by Wednesday morning.

...Central/Southern Plains to the Great Lakes...
Day 3...
Wednesday morning is expected to mark the onset of what may become
a significant winter storm impacting portions of the central U.S. 
Deepening moisture supplied by low-to-mid level southerly flow
from the Gulf of Mexico into the central U.S. is expected to
support precipitation developing north of a strong cold front as
it drops southeast through the central Plains, mid Mississippi
Valley, and south of the western Great Lakes Wednesday morning. 
Favorable upper jet forcing overlapping mid level frontogenesis is
expected to support an expanding area of wintry precipitation from
Kansas and Oklahoma to Lower Michigan.  While confidence in the
details in limited, at least light accumulations, including snow
and/or ice, do look probable by early Wednesday across this
region.

For days 1-3, the probability of significant icing is less than 10
percent.

Pereira


~~~ Key Messages for Feb 1-3 Winter Storm ~~

-- A large storm system is increasingly likely to affect much of
the central U.S. by the middle of this week.  While itâ€s too far
out for specific snow and ice forecasts, a large, impactful, and
potentially significant winter storm is possible from the southern
Plains through the lower Great Lakes.

-- All types of winter precipitation are possible, ranging from
heavy snow to sleet and freezing rain.  Significant snow and ice
accumulations are possible.

-- There is still uncertainty in the storm track and temperatures,
which will affect the location and potential amounts of snow and
ice.

-- Much below normal temperatures are also expected in the wake of
the storm, especially across the Plains where temperatures 20 to
30 degrees below normal are possible.

-- Begin to prepare for the possibility of winter weather and
hazardous travel conditions this week.