Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
313 PM EDT Wed Mar 19 2025

Valid 00Z Thu Mar 20 2025 - 00Z Sun Mar 23 2025


...Pacific and Interior Northwest...
Days 1-3...

A series of shortwave troughs will continue impacting the Pacific
Northwest and Interior mountains in-of ID/MT/WY over the next 72
hrs. Current WV satellite imagery shows a fairly robust upper
trough located off the Pacific Northwest coast with a well-defined
diffluent structure on the eastern flank of the trough axis. The
ridge that has been present downstream is beginning to feel the
affects of the upstream disturbance leading to some flattening of
the northern ridge extension and a realignment of the ridge
further east.
This general synoptic progression will lead to increasing mid and
upper ascent focused over a large portion of the west coast with
the primary impacts focused over Northern CA up through much of
OR/WA state. The beneficiary of the heaviest precip core over the
course of D1-2 will be situated within the Cascades with snow
levels
hovering between 3000-4000' MSL prior to the stronger height falls
that will occur as the shortwave progresses towards the coast with
the
mean trough taking on a more negative tilt as it eventually ejects
inland later this evening. The cold frontal progression associated
with the disturbance will move ashore around the time of the mean
trough swinging inland generating a period of falling heights with
snow levels dropping closer to 2000-3000' MSL leading to snow
accumulations becoming more prevalent in the higher valleys around
the Olympic Peninsula and Cascades. Snowfall accumulations of at
least
4" remain very high probabilistically (>70%) across the higher
elevations of the Cascades and Olympics in WA/OR, as well as the
Salmon, Siskiyou and Mount Shasta regions of CA. Mid-level probs
between 40-60% for at least 4" are located over the Northern
Sierra's with the highest chance in elevations above 7500' MSL.

Further inland, the prospects for heavy snow continue later this
evening as the shortwave propagates through WA/ID with the
greatest
forcing aligned over the Cabinet/Lewis/Bitterroot Ranges in the
Interior Northwest with the southern extent benefiting the
Absaroka
Range of northwest WY. Similar probs of >70% for at least 4" of
snowfall exist in those terrain focused regions with the impacts
falling within the back-half of D1 into much of D2. 

As this first trough shifts eastward, forcing will weaken across
the Northwest, but flow across the Pacific becomes increasingly
zonal due to squeezing between broad ridging well west off Baja and
a modest trough across the Gulf of Alaska. This zonal flow will
maintain onshore moisture advection to support rounds of
precipitation into the Northwest, with periodic vorticity lobes
swinging eastward (although maintaining latitude generally north
of OR)
to enhance ascent. Snow levels D2-3 will fluctuate generally
between 2500ft and 4500ft, with rounds of precipitation leading to
periods of heavy snowfall. WPC probabilities both D2 and D3 are
similar in magnitude and areal extent, reaching 70% or more for 4+
inches from the Olympics, to the WA/OR Cascades, eastward through
the Salmon River/Sawtooth Ranges, and into the Northern Rockies.
2-day snowfall in some of the higher elevations could reach 2-4
feet, with up to 1 foot at the higher passes of the Cascades.

Weiss/Kleebauer


...Central High Plains through the Great Lakes...
Day 1...

...Significant winter storm is producing blizzard across portions
of the Midwest today. Key Messages are being issued for this
system...

This powerful winter storm has been as-advertised with wind gusts
topping 50mph that are fostering blizzard conditions, numerous
cases of thundersnow, and prolific snowfall rates of 1-2"/hr
beneath the TROWAL over northern Kansas and eastern Nebraska. As
the 700mb low traverses northern Missouri this afternoon, a ribbon
of 700mb FGEN will pivot and extend over northwest Iowa, southeast
Minnesota, and as far north and east as northern Wisconsin.
Blizzard conditions will be most common from eastern Nebraska to
the Mississippi River between MN/WI. An additional 4-8" of snowfall
are forecast in these areas with localized amounts topping 10"
possible. Snow accumulations of 1-2" and wind gusts of 50-60 mph
are likely in southeast Nebraska and into east-central Kansas. WPC
continues to issue Key Messages for the ongoing winter storm and
they are available for viewing below.

The storm heads for the Great Lakes tonight with heavy snow from
north-central Wisconsin to the Michigan U.P.. Similar 1-2"/hr
snowfall rates are likely within the heaviest snow bands, along
with wind gusts topping 30 mph. Lake enhanced snowfall is likely
along the eastern half of the Michigan U.P. through Wednesday night
and possibly into early Thursday morning. By 12Z Thursday, the
residual TROWAL on the backside of thew weakening storm system will
keep some light-to-moderate snow in the forecast across western
Michigan and as far south as northern Indiana, but the progressive
nature of the snow bands and warmer soil temperatures should keep
any snowfall totals to minor amounts (coating to 3"). Still, wind
gusts surpassing 30 mph would result in reduced visibilities that
make for hazardous driving conditions Thursday morning. Aside from
periods of light snow traversing the Great Lakes and Ohio Valley,
most of the disruptive snowfall will have concluded by Thursday
morning.

Mullinax


...Interior Northeast...
Days 2-3...

By Thursday afternoon, a lobe of 500mb vorticity tracking towards
the Southeast will foster strong upper-level ascent over the
Northeast coast. At the same time, a frontal boundary approaching
from the west will align itself along a more baroclinically favored
area along the Northeast coast that will give rise to a developing
wave of low pressure Thursday night near Long Island. With the
developing low positioned beneath the diffluent left-exit region
of a 250mb jet streak, low pressure will develop quickly and
southerly flow off the Gulf Stream will advect rich Atlantic
moisture around the northern and western flanks of the low. After
initially starting out as rain, a transition to snow will ensue
from the Adirondacks on east through the Berkshires, Green, and
White Mountains on Friday. The storm is a quick mover thanks to the
next upper trough in the active jet stream pattern making its way
towards the Great Lakes. It is worth noting that the EC-AIFS does
show the potential for the storm's deformation axis to linger
longer over central Maine and the White Mountains, which could
lead to some locally heavy snow totals in elevated terrain through
Friday afternoon. Any lingering snow in parts of northern Maine
should come to an end Friday night. WPC probabilities shows
moderate-to- high chances (40-70%) for snowfall totals >2" in the
peaks of the Catskills, Adirondacks, Berkshires, Green, and White
Mountains. The tallest peaks of the Whites, most notably around Mt.
Washington, could see localized amounts approach 6" through Friday
afternoon.

Mullinax




...Winter Storm Key Messages are in effect. Please see current
 Key Messages below...

https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_1.png