FOUS11 KWBC 180828
QPFHSD
Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
328 AM EST Thu Dec 18 2025
Valid 12Z Thu Dec 18 2025 - 12Z Sun Dec 21 2025
...Blizzard conditions continue in the northern Plains today. See
Key Messages linked at the bottom of the discussion for more information...
...Northern Plains, Upper Midwest, Great Lakes... Days 1-2...
By the start of the forecast period (12z Thurs.) a very strong and
mature mid-latitude cyclone is expected to be located across
northern Minnesota, with an estimated central pressure in the low
980s mb. This would place it within record low territory for the
region in mid-late December. The depth of this low pressure system
alone will continue to exhibit a tight pressure gradient on the
northern and western flanks, creating very strong winds (gusts up
to 70 mph) where snowfall is also the primary precipitation type
and some lingering snowpack still exists.
Strong theta-e advection from the Gulf combined with moist eastern
Pacific inflow will result in precipitable water anomalies above
the 97.5th percentile upstream of a developing TROWAL on the
northwest flank of the low center. With the right entrance region
of a strengthening jet streak situated over the Canadian prairie, a
heavy snow band is expected along the MN-Canadian border today. Some
isolated snow squalls are also possible underneath the mid-level
circulation as it dives southeast from the Dakotas into southern
MN tonight. The latest WPC probabilities for >6" on Day 1 highlight
20-50% chances across northern MN. Although the total snowfall from
this event may look modest for this region, strong wind gusts
upwards of 70 mph will lead to dangerous travel due to blowing snow
and potential blizzard impacts, even outside of the area receiving
the most snowfall.
As this system continues eastward tonight into Friday, gusty winds
and developing lake effect snow are the most likely winter-related
hazards. 850 mb temperatures as low as -15C to -20C are expected
behind the strong cold front as lake temperatures remain largely
around 5C. This temperature delta and brief surge of west-
northwesterly flow will allow for heavy lake effect snow in the
typical snowbelts downwind of Lake Superior and Michigan, with
additional heavy snow possible downwind of Lake Erie and Lake
Ontario. The highest WPC probabilities for at least 6" of snow
through Saturday morning is across the Tug Hill Plateau downwind of
Lake Ontario, where chances sit at 40-70%.
...Cascades and Northern Rockies... Days 1-3...
An anchored -WPO/-PNA teleconnection pattern is the driver in the
seemingly endless barrage of atmospheric rivers that is delivering
copious amounts of snow to the mountains of the Pacific Northwest
and the Northern Rockies. The next surge of moisture is expected to
impact the Northwest during the day 1 period with a brief lull and
lowering snow levels on day 2 before the next round enters further
south across northern California on day 3. Meanwhile, moisture
continues to stream inland over the northern Rockies in order to
provide additional heavy mountain snowfall. Snow levels in the
core of this AR will rise to over 9000ft in Oregon this and 6000
to 7000ft in WA by this evening with a powerful cold front
shifting south over WA Thursday night crashing snow levels back
below 2000ft. Farther east, snow levels will rise to 6000t in the
Bitterroots by tonight and approach 7000ft in the Sawtooth. Before
the snow levels rise, however, strong 700mb FGEN will support
several hours of heavy snow at elevations as low as 6000ft in
central ID and 5000ft in the Blue Mountains through this evening.
Farther south, the Tetons, Absaroka, and Wind River Ranges will
reside closer to stronger 700mb jet and anomalous PWATs, giving
these ranges both an abundance of moisture and strong upslope
enhancement to keep heavy snow in the forecast through Saturday
morning for elevation at and above 7000ft.
Prolonged Pacific moisture flux continues to be directed at OR and
into the Northern Rockies on Friday with higher snow levels that
support heavy snow in the more remote reaches of the Cascades and
Northern Rockies. The lone exception will be ongoing westerly upslope
flow into the WA Cascades where snow levels as low as around 1500ft
are expected. The bulk of the heaviest snowfall in the WA Cascades
and Olympics is expected above 2500ft. WPC 72-hour probabilities
show high chances probabilities (>70%) for snowfall totals >24" at
elevations between 3000-4000ft, while similar high chance
probabilities exist above 4,000ft for snowfall totals >30". In the
Rockies, high chance probabilities (>70%) for >12" of snow on days
1 to 2 are present above 5,000ft in the Blue Mountains,
Bitterroots, and the Lewis Range, while those same probabilities
for >24" are present above 6,000ft in the Sawtooth. Snowfall in the
Tetons and Wind River Ranges are likely to range between 1-3 feet
with some localized amounts approaching 4 feet in the more remote
reaches of these ranges through Saturday. Strong winds are also
likely to be a concern across the Wyoming ranges, leading to
extreme impacts in the WSSI due to blowing snow.
The probability of significant icing is less than 10 percent.
Snell
...Winter Storm Key Messages are in effect. Please see current
Key Messages below...
https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_1.png
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