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FOUS11 KWBC 050758
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
258 AM EST Mon Jan 5 2026

Valid 12Z Mon Jan 05 2026 - 12Z Thu Jan 08 2026


...Upper Midwest/Great Lakes/Northeast...
Days 1-3...

Shortwave currently over Wisconsin will track rapidly eastward
while continuing to de-amplify this morning, likely moving off the
Maine coast by Tuesday morning. The weakening trend of this impulse
driven by the absorption into more pinched westerlies will
gradually weaken ascent such that ongoing heavy snow near the Great
Lakes will transition to primarily light snow from Upstate NY
through central/northern New England. Light accumulations of 1-3"
are expected in this region, with locally as much as 4" possible in
the Tug Hill Plateau due to lake enhancement and southern Greens
thanks to upslope flow. In general, however, the most substantial
impacts from this shortwave will end before the new D1 period
begins.

Almost as quickly as this first shortwave exits New England, a
second impulse following quickly in its wake will begin to
organize over the Upper Midwest Tuesday morning. This next impulse
stems from a weak vorticity lobe which ejected from the Pacific
trough late Sunday, crested the western ridge, and begins to deepen
as it moves towards the Great Lakes Tuesday. Unlike the lead
shortwave which weakens with time, this feature is expected to
gradually strengthen and gain amplitude as it moves eastward into
Wednesday. Additionally, this shortwave will be joined by an
impressive jet streak to its south (reaching 160 kts from the
Central Plains to the Ohio Valley) and accompanied by Pacific
moisture (PWs above the 90th climatological percentile according to
NAEFS). The resulting surface low which will develop will
additionally enhance ascent, and a swath of moderate to heavy
precipitation is likely from the western Great Lakes through New
England.

Thermally, the environment is marginal for wintry precipitation due
to antecedent ridging aloft and strengthening WAA, so p-type from
WI, across the Great Lakes, and into at least central New England
will likely be a mix of rain, snow, sleet, and freezing rain. The
mixed precip will result in some impacts, but WSSI-P indicates only
minor impacts expected due to the progressive nature and mixed
p-type in this region. Still, WPC probabilities for ice accreting
to at least 0.1" reach 30-50% from near the Twin Cities through
central WI and into lower MI. Locally 0.2" of ice is possible, but
snow amounts are expected to be very light as the guidance has
trended a bit warmer tonight.

During D3, secondary low pressure development in the Gulf of Maine
could make snowfall and impacts a bit more impressive over New
England. While there remains considerable uncertainty into the
timing of this secondary low development, a surge of cold air
wrapping behind (and a developing in-situ CAD) should keep p-type
primarily snow in northern New England and mixed
snow/sleet/freezing rain in the higher elevations of Upstate NY and
central/southern New England. This is reflected by an increase in
WPC snowfall probabilities, which, while still modest, are as high
as 10-30% D2 into D3 in the higher terrain of NH and ME. Icing to
the south of the snow may locally reach above 0.1" (30-50% chance
in the Adirondacks, Greens, and Monadnocks).


...California...
Day 1...

Amplifying trough off the Pacific Coast will deepen into a closed
low today, with this closed center drifting southeast towards Baja
California by Wednesday morning. Downstream of this evolution,
continued SW mid-level flow and aligned Pacific jet energy will
pump moisture northeast, reflected by high probabilities (>80%
chance) for IVT exceeding 250 kg/m/s surging into CA. Although this
IVT will be pushed onshore via WAA, snow levels will generally
remain around 5000 ft as the WAA is offset by slowly sinking
heights downstream of the trough axis. At the surface, of wave of
low pressure will drop along the CA coast, and while there is
considerable spread in the longitudinal placement of this feature,
sufficient additional ascent into the moistening column will
result in periods of heavy snow above 5000 ft in the Sierra and
northern CA ranges D1, and WPC probabilities are high (>90%) for at
least 6 inches more of snow, with more than 12 inches possible in
the higher terrain, especially around Mt. Shasta.


...Olympics, Cascades, and Northern/Central Rockies...
Days 2-3...

Mid-level flow becomes increasingly zonal across the Pacific,
directing energy and moisture into the Pacific Northwest beginning
on Tuesday. Aloft, a jet streak will intensify directly atop the
zonal mid-level flow, providing additional funneling of moisture
onshore before the jet starts to slowly sink southward on
Wednesday. This is reflected by a brief period of elevated IVT
(>90% chance exceeding 250 kg/m/s but less than 25% chance of 500
kg/m/s) Tuesday into OR/WA. As forcing for ascent increases D2 and
D3 through gradual height falls, left-exit diffluence, and
impressive upslope into the Olympics, Cascades, and Northern
Rockies, heavy snowfall will result in these areas, with snow
levels Tuesday 2000-3000 ft, falling to as low as 1000 ft late
Wednesday (higher but still just around 2500 ft in the Central
Rockies).

This cooling column, increasing ascent, and impressive moisture
indicates that heavy snowfall will become increasingly widespread
above these snow levels, especially in the upwind regions of the
Olympics, Cascades, and Northern Rockies. Forecast soundings
suggest steepening lapse rates up to as high as 750mb, which
indicates accumulating snow could occur even lower than these snow
levels, and the NBM 10th% fall to as low as 500 ft in the Pacific
Northwest, so lowland snow is possible late in the forecast period.
However, the most significant accumulations, which are likely to
be impressive, will be above 2000 ft, but will encompass most of
the Cascade and Northern Rockies Passes leading to challenging
travel later this week. WPC probabilities D2 for more than 6 inches
of snow are high (>70%) in the Olympics, Cascades of WA and OR,
the Northern Rockies, and as far south as the NW WY ranges (Tetons,
Wind Rivers), with 1-2 feet likely in the higher elevations of
these ranges. During D3, precip wanes a bit across the
Intermountain West, but persists in heavy fashion across the
Olympics and Cascades where WPC probabilities for 12+ inches remain
above 50%. As noted above, the falling snow levels will result in
dangerous travel across all of the important Cascades Passes this
week.



Weiss


$$

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