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FOUS11 KWBC 051907
QPFHSD

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

Valid 00Z Tue Jan 06 2026 - 00Z Fri Jan 09 2026


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

A progressive shortwave trough over southern Ontario is producing
weak PVA over the Northeast, along with minor 850-700mb WAA ahead
of the trough. Sufficient 850-300mb moisture is present to support
periods of light-to-moderate snow over the Northeast this afternoon
and evening, but snow should taper off not long after midnight.
Minor snowfall accumulations of 1-4" are expected with some slick
conditions on untreated surfaces possible.

As the trough in the Northeast exits east into the North Atlantic
tonight, another disturbance with Pacific origins follows on its
heels as it develops a wave of low pressure in the Midwest. Located
beneath the divergent left-exit region of a 150kt 250mb jet streak,
the storm will gradually strengthen at the same time as 850-700mb
WAA ahead of the low also increases. While this disturbance is
similar to the one over the Northeast in that it is progressive,
there will be a stronger warm nose aloft that makes ice the primary
concern over the Midwest and Great Lakes this time around. An icy
wintry mix is beginning over parts of the eastern Dakotas and
central MN this afternoon, but as WAA increases, so will the rates
of sleet and freezing rain. Look for icy conditions to unfold
across WI and over MI's U.P. (Upper Peninsula) tonight, then over
MI's L.P. (Lower Peninsula) by Tuesday morning. The wintry mix may
linger over the Great Lakes and Midwest through midday Tuesday, but
should taper off by Tuesday evening, meaning there could still be
lingering icy conditions for the Tuesday afternoon rush hour. WPC
probabilities show at least moderate chances (>50%) for ice
accumulations over one-tenth of an inch of ice from southern MN to
northern MI. The WSSI shows a large swath of at least Minor
Impacts (slick travel conditions possible, use caution) from
southern MN on east through northern WI and into central MI. There
is an area denoting Moderate Impacts (hazardous travel conditions,
closures possible) in the heart of WI where localized ice
accumulations could approach one-quarter inch.

As the storm tracks over southern MI Tuesday afternoon, the same
synoptically-forced mechanisms aloft will support periods of snow
over the Adirondacks and northern New England. Farther south, a
wintry mix of sleet and freezing rain will envelope central NY,
northern NJ, and northeast PA starting as early as Tuesday
afternoon, then advance east into the heart of New England with the
Green Berkshires, and Worcester Hills Tuesday night. Throwing a
wrench into the forecast is the expected development of a coastal
low along a coastal front off southern New England. This transition
from the primary low over southern Ontario to the new coastal low
off the MA Capes will be pivotal in how long central New England
stays a wintry mix and when/if they transition to snow. Northern
Maine and the White Mountains have the greater chances of seeing
snow as their primary precip type for this event Tuesday night and
into Wednesday morning. Through the daytime hours Wednesday, an icy
wintry mix is likely to linger over coastal ME but all
precipitation tapers off by Wednesday evening.

WPC probabilities show high chances (>70%) for ice accumulations
>0.01" over the Catskills, Adirondacks, and much of interior New
England. The Adirondacks, Berkshires, Green, and Worcester Hills
have moderate chances (40-60%) for ice accumulations over one-tenth
of an inch. In terms of snowfall, the tallest peaks of the
Adirondacks, northern Greens, Whites, and northern ME show moderate
chances (40-60%) for snowfall over 2" through Wednesday evening,
but should the coastal low strengthen faster, localized snowfall
totals of 4-6" could transpire in northern ME. WSSI shows these
winter hazards generally look to cause Minor Impacts, indicating
the potential for some areas of hazardous travel due to snow and
ice Tuesday night and through Wednesday.


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

A powerful storm system over southern AK will work in tandem with
an unusually strong subtropical ridge north of HI to create a
robust 160kt 250mb jet streak in the northeast Pacific. This
enhanced polar jet will direct a potent IVT that ranges between
250-500 kg/m/s at the Pacific NW, while at the same time, being
co-located beneath the divergent left-exit region of the
aforementioned 250mb jet streak. While moisture content is not
overly anomalous, the westerly IVT supporting enhanced upslope
flow, falling mid-upper level heights, and supportive jet streak
dynamics will support rounds of heavy mountain snow over the
Cascades and Olympics. Snow levels will fall to as low as 2,000ft,
although the heavier and more impactful snow will be observed above
3,000ft. The heaviest snowfall arrives Tuesday afternoon, and
following a brief break in the heavier snowfall rates early
Wednesday morning, another disturbance arrives later in the day
with more snow in the Cascades and Olympics. This time, with a
colder air-mass aloft, snow levels dip to as low as 1,000ft
Wednesday afternoon and continuing into Thursday.

With snow continuously falling in these ranges through Thursday,
WPC's 72-hour snowfall probabilities are quite impressive with high
chances (>70%) for snowfall totals >24" above 3,000ft in the
Cascades and Olympics, including passes such as Snoqualmie and
Stevens. Current WSSI shows Moderate Impacts at these passes
(hazardous travel, potential closures) but given the higher end
snowfall potential, the WSSI-P does depict a scenario (20-30%
potential) for Major Impacts that would imply more dangerous travel
conditions. Regardless, multiple days of heavy snowfall is
expected, so passes will likely contend with prolonged delays and
potential closures.

The Pacific moisture spills east into the Northern Rockies as well
through the first half of the week. There is already lingering
Pacific moisture leftover from the heavy rainfall and mountain snow
in CA that is supporting periods of snow today and into tonight in
the Sawtooth, Bitterroots, Tetons, Wind River, and as far south as
the more remote reaches of the CO Rockies. As Pacific moisture
arrives Tuesday afternoon thanks to 250 kg/m/s IVT extending as far
east as eastern WA, periods of heavy snow ensue above 4,000ft in
the northern Bitterroots, above 5,000ft in the Lewis Range, Blue,
and Sawtooth Mountains, and above 7,000ft in the Absaroka, Tetons,
and Bear River Ranges. WPC probabilities over the next 72-hours
show high chances (>70%) for over 12" of snow in these ranges with
moderate chances (>50%) for snowfall eclipsing 24" in the more
remote elevations of the Bitterroots, Sawtooth, Tetons, and Wind
River ranges. The peaks of the Tetons sport the best odds of seeing
localized snowfall totals over 3 feet.

By Wednesday evening, attention turns to the central Rockies where
they will be placed ahead of two approaching shortwave troughs; one
diving south and east from the Pacific NW and another approaching
from northwest Mexico. As the former disturbance deepens Wednesday
night and into Thursday, periods of mountain snow are likely to
envelope the Wasatch, Uinta, all of the CO Rockies, and even as far
south as the Mogollon Rim and the Rockies of NM. Guidance shows a
fair amount of uncertainty in the handling of these two features,
so confidence in totals remains low. That said, the pattern support
accumulating mountains snow (generally above 7,000ft) Wednesday
night and into Tuesday. Residents along the Front Range of the
CO/WY/NM Rockies will want to monitor the forecast closely as this
could result cause impacts to travel and commerce late week.


Mullinax





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