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FOUS11 KWBC 121909
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
209 PM EST Mon Jan 12 2026

Valid 00Z Tue Jan 13 2026 - 00Z Fri Jan 16 2026


...Great Lakes...
Days 1-3...

Slowly amplifying flow across the east will result in periods of
light synoptic snow, and more impressive lake effect snow (LES)
through the period.

Tonight, a surface trough will track rapidly eastward across the
eastern Great Lakes and into New England while weakening. Although
this feature is progressive and of modest intensity, the enhanced
south-westerly flow in its wake will help spawn LES, especially
downwind of Lakes Erie and Ontario through Tuesday morning. Slowly
rising heights within shortwave ridging Tuesday morning will bring
a quick end to this LES, but at least briefly heavy snow rates of
1"/hr (10-20% chance) will produce significant accumulations,
especially in the Tug Hill Plateau where WPC probabilities are
moderate (50-70%) for at least 4" of snow.

Thereafter, a series of fast-moving shortwave troughs will track
southeast downstream of an amplifying ridge across the western
CONUS. This will lead to a gradually deepening trough in the east,
with increasing cold advection within impressive cyclonic flow. The
first of these shortwaves will track across MI and into northern
New England late D1 into D2, pushing a surface low along the
US/Canada border through Wednesday. Some modest WAA will spread
light synoptically forced snow from WI into MI, but with only
modest accumulations.

More impressively, this low will drag an arctic cold front
southward behind it, aided by a secondary impulse which will track
towards the Gulf Coast helping to deepen the longwave trough with a
closed low over the Great Lakes. While there has been a lot of
uncertainty and latitudinal changes with this evolution the past
few model runs, impressive CAA behind this front will result in
impressive LES, especially in the north-wind lake effect belts
across the U.P., northern L.P., and south of Lake Michigan, with
additional LES likely into northeast Ohio and the Chautauqua Ridge
during D3. WPC probabilities for more than 4" of snow D2 reach
50-70% for parts of the U.P., and then expand to southeast of Lakes
Erie and Ontario D3, with the most significant snowfall likely in a
single band southeast of Lake Michigan (with possible Lake Superior
connection) across northern IN where 8+ inches of snow is possible
(30-50% chance).


...Central Appalachians through the Northeast...
Day 3...

Amplification of the mid-level pattern through Thursday will result
in an anomalous trough digging across the eastern CONUS, reflected
by NAEFS 500-700mb heights falling below the 0.5 percentile across
portions of the Mid-South and Southeast before 00Z Friday. While
this trough is impressive, there has been considerable variability
over the past several model cycles both in terms of the intensity
and placement of the core of this trough, most notably with the
position of the closed low likely to develop Thursday morning.

This closed low will manifest from a deepening shortwave tracking
almost due south out of Manitoba, while secondary energy rotates
towards the Gulf Coast. Together, these will amplify the trough as
noted above, with the lead shortwave closing off and forcing a
slightly negative tilt by the end of the forecast period. At the
same time, a powerful jet streak will arc increasingly poleward
over the Atlantic (downstream of this trough axis) to provide
intense left-exit diffluence overlapping the impressive mid-level
height falls and divergence. While this should support a deepening
surface low pressure, guidance has systematically backed off on the
intensity and southern latitude of this low, with any secondary low
development occurring too far east to bring heavy
snowfall/precipitation to the east coast despite the lead low
moving across northern New England.

The cluster analysis (00z/11 cycle) indicates that the GEFS is
likely underdispersive into D4 as 77% of its members make up one
cluster, which is also the most amplified and slowest due to
extremely different ridging intensity over northern Ontario. While
this solution can't be ruled out entirely, the trend in the GFS
heights combined with the more broad solution envelope of the other
ensembles indicates the more likely scenario is for a low pressure
moving through New England Thursday, with modest warm air aloft
(TROWAL) pivoting behind this low coincident with weak deformation
atop an inverted trough supporting heavier snow generally from
Lake Erie through northern New England. This robust ascent may
overlap effectively with a deepening DGZ as well, with the cold
column supporting fluffy SLR that can accumulate rapidly. While
confidence remains lower than usual at this time range, current WPC
probabilities are moderate to high (50-90%) for at least 4" of
snow in the vicinity of Lake Ontario and northeast into the St.
Lawrence Valley and parts of the Adirondacks.

Farther southwest, there is higher confidence in brief but
impressive upslope snow behind the arctic front on Thursday.
Forecast soundings indicate a deepening PBL with theta-e lapse
rates around 0C/km, coincident with impressive ascent into the DGZ
and then lifting into the terrain, especially from the Laurel
Highlands south into the Southern Appalachians. Initially some of
this precipitation may be rain, but will quickly dynamically cool
(and thermally cool behind the front) leading to periods of heavy
snowfall beginning early Thursday and persisting through much of
D3. WPC probabilities have dropped a bit as QPF trends have been
more to the north, but still indicate a 30-50% chance for at least
4" of snow across the higher terrain of WV, with high probabilities
(>70% or more) for 2+ inches along most of the Appalachians from SW
NC through the Laurel Highlands of PA.


Weiss


$$

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