FOUS11 KWBC 020703
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
203 AM EST Mon Mar 2 2026

Valid 12Z Mon Mar 02 2026 - 12Z Thu Mar 05 2026

...Ohio and Tennessee Valley's... Day 1...

Weak shortwave traversing through generally zonal flow from the
Central Plains to the Southern Appalachians will create a period of
modest ascent across the region. Current WV satellite and radar
composite shows the disturbance situated over the mid-Mississippi
Valley this evening moving due east with sights generally along the
central Ohio River Valley. Low-level baroclinicity along a cold
front stalled across the Lower Tennessee Valley will allow for
maintenance of surface low pressure in conjunction with the mid-
level shortwave, tracking eastward along the front allowing for an
enhancement of precipitation in the confines of the Ohio and
Tennessee Valley's, respectively. Despite the weak nature of this
surface low, downstream warm and moist advection will intensify on
850mb winds surging out of the Gulf, transporting moisture and a
warm nose northward, with increasing isentropic upglide leading to
an expansion of precipitation from the Mississippi River to points
east with the northern periphery of the precip field delegated to
the expected winter p-types. The column will remain marginally
supportive of winter weather, however, thanks to the warm nose
protruding the lower confines of the boundary layer meaning the
swath of snow or freezing rain will be relatively narrow,
especially south-central IL through southern OH. Total snowfall is
expected to be minimal at less than 2". However, WPC probabilities
indicate a 50-90% chance of at least 0.01" of ice, with some
locally higher totals approaching 0.1" for southern Ohio around the
proximity of Cincinnati and points north away from the immediate
Ohio River basin as noted via lower probs (10-25%) for the 0.1" threshold.

...Mid-Atlantic to Northeast... Day 1-2...

Mid-level trough over the mid-Mississippi Valley will advance
downstream into the Ohio Valley with an attendant surface low
migrating east along a stalled frontal boundary located over the
Lower Tennessee Valley as of early this morning. As this low moves
east in conjunction with its parent trough, downstream height
rises will occur through intensifying WAA, with the resulting
overrunning/upglide leading to an expansion of precipitation from
the Mid-Atlantic/Central Appalachians into the Northeast/New
England, especially as PWs surge to above the 90th climatological
percentile according to NAEFS. With Canadian high pressure quickly
retreating to the E/NE ahead of this system, the warm nose
accompanying the WAA will be able to surge quickly northeast, and
this will likely result in a rapid transition from snow at precip
onset, to a mix of sleet/freezing rain, and eventually rain, even
as far north as southern New England. Before that transition, some
impactful winter weather is likely through briefly heavy snow
(although accumulations should be modest) and the icy
sleet/freezing rain combination which will lead to some impactful
ice accumulations in the higher elevations of the Central
Appalachians and neighboring valleys where CAD signatures remain
prevalent through Tuesday morning.

WPC probabilities for snow exceeding 2" each day exceed 30% only in
a few isolated areas, the higher Central Appalachians D1, the
Greens and Berkshires on D2, and coastal/Downeast Maine on D2-2.5.
Total snowfall may reach 4" in a few of these areas, mainly in
elevations above 4000ft MSL.

The icing is expected to be more impactful, especially in the
Central Appalachians, where the probability for at least 0.1" of
ice exceeds 50-90% in the higher elevations of the Alleghenies,
the Blue Ridge of VA, and into the Laurel Highlands of PA. Latest
probs for >= 0.25" have come up towards 30-50% within a narrow
corridor along the spine of the Central Appalachians of east-
central WV, mainly as you move south of the Canaan Valley along the
eastern Continental Divide. More widespread icing exceeding 0.01"
is expected from far NW NC through southern New England, including
the I-95 corridor from Washington, D.C. through New York City where
the Tuesday commutes could be impacted by light icing and mixed
precipitation. Highest probabilities for >0.01" of ice accretion
will be found generally northwest of the fall line, especially as
you west of the Blue Ridge and Susquehanna Valley in PA.

...Central Rockies... Days 1-2...

A potent closed low emerging from the Pacific has begun to push
ashore this evening over Northern California with an expectation
of continuing eastward across the Great Basin today, eventually
ejecting into the Central Rockies by Tuesday morning. Although
this feature is now progged to weaken as it translates eastward, it
will still maintain sufficient amplitude to drive robust height
falls/PVA into the Central Rockies, which when combined with a
modest (90-100kt) jet streak placed favorably into the Central
Plains, will result in lee cyclogenesis Monday evening. This low
will deepen at least marginally as it advects E/SE into Tuesday,
while downstream moisture from the Gulf gets wrapped cyclonically
into the system to create anomalous PWs as high as the 97th
climatological percentile. The combination of synoptic ascent with
upslope enhancement north/northwest of the surface low will create
areas of heavy snow, especially above 7000 ft in the Uintas,
Tetons, Wind Rivers, Laramie Range, and across much of the CO
Rockies including the Park and Front Ranges. In these areas, WPC
probabilities are high (50-80%) for at least 4" D1 in NW WY,
expanding to include the terrain of UT and CO on D2. Locally as
much as 10" of snow is possible in the higher terrain.

...Pacific Northwest... Day 2-3...

An amplifying shortwave trough currently positioned over the Gulf
of Alaska will gradually advect southeastward, coming onshore
Wednesday morning. As this shortwave moves onshore, it will produce
impressive height falls which will overlap with the RRQ of a
meridionally strengthening jet streak (downstream of the primary
trough axis) to drive pronounced deep layer lift into the
Northwestern CONUS. At the same time, confluent flow immediately
ahead of the mid-level trough will gradually back to be more SW,
pumping elevated IVT onshore to provide the moisture needed for
heavy precipitation. Global deterministic and their ensembles are
starting to converge on a relatively modest IVt advection regime
~250 kg/ms, aligning with the ECENS outputs that have been
consistent within this range for the past few days. This scenario
should result in periods of heavy snow, especially in the
Olympics, Cascades, and Northern Rockies, with snow levels falling
steadily from around 5000 ft to 4000 ft beneath the upper trough
and a corresponding cold front. WPC probabilities D3 are high
(>70%) for at least 4" of snow along the spine of the Cascades of
OR and WA, the highest terrain of the Olympics, and parts of
OR/ID/MT from the Blue Mountains through the Sawtooth Region and
into the far Northern Rockies near Glacier NP.

Weiss/Kleebauer
$$
--- SBBSecho 3.28-Linux
 * Origin: Capitol City Online (618:250/1)