FOUS11 KWBC 012006
QPFHSD
Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
406 PM EDT Wed Apr 1 2026
Valid 00Z Thu Apr 02 2026 - 00Z Sun Apr 05 2026
...Northern Plains through the Great Lakes...
Days 1-2...
...Significant late-season snow and freezing rain likely to create
substantial impacts...
Significant winter storm begins tonight as a low pressure develops
in the lee of the Colorado Rockies and then tracks northeast into
the Upper Midwest and Great Lakes, reaching Ontario Friday
afternoon. This system is driven by a shortwave that will be moving
atop the Central Rockies Thursday morning and amplify into a
negatively tilted trough as it lifts northeast into Ontario by
Friday. The trends in the guidance have been for this shortwave to
be a bit deeper, leading to sharper height falls combined with the
LFQ of a modest but meridionally arcing jet streak. This will
produce significant deep layer ascent to deepen the surface low as
it tracks northeast, and the guidance has clustered to a slightly
slower but stronger surface low today.
As this low tracks northeast, impressive column PW will manifest=20
across the Upper Midwest in response to dual moisture streams
interacting into the region. Residual IVT from the Pacific will
continue to push inland with the shortwave over the Rockies, and
IVT probabilities for >250 kg/m/s remain high, bringing elevated
moisture into the region on the 700-500mb flow. In the lower
levels, return flow out of the Gulf begins to intensify as 850mb=20
winds surge northward, spreading a pronounced theta-e ridge
northward into the system. The overlap of these two moisture
streams will create PW anomalies that are above the 99th percentile
of the CFSR climatology according to NAEFS, and this is likely to
be a very wet early-spring system.=20
The primary driver of the associated precipitation will be
intensifying isentropic ascent, especially along the 290-295K
surfaces where mixing ratios of 4-5 g/kg will support heavy
precipitation anywhere within the system. The strongest ascent will
be where the 850mb winds and accompanying WAA produce intense fgen,
and this will result in an above-freezing warm nose surging
northward. The surface high pressure responsible for the cold/dry
antecedent airmass will retreat rapidly to the northeast, and=20
regional soundings indicate that a lack of sufficient dry-bulb=20
advection will promote a rapid transition from snow to freezing=20
rain, especially for eastern MN through MI, with snow remaining the
primary p-type for northern MN and the eastern Dakotas.
In the snow areas, heavy snow rates will develop as fgen=20
strengthens and then a modest deformation axis develops to drive=20
ascent into the modest TROWAL which will form as the theta-e ridge=20
wraps cyclonically into the system. With elevated PWs in place,=20
this should result in rates approaching 1"/hr at times as supported
by the WPC prototype snowband tool, and any local banding will
enhance the duration of snowfall. Overall snowfall amounts will be
modest due to the rapid progression of this system, but a slightly
slower track and some heavier snowfall rates will still support a
high risk (>70% chance) for more than 4 inches of snow from eastern
ND through northern MN and the Arrowhead, with locally as much as 8
inches possible (10-30% chance) across this same axis.
Farther east, the primary p-type will likely be freezing rain as
the warm air aloft floods northward without any strong forcing to
prevent this. The cold layer beneath the warm nose is quite deep,
above the 75th% for cold-layer depth for freezing rain, so there
may be some considerable sleet before changeover to freezing rain,
with 0.5" to 1.0" of sleet possible for northern WI and the U.P.=20
of MI. However, the greatest impacts are likely from the Buffalo=20
Ridge through the Twin Cities, into central WI, and the northern=20
L.P. of MI where WPC probabilities indicate a moderate to high risk
(50-90% chance) of at least 0.1" of ice, with 0.25" or even 0.5"=20
possible (50% and 20% respectively) across parts of WI.
Key Messages are in effect for this system and are linked below
(Key Messages #1).
...Northern New England...
Day 2...
Moisture streaming northward ahead of the large Midwest winter
storm will surge into New England Thursday night and Friday on
persistent warm advection. As the WAA intensifies through the
850-700mb layer, precipitation will expand from Vermont into Maine
in response to the maximizing fgen. During precipitation onset,
wet-bulb temperatures will be below freezing (with a full below-
freezing column across Maine) as Canadian high pressure only slowly
retreats to the northeast. As this high retreats and the WAA
continues, the accompanying warm nose should surge all the way into
Canada causing a p-type transition from snow to sleet to freezing
rain, and eventually rain. Before the changeover, a period of heavy
snow with rates around 1"/hr are possible, primarily just for
northern Maine, leading to WPC probabilities that are 50-70% for at
least 4 inches of snowfall. Farther south, from the White Mountains
of NH into the higher terrain of northern/central ME, a period of
freezing rain is expected which will lead to a moderate risk
(30-50% chance) of at least 0.1" of ice accumulation. Although the
snowfall by itself, or the icing by itself, may not result directly in warning-level impacts, the combination of a period of heavy snow,
followed by sleet, followed by freezing rain, will create
treacherous travel and some elevated snow load on trees/wires
leading to substantial impacts across parts of northern ME.
While the heaviest snow and ice are expected only in the higher=20
terrain or highest latitudes of northern New England, light snow=20 accumulations and light icing is expected for much of northern and=20
central New England before p-type transitions to all rain by late=20
Friday morning.
...Pacific Northwest/Sierra through Northern/Central Rockies...=20
Days 1-2...
Active winter weather continues through late-week as an anomalously
deep trough digs across the Northwest bringing widespread heavy
snow to the terrain through Friday.
At the beginning of the period /00Z Thursday/ a shortwave will be
positioned off the WA coast, with impressive confluent flow to its
south driving moisture onshore as reflected by IVT probabilities
for at least 250 kg/m/s exceeding 90% from the GEFS/ECENS lifting
into WA/OR D1. This shortwave is progged to amplify into a potent
closed low and dig into the Pacific and Interior Northwest by
Thursday morning, and then continue to move slowly but steadily
eastward with impressive height falls reaching the Northern and
Central Rockies by Friday morning. This feature will be expansive
and amplified, reflected by a large swath of 500mb heights falling
below the 10th percentile within the CFSR climatology according to
NAEFS.=20
As this closed low dives E/SE through the area, the accompanying
Pacific jet streak (which will be weakening from 140 kts early D1
to 110 kts late D1) will continue to be favorably positioned to
enhance deep layer lift through its diffluent LFQ, resulting in
sufficient ventilation for surface low development tracking from WA
to WY by early D2. This low will also drag a strong cold front
behind it, bringing colder temperatures and lowering snow levels
through the event.
With significant deep layer ascent in place, and moisture
increasing through the onshore flow from the Pacific, precipitation
is expected to be widespread Thursday into Friday. Initially, snow
levels are expected to be between 6000-8000 ft ahead of the cold
front, but will fall sharply as it tracks southeast, dropping to as
low as 2500-3000 ft across much of the region. It appears that the
heaviest precipitation will occur along and ahead of this front, so
the heaviest snowfall should remain at the mid-to-higher
elevations. However, some light snow is expected down to many of
the passes as the cold front progresses eastward, leading to
widespread hazardous travel before precipitation wanes Friday
morning.
On D1 /00Z Thu to 00Z Fri/ WPC probabilities indicate the highest
snowfall potential will be across the northern Sierra and Oregon
Cascades where the moisture will be directed orthogonally into the
terrain, leading to upslope enhancement, with additional
significant spillover leading to heavy snow as well into the=20
Salmon River/Sawtooth Ranges, and the Tetons/Wind Rivers. In these=20
areas, WPC probabilities are high (>70%) for at least 8 inches of=20
snow, with locally 12-18" possible in the highest terrain.=20
Elsewhere on D1, WPC probabilities suggest a high risk for at least
4 inches for the WA Cascades, much of the Northern Rockies, and=20
surrounding terrain as far south as the Ruby Mountains of NV,=20
Uintas of UT, and even into the Park Range and portions of the CO=20
Rockies.
By D2, the focus of heaviest snow shifts well to the interior,
leaving heavy snow only across the Northern and Central Rockies as
a significant lee cyclone develops across WY (more on this in the
section below). Additional snowfall D2 has a high risk (>70%
chance) of at least 6 inches across the Absarokas and Big Horns,
with lower probabilities extending into the Little Belts, Lewis
Range, and portions of the CO Rockies and Laramie range. The
heaviest snowfall D2 should be above 4000 ft.
...Northern Plains to the Upper Midwest...
Day 2.5-3...
...Significant late-season snow and freezing rain likely to create
substantial impacts...
A slow moving 500mb closed low over WY will generate healthy PVA=20
aloft and increased 700mb Q-vector convergence over the northern=20
High Plains on Friday. Snow will already be falling over central=20
MT and the Big Horns Thursday night, but as a surface low=20
strengthens along the KS/NE border Friday morning, 850-700mb WAA to
the north of the low will support banded precipitation on the=20
northern flank of the 500mb low. Guidance is in good agreement on=20
the presence of a very moist 700-300mb column with strong vertical
velocities aloft supporting snowfall rates of 1-2"/hr. On the=20
eastern flank of the storm, freezing rain and sleet will be more=20
prominent from central MN on north and east into northern WI and=20
the U.P. of MI. Snow will persist over northern MN into Saturday
with any ongoing ice changing over to snow in northern WI and the
western U.P. of MI. Cyclonic flow on the back side of the storm
will keep periods of snow in the forecast across the U.P. of MI
through early Sunday morning.=20
WPC probabilities show a large swath of at >50% probability for at
least 8 inches of snow from southern ND and norther SD on east into
northern MN. Where the pivoting deformation zone forms in southern
ND and northern SD sets up will determine who sees the most snow.
WPC probabilities show moderate chances (40-60%) for >12" of snow
in south-central ND and north-central SD at this time. In fact,
there are low chance probabilities (10-30%) for localized amounts
surpassing 18". Farther east, WPC probabilities for at least a=20
tenth of an inch of ice show moderate chances (40-60%) over=20
southeast SD/southwest MN but high chances (>70) over northern WI=20
and the U.P. of MI.. It is in northern WI and the U.P. of MI where
there are concerns for prolonged affects between the two winter
storms late week, given WPC probabilities show at least moderate
chances (>50%) for additional ice accumulations over one-quarter
inch. The Day 3 WSSI currently shows Moderate Impacts in southern=20
ND and northern SD due to the heavy snowfall, as well as in
northern WI and the U.P. of Michigan due to ice accumulations.
Weiss/Mullinax
...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...
https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!6kBIVWskrvb06emiItPe0iWe3MYfSSYFjc26_7QOJyA5S= 3uBhNh0vi7LP9MuEdmRbLblHu2pDu2m_865te55uqGdjmQ$=20
https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!6kBIVWskrvb06emiItPe0iWe3MYfSSYFjc26_7QOJyA5S= 3uBhNh0vi7LP9MuEdmRbLblHu2pDu2m_865te55qkvw7og$=20
$$
=3D =3D =3D
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