FOUS11 KWBC 040735
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
335 AM EDT Fri Apr 4 2025

Valid 12Z Fri Apr 04 2025 - 12Z Mon Apr 07 2025

...Portions of the Rockies and the High Plains...
Days 1-2...

This morning, a cold front tracking south through the central High
Plains with NErly CAA will cause temperatures to drop and modest
upslope ascent into the Front Range of the Rockies. This air-mass
will be essential for boundary layer wet-bulb temperatures being
cold enough to support snow in the central and southern High
Plains. Farther south, a closed upper low will slowly make its way
east through Arizona and New Mexico on Friday while also injecting
a healthy plume of 300-700mb moisture over the Rockies. This will
support periods of mountain snow from as far west as the Wasatch
and as far south as the Gila Mountains of eastern Arizona. As the
700mb low heads into western New Mexico Friday afternoon, low-mid
levels winds over southeast CO and northeast NM will turn easterly
at the same time as the aforementioned cold front to the north
continues its southerly progression. In addition, the southern and
central Rockies/High Plains will reside beneath the divergent left-
exit region of a 500mb jet streak. Guidance shows a moistening of
the 700-300mb layer Friday afternoon that coincides with what is
likely to be the start of heavy snowfall from the San Juans and
Front Range on south along the Sangre De Cristo and Raton Mesa
Friday afternoon and into Friday night.

By Saturday morning, snow will be falling not only in the Southern
Rockies, but across the southern High Plains thanks to a narrow
area of 700mb WAA to the north of the 700mb low tracking from
southeast NM into western TX. This will prompt the formation of a
deformation zone on the western and northern flanks of the 700mb
low. Note that, with the calendar reading early April and the
increasingly high sun angle, it will have to snow at an
exceptional clip (>1"/hr)for snow to accumulate outside of the
mountain ranges. Still, periods of moderate snow combined with
30-40 kt 850mb winds will cause significantly reduced visibilities
across the southern High Plains of eastern NM and the OK/TX
Panhandles through Saturday afternoon. Snow should finally taper
off by Saturday evening as the 700mb low tracks east over central OK.

The ECMWF EFI does suggest this is a rather anomalous event in
terms of snowfall for the late March to mid-April time period. The
EFI shows a large swath of 0.8-0.9 values from Raton Pass on south
through much of eastern New Mexico. WPC probabilities show high
chances (>70%) for snowfall totals >12" along the >9,000ft peaks of
the Sangre De Cristo and above 8,000ft in the Raton Mesa. The
latest forecast calls for as much as 12" of snow at the peak of
the Raton Pass along I-25. The WSSI does indicate Major Impact
potential (considerable disruptions; dangerous to impossible
travel) along the Raton Pass Friday night into Saturday morning.
WPC probabilities also show moderate-to-high chances (50-70%) for
snowfall >4" along the I-40 corridor in eastern NM. The WSSI shows
Minor to Moderate Impacts from a combination of Snow Amount and
Blowing Snow across the High Plains of eastern NM and the OK/TX
Panhandles through Saturday with Minor Impacts denoted (winter
weather conditions, hazardous travel possible) in and around the
Amarillo area.


...Northern New England...
Day 2...

Saturday will bring yet another round of wintry weather from the
White Mountains through much of western and northern Maine. While
the air-mass is not as cold as the more recent winter storm that
took place earlier this week, high pressure over Quebec will
provide a weak source of sub-freezing boundary layer temps. As
850-700mb WAA and 300K isentropic ascent amidst brisk SWrly flow
aloft increases, a ribbon of 850-700mb areal-averaged FGEN will
support a band of moderate-to-heavy precipitation that runs
directly over the marginally cold air-mass in northern New England
on Saturday. Precipitation may briefly start out as snow (staying
all snow longest over northern Maine), but the burgeoning nose of
>0C temps at low-levels will inevitably switch any snow to a
sleet/freezing rain mixture from the Whites to western Maine
Saturday afternoon. A weak CAD signature will linger longest along
the Maine/Quebec border that will linger through Saturday night. By
Sunday morning, the warm front lifts far enough north to have plain
rain be the primary precipitation type.

WPC probabilities show moderate-to-high chances (50-70%) for ice
accumulations >0.1" from the Whites through western Maine. Some
minor ice accumulations (generally <0.1" are possible in the Green
Mountains and even as far south as the Berkshires. However, if any
locations are to see localized ice accumulations >0.25", it would
be the White Mountains and western Maine where low-to-moderate
probabilities (10-40%) are present. The probabilistic WSSI (WSSI-P)
does indicate moderate-to-high chances (50-70%) for Minor Impacts
as a result of the >0.1" of ice accumulations.

...Northern Great Lakes...
Day 3...

A potent 500mb vort max with origins out of the Arctic Circle will
dive south from south-central Canada towards northern Minnesota
Sunday evening. A 250mb jet streak oriented N-S will place its
divergent left-exit region over the Midwest Sunday night and aid in
the development of low pressure along a strengthening 850mb front.
A narrow band of moderate snow should manifest on the northern
periphery of low pressure as it tracks through Wisconsin and
northern Michigan. In addition to the band of snow, CAA via brisk
northerly winds will trigger lake-enhanced snow showers over
northern Wisconsin and the Michigan U.P. Sunday night and Monday
morning. WPC probabilities highlight low chances (10-30%) for >4"
of snowfall through 12Z Monday in the Michigan U.P. and the tip of
Michigan's Mitten with additional snowfall possible across northern
Michigan through Monday afternoon.


Mullinax

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