FOUS11 KWBC 040726
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
326 AM EDT Sat Apr 4 2026

Valid 12Z Sat Apr 04 2026 - 12Z Tue Apr 07 2026

...Northern Plains, Upper Midwest, & Western Great Lakes... Day 1...

...Second of back-to-back systems will bring additional heavy snow
and icing to portions of the region today...

Significant late-season winter storm is ongoing this morning extending
from the Dakotas across the Midwest towards the MI U.P.. Moderate
to heavy snow occurring across the Dakotas is expected to diminish
by midday as snowfall continues across central and northern MN
through this evening. Meanwhile, to the north and northeast of the
associated low pressure system, freezing rain will be the primary
winter precipitation type throughout northern WI and both the U.P.
and northern L.P. of MI. This significant low will track northeast
from the Midwest through the Great Lakes by this evening and
quickly exit into southeast Canada tonight while hazardous winter
precipitation concludes as well.

As this low pressure system and accompanying upper low track E/NE
today, continuing downstream moisture advection will peak later
this morning leading to impressive isentropic ascent, especially
along the 290-295K surfaces, lifting into the Upper Midwest. Mixing
ratios within these layers of 3-5 g/kg reflect the anomalous
moisture being wrapped into the system, and it is likely that
precipitation will become even more widespread by sunrise this
morning. At the same time, the accompanying theta-e ridge will
wrap cyclonically around the system and lift into a TROWAL, while
the impressive upper low forces intense deformation to drive
tremendous ascent into the TROWAL. The combination of the deep
layer ascent with robust mesoscale forcing will result in banded
structures with snowfall rates for which the 00z HREF suggests
will reach 1-2"/hr at times, especially from eastern ND into
northern MN where some pivoting of these bands may also occur. This
will result in heavy total snowfall accumulations around one foot.
However, just outside of these pivoting heavier bands and within
lighter snow rates, totals will likely be limited by the early
April sun- angle combined with surface temperatures in the low-30s.
WPC probabilities start at 12Z today (heavy snow is ongoing before
12Z as well) and indicate a 50-80% chance of at least 8 inches of
additional snow in northern/northeastern MN today.

Farther southeast, the strong WAA east of the upper low and a warm
nose pushing northward is leading to an area of heavy mixed
precipitation including sleet and freezing rain. Even with a deep
cold layer and period of sleet, warm nose energy rapidly increases
this morning leading to a changeover to an extended period of
freezing rain before the dry slot pushes northward (likely
preventing a changeover to rain in some areas) this afternoon.
While sleet accumulations on both shores of Lake Superior may reach
0.5", the more significant hazard is expected to be freezing rain
where the latest WSSI depicts widespread Moderate Impacts
associated with freezing rain from northern WI to the eastern
U.P.. This icing could be damaging where totals exceed a quarter
inch, causing power outages and tree damage, and will likely
exacerbate and prolong impacts ongoing from the ice/snow which
occurred with the earlier system on Thursday.

Key Messages are in effect for this system and are linked below.

...Northern New England... Days 1-2...

A warm front extending eastward from a significant low pressure
across the Great Lakes will result in expanding precipitation
tonight into Sunday. Although the low itself will track well
northwest of the region, impressive warm/moist advection surging
northward from the Gulf will spread PW anomalies to as much as +3
sigma on an 850mb LLJ reaching as high as 50 kts. As this occurs, a
Canadian high pressure initially placed just north of the region
will rapidly retreat to the northeast, allowing the warm air to
flood unimpeded northward, lifting a warm nose above 0C all the way
into Canada. This suggests that precipitation will begin as a
period of snow across northern Maine, but will otherwise be a
combination of sleet/freezing rain, especially in the higher
elevations, before transitioning to all rain by Sunday aftn.

Total accumulations of any individual wintry precipitation type
will likely be modest as the warm air overwhelms the column, but
impactful ice is most likely. This is reflected by WPC
probabilities for ice exceeding 0.1" reaching 30-60% in the higher
terrain of northern NH and interior/western ME.

Snell/Weiss

...Winter Storm Key Messages are in effect. Please see current
Key Messages below...

https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_2.png

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