Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
205 PM EDT Sun Mar 15 2026
Valid 00Z Mon Mar 16 2026 - 00Z Thu Mar 19 2026
...Upper Mississippi Valley through the Great Lakes...
Days 1-3...
...Historic blizzard ongoing through Monday with widespread major
impacts and record-breaking snowfall for portions of the Upper
Midwest and Great Lakes...
Confidence continues to be high for a widespread major winter
storm across the Upper Midwest and Great Lakes as a lee surface
low lifts northeast and rapidly deepens into an increasingly moist
column. Snowfall from Minnesota through Wisconsin and northern
Michigan, including the U.P, will breach 12" in many locations with
areas of northern WI into the U.P. likely to reach 2-4 feet of
accumulation through Monday night.
A rapidly developing surface low, currently centered near the Quad
Cities of Iowa/Illinois, is being supported both by a digging
upper level trough to its west over Nebraska and Kansas and the
RER of a 160 kt jet streak to its north and east. A couple of lines
of showers and storms are moving across Iowa and eastern Illinois,
supported by a southwesterly low level jet, pumping in Gulf
moisture and locally increasing both shear and unstable, warm air,
feeding the storms. As the shortwave trough digs further to the
southeast, flow will become increasingly meridional over the
Central Plains to Mississippi Valley with the trough axis forecast
to tilt neutral to eventually negative with the 500 mb height
pattern expected to close off near or over IA by later this
evening. Meanwhile, a maturing "comma-head" has emerged that is
largely snow from Nebraska through the U.P. and into Ontario. There
have already been reports of snow rates of 4 inches per hour, as
several locations have eclipsed the 20 inch mark for accumulations
into Minnesota and Wisconsin.
The surface low center will track east into this evening,
intensifying as it then turns northeast towards the Straits of
Mackinac by Monday afternoon. As the upper pattern takes on the
negative trough orientation, the surface low will rapidly
intensify as it begins to enter into its full maturation phase.
The primary heights from 850mb to 500mb become more vertically
stacked into Monday morning. The cyclone will finally reach
occlusion phase by Monday afternoon, but surface low pressure will
likely be down into the upper 970s by this juncture over the
western Great Lakes, solidifying its presence with an all-out
blizzard for a large chunk of the Midwest and Great Lakes region.
A classic comma-shaped storm will develop, with cold conveyor belt
supplying ample Gulf moisture into some unusually cold air for this
time of year on the north side of the storm. Thus, expect multiple
bands of heavy snow to develop, which will likely remain nearly
stationary as they pivot around the northeastward-tracking surface
low. Where these stationary bands remain in place the longest is
where the highest snow totals with this storm will be realized.
There has been little change in the relevant synoptic details
referenced in the last forecast as guidance remains steadfast in
all facets of this storms anticipated evolution. The synoptic setup
is extremely favorable for a classic Midwest winter storm with
widespread intense snowfall. Embedded bands with snowfall rates of
1-3"/hr are expected as reflected by high potential for CSI and
even CI in model cross- sections Sunday aftn into Monday which
drives intense omega into the TROWAL. There remains high confidence
in a pivoting band over eastern MN and WI/Michigan U.P. this
evening into Monday. It is in this area where the heaviest snowfall
is expected, and potentially record, or near- record 2-day
snowfall is possible from eastern MN through WI and northern MI.
Elsewhere, snowfall rates of 1"/hr or more are still likely at
times, just with lesser duration. These snowfall rates combined
with gusty winds reaching up to 60 mph will create blizzard and
near-blizzard conditions and whiteouts, with major to extreme
impacts progged by the recent WSSI-P. Even in areas that get lower
snow totals, the blowing snow potential will still result in
difficult travel, and it is likely that most forms of
transportation will be treacherous at best, and impossible at
worst, through the event across a large area from Montana to
Michigan, and everywhere in between.
Event-total snowfall is likely to be extreme in some areas. This is
reflected by 72-hr WPC probabilities (ending 00Z Wednesday) that
are high (>70%) for at least 12" from southeast MN to points
northeast through north- central WI, and the entirety of the U.P.
of MI. Where snowfall is most prolific, likely in northeastern WI
and the U.P of MI, WPC probabilities indicate a 70-90+% chance of
at least 24", and localized totals of 3-4 feet are possible before
this event ends with the maxima positioned across the Huron
Mountains downwind of Lake Superior. This could result in record
snowfall in some places, and with SLRs being near to slightly below
climo, combined with the strong winds, power outages and long-
lasting impacts are expected. For these reasons, Winter storm key
messages are in effect, and are linked below (Key Message 1).
After 00Z Tuesday, snowfall rates will be waning rapidly in direct
association with the storm, transitioning more and more to lake-
effect snows downwind of all of the lakes. Pronounced CAA on NW
flow in its wake could result in some lake effect snow in the
favored NW snow belts downstream of all the Great Lakes. WPC
probabilities are moderate (50%) for at least 4" of snow from LES
in SW MI, as well as along the Chautauqua Ridge and into the Tug
Hill Plateau. Additional heavy snow will occur near Marquette, MI
as well, adding onto the extreme snowfall event there the next few
days bring storm and LES combination totals towards the 4-5ft range
by Tuesday afternoon. The lake- effect will continue into Tuesday
morning before largely dissipating.
On the S/SE side of this snowfall swath, an axis of mixed
precipitation is likely, leading to icing accretion from central IA
through southern WI and into the northern mit in lower MI. The
most significant icing is expected for the northern mitt of MI
where WPC probabilities for at least 0.25" of ice have settled
between 40-70%, and the axis of higher probabilities for at least
0.10" of ice have extended back into southern WI.
...Post-storm lake-effect...
Behind the storm, a very cold air mass, characterized by 850 mb
temperatures within a couple degrees on either side of -20C, will
plunge across all of the Great Lakes for the Days 2 and 3 periods
from Monday night through Tuesday night. Widespread multi-bands are
expected along the long axis of all of the upper Great Lakes, while
the lake-effect will eventually congeal into single bands downwind
of the lower lakes, especially Ontario. Fortunately, as far as
lake-effect snowstorms go, this will be relatively short-lived,
with the lake-effect ending on the upper lakes by late in the day
Tuesday and on the lower lakes by Wednesday morning as 850 mb
temperatures warm sufficiently to end the lake-effect. WPC
probabilities for 4 inches of snow are high (>70%) for the
southwest corner of Michigan, the Chautauqua Ridge of far western
New York, and east of Lake Ontario. The Tug Hill region
probabiliites are over 90% for 4 inches of snow.
...Central Appalachians...
Day 2...
A powerful cyclone over the Great Lakes will send a strong cold
front eastward through much of the country east of the
Mississippi. Once the cold front advances beyond the spine of the
Appalachians, a strong cold air advection (CAA) regime will
transpire with rain changing to snow for the mountains of western
PA down through western MD and the adjacent WV Highlands.
Elevations >2000ft will see some snowfall with the greatest accums
focused over areas >2500ft, a general climo output for this type of
evolution. WPC probabilities for >4" of snowfall are between
moderate to high (60-80%) from far western Maryland through WV. The
setup and magnitude of the upslope flow is classic for this
scenario allowing for growing confidence in at least minor impacts
for the terrain of the Mid Atlantic.
Wegman
...Winter Storm Key Messages are in effect. Please see current
Key Messages below...
https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_1.png
