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QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
257 AM EDT Thu Mar 20 2025

Valid 12Z Thu Mar 20 2025 - 12Z Sun Mar 23 2025


...Pacific and Interior Northwest...
Days 1-3...

Progressive pattern out of the North Pacific will maintain an
unsettled period for the Pacific Northwest into the northern
Rockies. Initial front has moved past the Cascades as of early this
morning and will continue eastward across the Divide later today.
Next system will be forced by a modestly strong incoming jet
(130kts) tonight with westerly flow focusing into the Cascades,
followed by height falls from the northwest (southwestern Canada)
late Fri into early Sat. That system will dig much farther west out
ahead of incoming ridging into WA/OR, finally setting up some
drier periods on Saturday.

Low snow levels in the Cascades of around 2000-3000ft this morning
will rise through the day and overnight to around 3500-4500ft
(north to south) coincident with the next surge of moisture. Snow
levels will fall again late Fri into early Sat as the Canadian
height falls push into WA then into northern ID, down to around
1500-3000ft from north to south as the precipitation gradually
ends.

Three-day totals of at least 12 inches of snow are likely (>70%
chance) above 3500-4500ft or so from north to south along the
Cascades with some higher elevations receiving more than 2-3 ft.
Significant snow is also possible at many passes given the lower
snow levels. There is a >60% chance of at least 8 inches of snow
above 2500-3000ft or so. Farther east, significant snow in excess
of 12 inches is likely (>70% chance) across the Blue Mountains,
central/northern Idaho, northwestern Montana, and into western
Wyoming. The southern extent of the snow will clip northern Utah
and the CO Rockies as well with light/modest amounts near 6 inches
(UT) and nearing 12 inches into CO, especially above 10,000ft.


...Upper Midwest...
Day 3...

The system exiting the High Plains late Sat will continue to dig
into the northern Plains overnight into early Sun. Low pressure
will coalesce over eastern SD Saturday evening and lift into MN
thereafter, bringing WAA-driven snow to northeastern MN, northern
WI, and the western U.P. of Michigan. Amounts will generally be
light through 12Z Sun, perhaps 1-2.5", and the probability of at
least 4 inches is less than 10%. Additional accumulation is likely
beyond this forecast period.


...Great Lakes/Appalachians/Northeast...
Days 1-2...

Exiting system responsible for blizzard conditions over the
central Plains will move into Canada with snow ending over Michigan
this afternoon. Additional snow accumulations will be light (an
inch or so). To the south, colder air will change rain to snow over
the central/southern Appalachians with upslope-driven
accumulations persisting into early Friday. Several inches of snow
are possible at the higher elevations above 3500ft, but WPC
probabilities for at least 4 inches are low (10-40%) along the
TN/NC border. By day 2, low pressure over Cape Cod early Fri will
lift into Nova Scotia with backside snow over northern New England,
but mostly at higher elevations above 2500ft and amounts will
generally be light (<3 inches). The highest peaks of the White
mountains may see more than 4 inches (probabilities generally
10-50%).


For days 1-3, the probability of significant icing of at least
0.10" is less than 10 percent across the CONUS.


Fracasso

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