Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
346 AM EDT Tue Apr 05 2022

Valid 12Z Tue Apr 05 2022 - 12Z Fri Apr 08 2022

...Northwest to the northern/central Rockies...
Day 1...

Strong jet that carried a cold front quickly through the Northwest
yesterday will weaken and lift northeastward as upper ridging
builds into the PacNW this afternoon/evening. Any precipitation
early in the day will end by then as high pressure builds in off
the northeastern Pacific. Snowfall will still be heavy over the
northern Cascades just after 12Z today where an additional 6+
inches of snow is likely. Downstream, some additional amounts over
four inches are likely into the Bitterroots and western Montana as
well as western Wyoming and Colorado as forcing wanes by evening.


...Northern Plains/Upper Midwest/Western Great Lakes...
Days 1-3...

Closed low forming over southwestern Saskatchewan this morning
will merge into the sheared vort out of the northern Rockies today
spurring cyclogenesis into Minnesota today. By Wednesday, another
smaller closed low over northern Ontario will rotate into the
western side of the deepening closed low over Minnesota as the
system becomes stacked up to jet level. The multiple axes of
vorticity will result in a deformed ellipse at 500mb with
different foci for lift. On Day 3, the expanding upper low will
sink southeastward into the eastern Great Lakes.

Life cycle of the system through the period will start with strong
PVA and jet expansion into the Upper Midwest and Great Lakes with
an increase in moisture from the southwest back to northeast Texas
(PW anomalies +1 to +1.5 sigma). WCB will bring sufficient
moisture to the Arrowhead where temperatures will be marginally
cold for snow, with lower amounts over northern Minnesota. By Day
2, upper pattern will amplify as the surface low wobbles eastward
but the cold front swings into the eastern Great Lakes. This will
stretch the moisture plume that taps the Gulf (+1 to +2 sigma) but
displaced into the Northeast. On the backside of the broad
circulation, second vort max (old upper low) will provide
additional lift combined with upslope flow into the Black Hills
for several inches of snow. With the wrapped occlusion over the
Great Lakes, TROWAL development will try to ensue before the
system overturns and a new area of low pressure forms along the
Mid-Atlantic coast. On Day 3, leftover parent low will drift into
the Midwest with northerly to northeasterly flow over
Michigan/Wisconsin supporting lake-enhanced snow and a rather
expansive area of light snow beneath the cold pool.

WPC probabilities for at least four inches of snow are moderate
over the Arrowhead of Minnesota and low over parts of the rest of
northern Minnesota. Probabilities increase by Day 2 everywhere as
the system reaches maturity -- moderate to high over the
Arrowhead, low over northern Minnesota, and moderate over the
Black Hills. On Day 3, moderate to high probabilities of at least
four inches of snow are focused over the Gogebic Range across
northern Wisconsin into the U.P. of Michigan. Three-day totals of
over eight inches are low to moderate over similar areas.


For Days 1-3, the probability of significant icing of at least
0.25" is less than 10 percent.

Fracasso