Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
530 PM EDT Sun Mar 13 2022

Valid 00Z Mon Mar 14 2022 - 00Z Thu Mar 17 2022

...Upper Mississippi Valley into the Upper Great Lakes...

Day 1...

A 110-120kt 250mb jet streak traversing northern MN, far northern
WI, and Upper MI and ensuing right-entrance region forcing to the
south will focus deep-layer ascent in a narrow ribbon across
central to southeast ND into central MN, then eastward through
portions of northern WI, far southern Upper MI, and northern Lower
MI. Given the narrow nature of the most favorable low-mid level
frontogenesis, there continues to be some latitudinal spread among
the guidance in terms of where the best band(s) will set up, which
is largely dependent upon what layer(s) the models are indicating
the strongest vertical motion. The GFS and corresponding high-res
CAM (FV3) show stronger ascent within the dendritic growth zone
(DGZ), and as a result, is a wet outlier with the QPF (>0.50") and
SLR, and as a result has heavier max snow totals (6-7" per GFS,
8-9" per the FV3). Most of the other models show max UVVs either
above or below the DGZ. The latest WPC forecast, owing to the NBM
and HREF trends, was a little farther south with the highest 24
hour probabilities of 4+ inches compared to last night's forecast
(>50% from portions of north-central WI into Charlevoix, southern
Emmet, northern Antrim Counties in northwest Lower MI). 700-500 mb
theta-e lapse rates between +1 to +2C would imply weak symmetric
stability, and as such anticipate one main west-east frontogenetic
band, likely leading to an average of 4-6" of snow with locally
higher amounts. The latest (12Z) HREF in fact shows a few members
showing >0.05"/hr QPF within this region between 13-20Z Monday,
imlying potentially 0.5-1.0"/hr snowfall rates for at least a few
hours during the peak of the event.

The probability of freezing rain exceeding 0.10" is less than 10
percent during days 1 through 3.

Hurley