Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
457 AM EDT Thu Oct 10 2019

Valid 12Z Thu Oct 10 2019 - 12Z Sun Oct 13 2019

Days 1-3...

...Major early season snowstorm spreading into the Northern
Plains...

...Northern Plains...

A powerful, early-season winter storm will continue to take shape
on Thursday, with heavy snow spreading into the Dakotas Thursday
and Friday. Snowfall over the Dakotas is expected to linger into
Saturday as the system becomes occluded...resulting in heavy,
potentially historic accumulations for early October.

Overall...the 00Z suite of guidance was again good agreement with
the large-scale features. Strong low to mid-level frontogenesis
will support a band of moderate snows dropping into the western
Dakotas early today, with snowfall rates increasing across the
Dakotas, especially over parts of North Dakota, as a well-defined
deformation zone develops. That should decrease the chances of
multiple precipitation types. The models are also pointing to
coupled left exit region and right entrance region upper level jet
streaks south and north of the eastern ND respectively, as
deep-layer frontogenesis coincides with a layer of negative
Saturated Geostrophic Equivalent Potential Vorticity. The robust
dynamical forcing will favor a region favored for enhanced
snowfall rates in banded precipitation. 

By Saturday, the mid/upper level circulation center continues to
drift out of the Dakotas and across northwest Minnesota to the
Canadian border. This will allow for snows to gradually taper off
across the Dakotas as drier air works in from the west. Farther
east, the risk of snows will start to be limited by a developing
dry slow as the entire system occludes.

70+ percent probabilities of exceeding 8" over the next 3 days
(12Z Thu-12Z Sun) encompass the eastern half of ND, while also
clipping north-central and northeast portions of SD. Probabilities
of exceeding 2 feet are now over 50% across a good chunk of
eastern ND, where quite a few models show spotty totals around or
exceeding 3 feet.

The probability of significant icing is less than 10 percent Days
1-3.

Hurley/Bann