Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
407 PM EDT Wed Apr 17 2019

Valid 00Z Thu Apr 18 2019 - 00Z Sun Apr 21 2019

A longwave trough will edge east across the central CONUS today
through Thursday. Residual energy will exit New Mexico shifting
into the Texas Panhandle. Weak surface low development in north
Texas will provide continual upslope across the higher terrain of
the Sangre de Cristo tonight into early Thursday (Day 1).  Farther
north, a deepening surface low associated with the aforementioned
trough will move through the Upper Midwest/Great Lakes region
resulting in snow showers across northern Minnesota/Wisconsin and
the UP of Michigan Thursday into Thursday night.

The next storm system will approach the Pacific Northwest early
Friday with a potent jet axis of 130 knots which sharpens
throughout the day as it moves northeast. This will aid in ascent
as precipitable waters of 1 inches advect into the coast of
Washington and Oregon.  This combined with orthogonal moisture
transport should result in enhance orographic lift.  With snow
levels fairly high, around 9000ft, this will limit the overall
snowfall coverage to the highest terrain of the Olympic Mountains
and Cascades.  Snow levels fall throughout the day on Friday to
around 7000 feet as the front crosses.  Strong mid-level vorticity
starts to shift quickly east across the Pacific Northwest into the
Northern Rockies late Friday into Saturday. It becomes better
aligned with the jet axis resulting in enhanced atmospheric ascent
and thus precipitation amounts. Snow levels should fall from
around 9000ft to 7000ft across the Bitterroot, Lewis and Absaroka
Ranges. WPC probabilities suggest a Medium chance for 4 inch or
more across these ranges on Day 3, ending 00Z Sunday. 

Pagano