Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
436 AM EDT Tue Mar 17 2020

Valid 12Z Tue Mar 17 2020 - 12Z Fri Mar 20 2020


...Northern California, Northeastern Nevada, into Southern
Oregon...
Day 1...

The northern portion of the low that has been stalled off CA for
the past couple days shifts inland to northeastern NV today as it
fills/weakens. Remnant wrap around moisture and lift will
encounter the terrain of northeastern NV and in CA the Warner
Mtns, Modoc Plateau and the eastern slopes of the CA Cascades and
the Fremont Mtns of southern OR. Snow levels will be around 3000ft
today with moderate to heavy snow above. Day 1 probabilities for 8
or more inches are moderate to high in this area, particularly for
the Warner Mtns and CA Cascades.


...Four Corners States to the North-Central Plains and Upper MS
Valley to Lake Superior...
Days 2/3...

A reinforcing shortwave swings well off the CA coast today before
crossing the northern Baja Peninsula Wednesday before ejecting
northeast across Four Corners Wednesday night and the central
Plains Thursday before interacting with a northern stream trough
approaching from the eastern Canadian Prairies Thursday night. The
falling heights and increasing south to southwest flow leads to
Pacific moisture fluxes across far northwestern Mexico into AZ/UT
Wednesday before shifting across CO Wednesday night. Precip breaks
out in the Desert SW early Wednesday with snow levels 5000 to
6000ft and AZ/UT and 6000 to 7000ft in CO. Day 2 snow
probabilities for 8 or more inches are moderate to high for the
Mogollon Rim and White Mtns of AZ and Kaibab Plateau (north of
Grand Canyon North Rim) up the UT Wasatch to the Uintas before
expanding to the San Juan/Sangre De Christos and west-central CO
Ranges to the Front Range. 

Wed night-Thu, the system crosses the CO Rockies with lee side
surface low pressure developing in eastern CO late Wednesday
night. This low will combine with sprawling high pressure centered
over the northern Canadian Prairies to produce east-northeasterly
upslope flow over the High Plains/eastern slopes of the WY and the
Black Hills of SD where snow breaks out late Wednesday night and
continues to spread across the high plains Thu. Day 3
probabilities for 8 or more inches are moderate to high for all
ranges in central/northern CO with low to moderate probabilities
for the central/northern CO High Plains and southeast WY. Moderate
risks for 6 or more inches extend east-northeast across the NE
panhandle and then along the NE/SD border to Sioux Falls. Renewed
surface low development around Lake Superior Thursday night as the
northern stream trough interacts with leading shortwave brings
moderate risks for 4 or more inches over northern WI/the UP of MI
as well as the MN Arrowhead. The exact track will make notable
details such as lake enhancement which should be better determined
over the next day. Light icing is likely in southerly flow ahead
of the lead shortwave Wednesday night-Thursday in the eastern
Dakotas/MN and WI/MI Thursday.


...Northeast...
Day 1...

An upper trough swings east from the northern Great Lakes this
morning and shifts north of Maine this afternoon. Strong warm
advection with this quick moving system will limit snow fall. A
low-moderate risk of 4 inches of snow on Day 1 remains in effect
for the highest elevations along the Quebec border with NH/Maine
the ranges of northwest ME.

For Days 1-3, the probability of significant icing (0.25-inch or
greater) is less than 10 percent.

Jackson