Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
401 PM EST Sun Feb 02 2020

Valid 00Z Mon Feb 03 2020 - 00Z Thu Feb 06 2020

...Northern Rockies through the Southern Plains...
Days 1-3...

A positively tilted trough axis currently over northern CA per
GOES-17 water vapor imagery will close into a mid-level low
tonight over the Great Basin. Reinforcing shortwaves rounding the
low will keep the trough positively tilted and slow moving as it
drifts to the Four Corners and northwest Mexico through Tuesday.
The trough axis will only begin to eject east to the southern
Rockies on Wednesday. Tropically sourced Pacific moisture will
stream across Mexico into the southern CONUS tonight through
Tuesday. Some of this moisture, combined with lift from the right
entrance of a westerly jet over the northern tier of the CONUS as
well as upsloping easterly flow from a lee low in CO and surface
ridge extending from the Canadian Prairies into the northern
Plains will enhance snow through tonight across most of WY and for
terrain of UT/CO as well as the Great Salt Lake Basin. The slowing
movement of the system as it closes will maintain snow over these
areas through Monday and result in notably heavy snow,
particularly for the eastern slopes of the WY Rockies/High Plains.
The Day 1 WPC snow probs are moderate to high for 12 or more
inches over much of WY northeast of the Wind River Range as well
as the higher terrain of southeast ID and northern UT where snow
levels will crash from around 6000ft now to the ground tonight.

The trough amplifies into northwest Mexico Monday night as
everything shifts south, the next lee surface low develops over
eastern NM and the Canadian surface high shifts into the Dakotas.
Broad southwesterly flow shifts precip across much of the
east-central CONUS, but into the ridge where it will be warmer and
thus rain. Lighter bands of snow can be expected across the
central high Plains with moderate Day 2 probabilities for 2 or
more inches over eastern CO/WY into NE/KS, but the heavy snow
looks limited to the eastern slopes of the CO Rockies where
upslope enhancement leads to moderate to high snow probs for 8 or
more inches. There is a signal for persistent snow into the Front
Range of CO with 20 to 30 percent Day 2 snow probs for 6 or more
inches over the greater Denver area north from the Palmer Divide
to around Greeley.

The upper trough will shear over the Four Corners Tuesday night
allowing a focus of the southern portion which begins to eject
east over the southern Rockies/northern Mexico. This will allow
the southwesterly mid-level flow to overrun the surface cold front
and focus swaths of snow from southeast NM across west TX Tuesday
night that shift east to the Ozarks Wednesday. This ascent
combined with intensifying low to mid level frontogenesis and a
secondary jet streak lifting into the Central Plains will place
parts of NM/TX/OK in a region favorable for heavy snowfall.
Preference is for a non-GFS solution which is farther north from
southeast NM across the TX Panhandle into OK. Day 3 WPC snow probs
for six or more inches are moderate on eastern slopes of the
Sacramento and Guadalupe Mtns and 10 to 30 percent over the
southern TX Panhandle with 20 percent probs for four or more
inches extending into western OK.


...Pacific Northwest...
Day 3...

The next atmospheric river reaches western WA Tuesday night on the
back side of a broad northeastern Pacific Ridge. Snow levels will
rapidly rise from near the surface with this tropically sourced
moisture that reaches the northern Rockies of ID/MT Wednesday. Day
3 snow probs are moderate to high for 12 or more inches the
highest WA Cascades, Blue Mtns in OR, and northern ID.


The probability of significant icing (0.25-inch or greater) is
less than 10 percent.

Jackson