Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
354 AM EST Wed Dec 28 2022

Valid 12Z Wed Dec 28 2022 - 12Z Sat Dec 31 2022


...The West...
Days 1-3...

An atmospheric river progressing into Baja California will
continue to feed moisture into the Southwest today ahead of a
digging trough over the Great Basin that reaches the south-central
Rockies tonight. Continued onshore flow over the Pacific Northwest
and impulse energy in the trough allows morning snows to continue
to shift across the northern Rockies. Day 1 snow probabilities are
moderately high for 6"+ across the CO Rockies and higher ranges
near the Four Corners as well as northern ID/northwestern MT.

After brief shortwave ridging today over much of the West Coast,
successive shortwave troughs push over the Pacific Northwest and
northern CA late tonight and again Thursday evening. The second
shortwave directs an atmospheric river into far northern CA Friday
that sags south over the rest of CA through Saturday night. Snow
levels linger around 3500ft for much of the West coast into
tonight with the rise looking to lag the precip from the next
shortwave a bit, rising after 12Z Thursday. This rise is pretty
steady, particularly over CA where snow levels top 8000ft Thursday
night through Friday night. Day 2 snow probabilities for over 8"
are moderately high for the WA/OR/CA Cascades,Klamath, and Sierra
Nevada then are high on Day 3 for the WA Cascades, southern Sierra
Nevada, ranges in northeast NV, the Wasatch, Tetons, and moderate
for the OR Cascades, most ID ranges, and western CO Rockies.


...Central Plains & Upper Midwest...
Days 1-2...

The digging trough moving across the Intermountain West today will
drive lee cyclogenesis in eastern CO by this evening. This surface
low will then quickly swing through KS before turning northeast to
cross IA Thursday and WI Thursday evening. Non-NCEP guidance is
much stronger/wetter with this CO low with northeast flow that
spreads over northeast CO through the Front Range/Palmer Divide
and then over the central High Plains into Neb. NCEP guidance is
notably weaker/drier with this activity. However, given consensus
and even increasing precip with the 00Z suite, the non-NCEP
guidance is preferred on this shift. Moderate Day 1 snow
probabilities for 6 or more inches are along the Palmer Divide
with moderate probabilities for 4" over much of the Denver metro,
and 2" then across the rest of northeast CO. Day 1.5/2
probabilities for 2" are 30% or less in a northeast swath across
Neb and then less than 5% over northeast IA/MN. Confidence for
snow outside the highest central Plains is low given the marginal
thermal profile, but should sufficient banding develop, there
could be locally moderate snow bands over far northwest KS and
into central Neb, particularly through mid-morning Thursday. Warm
air advection ahead of the low brings a risk for freezing rain
over the Upper Midwest with low Day 1.5 chances for a measurable
glaze over south-central MN and the Arrowhead of MN.


Jackson