Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
402 AM EST Sat Feb 08 2020

Valid 12Z Sat Feb 08 2020 - 12Z Tue Feb 11 2020

...Southern Appalachians...

Day 1...
A clipper will shift east from the Mid-South States to the
southern Appalachians this morning before lifting northeast over
the Carolinas this afternoon and evening. Gulf moisture will be
drawn into the system which features lift from decent mid-level
vorticity advection and the left exit region of a northwesterly
jet on the back side of the trough axis over the southern
Appalachians and Atlanta metro this morning into the afternoon.
Low level southwesterly flow will encounter topographic lift and
cooling, aiding snow development roughly northeast from Atlanta.
Moderately high probabilities for 2 inches are across northeast GA
and far western NC which would occur in 12 hrs or less.


...The West...

Days 1-3...
A trough and embedded mid-level low will shear off northern stream
energy east while the main trough becomes rather positively tilted
as it digs south to southern CA where it closes late Sunday before
settling over the northern Baja Monday. Snow levels drop to around
2000ft behind the trough through tonight over northern CA/the
Great Basin. Snow levels are closer to 4000ft over southern CA/AZ
Monday. Abundant Pacific moisture has been streaming inland ahead
of this trough for the past several days though that becomes cut
off as ridging builds into the Pacific northwest. Day 1 snow
probabilities are high for 8 or more additional inches for the
WA/OR Cascades, the Blue Mountains of eastern OR, north-central
ID, western MT, and northern WY. Surface ridging spilling onto the
northern Plains Saturday night directs an upsloping easterly flow
to CO Sunday. Day 2 snow probs are focused in a swath south of the
trough axis from CO to southern UT. Moderate probabilities for
four or more inches are on the eastern slopes of the CO Rockies
(including the Front Range metro areas) with high probabilities
for the central/southern Co Rockies.

Pacific moisture streams into the Desert SW Sunday night through
Monday below the closed low. Convergent upsloping flow over
terrain in southern CA and AZ and especially the southern Rockies
of NM/southern CO where Gulf moisture also reaches, warrants
moderate to high Day 3 probabilities for six inches or more over
the higher terrain above the snow level of 4000 to 6000ft.


...Northern Great Plains through the Great Lakes and the
Northeast...

Days 1-3...
Northern stream shortwave energy ejects east across WY today and
SD tonight, the Upper Midwest/Great Lakes Sunday/Sunday night and
the Northeast Monday. The small vort lobs will wrap Gulf moisture
around the surface reflection and create a decent snow band on the
north side of the low level track. Mesoscale enhancement will
result in narrow heavy snow bands with locally higher totals (10+
inches) within a swath of snowfall averaging 6-8 inches.
Probabilities of 6 or more inches are moderate over east-central
SD into southwest MN Day 1, increasing in confidence and coverage
as jet dynamics increase across southern MN into western WI on Day
1.5 and the rest of WI for the Day 2 snow probabilities. The
impulse gets sheared out in the increasing jet Sunday night with
rather weak forcing as it tracks across the Northeast. Lake and
topographical enhancement lend to spotty coverage of Day 3 snow
probabilities for four or more inches including the tug Hill,
Adirondacks, and White Mtns.


The probability of ice accumulations of 0.25 inch or greater is
less than 10 percent all 3 days.

Jackson