Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
417 PM EST Mon Feb 03 2020

Valid 00Z Tue Feb 04 2020 - 00Z Fri Feb 07 2020

...Central Rockies through the Southern Plains and Missouri...
Days 1-2...

A positively tilted long wave trough will continue to drift
southeast from its current position over the Great Basin to
southern CA across the Four Corners and northern Mexico through
Tuesday night before ejecting east across the southern Plains
Wednesday. Much better consensus in evolution through this time is
seen in the 12Z global guidance suite.

As this feature shifts eastward, the strong southwesterly jet
streak downstream of the main trough axis will intensify and
become increasingly anticyclonic, especially on Tuesday, with
secondary, stronger, jet streak development occurring Wednesday
over the Southern Plains. This forcing will interact with a rather
moist column provided by tropical Pacific moisture transported
across Mexico as well as western Gulf moisture and cross and be
lifted over the cold air currently pushing down the southern high
Plains and produce an expansive area of moderate to heavy snow
Tuesday night/Wednesday across the southern Plains into MO.

The drift of the trough and developing lee side low in NM with
strong high spilling down the northern Plains from Canada will
focus an upsloping flow and south shifting snow bands down the
eastern slopes of the southern WY/CO/into NM Rockies through
Tuesday. Day 1 snow probs are moderate to high for 8 or more
inches particularly across the eastern slopes of the CO Rockies.

Shortwave energy rotating around the base of the positively tilted
trough over northern Mexico will send a surface low center down
the Rio Grande with the northern Plains ridge entrenching farther
south across the central Plains. A period of strong and moist
isentropic lift will spread snowfall from southeastern NM
northeast across northwest TX and central OK into MO. The column
will quickly cool with lift in the frontal convergence and strong
jet dynamics with snow expected at precip onset. Snowfall is
expected to be heavy at times in a broad stripe from the southern
TX Panhandle across central OK (increasingly likely across the OKC
metro) to southwest MO. Day 2 WPC snow probabilities have
increased again with moderately high risks for 6 or more inches
from the Sacramento and Guadalupe ranges of NM into TX across
northwest TX into central OK to the OKC metro. Probs for 4 or more
inches are moderately high for the rest of OK and low for
southwestern MO and southeastern KS.

Immediately along the surface cold frontal boundary is expected to
be a narrow stripe of wintry mix between the rain to the south and
snow to the north. Day 2 WPC ice probabilities are around 30
percent for a tenth inch or more accretion from central TX to
southeast OK and across southern MO and the OH Valley.


...Great Lakes and Northeast...

Day 3...
As the trough begins to lift northeast out of Mexico and across
TX, renewed surface low development is expected over the eastern
TX coast then rapidly developing as it tracks northeast across the
Ohio Valley Wednesday night to Upstate NY Thursday. Moisture on
the NW side of this low track will produce a swath of at least
moderate snow, as ascent is provided by rapidly intensifying jet
dynamics. The system moves quickly, so Day 3 WPC snow
probabilities for 4 or more inches are around 20 percent from
central MO across IL/northern IN and southeast MI as well as over
the Adirondacks.

The stripe of wintry mix continues south of the snow swath with
Day 3 WPC ice probabilities moderate for a tenth or more accretion
from central IN across northern OH, much of PA and down the
Allegheny Plateau in MD/WV, the Hudson Valley, and interior New
England. The greatest risk for a quarter inch of ice is over the
Allegheny Plateau of western MD/eastern WV north across the Laurel
Highlands of west-central PA.


...Pacific Northwest to the central Rockies...

Day 2...
The brief respite between systems affecting the Pacific Northwest
quickly ends Tuesday night as the next atmospheric river reaches
western WA on the back side of a broad northeastern Pacific ridge.
Snow levels for the Cascades and west will rapidly rise from near
the surface early Tuesday to as high as 7000 ft by Wednesday
morning in the tropically sourced moisture plume. Snow levels in
the northern Rockies will rise to around 3000ft on Wednesday as
the plume pushes inland. Above these levels, prolonged moist
advection will produce heavy snow in the Olympics and Cascades of
Washington, spreading into the Northern Rockies of ID/MT/WY on day
3. Day 2 WPC snow probabilities are moderate to high for 8 or more
inches across these areas.

Day 3...
A strong northwesterly jet will push this Pacific moisture in a
fairly narrow stripe arcing from western WA and down the Rockies
to CO through Thursday. Day 3 snow probabilities are slightly
farther east over the northern Rockies, but moderate to high again
for 8 or more inches for the highest WA Cascades and Rockies of
ID/MT/WY/northern UT/northern CO with snow levels generally 4000
to 5000ft across the Rockies and 5000 to 6000ft for the
Cascades/Olympics.


Jackson