Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
316 PM EST Tue Mar 03 2020

Valid 00Z Wed Mar 04 2020 - 00Z Sat Mar 07 2020


...Sacramento and Guadalupe Mountains...
Day 1...

Closed upper low crossing northern Mexico through tonight will
continue to have anomalously high moisture wrap around the system
with both Pacific and Gulf of Mexico sources. Enhanced jet-level
diffluence combined with the height falls/PVA invof the upper low
along with upsloping low level flow in the saturated environment
will produce localized heavy precipitation across far southern New
Mexico and far west Texas. Snow levels tonigh will generally be
around 7000 ft, which will confine the heavy snow to higher
portions of the Sacramento Mountains in NM and the Guadalupe
Mountains on the NM/TX border. Day 1 WPC snow probabilities are
high for 8 or more additional inches for the highest Sacramento
Mtns and moderate to high for 6 or more inches for the rest of the
higher eastern slopes of the Sacramento and the highest Guadalupe
Mtns.


...Washington Cascades and Northern Rockies...
Day 1...

The last in a series of shortwave troughs tracks southeast across
southern BC tonight. Half inch PW air streaming into western WA is
about one standard deviation above normal and promote moderate
snow above the snow levels of 4000 to 5000ft this evening that
drop to 3000 to 4000ft through tonight. Day 1 WPC probabilities
are high for 6 or more inches for the higher WA Cascades, the
Bitterroots along the ID/MT border, the Lewis Range/Glacier NP,
and moderate for the Tetons in NW WY.


...Western Washington...
Days 2-3...

Ridging behind the last trough means a break in precip over the
Pac NW Wednesday into Thursday with the next low dropping
southeast out of the Gulf of Alaska Thursday. This turns the flow
for the WA coast from NW to SW on Thursday, advecting enhanced
Pacific moisture into the Northwest with snow levels generally
2000 to 3000ft. Persistent onshore flow maintains moderate precip
across western WA late Thursday through Friday. Day 3 snow
probabilities for 8 or more inches are moderate for the highest
Olympics and higher WA Cascades with high probabililities for the
highest WA Cascades.


...Northern New England...
Day 1...

A northern stream trough swinging through the Great Lakes today is
taking on a negative tilt as it shifts to New England tonight.
This promotes rapid surface cyclogenesis as it takes an even
farther inland track than prior forecast. Therefore much of the
snow from this system will be on the back side and the progressive
nature will limit overall snow totals. Day 1 WPC snow
probabilities for 6 or more inches are moderately high for the
farthest northwest corner of Maine with moderate proabilities for
4 or more inches in the upslope zone of the Tug Hill and around
Mt. Washington, NH.


...Northern Great Lakes to the Northeast...
Days 2-3...

The last shortwave in a series moving southeast from BC amplifies
as it tracks across the far northern Great Plains Wednesday night
before closing off over the northern Great Lakes Thursday. This
system trails a southern stream trough that shifts off the
Mid-Atlantic coast Thursday night and fails to phase. Therefore
this will be more like a strong clipper for the Northeast on
Friday (and into Friday night). will race eastward in the fast
northern stream to move across the Great Lakes late Thursday into
Friday. A leading stripe of synoptic snowfall on warm air
advection Wednesday night through Thursday across far northern MN
and the UP of MI. Behind the departing system Thursday night and
early Friday, a brief period of lake enhancement snow is likely,
focused in the UP as northerly fetch develops across Lake
Superior. The temporal duration of this is short, temperatures are
modest, and inversion heights are low, so the potential for heavy
LES is low. Day 2 snow probabilities are moderately high for 4 or
more inches in the Arrowhead of MN and the eastern UP, then
moderately high for the central and eastern UP for Day 2.5. There
are low Day 3 probabilities for 4 or more inches over the higher
portions of NY/VT with moderate probabilities for the Allegheny
Plateau of WV into far western MN.


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

Jackson