Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
345 PM EST Mon Feb 04 2019

Valid 00Z Tue Feb 05 2019 - 00Z Fri Feb 08 2019

...Western States...
Days 1-2...

The final wave in a particularly active pattern from the Pacific
will push inland as a closed mid-level low over the Pacific NW
tonight and open as it shifts east to the Rockies through
Wednesday. A reinforcing low rounding the trough tonight will dig
into southern CA with continued onshore flow allowing coastal
precipitation through tonight. An arctic front beneath the low
will drive snow levels to around 2000ft with rare snows for the
northern and central CA coastal mountains tonight. Moisture
spreads into the desert SW through Tuesday with height falls also
allowing for lower than normal snow elevations in AZ and NM
through Day 2.

Snow continues on the Sierra Nevada through Tuesday with an
additional one to three feet depending on elevation. Day one and
two combined snows are likely to be one to two feet for the
southern Wasatch and Uintas of UT, as well as the Rockies in CO.
As the snow levels fall, accumulating snow is likely down to the
valleys of much of the inter-mountain West, and WPC probabilities
are high for 2 inches from north-central OR through northern New
Mexico. WPC Probabilities over 6 inches, however are limited to
higher terrain throughout the west.


...Northern Plains and Great Lakes...
Days 1-3...

The low currently over the Great Lakes will continue to shift
northeast with wrap around snow ending this evening. A weak
mid-level shortwave with surface trough will shift across the
Upper Midwest later Tuesday into Wednesday quickly bringing a
brief period of robust ascent through upper diffluence, WAA, and
isentropic lift atop cold high pressure. The temporal duration of
this event is limited, but strong omega is forecast as an 850mb
LLJ advects warm moist air which is lift. This will produce a
swath of snow from southern MN through WI and into the U.P. of MI,
where snow rates of 1/2" to 1" per hour are possible. Despite the
short duration event as drier air quickly works in from the west,
WPC probabilities are moderate for 4" of snowfall in south-central
MN on Day 1 (for late Tuesday) and from northern WI into the UP
for Day 2. South of this area, freezing rain is expected in a
stripe from northern MO through southern MI. The aforementioned
LLJ will drive 850mb temps above 0C, but surface cold air will
remain locked in as high pressure behind an arctic front persists
cool E/NE surface winds. Precipitation rates are forecast to reach
up to 0.25"/hr, which will accrete at a lower rate with runoff.
Moderately high Day 2 WPC probabilities for a tenth inch are
across northern IL including Chicago and across southern MI where
moderate probabilities for a quarter inch are in a stripe south of
Detroit.

A more robust surface low will develop Wednesday night along the
stalled front to the south bringing yet another round of snow and
ice to the same general areas through Thursday. Warm air advection
in advance of the low, should direct the leading front north a bit
with moderately high chances 4 inches of snow from WPC
probabilities from northeastern SD on Day 2 through north-central
MN to the western UP on Day 3. Moderate probabilities for a tenth
inch freezing rain SE of there from southern WI and across central
MI. Probabilities for a quarter inch are low for Day 3 as of now,
though this will need to be monitored.


...Upstate New York and New England...
Day 3...

The same storm system impacting the Midwest on Day 3 will drive a
warm front northward into New York and New England late Wednesday.
Surface temperatures will initially be cold and may be maintained
by a strong high over northern Quebec despite southerly low level
flow. Freezing rain is likely, with the terrain of the Catskills,
Adirondacks, and interior New England featuring the moderately
high probabilities for a tenth inch of ice through Thursday. Low
probabilities for four inches of snow north from central NH are
also in the Day 3 WPC probabilities where deeper cold air could
hang on.


Jackson