Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
338 AM EST Thu Feb 07 2019

Valid 12Z Thu Feb 07 2019 - 12Z Sun Feb 10 2019


...Central Missouri Valley to the Great Lakes...

A deep upper trough currently spanning the Rockies with southern
stream energy lifting onto the southern Plains will lift
northeast, crossing the Great Lakes tonight with a developing
surface low.  As strong northeasterly flow advects and maintains a
shallow dome of cold air west of the low, low-level warm air
advection will support freezing rain northeast from MO.  In
addition to the upper level dynamics, low to mid-level
frontogenesis will support a developing swath of moderate to heavy
snows northwest of the low, with the heaviest accumulations
expected to center across northern WI and the western UP. Day 1
WPC probabilities are high for more than six inches north from
north-central WI with moderate probabilities for a foot along the
northern UP shore where lake enhancement is expected (despite 50
percent ice coverage on Lake Superior). A wintry mix closer to the
low is expected to result in accumulating ice with low to moderate
probabilities for 0.25 inch ice accretions extending from
south-central WI to northern Lower MI.

The low and parent trough lift northeast through Friday with cold
air advection ending over the lakes Friday in continued westerly
flow. Some lake effect is expected with moderate to high Day 2
probabilities for two inches in the lee of all lakes, but Erie
which is over 80 percent covered.

...Northeast...

Abundant warm air advection east of low pressure tracking over the
Great Lakes tonight will bring rain to much of the northeastern
CONUS with freezing rain expected over interior New England and
the Adirondacks. Moderately-high probabilities exist for a tenth
inch of ice over these areas. Snow on the front end looks limited
to the northern and eastern New England border.

...Western U.S....

Another similar pair of features are expected to bring widespread
snows to the Pacific Northwest and northern California, including
lower elevations snows to western Washington, Oregon and the North
Coast of California late Friday into Saturday. Models show an
upper low dropping southeast from the Gulf of Alaska, reaching
Northwest California on Friday. As this system weakens and moves
across the region, snows are expected along the coastal ranges
into the southern Cascades and northern Sierra late Friday into
early Saturday. Meanwhile, an upper low is forecast to develop
over British Columbia late Friday and deepen as it moves farther
south along the Pacific Northwest coast on Saturday. This will
support low elevations snows across western Washington and Oregon
Friday night into early Saturday (including Seattle and Portland),
with additional snows reaching into Northwest California on
Saturday. Probabilities for greater than 8 inches increases from
Day 2 to Day 3 as the focus of snow moves from WA to OR/CA.

The active/wet/snowy pattern over the western US looks to continue
through at least the middle of the month.

Jackson