Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
332 PM EST Wed Nov 07 2018

Valid 00Z Thu Nov 08 2018 - 00Z Sun Nov 11 2018

...Central Plains to the Great Lakes...

A mid level impulse is expected to produce 700 mb warm/moist
advection and convergence, with low level upslope easterly flow
and a persistent strong southwest jet overhead leading to a band
of accumulating snow from northeastern Colorado to northern Kansas
and southern Nebraska tonight into Thursday. Snowfall rates may be
locally enhanced owing to some elevated instability and steeper
lapse rates, promoting more vigorous lift in the dendritic growth
zone. Moderate probabilities for four inches exist along the
western half of the KS/NE border. 

The disturbance tracks out of the central Plains across the
Midwest states Thursday night just ahead of a digging trough over
the northern Plains. The developing low shifts east over the Great
Lakes Friday through Saturday. A region of mid-level ascent is
expected in the moisture plume from Kansas, across northern
Missouri, and then over northern Illinois and southern Wisconsin.
Temperatures will be cold enough for light snow on the northern
edge of the precip shield, on the order of 1 to 2 inches in most
cases. 

On Friday, the northern and southern stream waves merge and a new
surface low forms and tracks across the lower Lakes. On the west
side of the low, temperatures will be cold enough for snow across
WI/MI. Several inches of snow are possible in lake enhanced areas
south of Lake Superior, centered on the UP of MI where moderate
probabilities for four inches exist for Day 2.

The upper low tracks east from MI Friday night setting up a short,
but potentially robust period of lake effect snow for the lee
sides of the Great Lakes Day 3 with a deep mixed layer and plenty
of cold air. Lake temperatures are in the mid to upper 40s, so a
near shore gradient with rain is possible. QPF from the NAM was
utilized particularly for the western LP of MI since it has the
best resolution of Day 3 guidance.

...Northern New England Day 3...

A low-mid level warm front moves north across New York and New
England Friday night. Well defined low-mid level warm/moist
advection and convergence leads to widespread precipitation. The
models indicate it is cold enough for snow at the onset across
northern New England. The warm advection leads to a good chance
the snow will change to rain ahead of the cold front.

The cold front crosses Saturday with wrap around snow continuing
over northern New England Saturday. This warrants high
probabilities for four inches over northern Maine for Day 3.

The probability of significant icing is less than 10 percent days
1-3.


...Northern Rockies and WA Cascades...

On Friday, a 700 mb wave and associated cold front move onshore
from the East Pacific across western WA.
Pre-frontal low level to 700 mb convergence leads to
precipitation, with snow in the WA Cascades expected, with several
inches possible in the northern Cascades. As the wave progresses
inland, light snow occur with the front as it crosses the ranges
of northern ID late Friday before shifting across MT Saturday.

Jackson