Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
432 PM EDT Tue Apr 02 2019

Valid 00Z Wed Apr 03 2019 - 00Z Sat Apr 06 2019


...Great Lakes/Northeast...

Models continue to show a surface low strengthening rapidly as it
moves quickly to the north along the Mid-Atlantic and Northeast
coasts over the next 24-hours.  This will produce a brief period
of wet snow from interior Connecticut/Rhode Island, central
Massachusetts and southern New Hampshire overnight, shifting
northeast across Maine through the mid to late morning hours on
Wednesday.  Marginal boundary layer conditions along with the
progressive nature of the system are expected to limit the
potential for widespread significant accumulations.  For the the
24-hour period ending 00Z Thursday, Moderate Risk probabilities
for accumulations of 4-inches or greater are largely confined to
the Maine/New Brunswick border.

Precipitation is forecast to return to the Great Lakes/Northeast
Thursday night, with warm advection precipitation spreading north
ahead of a weak wave lifting out of the mid Mississippi valley. 
High pressure sliding east from the Great Lakes will support a
period of mixed precipitation at the onset, with some models
showing some light snow/ice accumulations from the northern Great
Lakes region to the Northeast.

...Western U.S....

Mountain snows associated associated with an upper level shortwave
moving east through the Great Basin may result in some locally
heavy accumulations across portions of the central Rockies late
Wednesday into early Thursday.  Left-exit region upper jet forcing
along with low to mid level frontogenesis farther to the north are
helping to support some of the higher probabilities for heavier
accumulations across portions of the northern Colorado into the
southern and western Wyoming ranges.

Farther west, models show a pair of shortwaves impacting the West
Coast states and northern Rockies late Thursday night into Friday.
 The leading system is forecast to weaken as it moves inland
Thursday night, producing generally light high elevation snows
from the Cascades and northern Sierra to the northern Rockies.  A
more defined system is expected to follow, bringing snow back to
the higher peaks of Sierra by late Thursday.

Pereira