Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
408 PM EDT Sun Apr 14 2019

Valid 00Z Mon Apr 15 2019 - 00Z Thu Apr 18 2019

...Western U.S...

A sfc frontal boundary combines with moist confluent 700 mb flow
with embedded vertical velocity maxima and favorable upper jet
forcing to produce several inches of snow across the ranges of
western WY on day 1.  There is a Low to Moderate Risk for
accumulations of 8 inches or more during the Day 1 period.

Models show a higher amplitude mid-upper level trough moving
onshore late Monday, bringing snows back into the CA/OR Cascades
and CA Sierra, continuing farther east as the 700 mb wave tracks
inland across the ranges of OR and then into ID/NV and then
southwest MT/western WY/UT. Several inches are expected on Monday
night-Tue (day 2) in each of the ranges in these regions.

On Tue night through Wed (day 3), as the upper trough continues to
move east from the Great Basin across the CO/NM mountains, 
combined enhanced moisture and lift in advance of the trough are
expected to produce several inches of snow in the San Juan
mountains of southwest CO/northern NM, extending into the Sangre
DeCristo mountains of southeast CO/northeast NM.  The GFS, the
GEFS Mean and the parent NAM amounts are comparable and the
probabilities are weighted towards this cluster as a result.

...Great Lakes...

Models continue to show snow in mesoscale banding supported by low
to mid level frontogenesis, resulting in moderate accumulations in
northern lower MI along the northwest quadrant of a well-defined
low lifting northeast across the Great Lakes tonight and moving
across northern NY/New England on Monday.  The heavier amounts are
expected to be in northeast lower MI with longer duration snow
before ending as the system moves away Mon.  A trailing cold front
cross the lower lakes, with post frontal cold advection, allows a
change over from rain showers to snow showers.  A few inches of
snow are expected in the lee shore areas from northeast OH across
northwest PA and southwest NY.  Also, with moisture advection
continuing inland into upslope areas of the central Appalachians,
a few inches of snow are expected in the mountains of WV.

Petersen