Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
327 AM EDT Wed Apr 24 2019

Valid 12Z Wed Apr 24 2019 - 12Z Sat Apr 27 2019

...Day 1...Northern Maine...

Low pressure over southeastern Ontario will cross southern Quebec
across northern New England Wednesday morning, and then across the
coastal waters of Maine.
Initial temperatures aloft are too warm for snow.  A brief change
over is possible as the 850 mb low passes during the day
Wednesday, with cold advection commencing.  Day 1 probabilities
for two inches are low over far northern Maine.

The probability of 4 or more inches of snow is less than 10
percent day 2.


...Day 3...Northern Rockies...

A northern stream shortwave trough crosses the Pacific Northwest
and northern Rockies Friday and Friday night. Gulf moisture up the
Great Plains and Pacific moisture from the Great Basin converge to
allow precip to break out as the frontal circulation provides
ascent. Low to moderate probabilities for four inches are shown in
MT Rocky Mountain Front and Absarokas. 

As the system move east across the northern Plains, a low risk is
indicated near the North-South Dakota border as cooling once the
low level circulation passes eventually allows rain to have a
chance of changing over to snow.  The 00z NAM was most aggressive
but the GFS/ECMWF and most SREF/GEFS members have less snow
potential than the NAM, so probabilities are low given initial
conditions too warm for snow, leaving a limited window for snow to
occur.

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

Petersen