Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
402 AM EDT Sun Oct 27 2019

Valid 12Z Sun Oct 27 2019 - 12Z Wed Oct 30 2019


Days 1-3...

...Northern and Central Rockies/High Plains...
A positively-tilted shortwave trough will continue to drop
southeast through the Great Basin on Sunday and into the Four
Corners region by early Monday.  Upslope flow behind a strong cold
front, along with low to mid level frontogenesis will support
moderate to heavy snowfall from southeastern Wyoming to central
Colorado on Sunday into early Monday.  While the heaviest amounts
are expected to fall across the mountains - where WPC
probabilities show that amounts of 8-inches or more are likely -
several inches are likely to extend east of the foothills into the
High Plains along the I-25 corridor, including the Denver Metro. 
By late Monday, snows will begin to taper off across the central
Rockies/High Plains as the associated shortwave begins to
accelerate northeast away from the region.

Meanwhile, snows will have begun to redevelop and drop south
through the northern Rockies as a second shortwave trough
amplifies while moving south from Canada.  While widespread heavy
amounts are not expected, locally heavy accumulations are possible
over the western Montana into the northern Wyoming ranges by early
Tuesday. 

Models show this second system continuing to amplify as it drops
farther south, with a closed upper low developing over southern
Idaho-northern Utah on Tuesday into early Wednesday.  Snows are
expected to intensify ahead of the system, with heavy
accumulations likely to return to portions of southeastern Wyoming
to northern and central Colorado.  Model spread with this second
system is greater than the initial system, so confidence in the
forecast details is more limited.  However, the general consensus
of the overnight models shows heavier amounts setting up farther
to the east along the I-25 corridor from Casper to Denver.

...Central Plains to the Upper Midwest...
Models continue to show the leading shortwave in the West
producing a stripe of mainly light snow amounts as it accelerates
northeastward from from the central Plains late Monday to the
upper Midwest Tuesday morning.  Favorable upper jet forcing may
help produce some locally heavier totals centered across
northeastern Iowa and southern Wisconsin Tuesday morning. 
Otherwise, accumulations for most areas are expected to be around
an inch or less.

For Days 1-3, the probability of significant icing is less than 10
percent.

Pereira