Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
319 PM EDT Sat Oct 28 2023

Valid 00Z Sun Oct 29 2023 - 00Z Wed Nov 01 2023

...Central & Southern Rockies to the Central and Southern High
Plains...
Days 1-2...
As a positively-tilted upper trough approaches from the west,
periods of heavy snow are forecast to continue through tonight
across portions of the Colorado Rockies into the High Plains. 
Ascent is expected to increase across the region as the trough
axis progresses east from the Great Basin into the Four Corners
states this evening.  Additional heavy amounts are likely for the
central Colorado ranges, with WPC probabilities indicating
widespread high probabilities (greater than 70 percent) for
accumulations of 6 inches or more during the evening and overnight
hours.  More snow is forecast to spread across the Front Range
into the I-25 corridor as well, with WPC probabilities indicating
that another 4 inches or more is likely across much of the Denver
metro.  Meanwhile in the wake of the band now progressing across
Nebraska into southeastern South Dakota and eastern Iowa, expect
at least some light to moderate snow to develop near a low-to-mid
level front extending from eastern Colorado into southwestern
Nebraska and northeastern Kansas. 

Farther to the south, accumulating ice will be a greater concern,
with shallow cold air behind a strong cold front supporting the
transition from rain to freezing rain and sleet from southwestern
Kansas and southeastern Colorado into the western Oklahoma, the
Texas Panhandle, and northeastern New Mexico tonight into Sunday. 
While widespread heavy ice accumulations are not expected, many of
these areas are likely to see at least some minor ice
accumulations, with WPC probabilities indicating at least moderate
probabilities (greater than 40 percent) for accumulations of 0.01
inch or more.

Across the Rockies, the snow is expected to wane and shift farther
south as the upper trough axis moves across the Rockies and into
the High Plains by early Monday.  Meanwhile, areas of mixed
precipitation may continue to develop over the Plains across areas
as far south as the Stockton Plateau in southwestern Texas, where
some accumulating ice is possible on Monday.

...Northern New England...
Day 2...
Guidance shows a broad long wave trough centered over the upper
Midwest late Sunday.  As mid level energy moving through the base
of the through lifts out across southeastern Canada and the
northeastern U.S., a surface wave is forecast to develop over the
Mid Atlantic states and then track northeast off the coast. 
Thermal profiles indicate rain for most parts of the Northeast,
except for portions of the Adirondacks and interior northern New
England Sunday night into Monday.  The greatest chance for any
significant accumulations is expected to fall across the higher
elevations of northern Maine, where WPC probabilities are around
40 percent for amounts of 4 inches or more.

...Upper Great Lakes...
Day 3...
The long wave trough axis is expected to remain largely in place
across the upper Midwest and Great Lakes as the previously noted
shortwave lifting out on Day 2 is followed by another shortwave
diving south across central Canada into the base of the trough. 
Strong cold air advection and northwesterly flow in the wake of
this system is likely to spark more lake effect snows, with some
potential for heavy accumulations late in the period, especially
over the U.P. of Michigan.  However, models are far from agreement
on the timing and amplitude of this system and therefore
confidence is limited. 

Pereira