Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
418 PM EDT Mon Oct 22 2018

Valid 00Z Tue Oct 23 2018 - 00Z Fri Oct 26 2018


Day 1...

...Central Rockies...
Broad upper level trough across the west will shift eastward
through Day 1. Increasing moist advection on return flow ahead of
this feature will combine with the best jet level dynamics due to
right entrance region diffluence, to produce snowfall in the
highest terrain of Colorado and Utah. Accumulations will be
limited to the terrain above 9000 feet, and will be maximized
across the San Juans where orographic enhancement is likely on
southerly and moist 700mb winds. WPC probabilities are high for 4
inches of snow across the San Juans with 8 inches or more
possible. Lower amounts are likely in the high terrain of the
Rockies and Sangre De Cristos in Colorado, as well as the Uintas
in northeast Utah.

The probability of significant icing (0.25 inches or more) is less
than 10 percent.

Day 2...

...Northern New England...
Potent shortwave digging into New England will induce surface
cyclogenesis which will then lift northeast while strengthening
into New Brunswick, Canada. Heavy snow will develop within the
primary mid-level deformation axis northwest of the 700mb low
across far northern New Hampshire and much of northern Maine.
Although there remains some disagreement into the exact placement
of this heaviest band of snow, the best overlap of lift due to
height falls, sloped mid-level frontogenesis, and the presence of
a modest trowal occurs over far northern Maine. Here, WPC
probabilities show a moderate risk for more than 8 inches of snow.
Elsewhere across northern New England including the White
Mountains of NH, WPC probabilities are moderate for 4 inches of
snow.

...Central Rockies...
Upper trough will continue to slide eastward across the Four
Corners region Tuesday night before shifting into the Plains on
Wednesday. Moist advection will persist ahead of this feature
before the trough axis slides east, bringing with it drier air and
an end to the mountain snows. Jet level diffluence and subtle PVA
within a moistening column will produce high elevation snows
across the Colorado Ranges as well as the Sangre De Cristos in New
Mexico. The highest amounts are likely in the San Juans where WPC
probabilities are high for 4 or more inches of snow. Lighter
snowfall accumulations are likely elsewhere across most of the
high terrain above 9000 feet.

The probability of significant icing (0.25 inches or more) is less
than 10 percent.

Day 3...

...Northern New England...
Vertically stacked low pressure will drift slowly northeast away
from Maine on Day 3. Residual deformation snows are likely
Wednesday night across far northern Maine but WPC probabilities
are low for more than just a few inches of additional accumulation
before forcing lifts away and drier air advects in from the west.

The probability of significant icing (0.25 inches or more) is less
than 10 percent

Weiss