Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
406 PM EDT Sun Oct 21 2018

Valid 00Z Mon Oct 22 2018 - 00Z Thu Oct 25 2018


Days 1 through 3...

...Central Rockies...
Greatest potential for significant snow accumulations will be
confined mainly to the western and central Colorado ranges for
elevations above 10000 ft.  Increasing moisture and lift ahead of
a broader upper trough approaching from the west is expected to
increase the threat for locally heavy amounts, with WPC
probabilities indicating Slight risks for accumulations of
8-inches or more for portions of the region on Days 2 (ending 00
UTC Wed) and 3 (ending 00 UTC Thu) - including parts of the San
Juan, Sawatch and Elk ranges in Colorado.

...Northern New England...
Models show a well-defined shortwave trough diving southeast
across central Canada into the Great Lakes region on Monday.  As
the shortwave continues to amplify and shift east, a surface low
is expected to deepen and track north from the Gulf of Maine into
Atlantic Canada Tue night.  For most areas, thermal profiles will
support mostly rain.  However, deepening cold air on the back side
of the system should be sufficient for a transition to snow,
particularly across the mountains of northern Maine and New
Hampshire - where some guidance members, including the ECMWF show
the potential for locally heavy amounts.  However, models are far
from agreement here - showing a fair amount of spread with respect
to the track and amplitude of this system.  WPC probabilities
reflect this uncertainty with only a Slight Risk for accumulations
of 4-inches of more covering northern Maine and far northern New
Hampshire and a Moderate Risk confined to the northwest Aroostook
County, Maine on Day 3.

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

Pereira