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

Valid 12Z Sun Oct 21 2018 - 12Z Wed Oct 24 2018


Days 1 through 3...

***Central Rockies***

The broad closed mid-level low currently over California is
forecast to slowly move east and open up Monday into an open
trough as the ridge to its northeast breaks down some.  As the
upper level trough approaches the Four Corners region by Tuesday,
moisture advection and mid level dynamics are maximized over
western Colorado and will result in the greatest opportunity for
accumulating snow for elevations above 10000 feet.  The San Juan
Mountains will likely have the greatest amounts, with patchy areas
of greater than 4 inches possible above treeline by Wednesday
morning for southwest facing slopes.


***Northern New England***

A strong shortwave impulse tracking southeastward across Ontario
early in the week is forecast to amplify further upon reaching New
England by Tuesday night.  The accompanying surface low is
expected to re-form near Nova Scotia by Wednesday morning and
rapidly deepen.  A band of moderate snow is likely to the north
and west of the surface low across northern Maine and extending
westward to the White Mountains of northern New Hampshire, with
the greatest snowfall associated with where the low-mid level
frontogenesis sets up.  There is a slight probability of 4+ inches
across northern Maine Tuesday night.  A secondary area of light
accumulations is possible across the higher elevations of the
Adirondacks with post frontal upslope flow along with moisture
from Lake Ontario.

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

Hamrick