Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
355 PM EST Tue Mar 02 2021

Valid 00Z Wed Mar 03 2021 - 00Z Sat Mar 06 2021

...Northern New York/Vermont...
Day 1...

A low will move across southern Ontario and then southern Quebec
to just north of Vermont Wednesday before decaying as it moves
towards Maine. The trailing front south of the low crosses
northern NY and VT.  The post-frontal flow becomes westerly, with
moist upslope flow coming into both the Tug Hill and NY Adirondack
Mountains, followed by the northern green Mountains of VT.
Where ascent corresponds to the enhanced moisture in northern NY,
several inches of snow are expected.
The veering flow turns to the north tomorrow night, with drying
aloft simultaneously occurring. As a result, snow shower coverage
and intensity should quickly wane Wed night to Thu morning.  WPC
probabilities for 4 inches are as high as 60% in the northern
Adirondacks.

...CO Rockies...
Days 2-3...

A low-mid level circulation moves from Southern California and
across eastern UT and C. Enhanced low level convergence/ascent
near the 700 mb circulation center crosses southern Utah, the Four
Corners and the ranges of CO, leading to a period of snow across
the mountains, with the higher QPF centered on the San Juan
Mountains, where the strongest 700 mb convergence is forecast.
Secondary snow accumulation maxima are forecast in other ranges of
western to central CO, and Wasatch of southern Utah. WPC
probabilities indicate a high likelihood for 4" in the San Juan
Mountains, and moderate in the southern Wasatch, central Mogollon,
and other CO ranges.
The event winds down Thu as the 700 mb low moves east across the
high plains, with ascent departing the mountains.

...Pacific Northwest...

Day 3...

A closed mid-level low is expected to linger off the coast of
Washington and Oregon Thursday night and Friday. East of the low a
Pacific jet streak and warm/moist mid-level SW flow extends from
the coast of northern CA across western OR and WA. The slow
eastward progression of the low will allow for slow movement of
the bands of precipitation across western WA and OR.  Heavy
amounts of precipitation are possible in the mountains due to the
combination of enhanced moisture in the low level jet and ascent
from both the approaching front and also orographic lift in
windward terrain. However, the southerly component of flow leading
to warming, with snow levels likely to climb above 4000 ft,
limiting significant snowfall to the Olympics and far northern
Cascades, where 1 to 2 feet of snow is possible in the highest
terrain.
The probability of 8 inches is high in the WA Olympics. becoming
moderate in the northern WA Cascades.

For Days 1-3, the probability of significant icing (0.25 inch or
greater) is less than 10 percent.

Petersen