Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
302 PM EDT Fri Mar 15 2024

Valid 00Z Sat Mar 16 2024 - 00Z Tue Mar 19 2024

...Southern Rockies, Four Corners, and the Southwest...
Days 1-2...

***Heavy snow expands across the Four Corners region through the
 weekend***

The main closed low remains centered over the DEsert Southwest
today, increasingly cut off from the main flow that is becoming
increasingly amplified over the western U.S. today/tonight. So
while the significant upslope snow event over the Front Range winds
down, the second phase of this significant, long-duration winter
storm will begin to expand over the Four Corners region.

THis is a result of the deep/main upper level and the pronounced
and long duration of mid-level divergence downstream, across much
of the lower Colorado Basin into the Central High Plains. Confluent
flow southeast of this low will help surge moisture northward,
combining with modest jet-level diffluence to expand moderate to
heavy precipitation through Saturday. This will result in heavy
snowfall in much of the terrain from the Mogollon Rim and Kaibab
Plateau eastward into the Wasatch, San Juans, and Sangre de
Cristos, with heavy snow accumulations likely above snow levels of
6000-8000 ft in the region of strongest WAA/heaviest precip, but
may fall to 4000-5000 ft beneath the cold core low, especially as
it begins to eject east by Sunday.

WPC probabilities for more than 6 inches through Saturday evening
are above 90% in the southern Wasatch and much of the San Juans, as
well as the higher terrain of the Mogollon Rim, and White
Mountains. Probabilities for at least 12 inches are high (>70%)
for the southern Wasatch, where locally 2 foot totals are likely.

As the upper low finally begins to fill and eject eastward through
the Four Corners on Sunday, total forcing for ascent and moisture
should begin to wane. However, still sufficient moisture and
persistent ascent both due to height falls and steepening lapse
rates aloft will allow for precip falling as snow to continue to
pivot eastward, primarily falling in the San Juans and Sangre de
Cristos. Additional snowfall Saturday night into Sunday is
confined to the San Juans and Sangre de Cristos, where WPC
probabilities for 6+ inches are again 20-40%.


...Great Lakes and New England...
Days 2-3...

A fairly potent shortwave trough digging through southern Canada
today will amplify into a large scale trough over the Great Lakes
this weekend, driving a surface low pressure through Ontario and
Quebec. A passing cold front will have a modest amount of moisture
associated with it and the overlap of forcing for ascent and
moisture will bring widespread precipitation to the region.
Initially, marginal temperatures will lead to a mix of rain and
snow but as colder air seeps southeast, a mix or changeover to snow
is expected, particularly for northern Maine and northern New
Hampshire. Here, the latest WPC probabilities for at least 4 inches
is around 25%.

More impressive, although still somewhat modest, is likely to be
an increase in lake effect snow (LES) behind the front as strong
CAA surges southeast across the Great Lakes. This will result in
axes of significant snowfall accumulations in the favored N/NW snow
belts across the U.P. of MI, and along the Chautauqua Ridge and
Tug Hill Plateau. WPC probabilities for 4 inches within the LES
bands are as high as 20-30% downwind of Lakes Superior, Erie, and
Ontario, highest across the U.P. of MI.

The probability of receiving at least 0.1" ice is less than 10%
across the CONUS through Day 3.

Taylor

**Key Messages for the March 13-16 Winter Storm can be found on
our website
 at https://www.wpc.ncep.noaa.gov**