Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
444 AM EDT Mon Mar 18 2024

Valid 12Z Mon Mar 18 2024 - 12Z Thu Mar 21 2024

...New Mexico and Arizona... Day 1...

The cutoff closed mid-level low over Arizona will continue to
bring precipitation including higher elevation snowfall to
portions of Arizona and New Mexico through Tuesday as weakening
confluent flow east of the low results in diminishing precip
rates.
Snow levels rise from around 7000 ft to 8000 ft today. Day 1 PWPF
for an additional >4" are 20-40% for the highest portions of the
White Mtns of AZ and northern AZ mountains/plateaus.


...Eastern Great Lakes into New England...
Days 1-3...

Upper trough over the Great Lakes this morning shifts east through
New England today with continued westerly flow over the eastern
Great Lakes. Day 1 PWPF for >6" is 30-50% for the Tug Hill and
northern Green Mtns.

The next reinforcing shortwave trough is then expected to swing
east through the Great Lakes Wednesday and New England Wednesday
night. Flow ahead of this wave will remain Wly or WSWly flow over
Lake Ontario, bringing further LES into the Tug Hill with Day 2
PWPF for >6" there 50-80%.

There is a risk for enhanced lift as this trough axis becomes
negatively tilted east of the Great Lakes late Wednesday. Moisture
in this continental airmass should be fairly limited, but Great
Lakes moistening is expected. The 00Z Canadian Regional had much
more QPF than other guidance (even the Canadian - NH), but is
considered a possibility, so the WPC-based PWPF will have higher
Day 3 probabilities than most blends. Day 3 PWPF for >6" is 40-80%
for portions of Upstate NY and the Green/White Mtns.


...Montana...
Day 3...

Amplification of a potent ridge through eastern Alaska Tuesday
night causes height falls downstream over the Canadian Rockies into
MT. Low pressure off Vancouver Island will shift Pacific moisture
through the Northwest with northern MT in the right entrance region
of a NWly jet extending from Alberta to Ohio by late Wednesday. A
swath of snow is expected along a baroclinic zone near and north of
a stalled frontal zone in the immediate lee of the MT Rockies. Day
3 PWPF for >6" is 20-40% around Glacier NP and around 10% along the
northern MT border.

Snow here is expected to continue into Friday, before expanding
over much of the Northwest and northern Plains, so this is just
the first portion of a more significant storm.



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


Jackson