Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
345 AM EST Mon Jan 01 2024

Valid 12Z Mon Jan 01 2024 - 12Z Thu Jan 04 2024

...California & the Southwest...
Days 2-3...

An anomalous upper low barreling into California on Wednesday will
be the culprit for the next round of heavy snowfall into the
mountains ranges of California and as far inland as central
Nevada. The upper low is a stout one with <10th percentile heights
showing up at 250mb and 500mb Wednesday morning. This upper low
will already channel ample 850-700mb moisture flux out ahead of it
Tuesday night that will reach the Salmon and Trinity mountains. As
a surface cold front makes its way through northern California,
snow levels will fall and snow will pick up in intensity from
northern California Tuesday night to the northern and central
Sierra Nevada by Wednesday morning. As the upper low continues to
push east, so will the conveyor belt of moisture out ahead of the
storm system, leading to heavy snow enveloping the southern Sierra
Nevada and even as far south as the Transverse Ranges above
6,000ft. The upper low will remain progressive as it tracks into
southern Nevada Wednesday evening, resulting in accumulating
snowfall from the 7000ft ranges of central Nevada to as far south
as Mount Charleston.

Latest WPC PWPF sport high chances (>70%) for >6" of snowfall from
the Mendocino National Forest and the Trinity/Salmons Mountains to
the central and southern Sierra Nevada. In the peaks of the
Transverse Ranges, WPC PWPF does show low chances (10-30%) for >4"
snowfall amounts on Wednesday. Similar probabilities are depicted
in the >7,000ft ridges in central Nevada, around Mt. Zion National
Park in southwest Utah, and just north of Grand Canyon National
Park in northern Arizona. The Probabilistic WSSI shows as much as
a 60-80% chance for Minor Impacts in the California mountains
ranges and Moderate Impact probabilities are at low-to-moderate
odds (30-50%). Snow Amount and Snow Rate are the primary drivers
in the WSSI-P algorithm there. Moderate Impacts will would most
likely occur in the tallest peaks of the California Ranges.
Central Nevada is less likely to see Moderate Impacts, but the
Probabilistic WSSI does show as much as moderate chances(50-60%)
for Minor Impacts on Wednesday. Where Minor Impacts occur, some
treacherous travel conditions could occur and result in a few
inconveniences to daily life in these areas.

...Great Lakes...
Days 2-3...

A cold front tracking south and east out ahead of an approaching
upper level vort max will spur lake effect snow showers to develop
along the U.P. of Michigan Tuesday night. By Wednesday morning,
the upper level vort max will amplify as it tracks south through
the Upper Mississippi Valley. Surface winds over the eastern Great
Lakes will become increasingly convergent as the cold front
advances through the region and result in some lake effect
streamers off of Lakes Erie and Ontario during the day. However,
it will be the amplification of the 500mb trough over the Great
Lakes that fosters increased diffluent flow at upper levels over
the eastern Great Lakes and the Northeast. Snow will likely be at
its heaviest over the U.P. of Michigan and the top of Michigan's
Mitten as the cold front passes through, with the heaviest of the
Lakes Erie/Ontario streamers holding off until Wednesday night.
Latest WPC PWPF is highlighting the Tug Hill Plateau with having
moderate chances (40-60%)of receiving >4" of snowfall. Otherwise,
the Michigan U.P., the northern tip of Michigan's Mitten, and both
far northwest Pennsylvania and western New York show generally low
chances (10-30%) of receiving >2" of snowfall. Minor impacts,
including snow covered roads and resulting hazardous travel are
possible in the more heavily affected areas.

The probability of significant ice across the CONUS is less than
10%.

Mullinax