Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
320 AM EST Sun Jan 28 2024

Valid 12Z Sun Jan 28 2024 - 12Z Wed Jan 31 2024

...Northeast...
Day 1...

Mid-level closed low moving through the Ohio Valley this morning
will turn eastward across the Mid-Atlantic this afternoon and
continue along 40N this evening. At the surface, the current main
area of low pressure is nearing the Ohio border from KY, with a
warm front progression northward over NC. By this afternoon, the
triple point low will start to become the dominant low as the
Miller-B evolution unfolds, aided by a strengthening upper jet
just off the coast. That low will track right across the 40/70
benchmark around 06Z Mon, keeping the Northeast on its cooler NW
side. However, antecedent conditions are rather mild (32F Td line
currently north of I-90) and there is no surface high over
southern Canada to supply colder air. The end result will be a
transitional storm highly dependent on elevation before the flow
becomes northerly enough to drag down some colder air around on
the CCB near and after the peak in QPF. SLRs will vary as well,
trending higher with time and within more robust banded snowfall.
Models do show at least modest 700 FGEN aligned more or less along
a BGM-ALB-BOS line/arc northward, translating northeastward in
time as the surface low progresses south of SNE. WPC Snowband tool
also shows this quite well, suggesting the possibility of >1"/hr
rates in the Catskills and into central New England (also
supported from the HREF probs). Snow will dissipate by Monday
afternoon as the storm quickly pulls away, sending some light snow
to the MA coast.

WPC probabilities for at least 4 inches of snow are greater than
50% over the Catskills and greater Capital District region, though
with lower values in valley locations. Probabilities are higher
than 70% over much of the southern Green Mountains and Berkshires
eastward across the Rt 2 corridor in northern MA into southern NH
(Monadnocks, southern Whites, into the Merrimack Valley). Higher
end snowfall is quite possible, as the models struggle with
snowfall rates, ratios, surface/ground temperatures, and
melting/compacting during these marginal events. There could be a
very notable difference in amounts between lower
elevations/valleys and higher elevations above ~1000ft or so. WPC
probabilities for at least 12 inches of snow are low (10-20%) over
some higher areas.


...Southern Appalachians...
Day 1...

Northwest flow behind the exiting Northeast system will invigorate
upslope snowfall across the southern Appalachians/Smoky Mountains
today into very early Monday as the wraparound moisture in the
lower levels swings through. WPC probabilities for at least 4
inches of snow are highest above about 3500 ft. Above 5000ft, WPC
probabilities for at least 8 inches of snow are around 30-40%.


The probability of at least 4 inches of snowfall on days 2 and 3
are less than 10 percent across the CONUS.


Fracasso