Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
303 PM EST Fri Jan 26 2024

Valid 00Z Sat Jan 27 2024 - 00Z Tue Jan 30 2024


...Pacific Northwest...
Days 1...

Disturbance off the northwest Pacific will continue pressing
northeast towards British Columbia with persistent southwesterly
flow advecting mild, Pacific air into the northwestern U.S. Snow
levels will rise through the course of D1 with significant snow
confined to the highest elevations of the Cascades. The sheltered
valleys within the shadow of the Cascades of WA/OR will see a
period of light freezing rain with low probabilities for at least
0.1" of ice accretion. The best area for accretion will reside
across the shadow of the WA Cascades where shallow arctic air will
be tougher to remove. WPC probabilities are still only around
20-30% for reaching the 0.1" accretion threshold, so fairly low
probabilities for any significant impacts anticipated.


...Northeast...
Days 2 & 3...


Current WV satellite shows the next disturbance down the pike for
the northeastern U.S as it slowly pivots out of the southern
Rockies into the Southern Plains through the next 24 hrs. Steady
progression eastward, then northeast by tomorrow afternoon will
also deepen to a 5H ULL reflection as it moves into the Ohio
Valley. Strong difluent signature ahead of the mean trough will
advect rich, Gulf moisture poleward with widespread precip
extending from the Southeast U.S into the Mid-Atlantic and
Northeast by early Sunday morning. Weak surface ridging across the
northeast will vacate with marginally cold air in its wake leaving
a borderline setup for snowfall across the interior Northeast,
eventually moving into New England by Sunday night into Monday.
Surface low in the vicinity of the Ohio Valley will transfer
energy to the Mid-Atlantic coast with a classic Miller-B evolution
unfolding as we enter the end of the weekend. The maturation of
the coastal cyclone coupled with a favored 5H trough evolution
thanks to marginal confluence over northern New England will lead
to a rain to snow transition within the confines of northern PA
and points northeast with the most impactful zones located within
the higher terrain of the Catskills, Berkshires, and the Worcester
Hills in central MA through southern NH.

The spread within guidance makes this tricky, even as we approach
shorter leads due to the discrepancy in the handling of the 5H
trough/closed-low reflection over the eastern CONUS. There are two
distinct camps at this point; GFS/CMC in a further south solution
with a snow footprint confined across PA/southern NY state into
southern New England, and the ECMWF/ECS/UKMET which are further
north with greater amplitude to the mid-level trough and
accompanying PVA regime across southern NY state up into southern
and central New England. The latter is the most aggressive with
regards to appreciable impacts with WPC probabilities of at least
4" of snow of 30-60% encompassing a large area spanning
southwestern NY across the Hudson Valley into much of MA/southern
NH. A max of 70-80% of at least 4" is located within the
Catskills/Berkshires/Northern MA with at least 6" probabilities of
50-60% in the aforementioned zones. Ensemble means generally keep
the door open to a moderate impact event with WSSI showing a large
expanse of at least minor impacts, bordering moderate within the
zones capable of exceeding 4". Snow load will be a primary concern
as marginal thermals for most of the event will create lower SLRs
compared to climo until perhaps the tail end of the storm when
mid-level frontogenesis and matured axis of deformation reaches
peak as the coastal low intensifies and moves off the northeast.
This is most likely within the confines of interior southern New
England between the Berkshires and Worcester Hills. This has
allowed for Watches to be hoisted in those zones given the latest
probabilistic and deterministic trends within the 12z suite. This
will be a setup that is prone to large shifts in impact potential
due to marginal thermals and intricate details within the
mid-level evolution.

Kleebauer