Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
350 AM EST Sun Dec 10 2023

Valid 12Z Sun Dec 10 2023 - 12Z Wed Dec 13 2023

...Northwest through the Northern Rockies...
Day 1... 

Moderate atmospheric river (AR) plume axis shifts from southern WA
through OR today. Shortwave impulses help spread this moisture
east over the northern Great Basin and through the northern
Rockies down to northern CO. Snow levels exceed 8000ft in the
Cascades in the core of the AR and closer to 3000-5000ft over the
northern Rockies. Day 1 snow probabilities for >6" are moderate
(40-60%) for the higher Blue Mtns in northeast OR, and the
Clearwater/Salmon River/Bitterroots as well as the Tetons and
western WY ranges and Medicine Bow Mtns over southern WY.


...Central Appalachians through the Interior Northeast...
Days 1/2...

Multi-stream positively-tilted trough situated over the
Midwest-to-southern Plains this morning. The southern stream
section continues to dig to the central Gulf Coast today before
ejecting north over the Eastern Seaboard tonight into Monday. This
southern trough takes on a negative tilt by Monday morning over
the Mid-Atlantic as it zips north with an increasingly buckled
S-shaped upper jet over the Northeast and southeastern Canada.
Slowing surface front approaching the central/southern
Appalachians this morning will spur a wave in the Mid-Atlantic
that lifts north-northeastward across southeastern New England
early Monday in the right entrance region of the 130kt jet,
promoting deepening thereafter into eastern Maine and into Quebec
that afternoon. Strong CAA behind the front amid a sufficiently
moist column will turn rain to snow from west to east over the
central Appalachians and New York State late this afternoon into
Monday, especially in elevations above 500ft (and west of I-95).
Strong NW-tilted FGEN band from northeast PA into northern New
England will support snow rates >1"/hr as the rain changes to
heavy, wet snow (high snow load) especially from the Catskills
into the Adirondacks and Green Mountains. Day 1 WPC snow
probabilities for >6" are moderate (40-60%) for the WV crest of
the Appalachians as well as the VA Blue Ridge at Shenandoah NP
with Day 1.5 probs moderately high (40-80% from far northeast PA
north through Upstate NY including the Catskills and Adirondacks.
These values are high on Day 1.5 over much of VT into far northern
NH where there are also moderate (40-70%) for >12".

Though the system will be progressive despite the negative tilt,
minor fluctuations in the track of the front/low, speed of
incoming cold air (rate of changeover), and precipitation focus
would lead to large changes in the snowfall amounts. Lake effect
snow in typical northwest flow snow belts off Erie and Ontario
will persist on Monday before shifting westerly Monday night with
additional accumulation in the Tug Hill.


...Michigan U.P...
Day 3...

On upper low will move from Manitoba across far northern Ontario
late Monday through Tuesday with a surface cold front dropping
through northern MN and into the western Great Lakes. 850 temps
will be colder with this wave, dropping to around -12 to -15C
(into the DGZ) and supporting WNW to ESE bands post-FROPA
Tuesday/Tuesday night. WPC probabilities for >4" are moderate to
high in west flow snow belts around the Keweenaw Peninsula and far
eastern sections of the U.P. shoreline of Superior. 


Jackson