Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
302 AM EST Tue Mar 05 2024

Valid 12Z Tue Mar 05 2024 - 12Z Fri Mar 08 2024

...West Coast, Northern Great Basin, & Northern/Central Rockies...
Days 1-3...

Multi-stream westerly flow will give one more push of moisture
into NorCal/southern OR eastward to western WY today as the weak
IVT axis collocated near a weak surface boundary slowly dissipates
late tonight. Upslope enhancement will still be able to capitalize
on sufficient moisture out of the Pacific to yield modest snow
totals over the far northern Sierra into the
Klamath/Shasta/Siskiyous and southern OR Cascades eastward into
central Idaho. There, WPC probabilities for at least 8 inches of
snow are high (>70%) about about 5000ft or so. Over western WY,
combination of a bit stronger height falls and surface convergence
may elevate totals. There, WPC probabilities for at least 12
inches of snow are high (>70%), generally above 7000-8000ft.

Into D2, an upper low will move into SoCal with the rest of the
West relatively dry. Lingering light snow is forecast for a
similar area as D1, from NorCal eastward to WY, and also into the
CO Rockies. By D3, the upper low over the Southwest is forecast to
weaken a bit as it moves into NM, while a surface high builds
southward out of the northern Plains, helping to drive a cold
front southward east of the terrain and enhance easterly/upslope
flow. Temperatures will be marginal east of the Rockies, but trend
colder with time overnight Thu into early Fri. Through the end of
this period, 12Z Fri, WPC probabilities for at least 6 inches of
snow are >50% above 7500ft or so in the Rockies, with light snow
along the I-25 corridor except for the Palmer Divide which will
has moderate chances (40-60%) of at least 6 inches of snow. 


...Northern Plains...
Day 2...

A compact closed mid-level low over southern Canada just north of
MT early Wed will move eastward along the border but swing an
appendage of vorticity into ND and far northern MN. At the same
time, an area of low pressure is expected to lift northward along
its frontal boundary from central SD into northern MN. Models
continue to struggle with the placement and amount of QPF, with
the NAM/NAMnest driest and farther north with its QPF than most of
the other models. Still, the consensus is for more snowfall than
24 hrs ago, and amounts were raised over northeastern ND into far
northwestern MN where WPC probabilities for at least 4 inches of
snow are around 70%. The entire snow shield will likely be fairly
compact, and generally north of I-94. Still, these robust yet
short wavelength features have a habit of being underestimated by
the guidance, so trends will have to be noted in the next CAM
cycle.


...Northern New England...
Day 2.5...

Northern stream shortwave will carry a cold front into New England
as a coastal low takes shape over the VA Tidewater late Wed into
early Thu. Strengthening high pressure over Quebec will help draw
in colder, and drier, air down the St. Lawrence Valley, allowing a
changeover from rain to snow on the north side of the
precipitation shield early Thursday. Models continue to waver on
depth of cold air vs available QPF, and WPC probabilities for at
least 4 inches remain on the low side for now -- generally 10-40%
across northern Maine.


Fracasso