FOUS11 KWBC 050629
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
129 AM EST Thu Dec 5 2024

Valid 12Z Thu Dec 05 2024 - 12Z Sun Dec 08 2024

...Eastern Great Lakes and Northeast...=20
Days 1-3...=20

Strong low pressure moving through Quebec this morning will=20
continue eastward, with WAA-driven snow over northern New England.=20
500mb heights/wind are near the CFSR reanalysis min/max=20
(respectively) with this potent system. The associated cold front,=20
responsible for numerous snow squalls yesterday afternoon and=20
overnight, will help feed moisture into northern/interior Maine=20
where sub-freezing temperatures will support all snow this morning.
Low pressure will quickly translate into Atlantic Canada early=20
this afternoon, with the FROPA turning winds around to the=20
northwest and helping to enhance orographic lift across much of the
Northeast into the central Appalachians. Strong pressure gradient=20
will also maintain windy conditions with blowing/drifting snow over
the interior and near-blizzard/blizzard conditions in the higher=20
elevations (esp WV). Lake-effect snow, already in progress over MI,
will redevelop/strengthen over the eastern Great Lakes by this=20
afternoon on NW flow with some double (Lake) dip increase in=20
moisture. CAM guidance continues to depict some rather robust=20
single bands off some of the lakes with a far reach inland of at=20
least lighter snow. Winds will eventually back and lighten by=20
tomorrow with less coverage/intensity overall but still some more=20
potent bands possible. A trailing shortwave out of Canada will=20
swing through the Lakes late Friday, again enhancing some lake-=20
effect snows across MI into NY and NW PA.=20

WPC probabilities for at least 12 inches of additional snow after=20
12Z Thu are highest (>50%) east of Lake Erie (NW PA into SW NY) and
southeast of Lake Ontario (between ART and SYR). Moderate snow=20
(>8") is likely over the higher terrain of the Adirondacks into the
Green and White Mountains due to upslope flow. In addition, the=20
eastern U.P. of Michigan and the western side of Lower Michigan=20
show moderate (40-70%) and low (10-40%) probabilities,=20
respectively, of at least another 8 inches of snow through=20
Saturday.=20

Lastly, with the progression of the cold front this morning, the=20
threat of snow squalls remains for parts of the northern Mid-=20
Atlantic into New England. This may produce a quick drop in=20
visibility coincident with gusty winds and slippery travel.=20


...Pacific Northwest/Northern Rockies...=20
Day 3...

Upper low in the northeastern Pacific will stream eastward along=20
50N into British Columbia, bringing in a surge of moisture to the=20
Cascades then into the northern Rockies on Saturday. Snow levels=20
will be on the higher side, about 8000ft at precip onset, but will=20
lower to around 5000-6000ft Saturday afternoon as the front moves=20
in, and falling farther to around 3500ft as the precipitation=20
lightens into Sunday morning. Snow will likely affect the higher=20
passes, where the probability of at least 6 inches is >50% above=20
4000ft or so. East of the Cascades, some icing and/or a wintry mix=20
of sleet/freezing rain will be possible as colder surface=20
temperatures are overrun by mild air aloft. Into the northern=20
Rockies, moisture will get wrung out over the higher terrain with=20
several inches likely (>50% chance of 6 inches) on the higher=20
mountain ridges.=20


The probability of significant ice >0.25" across the CONUS is less
than 10 percent.=20


Fracasso



...Winter Storm Key Messages are in effect. Please see current=20
 Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late=
stKeyMessage_1.png__;!!DZ3fjg!_SE21lAdIfWr2_E8riMb_I83_oj2-e2RtStvv7M3CA5zx=
aP-iR8mkCa83hFy0rm25LoL5Zg-zgN9lFM2TYGyrW9ETZs$=20

$$

=3D =3D =3D
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