FOUS11 KWBC 020831
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
431 AM EDT Tue Apr 2 2024

Valid 12Z Tue Apr 02 2024 - 12Z Fri Apr 05 2024

... Great Lakes into the Northeast... Days 1-3...

...Significant late season winter storm this week...

A well-defined southern stream shortwave continues to lift
northeast across the central Plains this morning. This system is
expected to continue tracking northeast into the mid-to-upper
Mississippi Valley and western Great Lakes region, where it will
begin to interact with an equally defined northern stream trough
diving out of central Canada. As the two streams phase, models
show an upper low rapidly developing over the upper Mississippi
Valley and western Great Lakes this afternoon and evening. Strong
upper forcing overlapping low level frontogenesis will support rain
quickly changing to heavy snow on the backside of the associated
surface low as it tracks out of the mid Mississippi Valley toward
the Great Lakes this afternoon and evening. HREF guidance shows
heavy banded snow with rates of 1-2 inch/hour developing across
southern Wisconsin by the late afternoon, before gradually
expanding north into Upper Michigan during the evening into the
overnight hours. Following a significant western shift in the
guidance from the 00Z to the 12Z runs earlier today, the latest 00Z
guidance has shown overall better run-to-run continuity. However,
some models, including the GFS, continue trend west, raising
probabilities for heavy snow further west across Wisconsin. Snow
will continue to fall across the region through Wednesday, however
overall rates are expected to diminish as the low begins to drop
back to the southeast. A primary exception will likely be the
central to western U.P., which will be the focus for strong
easterly flow off of Lake Superior as the low meanders over
southern Wisconsin on Wednesday before drifting southeast toward
the Ohio Valley. WPC PWPF probabilities for snow accumulations of 8
inches or more are above 70 percent from southern Wisconsin to the
U.P. The highest probabilities are centered over the central U.P.,
where the PWPF even shows some 50 percent or greater probabilities
for 2 feet or more before the snow ends on Thursday.

Meanwhile, additional southern stream energy phasing with the low
will support the development of a triple-point low that will start
to become the primary surface feature as it tracks from the Mid
Atlantic to Long Island and southern New England late Wednesday
into early Thursday. Precipitation will begin to spread across
eastern New York into New England on Wednesday, with mixed
precipitation at the onset for much of the interior. Low-to-mid
level frontogenesis along with divergence aloft will support
stronger ascent and a transition to snow across northern New York
and interior central to northern New England. It is unclear how
much an intrusion of dry air and warm air aloft may impact amounts. Probabilities for heavy snow have retreated a bit further to the
north with latest run across from the Catskills eastward into
central Massachusetts, southern Vermont and New Hampshire.
Relatively lighter QPF and the potential for a more prolonged
period of sleet are contributing to the lower probabilities.
Heavy, wet snow still appears likely for at least portions of the
Adirondack, Green, and White mountains. WPC PWPF shows high
probabilities for 8 inches or more extending from these areas into
central Maine. Snow will continue across the region into Friday,
however rates should begin to diminish by late Thursday as the low
lingers but weakens over New England.

...Western U.S.... Days 2-3...

An amplified upper trough associated with a low dropping south from
the Gulf of Alaska will begin to dig into the northwestern U.S. on
Wednesday. Backing flow ahead of the advancing trough will support
deepening moisture and the increasing potential for snow along a
low-to-mid level front extending northeastward from the southern
Cascades on Wednesday. While widespread heavy accumulations are
not expected, locally heavy amounts are possible from the southern
Cascades to the Blue Mountains late Wednesday into early Thursday.

By early Thursday, models show a deep upper low centered along the
Northwest coast that will then dig further south into northern
California by early Friday. This will bring heavy snows into the
Sierra Nevada and parts of central and northern Nevada. Meanwhile,
energy lifting east of the low and a lingering frontal boundary
will support additional heavy amounts across northeastern Oregon.
For portions of the Sierra Nevada, southern Cascades, and the Blue
Mountains, WPC PWPF shows high probabilities for 8 inches or more.


Pereira

*** Key Messages for Early April Nor'easter ***

---Long duration winter storm

A large storm system will produce gusty winds and late-season
heavy snow across portions of the Great Lakes and the Northeast
beginning later today and continuing through midweek.

---Western Great Lakes heavy snow Tue night

Heavy snow will likely develop over Wisconsin by this
afternoon and expand into Upper Michigan overnight. Snow will
continue over much of the region through Wednesday, with additional
heavy snow across portions of Upper Michigan, before ending on
Thursday.

---Northeast snow and wind Wednesday-Friday

Secondary low pressure development along the Mid-Atlantic coast
will likely bring heavy, wet snow and some sleet to the Northeast
Wednesday afternoon through Friday. Significant snow accumulations
are likely over parts of northern New York and New England.

---Significant impacts from heavy snow and wind

The combination of heavy snow rates and gusty winds will likely
result in hazardous travel due to low visibility and snow-covered
roads. The wet snow and high snow load may cause tree damage and
impact infrastructure.

$$
--- SBBSecho 3.20-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (21:1/175)