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Winter Weather Forecast Discussion
 
(Latest Discussion - Issued 1907Z Apr 12, 2024)
 
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Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
306 PM EDT Fri Apr 12 2024

Valid 00Z Sat Apr 13 2024 - 00Z Tue Apr 16 2024

...Western NY & Northwest PA...
Day 1...

Strong cyclonic flow on the backside of a storm system tracking
north into the heart of southeast Canada will lead to a brief but
potent surge of CAA across the eastern Great Lakes this evening.
Accentuated beneath a TROWAL overhead, a pivoting band of heavy
rain will changeover to snow as WNW winds favorably upslope into
the Chautauqua Ridge in the western portion of NY's Southern Tier
and strong dynamic cooling within the column ensues. Latest CAMs
are showing the potential for as much as 1-2"/hr snowfall rates
along the Chautauqua Ridge tonight, and snowfall rates that heavy
can rapidly cool boundary layer temperatures closer to freezing to
support rapid accumulations. As with most snow events this late in
the season, elevation will be a massive factor in which areas see
a coating to a couple inches or as much as localized amounts
between 6-8" by Saturday morning. Latest WPC PWPF sports moderate-
to-high chances (50-70%) for >4" of snowfall along the Chautauqua
Ridge at elevations >2,000ft through Saturday morning. Areas in
northwest PA, including Bradford, PA and Allegany State Park,
feature low-to-moderate chances (30-50%) for >4" of snowfall. The
WSSI sports Minor to even Moderate Impact potential in western NY
to the south and east of Buffalo, NY. These areas in particular can
expect some hazardous travel conditions tonight and into early
Saturday morning. Periods of snow will gradually taper off
throughout the morning, which given the mid-April sun angle will
all but end the accumulating snowfall potential from late morning
on.

...California...
Days 1-2...

A compact and potent 500mb low approaching the Golden State today
will result in an unsettled weather pattern this weekend. NAEFS
continues to depict the 500mb low tonight and early Saturday
morning that features 500mb heights that are below the observed
CFSR climatology (1979-2009) just WNW of San Francisco. This
impressive upper low will accompany a strong IVT (topping out
around 400 kg/m/s) that according to NAEFS will top the 99th
climatological percentile over central California. The upper low
will gradually weaken throughout the day, but not before it
provides ample Pacific moisture flux into California that leads to
heavy snow >6,000ft from the Salmon/Shasta/Siskiyou Mountains on
northern California on down the spine of the Sierra Nevada Saturday
and into Sunday. As the upper low weakens Saturday night and into
Sunday, snow levels will gradually rise and strong synoptic-scale
ascent will weaken, keeping periods of heavy snow strictly confined
to elevations >6,000ft. Meanwhile, periods of moderate-to-heavy
snow will still occur in parts of the northern Sierra Nevada, the
Warner Mountains of northern California, and the tallest >7,000ft
peaks of the Great Basin in Nevada. Snow looks to conclude in these
regions by Sunday night.

WPC PWPF shows high chances (>70%) for snowfall totals >8" in
elevations >7,000ft in the Sierra Nevada and the aforementioned
northern California ranges. The WSSI sports Moderate Impacts in the
southern Sierra Nevada (elevations >7,000ft) where a combination
of Snow Amount and Blowing Snow are the primary components driving
the algorithm. Otherwise, most impacts as low as 5,000ft in the
northern California ranges are likely be Minor Impacts, implying
there could be a few inconveniences to daily life and caution is
urged while driving in affected areas.

For days 1-3, the probability of significant icing is less than 10
percent.


Mullinax