Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 190629

Area Forecast Discussion
National Weather Service Buffalo NY
129 AM EST Fri Jan 19 2018

The cold weather and areas of lake snows from the past several days
will give way to a pronounced warming that will begin on
Friday. High pressure settling off the coast of the Carolinas will
pump progressively milder air into our region during the course of
the weekend so that temperatures will finally push into the 40s.


As we move through tonight...a rather well-defined shortwave
will weaken while quickly rippling eastward across our region.
The brief boost in moisture and lift provided by this passing
feature will bring some short-lived scattered snow showers to
areas from roughly about the New York State Thruway northward.

As for the lake snows...warm advection has already shut down the
snow off Lake Erie and has seriously weakened the snows to the east
of Lake Ontario. While the very weak lake snows near the Tug Hill
should flare back up for a few hours towards daybreak as a result of
the passing shortwave...the winter weather advisory has been
discontinued as additional snowfall should only be an inch or two.

On Friday...heights will rebound across our region in the wake of
the shortwave...and this in concert with continued steady low level
warm air advection will help to steadily wear down the Lake Ontario
lake snows...with these producing another inch or so of accumulation
before finally disintegrating into some leftover scattered snow
showers. Otherwise the day will be largely dry with morning clouds
giving way to some partial sunshine south of Lake Ontario...with the
aforementioned warm air advection also helping to boost temperatures
back into the lower to mid 30s in most places...and possibly even to
the upper 30s across interior portions of the Genesee Valley.


Friday evening there may still be a few light lake effect snow
showers east of Lake Ontario. These will quickly end during the
evening as inversion heights drop below 4K feet and low level
moisture is stripped away as a warm front moves northeast across
the area. Otherwise it will be dry Friday night, with more in
the way of clouds near the Canadian border in closer proximity
to the retreating warm front, and more clearing near the PA
state line. It will become quite windy again with a tight
pressure gradient and a 50+ knot low level jet crossing the
area. An inversion and poor low level lapse rates will not allow
for full mixing, but nonetheless expect gusts in the 35-40 mph
range overnight. Expect lows of around 30 on the lake plains of
Western NY, and mid to upper 20s elsewhere. These lows will
occur during the evening, with mixing and warm advection forcing
slowly rising temperatures overnight.

On Saturday the warm frontal boundary will sag back to the south
across Lake Ontario and the eastern Lake Ontario region as a weak
backdoor cold front. Convergence and frontogenesis will be very
weak, but there may be just enough when combined with lake moisture
and upslope flow to produce some very light precip east of Lake
Ontario. The cloud bearing layer may be too warm to support ice
nuclei, so if precip materializes it may be in the form of drizzle
or freezing drizzle. For the rest of the region, expect dry
conditions with low clouds increasing as low level moisture
increases. It will remain quite windy, with gusts of 35-40 mph in
the morning slowly coming down through the day as the low level jet
core moves off to the east. Expect highs within a few degrees of 40
in most areas, with mid to upper 30s for the North Country.

Saturday night will be dry with a weak surface ridge in place across
the eastern Great Lakes. Expect a good deal of cloud cover with NAM
and GFS BUFKIT soundings showing a rather extensive layer of low
level moisture in place, which is a common occurrence during a mid
winter warm-up with warm air crossing cold, snow covered ground. The
majority of the day Sunday will be dry and cloudy with a few
exceptions. A warm frontal segment will sharpen across the Saint
Lawrence Valley, and this may bring some light snow or rain to the
North Country where colder temperatures hang on. Another warm
frontal segment may bring rain showers to Western NY by late in the
day. Highs will again be within a few degrees of 40 in most areas,
with mid 30s for the North Country.

Monday and Monday night a more significant trough will advance into
the central Great Lakes. Warm advection and moisture transport will
increase across our region Monday, which may support a few showers
from time to time. A cold front will then cross the region late
Monday or Monday night, with the ECMWF a little slower on timing
than GFS based guidance. A plume of deep moisture ahead of the front
combined with increasing ascent will produce periods of rain. Monday
will likely be the warmest day of the stretch, with at least mid to
upper 40s likely in Western NY.

The combination of rain, and increased snowmelt from higher
temperatures and dewpoints may bring some flood concern by later
Monday and Monday night. This warm-up is not as dramatic as last
weekend, and rain amounts are also likely to be lower given the fast
passage of the cold front. Nonetheless, there may be some potential
for ice jam flooding by late Monday and Monday night.


Tuesday into Wednesday, colder air will rush back into the region
with a blustery southwest to west wind behind the cold front. This
will bring a return to more typical mid-winter temperatures for mid-
week along with lake effect snow within wraparound moisture and
lowering 850mb temps. Will have to keep an eye on how the ice cover
on Lake Erie evolves over the early week warmup, as it will have an
impact on the magnitude of whatever lake effect snows develops in
Western NY.


A fast-moving upper level disturbance will continue to track east of
Lake Ontario early this morning. Veering southwesterly flow behind
this system will allow for the re-development of lake effect snow
showers east of Lake Ontario this morning, bringing MVFR conditions
to KART. Snow showers should dissipate after 15Z, as temperatures
aloft warm in the wake of the disturbance, though MVFR cigs will
linger through much of the day, before lifting into a VFR deck after
00Z Sat.

Elsewhere, VFR conditions will prevail throughout the TAF period, as
dry air and warm advection aloft will stifle any lake effect
activity. However, strong westerly flow aloft will continue
throughout the period. These winds will mix down during the day on
Friday, producing gusts to 30 kts. Gusts will subside after sunset
on Friday, however the strong winds aloft will remain, and the low-
level jet will strengthen to in excess of 50 kts Friday night,
resulting in widespread areas of LLWS after 00Z Sat.


Saturday through Sunday...Widespread MVFR ceilings redeveloping on
Saturday...then persisting through Saturday night and Sunday.
Monday and Monday night...VFR/MVFR with rain showers developing.
Tuesday...MVFR/IFR with rain showers changing to snow showers before
ending...then areas of lake effect snow also developing east of the
lakes Tuesday night.
Wednesday...VFR/MVFR with a chance of snow showers.


A persistent pressure gradient will maintain brisk west-
southwesterly flow across the lakes into the upcoming weekend, and
small craft advisories remain in place into Saturday. High pressure
nosing across the region will relax the winds Sunday before winds
freshen once again on Monday ahead of a strong low pressure system
tracking out of the central Plains.


MARINE...Small Craft Advisory until 10 PM EST Saturday for LEZ040-041.
         Gale Watch from this evening through Saturday morning
         for LOZ062-063.
         Small Craft Advisory until 4 AM EST Sunday for LOZ042>045.



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