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Area forecast discussion
National Weather Service Buffalo New York
509 PM EDT sun Sep 22 2019

Synopsis...
a slow moving cold front will cross our region on Monday...and this
will not only generate some showers but will also bring an end to
our spell of late Summer weather. Notably cooler air will follow the
front Monday night and Tuesday when temperatures will fall back
towards normal. This cool down will be short lived however...with
temperatures expected to average above normal for the remainder of
the week.

&&

Near term /through Monday/...
our fine late Summer weather will only very slowly deteriorate
tonight...as a cold front over the upper Great Lakes will ease
across southern Ontario. While the vast majority of the region will
remain very warm and dry out ahead of this boundary...it may get
close enough during the wee hours of Monday morning to allow for
some showers to get into the Niagara Frontier. With respect to
temperatures...the warm southwesterly flow across our region will
keep overnight mins well above average...with temperatures averaging
a full 20 degrees above where they should be for the autumnal
equinox...which occurs at 3:50 am Monday morning.

The cold front will then finally push across our region during the
day Monday. In the process it will help to generate fairly numerous
showers...with a few embedded thunderstorms also possible given the
presence of some weak to modest instability. While a moisture rich
environment (pwats of 1.5 to 2 inches) and a deep warm cloud layer
will be in place out ahead of the front...the fast flow aloft will
help to keep the precipitation moving along...and therefore should
help limit basin-average rainfall amounts to a tenth of an inch or
two...though locally higher amounts could be possible within any
heavier showers or storms. Expect the bulk of the showers to come
between the morning and early afternoon hours...with the precip then
diminishing from west to east following the frontal passage as
strong dry slotting aloft overspreads the region.

Otherwise Monday will be a breezy to windy day across our region...
with modest cool advection and steepening lapse rates in the wake of
the front allowing for more efficient mixing of lingering higher-
momentum air from aloft down to the surface...thereby leading to
some gusts to 30-35 mph. As for temps...these will be notably cooler
than those of the past several days...but should still mostly top
out at above average levels in the 70s given the only very modest
cool air advection regime.

&&

Short term /Monday night through Wednesday night/...
colder air wraps in behind the departing system on Monday night. As
temperatures off the deck fall toward and below +6c, this should
start to provide some lake response...especially in the Lee of Lake
Ontario. Lake effect showers in cyclonic flow will continue through
the first half of Tuesday before incoming drier air starts to allow
for them to wind down. A cool boundary layer and over-lake flow will
keep boundary layer temperatures in check on Tuesday, though, as
lake enhance stratocumulus inhibits insolation. That will keep
temperatures back in the 60s.

Drier air and warm advection quickly returns to the area by
Wednesday as 850 hpa temperatures catapult up toward +15c in short
order. While ridging will be abrupt, it won't last, however. Another
weak system looks to come back bashing at the ridge axis by
overnight Wednesday night and into the long term forecast with
rapidly increasing chances of showers.

&&

Long term /Thursday through Sunday/...
a broad long wave trough forecast to advance across the Great Lakes
region will drive a cold front across the area early Thursday.
Moisture content will be limited, but enough to support a chance of
a few showers early in the day. Showers will end from west to east
later Thursday behind the cold frontal passage as drier air starts
to build in. High pressure will then build into the Ohio Valley and
eastern Great Lakes Thursday night and Friday, bringing a dry end to
the week. There are some slight timing differences with the arrival
of the next front over the weekend, with the European model (ecmwf) slower than the
GFS.

After a brief cool down Thursday and Thursday night, a warming
trend starts with temperatures warming to above normal Friday
and likely lasting through the weekend.

&&

Aviation /21z Sunday through Friday/...
VFR weather will remain in place through tonight...although high
pressure off the Carolinas will slowly lose its grip on our weather.
The only only concern tonight will be the risk for some low level wind
shear. Southwest winds of 40 knots will be found above 1500 ft after
06z...but at least a portion of these winds should mix to the sfc. Have
not added this marginal risk to the tafs...but this will need to be
monitored.

Conditions will deteriorate Tuesday morning though...as a cold front
will ease across the region. Cigs will lower to MVFR levels during the
course of the morning with the likelihood of showers. There will be the
risk for an isolated thunderstorm...mainly during the midday and
afternoon for sites east of the Genesee Valley. By the end of the
day...cigs will range from IFR to MVFR levels.

Outlook...

Monday night...VFR to MVFR cigs with a chance of showers.
Tuesday...mainly VFR but a chance of showers east of Lake Ontario where
MVFR cigs will be possible.
Wednesday...VFR.
Wednesday night and Thursday...mainly VFR with showers likely.
Friday...VFR.

&&

Marine...
a cold front will gradually approach our region tonight...then will
slowly push across the area during the day Monday. As the front
approaches tonight...southwesterly winds will freshen to moderately
brisk levels...before veering to westerly following the passage of
the boundary on Monday. This will result in a period of fairly
widespread advisory-level conditions that will begin tonight and
continue through Monday...before diminishing from west to east later
Monday night and Tuesday as high pressure builds into the region and
brings diminishing winds and wave action. With all this in mind...
small craft advisories are in effect as outlined below.

&&

Buf watches/warnings/advisories...
New York...none.
Marine...Small Craft Advisory from 11 PM this evening to 11 am EDT
Tuesday for lez040-041.
Small Craft Advisory from 6 am to 8 PM EDT Monday for
lez020.
Small Craft Advisory from 8 am Monday to 5 PM EDT
Tuesday for loz043-044.
Small Craft Advisory from 2 am Monday to 11 am EDT Tuesday
for loz042.
Small Craft Advisory from 5 am Monday to 2 PM EDT Tuesday
for loz045.

&&

$$

Synopsis...jjr/rsh

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