Area Forecast Discussion
Issued by NWS Buffalo, NY

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313
FXUS61 KBUF 211448
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1048 AM EDT Mon May 21 2018

.SYNOPSIS...
High pressure will bring fair weather to the region today with a
good deal of sunshine and light winds. A complex of showers and few
thunderstorms will propagate across Western New York tonight, with a
few of these storms potentially bringing heavy rainfall. These
storms will push east across Eastern Lake Ontario region tomorrow,
with additional showers and thunderstorms possible along lake breeze
boundaries tomorrow afternoon.

&&

.NEAR TERM /THROUGH TUESDAY/...
Surface high pressure over the Central Great Lakes will bring
pleasant and seasonal conditions along abundant sunshine.
Temperatures should top off in the low to mid 70s.

A shortwave trough over the Upper Mississippi Valley this
morning will advance eastward, rounding a SE ridge of high
pressure tonight. Meanwhile at the surface, a warm front will
be moving across the Ohio Valley. This shortwave will bring a
cluster of showers and thunderstorms forming within 500 J/KG of
elevated instability. A LLJ of 35 knots riding along the front
will enhance precipitation, with an axis of heavy rain possible
along leading edge of the jet, and just to the north of the
surface warm front. PWATS will rise to 2 to 2.5 SD above normal,
with an axis of 1.25 to 1.50 inches crossing WNY tonight.
Placement of heavy rain is still uncertain with varying
convective allowing model output, so will blanket WNY with a
chance for heavy rain tonight. Overall rainfall amounts will
range from a half to one inch. Localized heavier storms or
training of storms will likely exceed an inch.

Timing...Showers and thunderstorms tonight will likely reach SW
NYS around an hour or two before midnight, then across other
sections of WNY overnight. Storms should weaken some later in
the night with less instability to the east while crossing the
Finger Lakes region, and near the Eastern Lake Ontario area
around dawn.

Model consensus has trended north with a convectively driven wave of
low pressure, with this low likely to track from Buffalo to
Watertown on Tuesday. The forecast reflects this track, however
given the convective nature of this system, minor adjustments to the
track still may be needed. A cold front trailing this low will
drop southward across the western Southern Tier and into central
New York Tuesday afternoon. This is likely to result in another
round of showers and thunderstorms. There is a marginal risk
for severe with this, with a narrow window of ample instability
and ample winds aloft ahead of the cold front. The lake breeze
may also provide a focus for convection. Otherwise, some
scattered showers may linger into Tuesday afternoon. Highs will
be within a few degrees of 70 across the region.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/...
After a wet and unsettled day on Tuesday...we can fully expect
significant improvement in our weather as we work through this
period.

A ridge centered over the middle of the country Tuesday night will
amplify and drift east Wednesday and Thursday. After a leftover
shower or two Tuesday evening...this scenario will lead to clearing
skies during the overnight with absolutely beautiful weather to
follow for Wednesday and Thursday. Temperatures both days will
average above normal as max temps will end up between 75 and 80.

The only potential fly in the ointment will be across parts of the
Niagara Frontier Wednesday afternoon...as a localized convergence
zone could support some enhanced cloud cover within a few miles of
Tonawanda Creek. A relatively dry airmass and subsidence inversion
should be enough to preclude the risk for any showers though.

&&

.LONG TERM /FRIDAY THROUGH SUNDAY/...
While the start of this period will feature fair weather with
comfortable temperatures and low humidity...conditions will
deteriorate during the course of the weekend. In fact...guidance has
been fairly consistent with a scenario where our region could pick
up a significant amount of rain. More on this in a moment.

As we open this period Thursday night and Friday...a flattening
ridge will make its way across the Lower Great Lakes. This will keep
nice weather in place for our region to end the work week as
temperatures will average a few degrees above normal.

A weak warm frontal boundary will extend southeast across our region
Friday night. While this could lead to some showers during the
overnight...there is low confidence with the placement of the
boundary.

A broad area of low pressure over the Upper Great Lakes on Saturday
will push the warm frontal boundary to the north of our region by
afternoon. This will place our region well within a notably warmer
and more humid warm sector where H85 temps in the vcnty of 16c
should easily support highs in the 80s (bit cooler higher terrain
and North Country). Being in the warm sector...the vast majority of
the day should be rain free. A shower or two cannot be ruled out
though...especially in the North Country in the vcnty of the exiting
warm front during the morning...and across the Southern Tier in the
afternoon where the most unstable environment will be in place.

The aforementioned area of low pressure will track to the east to
Quebec Saturday night and Sunday...dragging its associated cold
front across our region in the process. There is a good
representation of ensemble members from the GEFS/ECMWF that suggest
that this front could contain a few subtle waves...which would help
to slow its eastward progress through our region. Meanwhile...a
potentially worrisome combination of systems over the sub tropics
(30 N) will pump copious amounts of tropical moisture out of the
eastern GOMEX. A nearly stationary mid level low near New Orleans
and a newly formed Bermuda High centered 500 miles east of Florida
will establish a deep plume of tropical moisture that will be
directed to the north along the spine of the Appalachians. This
moisture will then interact with the aforementioned cold frontal
boundary...the same one that could slow or temporarily stall over
our forecast area.

There is the risk that the timing of the front and arrival of the
tropical moisture could place part of our region in an area of heavy
rain for Sunday/Sunday night. Stay tuned.

&&

.AVIATION /15Z MONDAY THROUGH FRIDAY/...
High pressure today will bring VFR flight conditions with light
winds. A complex of showers and thunderstorms will near the
region tonight...generally after midnight. Some of this activity
may become heavy with visibilities dropping to IFR.

Outlook...

Tuesday...Areas of MVFR with showers likely and a chance
of thunderstorms.
Wednesday through Friday...VFR.

&&

.MARINE...
High pressure will bring fair weather to the lakes and rivers today,
with light winds and minimal waves on the lakes. An easterly wind
developing tonight ahead of a surface warm front will bring a
moderate chop to the western Lake Ontario waters...possibly to near
small craft advisory threshold by early Tuesday morning. These winds
will quickly veer to westerly and diminish Tuesday with another
period of fine boating weather expected through much of the work
week.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...None.

&&

$$

SYNOPSIS...Thomas
NEAR TERM...Apffel/Thomas/Zaff
SHORT TERM...RSH
LONG TERM...RSH
AVIATION...Thomas
MARINE...Thomas



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