Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 182338
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
738 PM EDT Thu Apr 18 2019

.SYNOPSIS...
Unseasonably warm and mainly dry weather will dominate our region
through tonight with just a few widely scattered showers possible at
times across far western and north central New York. A wavy frontal
boundary will then slowly cross the region Friday and Friday night
while generating increasingly widespread showers and a few isolated
thunderstorms...with a period of locally heavy rainfall possible
across the North Country. Unsettled weather will then continue over
the weekend as a weakening upper level low makes its way across our
region.

&&

.NEAR TERM /THROUGH FRIDAY/...
As we move into tonight...a sharpening upper level trough will make
its way into the Mississippi Valley...while at the lower levels an
initial surface low will drift northeastward across Quebec and a
secondary wave will develop across the Ohio Valley in response to
increasing DCVA/height falls aloft. The latter system will help to
further slow the eastward progress of the main frontal zone...with
the latter likely only making it to our northwestern periphery (if
that) by 12z Friday. As such our region will remain embedded within
the warm sector through the night...with unseasonably mild
conditions persisting...and just some additional widely scattered
showers possible across far western and northern New York...which
will lie closer to the slowly encroaching frontal boundary.
Overnight lows should range from the mid 50s along the lakeshores to
the upper 50s and lower 60s elsewhere.

On Friday...the deep upper level trough will continue to sharpen and
begin to cut off into a deep closed low centered over the Tennessee
Valley. Meanwhile at the surface...the slow-moving frontal boundary
will ever-so-slowly ease its way into our region as the secondary
surface low takes further shape upstream...with the former feature
only making it to a rough Bradford PA-Dansville-Fulton line by the
end of the day. The deep southerly flow out ahead of the surface
low/front and upper level trough will help to pump plentiful amounts
of Gulf and Atlantic-based moisture into our region...which will
then be lifted by these boundaries and lead to increasingly numerous
to widespread showers as the day progresses...with weak instability
also possibly allowing for a few embedded isolated thunderstorms.
The showers will arrive first along and to the north of the main
surface front between the morning and early afternoon hours...before
spreading across the remainder of the area through the rest of the
day as a low level jet/another attendant slug of deeper moisture
approaches from the mid-Atlantic states. Basin average rainfall
amounts through the day look to range from a tenth or two of an inch
across interior portions of the Southern Tier/Finger Lakes to around
a half inch across northern portions of the Niagara Frontier and the
North Country...where the showers will be most persistent. As for
high temps...the slowly advancing frontal boundary will lead to a
marked dichotomy in readings...with these ranging from the mid/upper
50s to its north to the upper 60s to mid 70s where it arrives last.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
Friday night and early Saturday the cutoff low over the Tennessee
Valley will move steadily NNE into the Ohio Valley, with a
downstream surface trough drifting across the eastern Great Lakes
and stalling. Deep southerly flow will be in place to the east of
the cutoff low, transporting Gulf and Atlantic moisture northward
along the eastern seaboard and into our area. Increasingly diffluent
mid/upper level flow and a plethora of mid level vorticity maxima
will overspread the eastern Great Lakes, supporting periods of
enhanced large scale ascent.

The abundant moisture and dynamics all point towards fairly
widespread showers Friday night, but model guidance differs
significantly and the potential for a concentrated area of heavy
rain. The greatest potential will be found across the Mid Atlantic
beneath the deepest plume of Atlantic moisture. There is some
potential a northern extension of that may clip the eastern
portion of our CWA per GFS based solutions, although some of the
higher-res NAM based guidance does not develop this area. If
the heavy rain were to materialize east of Lake Ontario there
may be some minor flood risk, but the greater risk appears to be
east and southeast of our area.

Saturday the upper level low will drift north across Ohio. The bulk
of the deeper moisture and steadier rain will rotate out of our area
as an extensive dry slot moves from the Mid Atlantic into the
eastern Great Lakes. This will allow for a good amount of dry time
by Saturday afternoon, although a few stray showers cannot be ruled
out. The position of the cutoff low and associated wind field will
produce a big temperature spread across the region Saturday. The
Niagara Frontier and much of Western NY, and also the Saint Lawrence
Valley will become captured by northeast low level flow to the north
of a baroclinic zone, keeping temperatures in the 50s, and even 40s
near the south shore of Lake Ontario. Meanwhile, warmer boundary
layer air will rotate through Central NY, with 70s probable
southeast of Lake Ontario. The Genesee Valley, including Rochester
will be right near the baroclinic zone making for a difficult call
on temperatures.

Saturday night and Sunday the cutoff low will move from Ohio
eastward into the Mid Atlantic. Moisture associated with the upper
low circulation will increase again from west to east, with the
greatest chance of showers Saturday night across Western NY, and
then Sunday from the Southern Tier through the western Finger Lakes
to points southeast of Lake Ontario. The lake plains may end up
mainly dry Sunday with northeast stabilizing flow off the lakes, but
for now will maintain low chance POPS given inherent uncertainty
with the track of cutoff lows. Highs Sunday will be in the upper 50s
to lower 60s in most locations, cooler along the south shore of Lake
Ontario.

Sunday night will turn mainly dry as the upper level low drifts off
the Mid Atlantic coast, and the next system remains upstream. Lows
will be in the mid 40s in most locations.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
Strong north Atlantic ridging(blocking pattern)will play a huge role
in the speed and timing of systems crossing and ejecting out of the
eastern Great Lakes over the course of this time period.

Monday, a cut off low will reside along the Mid-Atlantic which will
ever so slowly track NNE along the coast as it fights the strong
north Atlantic ridge. Meanwhile, an upstream mid-level trough will
track east across Ontario Canada. With that said, lots of model
spread with a strong blocking pattern in place over the north
Atlantic. Per latest GFS guidance, the upstream trough sends a
weakening cold front through the lower lakes which brings in a
chance for showers Monday into Tuesday and also kicks the cutoff low
out to sea. However, the ECMWF draws the cut off low inland and it
then merges it with the upstream trough. If this occurs it will keep
it cloudy and a bit cooler across our region with the potential for
showers through Thursday. Have kept chance POPs in the forecast with
such significant model differences for now. High temperatures will
also be highly depended on the movement of these two systems across
our forecast area. Monday will be mild ahead of the upstream trough
with temperatures climbing into the 60s near 70F. After that, a bit
cooler Tuesday through Thursday with a mix of clouds and the
potential for showers each day.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
Through the bulk of tonight our area will remain embedded within
the warm sector of a complex frontal system...which will result in
VFR conditions and mainly dry weather largely prevailing...with just
a few widely scattered showers possible at times.

Very late tonight and Friday a slow-moving frontal boundary will
gradually ease its way southeastward across our region. As it does
so showers will become more numerous to widespread from northwest
to southeast...with a few isolated embedded thunderstorms also
becoming possible. More importantly...VFR flight conditions out
ahead of the front will tend to deteriorate to MVFR and possibly
even IFR behind it owing to the increasing shower coverage and
developing moist northeasterly low level flow.

Outlook...
Friday night...IFR/MVFR in low clouds/showers and fog.
Saturday...MVFR/VFR with scattered to numerous showers.
Sunday...VFR/MVFR with a chance of showers.
Monday and Tuesday...Mainly VFR with a chance of showers.

&&

.MARINE...
A weakening surface pressure gradient and a stabilization of the
lower portion of the boundary layer has resulted in notably lower
winds early this evening. This will enable small craft advisories to
be discontinued for all areas but the far eastern portion of Lake
Ontario...but even that area should experience a similar trend in
winds and waves as the evening progresses.

On Friday...a slow moving frontal boundary will cross our region...
with a period of moderate northeasterlies then developing in its
wake Friday night as low pressure strengthens and lifts into the
Ohio Valley. This will likely result in another round of advisory-
worthy conditions...before winds relax later Saturday and Saturday
night as the low tracks into Southern Ontario and weakens.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory until 2 AM EDT Friday for LOZ045.

&&

$$

SYNOPSIS...JJR/RSH
NEAR TERM...JJR/RSH
SHORT TERM...Hitchcock
LONG TERM...AR
AVIATION...JJR/RSH
MARINE...JJR/RSH


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