Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 211902
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
302 PM EDT Sun May 21 2017

.SYNOPSIS...
Widespread showers and embedded thunderstorms will spread from west
to east across the area this afternoon into this evening, ahead of a
cold front that will cross the region late tonight into Monday.
Another round of showers will be possible Wednesday into Thursday,
as an upper level trough crosses the region.

&&

.NEAR TERM /THROUGH MONDAY/...
Regional radars showing the main axis of precipitation focused along
the approaching pre-frontal trough arriving into far Western New
York. No associated lightning at this time within the band, just
moderate to occasional heavy showers. This may change as the
activity shifts slowly to the east where just a bit better
instability exists, but any thunderstorms that do manage to develop
will remain isolated. Model consensus suggesting anywhere from a
quarter to a half inch of precipitation for most locations with this
activity.

Upstream radars showing that there will be a short break in the
precipitation late this evening before the arrival of a second round
later tonight, as the main surface cold front pushes into the
forecast area. It will remain mild tonight, as the cooler air behind
the front will not arrive in earnest until Monday. Overnight lows
should remain in the 50s.

Monday, behind the cold frontal passage, a broad west-southwesterly
flow regime is expected to develop across western and north
central New York. There could be a few lingering showers during
the morning hours across eastern areas, but with a building
bubble of high pressure and associated drier air being sent into
the area, should overall be a dry day. Cold air advection will
keep temperatures below normal with most highs only in the lower
to mid 60s, with a brisk afternoon wind to 35 mph downwind of
the lakes.

&&

.SHORT TERM /MONDAY NIGHT THROUGH THURSDAY NIGHT/...
As this period opens Monday night...narrow surface-based ridging
and attendant drier air/subsidence will slowly ease its way across
New York State. This will provide our region with a dry and quiet
night...with low temperatures ranging from the mid 40s across the
normally cooler interior portions of the Southern Tier and North
Country to around 50 along the Lake Erie lake plain.

On Tuesday the axis of the surface ridge will edge a touch further
southeastward into the Poconos and Catskills...while broad/subtle
mid and upper level ridging develops aloft. This should translate
into continued dry weather for our region...with temperatures also
rebounding back into the lower to mid 70s in many areas as modest
warm air advection develops aloft.

After that...the remainder of this period will then feature a
gradual return back to somewhat cooler and more unsettled weather...
as the next mid/upper level low drops southeastward from the Upper
Mississippi Valley...and eventually leads to reamplifying upper
level troughing across our region by Thursday and Thursday night.
Digging a bit further into the forecast details...

Tuesday night lingering ridging at the surface will begin to recede
northeastward into New England...as double-barrelled surface low
pressure extending from the Upper Midwest to the Carolinas begins
to progress northeastward...with one weak surface low working its way
northeastward along or a bit offshore of the mid Atlantic coastline...
and the other developing into the Ohio Valley. As moisture increases
around the periphery of the advancing coastal system...lower-end
shower chances should develop into the Southern Tier and interior
portions of the Finger Lakes...while the remainder of the region
should remain more under the influence of the departing surface
ridge/lingering weak upper level ridging...and thus largely dry.
Otherwise...low temperatures will range from the upper 40s to mid
50s.

On Wednesday the coastal low will slide northeastward along or a
bit offshore of the New England coastline...while the Ohio Valley
low will gradually make its way to western Lake Erie while also
becoming a bit better organized...thanks to its favorable location
under the eastern flank of the digging upper level trough. As a
result...the best shower chances (mid-high chance PoPs) for our
region on Wednesday will lie along our southeastern periphery (along
the perimeter of the passing coastal low) and across Chautauqua county
(closest to the Ohio Valley low)...with a relative minima in shower
potential (low chance PoPs) otherwise found across the remainder of
the region. While this is not to say that the day will be completely
rain free...it may well turn out to be mostly dry across the Niagara
Frontier...portions of the Genesee Valley and western Finger Lakes...
and northern portions of the North Country and Saint Lawrence Valley.
Temperature-wise...readings should remain near to slightly above
normal...with highs in the upper 60s to lower 70s expected.

Greater deterioration in our weather is then expected for Wednesday
night and Thursday as the burgeoning upper level trough makes its
way into our region along with its attendant (Ohio Valley) surface
low. This will result in periodic showers becoming more likely across
our region from southwest to northeast Wednesday night and Thursday...
then lingering into...if not right through Thursday night as the axis
of the surface/upper level lows pivot across New York State. As for
temperatures...expect lows Wednesday night to range in the lower
to mid 50s...highs on Thursday to mostly be between 65 and 70...
and lows Thursday night to range in the upper 40s to lower 50s.

&&

.LONG TERM /FRIDAY THROUGH SUNDAY/...
The lumbering closed low will exit across New England Friday and
Friday night...with waning shower chances from west to east.

Later Friday night into Saturday, a narrow progressive ridge will
make its way across the eastern Great lakes region favoring fair dry
weather which should hold at least through Saturday morning. Slight
chance POPs are held due to potential faster timing with the arrival
of the next system. 00z GFS/EC shows this next system could bring in
rain as early as Saturday afternoon across western NY where chance
POPs have been included.

In regards to temperatures...the mercury will average close to...or
just a bit below normal for Thursday and Friday...as max temps will
be mainly in the mid 60s. Some warming is then expected Saturday
when highs will be upper 60s to lower 70s. Mins will be within a few
degrees either side of 50 both Thursday and Friday nights.

&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
A concentrated band of precipitation is expected to cross the
forecast area from west to east into this evening, as a pre-frontal
trough fed by a 30-40kt low level jet moves across the forecast
area. A few embedded thunderstorms may accompany the showers within
this band, though any thunderstorms should be isolated in nature.
Timing for KIAG/KBUF/KJHW between 18z and 21z, KROC between 20z and
23z, and KART between 22z and 01z.

In addition, the strengthening south-southeast low-level jet will
bring gusty winds into early evening, particularly along downslope-
prone areas along the Lake Erie shoreline.

Expect another round of showers later tonight, accompanied by MVFR
cigs, IFR over higher terrain, as a cold front begins to cross the
forecast area.


Outlook...

Monday morning...MVFR. Showers likely with a chance of
thunderstorms.
Later Monday and Tuesday...Mainly VFR.
Wednesday...VFR/MVFR with a chance of showers.
Thursday...VFR/MVFR with showers likely.
Friday...VFR/MVFR with a chance of showers.

&&

.MARINE...
A brisk southeasterly flow will continue into tonight. Associated
warm advection and offshore flow will keep wave action negligible
for into early tonight, with wave action being focused on the
Canadian shores of the lakes, though we may see some choppy waters
develop near the entrance to the St. Lawrence late tonight, just
ahead of a cold front that will cross the region early Monday.

Winds backing to the southwest may produce some light to moderate
chop across the northeastern end Lake Erie Monday afternoon into
Monday night, though conditions should remain sub-advisory.

Waves will then diminish Tuesday, with tranquil conditions
persisting on the lakes through the middle of the week as a weak
area of high pressure moves across the region, followed by a broad
area of low pressure.

&&

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

&&

$$

SYNOPSIS...TMA
NEAR TERM...TMA
SHORT TERM...JJR
LONG TERM...RSH/SMITH
AVIATION...TMA
MARINE...TMA



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