Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 212354

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

Widespread showers and isolated thunderstorms will advance across
the region tonight and into Monday morning, 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.


Regional radars this evening display an area of showers across the
region, concentrated from about the Genesee Valley eastward. A brief
break will be found between the western edge of these showers, and a
cold front and associated showers. There is little to no thunder
activity with the prefrontal trough showers this evening, but
upstream there continues to be isolated areas of thunder with the
cold front. Will maintain these slight chance for thunder across far
western portions of WNY late tonight. This cold front and associated
showers will cross the region in the dawn hours tomorrow, and
through Monday morning east of Lake Ontario.

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. A building bubble of high pressure and associated drier
air will clear and dry out the region through the midday hours
Monday. 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.


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 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

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 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.


As has been the case for the past several days...the medium range
guidance packages are not in good agreement with the overlying
synoptic pattern. They were at odds over the handling of a closed
low...and now they differ on the amplification of an ensuing mid
level ridge. Without getting into too much detail...the ECMWF favors
a flatter ridge with the passing of a shortwave...while the GFS
features a higher amplitude ridge that would protect our region for
the bulk of the weekend. This will lead to relatively low forecast
confidence for this period...particularly for Saturday and Sunday.

That being said...there is fairly strong conviction that the slow
moving storm system from earlier in the week will gradually work
across New England Friday and Friday night. Showers associated with
this feature will taper off from west to east in the process...with
the bulk of western New York expected to be rain free.

Temperatures during this three day period should experience subtle
day to day warming...with max temps during the weekend forecast to
be in the 70s.


For the 00Z TAFS an area of showers continue to push across the
region, with the more concentrated and heavier activity from about
KROC eastward. There may be periods of MVFR flight conditions within
this activity, but for the better part VFR flight conditions will

A cold front will cross the region late tonight and early Monday.
Another brief line of showers will be upon this front. MVFR flight
conditons will be more prevalent with this front, possibly dipping
to IFR across the So. Tier, including the KJHW terminal.

An area of high pressure will press towards the Lower Lakes
tomorrow, bringing clearing skies and a return to VFR flight
conditions. Westerly wind gusts will increase tomorrow, to around 20
to 25 knots with the clearing through the afternoon.


Monday night 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.


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.





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