Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 202124

Area Forecast Discussion
National Weather Service Buffalo NY
524 PM EDT Sun May 20 2018

High pressure will build into the region tonight and Monday and
bring a period of dry weather. A weak area of low pressure will then
cross the eastern Great Lakes late Monday night and Tuesday, with
showers and a few scattered thunderstorms. Another area of high
pressure will then build into the Great Lakes Wednesday through
Friday with a dry second half of the week.


Strato-cu deck across the forecast area will continue to slowly
diminish for most locations into tonight. GOES-16 visible satellite
imagery is already shows this occuring with clearing along the lake
plains and across some interior locations southeast of both lakes
with sunshine peaking through early this evening. This low cloud
deck is unfortunately likely to linger a bit longer across the
Western Southern Tier and far southeast of the lakes into tonight.
Temperatures will remain in the upper 50s to lower 60s in most areas
as long as the clouds remain. The lake plains should jump into the
mid 60s with the sunshine.

Tonight high pressure will build from the Upper Great Lakes into the
Lower Great Lakes. Associated subsidence and a drier push of air
moving south out of Ontario will allow any remaining low clouds to
clear late this evening on the Lake Plains. The clearing will take
longer across the higher terrain of the western Southern Tier and
western Finger Lakes, where a shallow layer of low level moisture
and weak northwest upslope flow may allow low clouds to linger into
tonight. Some patchy fog may also develop across the western
Southern Tier later tonight where more abundant low level moisture
remains. Expect lows in the mid 40s in most locations, with a few of
the colder spots east of Lake Ontario dropping to around 40.

Monday the surface high will remain in place from the Upper Great
Lakes to the Lower Great Lakes. Any remaining low clouds and fog
across the western Southern Tier will dissipate by mid morning.
Otherwise expect sunshine for the bulk of the morning with
subsidence and dry air in place. Meanwhile, a de-amplifying mid
level trough and associated weak surface low will reach Illinois and
Indiana during the afternoon. Mid level clouds will then overspread
the area from west to east during the afternoon as a wing of warm
advection and mid level moisture transport spreads east ahead of
this system. Isentropic upglide and weak mid level DPVA may produce
some virga across Western NY later in the afternoon, but a very dry
sub-cloud layer should prevent this from reaching the ground, with
any showers holding off until later Monday night. Expect highs to
reach the mid 70s across the lower elevations of Western NY, and
around 70 on the hills and east of Lake Ontario.


Forecast models continue to trend a bit faster with the arrival of a
shortwave trough Monday night into Tuesday. Initially Monday night,
broad lift along the warm frontal feature ahead of the wave,
combined with some elevated instability, will result in an area of
showers and thunderstorms spreading across the region after
midnight. Precipitation will be most widespread during the midnight
to sunrise time frame across WNY, and into mid morning across the
North Country. A trailing cold front will then cross the region from
west to east during the day Tuesday. As this boundary interacts with
the developing lake breezes, expect a narrow band of showers and
thunderstorms to develop across the western Southern Tier and
quickly track off into central and eastern NY. Thus for most, expect
plenty of dry time during the day Tuesday aside from some nuisances
scattered showers. Any limited severe weather potential appears as
though it will be contained to areas southeast of the forecast area
with the earlier timing of the wave.

High pressure will quickly build in across the region Wednesday and
Thursday bringing a stretch of dry and warm weather. High
temperatures will be largely in the 70s through this period, with
Wednesday likely the warmest day before a weak and dry backdoor cool
front pushes in on Thursday. Nightly lows will be in the 50s.


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

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.


Sct-BKN deck of diurnal strato-cu across the eastern Great Lakes will
slowly diminish for most locations late this evening with VFR
conditions expected into Monday. Low clouds may linger into tonight
across the higher terrain of the western Southern Tier and the
western Finger Lakes, with areas of MVFR-IFR. Additionally, some
patchy fog may also develop overnight across the western Southern
Tier, with local IFR VSBY.

Monday any remaining low clouds and fog across the western Southern
Tier will dissipate by mid morning. This will leave VFR to prevail,
with mid level clouds increasing from west to east during the


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


WNW winds will diminish with lighter wave action along the south
shores of Lake Ontario and Lake Erie tonight. With high pressure
building into the eastern Great Lakes tonight and Monday expect
light winds and flat wave action.





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