Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 210302

Area Forecast Discussion
National Weather Service Buffalo NY
1102 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.


Low cloudiness from earlier has significantly been reduced in
coverage as drier air and subsidence from high pressure over the
Upper Great Lakes influences the lower lakes tonight. Some patchy
fog may develop across the western Southern Tier late tonight where
more residual 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.


Low cloudiness from earlier has significantly been reduced in
coverage as drier air and subsidence from high pressure influences
the lower lakes tonight. Overall, no issues for a majority of the
CWA with VFR holding for most locations overnight. There will be
some high cloudiness streaming from west to east across Western New
York into the Finger lakes region but that will not affect aviation
operations. Otherwise, the only area of concern going forward will
be the potential for some patchy fog to develop across the western
Southern Tier, with localized IFR VSBY.

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


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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