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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KBUF 211857
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
257 PM EDT Sun Apr 21 2024

.SYNOPSIS...
A moisture starved cold front will cross the area tonight with one
more reinforcing shot of cooler air that will keep temperatures
below average through the start of the new work week, before warmer
weather returns for Tuesday. Otherwise, high pressure will build
across the area providing mainly dry weather through Tuesday, before
unsettled and much cooler weather returns by midweek.

&&

.NEAR TERM /THROUGH MONDAY/...
Weak surface trough now moving east of our area, with dry weather
across all of western and northcentral NY expected through the
remainder of the afternoon. Well established lake shadows east of
both Lakes with fairly dense stratocu decks along and inland of any
lake breeze boundaries, with a good deal of sunshine along the east
end of both Lakes. Otherwise, cyclonic flow associated with upper
level trough will maintain cool and breezy conditions through early
evening with west to southwest gusts to 25-30 mph. Cool finish to
the day with highs ranging through the 40s, with some upper 30s
across the higher terrain.

A moisture starved cold front will cross the area tonight bringing
one last shot of cooler air that will keep temperatures below normal
through the start of the new work week. Other than a stray light
rain or snow shower toward the Saint Lawrence Valley tonight, high
pressure builds across the region providing dry weather and lighter
winds for tonight through Monday. Chilly night on tap with mid and
upper 20s higher terrain and low to mid 30s elsewhere. As mentioned,
temperatures will remain below average for Monday, however airmass
will modify some. This will yield highs ranging from the mid and
upper 40s across the higher terrain, to the low and mid 50s
elsewhere.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/...
While this period will start innocent enough with fair dry weather
and moderating temperatures...a relatively flat upper level pattern
will experience significant amplification that will lead to very
active weather for the middle of the week. This will include a
general quarter inch dousing of rain to add to our already very
soggy start to Spring. The details...

A wedge of high pressure extending from Nova Scotia and coastal New
England to the Deep South will continue to provide fair dry weather
to the region Monday night through at least early Tuesday afternoon.
The return flow around the backside of this fair weather feature
will combine with a developing storm system over the Upper Great
Lakes to direct a deepening southerly flow of notably milder air
into our region. After several days of temperatures topping out in
the 40s to lower 50s...a well mixed (35-40 LLJ) environment of H85
temps arnd +2c will allow us to look forward to widespread readings
in the 60s Tuesday afternoon. This is where the `party` will end
though.

A vigorous Pacific based shortwave crossing the Upper Great Lakes
Tuesday afternoon will phase with an already established longwave
trough over eastern Canada during the course of Tuesday night. In
the process...a wavy sfc frontal boundary along the leading edge of
a sharp baroclinic zone will SLOWLY press through our forecast area
through midday Wednesday.

Initially...a large swath of widespread rain will advect into our
area from Ohio late Tuesday and especially Tuesday night. The
precipitation will be supported by low level convergence along and
ahead of a pre frontal sfc trough with significant reinforcing upper
level lift  in the vcnty of the left front exit region of a
cyclonically curved 120kt H25 jet. PWAT values will hover just below
1.0" in the environment...thus supporting some moderately heavy rain
at times. Will use 100% pops for the overnight period. While not
overly impressed with the potential for convection...there is just
enough elevated CAPE being advertised to maintain slgt chc wording
for thunderstorms...mainly for the western counties and more
directly for the Srn Tier. Basin average rainfall will be in the
vcnty of a quarter inch...with local amounts as high as a half inch.

As the last sfc wave exits our region along the slow moving frontal
boundary Wednesday morning...strong H925-70 frontogenetic forcing
will take over on the backside of the system. While the deepest
moisture will have been pushed across New England by this time...
there should still be enough moisture left behind during the morning
hours to support leftover showers and possibly some steadier pockets
of rain...mainly from the Finger Lakes eastward. The bulk of the
moisture will then be stripped away by midday Wednesday...while very
strong cold advection on gusty northwest winds will send H85 temps
plunging below zero. The leftover rain showers could end as a bit of
graupel or wet snow in the afternoon...especially across the
elevated terrain. The cold advection should also promote a
neutral...if not a non-diurnal temp trend for the afternoon with
temps slowly falling through the 40s during a time of partial
clearing.

A large Canadian sfc high centered over the Great Lakes Wednesday
night will be accompanied by an influx of very dry air...and this
will help to counteract a minimal lake response from a north-
northwest upslope flow over Lake Ontario. The result will be fair
dry weather...albeit it chilly with temperatures away from the lakes
falling below freezing.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
-- Changed Discussion --
A large Canadian sfc high along with increased ridging will provide
dry weather for Thursday and most of Friday. The sfc high will
center over the forecast area by Thursday night and track to the New
England coast by Saturday morning.

A weakening trough and sfc low will track across the plains on
Friday and center over the Great Lakes on Saturday night. This will
result in increasing rain potential starting later Friday
evening/overnight as the warm front out ahead of the system
approaches/crosses the region. Showers and periods of steadier rain
will continue through much of Saturday as a plume of GOMEX moisture
pushes north across the Ohio Valley. With the warm sector of the
system over the region, there will be the chance for some
thunderstorms on Saturday, with the best chance for some storms over
the southwestern portions of the area. Still some uncertainty as far
as shower/rain amount goes among guidance with the GFS keeping the
sfc low track closer to the forecast area and keeping the trough a
bit stronger as well. Other forecast models limit the moisture
influx and pull the sfc low farther north, resulting in less precip
overall. Showers should continue into Sunday with more breaks,
especially into the afternoon.

Temperatures during the period will be below normal to start with
warming each day to above normal by the weekend.
-- End Changed Discussion --

&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
Mainly VFR conditions will continue across western and northcentral NY
through the remainder of the day, with widespread VFR expected
tonight through Monday.

Stable lake shadows have developed this afternoon east of both Lakes
with stratocumulus remaining along and inland of any lake breezes,
with CIGS again in the 4-6 kft range for KBUF/KIAG over to KROC,
with some isolated MVFR CIGS found across the higher terrain (KJHW).
Southwest to west wind gusts to 20-25 knots will be common
across the terminals this afternoon.

Winds diminish for tonight and Monday. Aside from a stray rain or or
wet snow shower toward the Saint Lawrence Valley as a moisture
starved cold front pushes south across the area first half of
tonight, dry weather is expected through Monday as high pressure
builds in behind the boundary.

Outlook...

Monday night...VFR.
Tuesday...Mainly VFR. A chance of showers later in the afternoon.
Tuesday night and Wednesday...Areas of MVFR with showers.
Thursday and Friday...Mainly VFR.

&&

.MARINE...
Westerly winds will again be on the increase this afternoon with
another period of Small Craft Advisory conditions on Lake
Erie and the Upper Niagara River, as well as the eastern end of Lake
Ontario through tonight. Weaker winds and waves will reside across
the waters Monday through Monday night. Southerly winds will freshen
on the waters Tuesday and will likely result in Small Craft Advisory
conditions into midweek.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory until midnight EDT tonight for LEZ020-040-
         041.
         Small Craft Advisory until 6 AM EDT Monday for LOZ044-
         045.

&&

$$

SYNOPSIS...JM
NEAR TERM...JM
SHORT TERM...RSH
LONG TERM...SW
AVIATION...JM
MARINE...HSK/JM