618
FXUS61 KBUF 050238
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1038 PM EDT Sat May 4 2024

.SYNOPSIS...
A wave of low pressure will move from the Ohio Valley across the
eastern Great Lakes overnight through Sunday, bringing a round of
widespread rain to the region. The rain will gradually taper off to
scattered showers from west to east Sunday, before ending entirely
Sunday night. High pressure will then build into the Great Lakes
Monday with a return to dry weather.

&&

.NEAR TERM /THROUGH SUNDAY/...
A dreary night on tap as a sharp mid-level shortwave trough
slides out of the Ohio Valley overnight and across the eastern
Great Lakes through Sunday morning. Deepening moisture and broad
scale ascent along the system`s strengthening LLJ will cause
rain to overspread the forecast area from south to north.
Regional radar and surface obs late this evening indicate the
leading edge of this precipitation shield is currently advancing
through the Southern Tier towards the Niagara Frontier and
Finger Lakes region. While a few widely scattered showers
associated with a weaker shortwave linger east of Lake Ontario,
the more widespread rain will eventually move into the region in
the second half of the night. As it does so, the LLJ will begin
to approach its peak expected strength at around 45kts, which
will likely cause precip across portions of the North Country to
be locally heavier compared to surrounding areas. Otherwise,
lowering cloud bases may intersect the higher terrain across the
Southern Tier and North Country, leading to patchy fog through
Sunday morning.

Owed to a stiff southeasterly surface wind, temperatures tonight
will average warmer than normal with mainly upper 40s to low 50s for
lows. Across far western NY and along the Lake Erie shoreline,
temperatures will be a bit warmer, likely only dipping into the
mid/upper 50s.

The system`s 850H jet will begin to wane in strength and slowly
slide east into central NY Sunday morning. Rain coverage will taper
off across the western zones in tandem though remain persistent east
of Lake Ontario for most of the day. By Sunday afternoon however, an
upstream cold front currently over the central Great Lakes will
begin approach western NY. The additional forcing combined with
waning diurnal instability should cause an additional round of
showers to arrive across from the far western counties by mid to
late afternoon. While poor diurnal timing, weak deep-layer shear and
a wealth of cloud cover will preclude stronger or more widespread
thunderstorm development, 300-500J of SBCAPE building ahead of the
front could still allow for a few rumbles of thunder and/or locally
heavy downpours.

Rainfall totals overnight through early Sunday afternoon are
expected to be greatest east of Rochester and across the North
Country, generally averaging 0.5-1" in these areas, potentially
exceeding an inch across far eastern Oswego and southern Lewis
counties. Rainfall amounts under half an inch elsewhere are expected
to the west.

In regards to temperatures...A large spread in daytime highs is
expected Sunday, owed to the expected steady rains across the
eastern zones during the day. Temperatures will top out mainly in
the mid to upper 60s across far western NY and the Niagara Frontier
east to Rochester. Across the interior Southern Tier, eastern Finger
Lakes, and North Country, a range of 50s is expected.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
A mid level trough will slide across Hudson Bay and into
northern Quebec Sunday night...with its associated modest
surface low pivoting a weak trailing cold front across our area.
This boundary will generate some additional scattered showers
and possibly an isolated thunderstorm or two as it passes
through our region. The greatest pcpn potential will be found
across the North Country... which will lie in closest proximity
to the base of the supporting upper level trough and where the
showers may become briefly more numerous during the late evening
and early overnight hours. Otherwise expect fairly cloudy skies
Sunday evening to give way to some limited clearing across far
western New York overnight...with lows ranging from the upper
40s to lower 50s in most places.

By Monday morning the cold front will be making its way across
eastern New York. While a leftover spotty shower or two cannot be
ruled out across our far eastern zones early in the day...in general
the day should feature dry weather along with increasing amounts of
sunshine from northwest to southeast as high pressure and drier air
over the central Great Lakes ridges eastward into our region. With
850 mb temps ranging from +6C north to +10 south...highs will
largely be in the upper 60s to lower 70s...though readings will be
cooler along the lakeshores due to onshore flow.

Monday night the axis of the surface ridge will slide directly
overhead...promoting dry and tranquil weather along with excellent
conditions for radiational cooling. This will allow lows to dip into
the 40s areawide...with a few readings in the upper 30s not out of
the question across the North Country.

On Tuesday the surface ridge axis will slowly drift east across New
England...while the leading edge of a sprawling mid level trough and
associated surface low over the north-central states slowly works
its way into the Upper Mississippi Valley. As this does so...a warm
frontal boundary snaking southeastward from this system will slowly
push northeast across the Ohio Valley. While this latter feature
could draw close enough to support the potential for a couple widely
scattered showers across the Southern Tier later on in the
afternoon...the day should otherwise feature continued dry weather
with just a modest increase in cloud cover across far western New
York. With our airmass starting to warm again highs should generally
range through the 70s...though it will again be a bit cooler along
the lakeshores due to onshore flow.

Tuesday night the various guidance packages suggest that the warm
frontal boundary will lift further northeastward and into our region
while also becoming increasingly wavy as a supporting mid-level
shortwave ripples eastward across the central/eastern Great Lakes.
This will bring a general southwest-northeast increase in cloud
cover and eventually the likelihood of some showers as the night
progresses...with a few thunderstorms also becoming possible due to
the arrival of some weak elevated instability. Otherwise it will be
a notably milder night with lows ranging from around 50 across the
North Country to the mid and upper 50s south of the NYS Thruway.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
A wet pattern for the long term period with at least a chance of
showers for the entire forecast area each day. A mid/upper level low
over the northern Rockies will slowly track east, opening to a large
scale trough through the second half of the week.

Earlier in the week with the trough/mid-level low to the west,
periods of weak ridging over the region will give way to developing
sfc lows and shortwave troughs that will bring an influx of GOMEX
moisture north into the region. Moisture and large scale synoptic
lift will provide for periods of showers with some breaks in the
precip.

The larger trough will setup over the region by Friday, and persist
through at least the weekend. This will provide for several rounds
of showers, especially as different shortwave troughs track
through/around the larger trough. Cyclonic flow and the trough in
general over the region will also result in cooler temperatures.

Embedded thunderstorms will be possible at times, especially during
the middle of the week when instability will be a bit better than
later in the week.

Temperatures will start out well above normal with highs in the mid
60s to near 80 from the higher terrain east of Lake Ontario to the
lower elevations of WNY respectively. Day-to-day cooling is then
expected through the rest of the period as the trough moves into the
region. Below normal high temperatures are expected for Saturday
with temperatures only reaching the low 50s to near 60 for the
afternoon.

&&

.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
Flight conditions across the forecast area will slowly deteriorate
from mainly VFR to a mix of MVFR and IFR tonight as a low pressure
system tracks out of the Ohio Valley and across the eastern Great
Lakes. This system will bring a large shield of rain through the
region from southwest to northeast, with locally heavier embedded
showers. While the precipitation and increasing saturation of the
boundary layer will cause CIGS and VSBYS to decrease, a stiff
southeasterly breeze off the higher terrain areas should prevent IFR
conditions from developing at the TAF sites with the exception of
KJHW. Meanwhile, IFR CIGS are expected to develop across the higher
terrain areas of the Southern Tier and east of Lake Ontario. Patchy
fog with IFR VSBYS is possible where the lower CIGS intersect the
hilltops.

The widespread rain will taper off across much of western NY Sunday
morning while remaining steady east of Lake Ontario for much of the
day. CIGS are expected to remain in primarily MVFR range through the
day as precipitation coverage becomes sparser, while IFR conditions
linger across the higher terrain areas. An approaching cold front
will then likely cause additional showers and possibly a few
thunderstorms to redevelop later in the afternoon in the vicinity of
the far western terminals (KIAG/KJHW/KBUF), which may cause
brief IFR conditions.

Outlook...

Sunday night...VFR/MVFR. A chance of showers, mainly early.

Monday and Tuesday...VFR.

Wednesday...VFR/MVFR. Chance of showers with a chance of
thunderstorms.

Thursday...VFR/MVFR. Showers likely with a chance of
thunderstorms.

&&

.MARINE...
Moderate southeast winds through Sunday morning will produce
choppy conditions on the lakes, mainly in the offshore and
Canadian waters given the largely offshore wind component. Winds
will then become southwest and decrease from west to east
Sunday as a weak trough moves across the eastern Great Lakes.

Generally light winds are then expected Monday through Tuesday with
a weak pressure gradient in place across the eastern Great Lakes.

&&

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

&&

$$

SYNOPSIS...Apffel/Hitchcock
NEAR TERM...PP
SHORT TERM...JJR
LONG TERM...SW
AVIATION...PP
MARINE...Apffel/Hitchcock