259
FXUS61 KBUF 042009
AFDBUF

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

.SYNOPSIS...
A wave of low pressure will move from the Ohio Valley this evening
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/...
High pressure ridging will continue to drift east into New England
through tonight. A weak trough on the backside of the ridge is
currently lifting across north-central NY, generating some widely
scattered light showers. Hi-res guidance is struggling to resolve
this activity, while continuing to indicate lake breeze induced
shower/thunderstorm potential back across the Niagara Frontier from
Buffalo to Rochester and northward. Latest mesoanalysis seems to
indicate there is presently just enough CIN to preclude this
activity. Thus, have included a broad area of low-end (15-30%) PoPs
south and east of Lake Ontario through the remainder of the
afternoon hours due to uncertainty in overall shower potential and
coverage.

A more well defined mid-level shortwave will then move from the Ohio
Valley this evening northeast across the eastern Great Lakes
overnight, generally following the path left by the remnants of the
trough that washes out over the area today. A 45+ knot southerly low
level jet ahead of the trough will bring a period of enhanced
convergence and low level moisture transport overnight. This will
combine with forcing from the shortwave to produce a fairly
widespread area of rain moving from southwest to northeast across
the region. Low stratus may intersect some of the higher hills
overnight through Sunday morning, resulting in patchy fog across
higher terrain.

Sunday, the mid level trough and associated forcing and deep
moisture will continue to move slowly northeast. Widespread rain
early in the day will gradually taper off to scattered showers from
west to east. The widespread rain should end in Western NY fairly
early in the day, while it will continue most, if not all day east
of Lake Ontario.

While the widespread rain will end across Western NY, an upstream
cold front will move into the far western end of the state by late
afternoon. This will combine with modest diurnal instability and
lake breeze convergence zones to support a few more scattered
showers in the afternoon and evening. Enough instability may develop
to support a few thunderstorms as well across Western NY.

Storm total rainfall amounts should average around a half inch,
but locally higher amounts of around an inch are possible east
of Lake Ontario where the rain will last longer.

&&

.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 /20Z SATURDAY THROUGH THURSDAY/...
VFR will prevail for the bulk of the area late this afternoon,
although there will be some lingering MVFR cigs across the
Southern Tier. A wave of low pressure will move from the Ohio
Valley this evening across the eastern Great Lakes tonight. This
will bring a period of fairly widespread rain spreading from
southwest to northeast across the area from late evening through
the overnight. CIGS will deteriorate to widespread MVFR/IFR
shortly after the rain begins. Any pockets of moderate rain will
bring short term VSBY restrictions, and the low stratus may
intersect some of the higher hilltops overnight through Sunday
morning with some patchy fog/mountain obscuration across the
high terrain.

Steady rain will taper off from west to east, with cigs also
lifting some into the MVFR/VFR flight category during the
afternoon. Some instability will develop in the afternoon, with
widely scattered thunderstorms possible across Western NY.

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