Port Byron, New York Weather Forecast Discussion

873
FXUS61 KBUF 211755
AFDBUF
Area Forecast Discussion
National Weather Service Buffalo NY
155 PM EDT Sun Sep 21 2025
.SYNOPSIS...
A pattern shift is expected to bring on and off showers and
thunderstorms through mid-week.
&&
.NEAR TERM /THROUGH MONDAY/...
Weak instability developing this afternoon across far western New
York with a subtle increase in moisture within southerly. Higher-
resolution guidance continuing to suggest the potential for some
isolated convection across far western New York late this afternoon.
Low confidence where this may occurs as there is no real distinct
boundary to focus convection.
A broad southwesterly flow will develop across the region tonight.
Mid-level moisture will increase ahead of an approaching mid level
trough. Activity developing across the Ohio Valley this afternoon,
may move into western New York later tonight.
Broad southwest flow continues on Monday, continuing to transport
moisture into the region. Shortwave expected arrive into the region
Monday afternoon. This jet-induced lift combined with a seasonably
warm and moist airmass should lead to at least scattered convection
as diurnal instability increases. Moderate instability, and a modest
shear environment could lead to low end severe threat, especially
across far western New York. Would not rule out a localized
heavy rainfall potential, though dry antecedent conditions and
progressive storm motion should greatly reduce any flood
concerns.
&&
.SHORT TERM /MONDAY NIGHT THROUGH THURSDAY/...
Several distinct shortwaves north of the Gulf states will form an
aggregate, positively tilted troughing pattern across much of the
CONUS through midweek. Deep southwesterly flow of moist air into the
eastern Great Lakes (PWATs increasing to 1.5-1.75") combined with
weak but favorable upper level jet dynamics will bring periods of
rain and possibly a few thunderstorms to the region. The complex
nature of the partially phasing shortwave pattern lends overall
lower confidence in the more granular forecast details with large
run-to-run jumps noted among the deterministic models, especially in
regards to QPF magnitudes and placement. Fairly widespread total
rainfall amounts of 0.5-1" inch seem probable through Tuesday,
though higher end totals will certainly be possible where embedded
heavier convection ultimately sets up. Based on NBM ensemble
probabilities, chances for rainfall >1.5" appear low across the
North Country while highest (20-30%) from roughly the Buffalo Metro
area southward to the NY/PA border.
Shower coverage and intensity will trend downward Tuesday night
through Wednesday as the eastern portion of the trough and deeper
plume of moisture shifts eastward, though with one of the
aforementioned shortwaves still hanging over the Upper Great Lakes
lower-end chances for showers will linger. As this shortwave begins
to merge with additional energy rippling eastward from the central
Plains, the system will likely form a cutoff low somewhere over the
Mississippi Valley. Uncertainty remains high in the evolution of
this system, though after a brief period of mostly dry weather
between Wed - Wed night, chances for rain increase again through
Thursday as it tracks eastward and deep moist SW flow is
reestablished across the region.
Otherwise...temperatures this period will be cooler than early in
the week though still average above normal. Daytime highs will be
seasonable within a few degrees of climatological averages, though
with nighttime lows on the warm side owed to southerly flow and/or
increased cloud cover.
&&
.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
Longwave troughing initially centered over the Mississippi Valley
will slowly cross through the Great Lakes this period, forcing a
broad wave of sfc low pressure through the region. Model certainty
remains quite low in how this system ultimately evolves, with some
depicting an initial cutoff low as opposed to an open wave, though a
general weakening trend with time is noted among the long range
solutions. Greatest chances for additional appreciable rainfall and
possibly some isolated deeper convection will be Thurs night -
Friday, though given low confidence will maintain NBM`s chc PoPs
into Saturday night, with lower-end sChc/Chc PoPs lingering through
Sunday.
&&
.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
VFR conditions will continue across western and north-central
New York through tonight, with ceilings gradually lowering to
between 4K and 7K by 12z Monday morning. Some MVFR ceilings may
develop across the Southern Tier.
Dry weather is mainly expected across the region, with a chance
for showers and a thunderstorm at KBUF and KIAG through tonight.
Chances for showers and thunderstorms may extend eastward to
KROC and KJHW later tonight (mainly after 04Z). Southerly winds
may gust 20-25 knots.
Outlook...
Monday and Tuesday...VFR/MVFR with showers likely along with a few
thunderstorms.
Wednesday through Friday...Scattered showers and thunderstorms with
restrictions possible.
&&
.MARINE...
A moderate southeasterly flow is expected to veer more southerly and
picking up a bit across both Lake Erie and Lake Ontario tonight.
Speeds should remain below 15 knots through this evening, though
winds will increase to up to 20 knots tonight, especially in the
eastern basins of Lake Erie and Lake Ontario. A Small Craft Advisory
is in effect for the eastern basin of Lake Erie and the eastern
shore of Lake Ontario tonight.
&&
.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory from 8 PM this evening to noon EDT Monday
         for LEZ040-041.
         Small Craft Advisory from 8 PM this evening to noon
         EDT Monday for LOZ045.
&&
$$
SYNOPSIS...HSK/TMA
NEAR TERM...TMA
SHORT TERM...PP
LONG TERM...PP
AVIATION...TMA
MARINE...EAJ/HSK/TMA

NWS BUF Office Area Forecast Discussion