Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 191827
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
227 PM EDT Wed Jul 19 2017

.SYNOPSIS...
While most areas will remain dry today...a weak frontal boundary
could generate some widely separated showers or thunderstorms during
the afternoon and evening. A higher chance for thunderstorms will
come Thursday afternoon. After a dry uneventful day on Friday...the
weekend will likely turn unsettled with showers and thunderstorms
becoming rather widespread.

&&

.NEAR TERM /THROUGH THURSDAY/...
A weak frontal boundary over southern Ontario this morning will
settle to the south across our forecast area later this afternoon
and evening. As of 1430z...convection near and ahead of the front
continued to be suppressed by a robust 2-3 deg C cap at 5k ft.
While this cap will eventually be eroded as we work through the
afternoon...a second inversion around 15k ft (see KBUF 12z sounding)
should keep any convection from getting very strong.

As we push through the mid and late afternoon and the front makes
its way across Lake Ontario...the eroded lower cap will allow for
some spotty convection that will be generated as a result of weak
convergence along the front. Some enhanced lift will be found from
Niagara to Monroe counties in the vcnty of a lake breeze boundary.
Have thus raised pops to chc for some of these areas. Otherwise...
visible sat imagery shows a wealth of clouds moving in from southern
Ontario so have raised sky cover to go no more optimistic than
partly sunny. It will be warmer and more humid than yesterday (Mon)
as H85 temps in the mid teens will support afternoon highs in the
mid to upper 80s.

Whatever limited convection that does form this afternoon/evening
should quickly diminish this evening with the loss of heating and
the passage of the weak trough...with dry conditions then ensuing
for the balance of the night. With little in the way of an airmass
change...the upcoming night should be a warmer  with overnight lows
mostly ranging in the lower to mid 60s.

A weak surface ridge will remain in place Thursday morning through
at least early afternoon, supporting dry weather across the region.
By late in the day a weak mid level shortwave will approach the
region, with this feature likely the remnants of an organized
complex of storms across the western Great Lakes early in the day.
This system will be moving out ahead of the better large scale
forcing and reservoir of strong instability over the Midwest, with a
steady weakening trend expected with eastern extent. There may be
just enough forcing and moisture when combined with local lake
breeze convergence to support a few widely scattered showers and
storms late Thursday afternoon.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SUNDAY/...
The remnants of a potential convective complex are likely to be
across the Southern Tier Thursday evening before exiting to the
south and east of the area later in the night. This will be
followed by a gradual clearing trend from W-E as a weak ridge of
high pressure builds into the area. 12Z model consensus
continues to keep our area dry late Thursday night through
Friday. There will be some afternoon clouds along and inland of
lake breeze boundaries, but still a fair amount of sunshine
across the region. Lows will be in the mid to upper 60s on the
lake plains and lower 60s in the cooler Southern Tier valleys
and Lewis County. Friday should be a rather pleasant day, with
moderate humidity and highs in the upper 70s to lower 80s.

A subtle frontal boundary will sharpen across or just south of the
Great Lakes with 12Z model consensus bringing another convective
wave across Western New York or Pennsylvania on Saturday. This
convective wave is more or less shown by NAM/ECMWF/GGEM
guidance, and if it develops it does have the potential to bring
another round of heavy rain in the 1-2 inch range. This may
result in flooding, with isolated severe storms a lesser but
still plausible risk.

This wave is likely to exit late in the day Saturday, potentially
resulting in a brief dry period. While model guidance differs, there
may still be a weak boundary near or just south of the area with
additional mid-level waves possible in cyclonic flow aloft. As such,
it will be difficult to rule out a shower or thunderstorm Saturday
night and Sunday, even though a good part of the time is likely to
be dry.

Temperatures over the weekend will remain rather seasonably with a
significant cold frontal boundary expected to remain to the north.
Highs depend on the development and track of any convection, areas
which remain dry likely to reach 80 while rainy areas will be quite
a bit cooler.

&&

.LONG TERM /SUNDAY NIGHT THROUGH TUESDAY/...
By early next week the pattern will begin to amplify, with a trough
sharpening over the Great Lakes Monday and New England Tuesday. The
sharpening trough and associated surface cold front will continue to
support shower and thunderstorm chances through Monday, with cooler
and drier air arriving for Tuesday. Expect slightly below normal
temperatures early next week.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
VFR conditions will be found across the region through this evening
although there will be a low chance for showers or thunderstorms
near lake Ontario after 18z.

Any convection that develops later this afternoon and evening will
then give way to clearing skies overnight. While VFR conditions will
be found across the majority of the region...IFR conditions in fog
and low stratus will be possible for portions of the Western
Southern Tier, including sites such as KJHW, KOLE and KELZ.

Outlook...
Thursday and Thursday night...Mainly VFR...with a chance of showers
and thunderstorms/attendant MVFR south of Lake Ontario.
Friday...Mainly VFR.
Saturday and Sunday...VFR/MVFR with a chance of showers and
thunderstorms.

&&

.MARINE...
Departing high pressure will maintain light to modest winds and
relatively minimal waves through most of today...with a passing
weak cool front only producing a few isolated to widely scattered
showers or thunderstorms this afternoon and early this evening.

While some additional rounds of scattered showers and storms will
then be possible Thursday/Thursday night and again over the weekend...
winds and waves are otherwise expected to remain at unremarkable
levels through Sunday.

&&

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

&&

$$

SYNOPSIS...RSH
NEAR TERM...HITCHCOCK/JJR/RSH
SHORT TERM...APFFEL
LONG TERM...HITCHCOCK
AVIATION...JJR/RSH
MARINE...JJR



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