Area Forecast Discussion
Issued by NWS Buffalo, NY

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743
FXUS61 KBUF 290620
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
220 AM EDT Mon May 29 2017

.SYNOPSIS...
Low pressure will slide by our northwest overnight and Monday...with
occasional showers and some embedded thunderstorms spreading across the
region through early Monday morning...then tapering off from west to east
on Monday following the passage of this system`s trailing cold front.
After this system exits our area...a large upper level trough will then
meander its way across the region through much of the upcoming week...
bringing periodic opportunities for additional showers and storms
along with near to slightly below average temperatures.

&&

.NEAR TERM /THROUGH TODAY/...
As of 06z...regional surface analysis shows weak low pressure extending
across Lake Huron and nearby southern Ontario...with its attendant warm
front draped across far western New York...and its trailing cold front
extending across western Lake Erie and central Ohio.

Regional radars currently show only widely scattered showers across
our region...though more widespread activity is found across northern
Pennsylvania...and also further west across southern Ontario/Lake Erie
out ahead of the surface cold front. While precip coverage should tend
to remain relatively minimal for the next couple of hours with only
widely scattered to scattered showers and storms expected...activity
should still tend to become more widespread from west to east very late
tonight and early Monday morning as the cold front approaches and
increasing height falls/shortwave energy overspread our region aloft.
For this reason have maintained high-end categorical PoPs...albeit
with these later than previously indicated. Given the warm and moist
air that will remain in place overnight...am still only expecting
overnight lows to bottom out in the upper 50s to lower 60s.

Shower and thunderstorm activity is expected to taper off from west
to east during the day on Monday as an upper level shortwave driving
the frontal system and precipitation moves overhead, with NVA and
associated subsidence behind the wave drying things out. While much
of the precipitation will be convective in nature at least through
the evening hours allowing for locally higher QPFs, a general
quarter to half inch can be expected across the forecast area though
tonight and Monday morning.

Drier, but still relatively warm air will move in behind the departing
mid/upper level troughing on Monday, and temperatures should top out
in the low to mid 70s away from the lakes. However, with southwesterly
winds strengthening behind the trough, cooler readings will be found
downwind of the lakes, with upper 60s prevailing.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/...
An upper level closed low over the southern shore of Lake Winnipeg
this afternoon will drop across the Great Lakes and influence our
weather for the Monday night through Wednesday night time period.
Several shortwaves rotating around the upper level low will give
increase chances for showers and thunderstorms. Though this wet
month of May will close out with thunderstorms, much of the time
will be rainfree.

Monday night the first such shortwave, and associated low level wind
speed max, will near our region. Convergence along this little speed
max in the lower levels and around 100 to 250 J/KG of MUCAPE may
produce a shower or thunderstorm, with activity later in the
evening across WNY, and in the predawn hours east of Lake Ontario.

Another shortwave impulse on Tuesday, combined with the upper level
low drawing closer will bring increasing chances for showers and
thunderstorms. The bulk of this activity will likely form on lake
breeze boundaries through the afternoon and evening hours. MLCAPE
values of 500 to 750 J/KG and PWAT values around three quarters of
an inch will provide the instability and moisture that when
interacting with the lift along lake breeze boundaries, convection
is likely to form. A morning inversion will likely keep this
convection at bay, but by noontime convection should be able to
overcome the decreasing capping inversion. Moisture is not overly
impressive, and activity may be just scattered in nature. Northeast
of the lakes, a southwest stabilizing wind flow will promote
sunshine and likely a dry day for areas such as metro Buffalo, and
north of Watertown. Winds will also be gusty within the sunshine
northeast of the lakes, with gusts 30 to 35 mph.

Wednesday may be a bit more active as upper level heights fall in
response to the upper level low reaching the region, and its trough
axis crossing the Lower Lakes. Similar to Tuesday, much of the
activity will be upon lake breeze boundaries, with showers and
thunderstorms sprouting in the afternoon heating. Northeast of the
lakes, a stabilizing lake induced airmass will maintain metro
Buffalo, and areas north of Watertown dry through the day, with a
gusty breeze. With the upper level trough axis passing through
chances for storms will be possible across the region through the
evening hours.

Temperatures will be held in check by the upper level low, with
highs in the 60s, (cooler Wednesday with the upper level low upon
us) and overnight temperatures back into the mid 50s to upper 40s.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
The region will be in a longwave cyclonic flow during the
period with frequent chances for precipitation and slightly
below normal temperatures. There will be periods of dry weather
too, however timing embedded shortwaves is difficult this far
out.

On Thursday the upper level low will be centered just south of
Hudson Bay with a ridge of high pressure at the surface across
the Appalachians. For the most part, this surface ridge should
keep the area dry, with a small chance for showers across the
North Country Thursday afternoon with the passage of a weak
shortwave. Highs will be in the mid 60s to around 70.

Model consensus drops the upper level low into Southern Quebec by
late Friday, which will eventually push a cold front southward
across the region. Model guidance differs on the timing, with a
chance of showers and possibly a thunderstorm along and ahead
of the cold front late Thursday night through Friday evening.

This front is likely to stall to the south of the area late
Friday night and Saturday. It will be close, but as long as it
remains to the south surface ridging will keep Saturday dry.
Highs on Friday and Saturday will be on the cool side behind
this front...mainly in the 60s.

The front should meander northward back into the area on Sunday.
Some guidance develops a wave along this front, with another chance
for showers and possibly a thunderstorm. The best chance will be
across southern portions of the cwa which will be closest to the
boundary.

&&

.AVIATION /07Z MONDAY THROUGH FRIDAY/...
As of 06z...regional surface analysis shows weak low pressure extending
across Lake Huron and nearby southern Ontario...with its attendant warm
front draped across far western New York...and its trailing cold front
extending across western Lake Erie and central Ohio.

While regional radars currently show only widely scattered showers
across our region...more widespread activity is found across northern
Pennsylvania...and also further west across southern Ontario/Lake Erie
out ahead of the surface cold front. While precip coverage should tend
to remain relatively minimal through about 08z with only widely scattered
to scattered showers and storms expected...activity should still tend to
become more widespread from west to east very late tonight and early
Monday morning as the cold front approaches our region. Consequently...
our current general VFR conditions with spotty IFR/MVFR should tend to
deteriorate to more widespread MVFR/IFR late tonight and early Monday.

On Monday...showers and thunderstorms will taper off from west to east
following the passage of the cold front. Expect a mix of IFR/MVFR
ahead of and along the front to improve back to VFR from west to east
as much drier air overspreads the region in the wake of the front.

Monday night...expect mainly dry VFR conditions during the evening...
before a secondary cold front pushes into the region overnight and
brings a renewed opportunity for some additional scattered showers and
thunderstorms. While mainly VFR flight conditions should continue to
predominate overnight...some brief/localized reductions to MVFR cannot
be totally ruled out within any showers or storms.

Outlook...
Tuesday through Friday...Mainly VFR...with localized MVFR possible
in scattered to numerous showers and thunderstorms at times.

&&

.MARINE...
Low pressure will move across southern Ontario overnight and Monday...
with occasional showers and embedded thunderstorms tapering off from
west to east behind its trailing cold front on Monday. In the wake
of the front...winds will veer to southwesterly and freshen to around
15 knots...resulting in light to moderate chop on the northeastern
ends of the lakes.

The SW flow will strengthen further Tuesday, as a cold front moves
through, potentially generating small craft conditions on the east
end of Lake Erie. In fact, an upper level trough will linger through
much of the coming week, with SW flow continuing as a result. This
will serve to reinforce afternoon lake breezes northeast of the
lakes, resulting in at least near-SCA conditions each afternoon
through the rest of the week.

&&

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

&&

$$

SYNOPSIS...JJR
NEAR TERM...JJR/SMITH/WOOD
SHORT TERM...THOMAS
LONG TERM...APFFEL
AVIATION...JJR
MARINE...JJR/WOOD



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