Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 181900
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
300 PM EDT Tue Jul 18 2017

.SYNOPSIS...
Weak high pressure will move across the region through Wednesday
morning bringing dry and seasonable weather. A weak cool front will
move through with isolated to scattered thunderstorms late Wednesday
into Wednesday night. More scattered showers or thunderstorms are
possible Thursday as a wave of low pressure move south of the
region. High pressure then builds in Friday brining dry weather. A
frontal boundary will stall across the region for the weekend
brining more shower and thunderstorm chances.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
High pressure surface and aloft will continue to provide pleasant
summer weather across western and north central NY this afternoon.
Visible satellite shows shrinking fields of diurnal cumulus clouds
across the Niagara Frontier/Genesee Valley and east of Lake Ontario
where lake shadows are expanding and drier air aloft is mixing out
the clouds. Temperatures are running comfortably in the upper 70s to
low 80s with dewpoints in the mid 50s to low 60s.

Tonight, surface high pressure will continue to influence our region
with dry weather and clear skies. The clear skies along with light
winds will result in another optimal radiational cooling night for
the Southern Tier River valleys. Otherwise, with dry air in place,
overnight lows will fall comfortably into the low 60s in the lake
plains and 50s in the interior valleys.

Wednesday, Weak surface high pressure will remain in place over
western and north-central NY through the morning. The surface high
will keep dry weather with any lingering valley fog quickly
dissipating after sunrise. A few features of interest will bear
watching for isolated to scattered shower and thunderstorm activity
going into the afternoon. The first is a leading weak mid-level
trough/shortwave which the 12z GFS pushes across our region midday
and the second is a weak surface cold front that trails by about 6
hours. Have included slight/low chance POPs focused along the PA
line in the western Southern Tier which could be triggered by a
combo of the mid-level trough and a surface lake breeze east of Lake
Erie. Later in the afternoon, the Niagara Frontier and Saint
Lawrence Valley also have slight/low chance POPs for some
isolated/scattered activity ahead/along the approaching front.

Otherwise, expect largely dry weather to continue through the
afternoon. Southwest flow of 10-20 mph will help boost dewpoints
back into the mid 60s which will bring back a return of more
uncomfortable humidity levels. 850mb temps around +16C will support
highs in the mid 80s at lower elevations and lower 80s higher
terrain.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
A weak mid level trough across the area Wednesday evening will move
eastward to New England late Wednesday night. Some model guidance
shows a weak surface trough as well, with some light QPF while other
guidance has the surface trough and associated QPF washed out by
Wednesday night. Either way the areal coverage of any showers will
be sparse with this feature. Expect lows in the mid 60s for most
areas, and around 60 in the coolest Southern Tier valleys.

After this, a weak frontal boundary will develop roughly from Eastern
Michigan to northwestern Pennsylvania. This boundary will be
diffuse and meander at times, and also will serve as a focus for
subtle convection in the Thursday and Friday timeframe. Model
guidance is in poor agreement on the specifics of any convective
waves which may develop along this boundary. Although it is possible
convection along this boundary will be significant, there is low
confidence in timing these waves at this timeframe since they will
be convectively driven. Due to the sparse nature of this convection,
the forecast carries an extended period of chance PoPs which is
highest across southern portions of the cwa which is closest to the
consensus position of the boundary.

Temperatures for Thursday and Friday will be near to slightly above
normal with daytime highs in the lower to mid 80s. It also will be a
bit more humid with dew points climbing to the mid to upper 60s.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
The region will remain southern edge of a cyclonic flow aloft which
will maintain a risk of showers and thunderstorms Friday night into
Saturday. Model guidance continues to differ on convective
development. After this there is some consensus on the pattern, but
overall low forecast confidence for PoPs during the long term
forecast period.

Model consensus suggests there will be a 12-24 hour period of dry
weather of the weekend with surface high pressure across Southern
Ontario ridging into the region. This will most likely occur late
Saturday into Saturday night. With this will be a northerly flow
with slightly drier air but still warm temperatures.

This ridge is likely to break down, with most model guidance
bringing a more significant wave across the region on Sunday as the
upper level trough starts to dig across the region. There is a good
chance of showers or thunderstorms with this wave Sunday and Sunday
night.

Cooler air will build into the region early next week with the upper
level troughing and a northerly component flow. Surface high
pressure building to our north is likely to bring mainly dry
weather, especially across northern portions of the forecast area.
Meanwhile temperatures will be notably cooler, with highs in the 70s
on Monday and Tuesday.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
VFR in place this afternoon thanks to high pressure over our region.
VFR will continue tonight with high pressure lingering, except for
more Southern Tier river valley fog developing late tonight. This is
expected to bring IFR to KJHW similar to last night.

On Wednesday, VFR will again remain in place. Some diurnal cumulus
clouds will again develop inland of lake breezes while some high and
mid level clouds arrive in advance of a weak cold front approaching
from the west. Some isolated showers/storms may be possible near the
PA state line and in the Niagara Frontier during the afternoon but
too isolated to include in TAF at this time.

Outlook...
Wednesday night and Thursday...VFR/MVFR. A chance of
showers and thunderstorms with possible MVFR.
Friday...VFR. A chance of TSRA in the western Southern Tier.
Saturday and Sunday...a chance of showers and thunderstorms with
possible associated MVFR.

&&

.MARINE...
High pressure will maintain fine boating conditions through much of
Wednesday with light winds and little wave action. A weak cool front
will cross the lakes Wednesday afternoon into Wednesday night
brining isolated to scattered showers and thunderstorms. Several
rounds of scattered thunderstorms remain possible Thursday into the
weekend but no significant marine concerns are expected outside the
storms.

&&

.EQUIPMENT...
The KBUF WSR-88D has returned to full service. Repair of some
critical parts which control its rotation is now completed.

&&

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

&&

$$

SYNOPSIS...SMITH
NEAR TERM...SMITH
SHORT TERM...APFFEL
LONG TERM...APFFEL
AVIATION...SMITH
MARINE...SMITH
EQUIPMENT...SMITH



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