Area Forecast Discussion
Issued by NWS Buffalo, NY

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000
FXUS61 KBUF 200346
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1146 PM EDT Mon Jun 19 2017

.SYNOPSIS...
A mid level trough will slowly cross the region and produce a few
scattered showers and isolated thunderstorms this evening through
Wednesday. A better chance of more widespread showers and
thunderstorms will arrive Friday and Saturday as low pressure moves
through the Ohio Valley. Temperatures will be cooler through the
middle of the week before warmth and humidity briefly returns at the
end of the week.

&&

.NEAR TERM /THROUGH TUESDAY/...
A shortwave crossing southern Ontario at 03z will generate some
showers and possible thunderstorms across the region into Tuesday
morning. Those areas that do receive any pcpn will pick up less than
a tenth of an inch. Temperatures by daybreak will be close to 60
across the lake plains...with readings in the mid 50s found across
much of the Southern Tier as well as across parts of Lewis County.

On Tuesday...the aforementioned shortwave will push off to the east
within the front side of supporting longwave trough. Any leftover
showers from this feature will end from west to east during the
morning hours...leaving mainly dry weather for the midday and
afternoon. The exception will be across the North Country where the
showers could linger into the late afternoon hours. 850mb temps will
lower to around +8C...which will only support highs in the mid 70s F
on the lake plains and upper 60s to around 70 on the hills.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/...
The axis of a Great Lakes longwave trough is forecast to cross
western and central New York Tuesday night. Forecast models continue
to show a nice vort max at the base of the trough axis with
additional forcing support from a surface trough crossing our region
00-06z. This brings the potential for a broken line of showers and
possible thunderstorms Tuesday evening. Have gone with high chance
range POPs during this time period along with maintaining the
enhanced wording for gusty winds from continuity. SBCAPE should be
very weak but forecast bulk shear of 40-50 knots could support some
gusty showers or isolated storms. A lingering wing of low-mid level
moisture and upslope flow has kept a chance for showers east of Lake
Ontario through the second half of the night while western NY dries
out. Low temperatures are expected to dip into the low to mid 50s as
dewpoints fall behind the surface trough.

A cool airmass with 850mb temps down to +8C will arrive behind the
mid level trough axis and continue comfortable temperatures
averaging a few degrees below normal as astronomical summer begins
Wednesday. Surface highs are forecast to run in the low to mid 70s.
A fresh shot of Canadian air will also continue to filter across our
region with dewpoints slipping back into the low to mid 50s which
will provide very comfortable humidity for summer standards. This
drier airmass will allow overnight temperatures to slip back into
the low to mid 50s Wednesday night. Have included a slight chance
for an isolated shower or thunderstorm Wednesday which would be
mainly diurnal influenced as the cooler air aloft steepens lapse
rates during the afternoon. Highest POPs in the low chance range
will continue to be across the eastern Lake Ontario region where
best moisture and coolest air aloft will be found. Diurnal
influences showers/storms should end after sunset Wednesday with
mainly clear skies arriving overnight within weak high pressure.
This may bring some patchy Southern Tier river valley fog.

A warm front is then forecast to lift across western and central NY
on Thursday. This front will be associated with low pressure over
western Ontario province. The warm front will bring a return of
warmer temperatures and increasing humidity along with a potential
for some showers and thunderstorms along the front and within the
trailing warm sector into Thursday night. Instability and shear is
not forecast to be particularly high so only including a general
thunderstorm risk for now. An incoming cold front sometime late
Thursday night or Friday morning will keep elevated chances for
showers and storms into Thursday night. Highs Thursday are forecast
to reach into the mid 70s to around 80 with dewpoints climbing back
toward 60. The increased humidity and southerly flow will keep
warmer temps in place overnight Thursday with lows only forecast
down to the low to mid 60s.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
Long range models are in good agreement on a overall broad troughing
pattern over the Hudson Bay through the weekend. The forecast area
will be located on the southern periphery of this broad low, and
generally embedded within the west-southwesterly flow aloft. This
will allow for several fast-moving Pacific sourced shortwaves
embedded with the flow to cross near the region. The day-to-day
temperature trend will be generally cooler through the weekend,
while daily details are bit fuzzy depending on individual shortwave
timing and the close proximity to a stalled frontal boundary. The
same goes for precipitation forecasts, as scattered showers and
thunderstorms are likely at times with the wave passages, with ample
dry time in-between.

Specifically, the first of these systems will be a cold front that
will plow across the Lower Great Lakes on Friday. While it is
too early to get specific with the amount of instability or
shear that will be present...it is worth noting that the
frontal passage should take place within a west to northwest
flow...and these inherently include a higher than normal amount
of directional shear. This could make the event more
`interesting`.  Given the consistency between the medium range
models...have raised pops to likely for this event.

A wedge of high pressure over the Lower Great Lakes will promote
nice weather for the first day of the weekend...as a fair amount of
sunshine will combine with H85 temps around 12c to support afternoon
highs in the upper 70s to around 80. Overall the weekend will be
mainly dry with shower and thunderstorm changes increasing through
the day Sunday. Its fair to say at this point that Sunday will be
the less favorable day for outdoor activities. Stay tuned.

Cooler drier air will filter into the region for the start of the
work week behind a cold front passage Sunday night.

&&

.AVIATION /04Z TUESDAY THROUGH SATURDAY/...
While VFR conditions will prevail across the region through the
remainder of the overnight...some showers and possible thunderstorms
will cross the region.

Leftover showers Tuesday morning will give way to increasing amounts
of sun from west to east during the midday and afternoon. The
exception will be across the North Country where some showers could
linger through much of the day. Otherwise...VFR conditions can be
expected.

Outlook...

Tuesday night and Wednesday...Chance of showers with mainly VFR.
Thursday through Saturday...A chance of showers and thunderstorms
with local MVFR.

&&

.MARINE...
Low pressure will stall across northern Quebec tonight through the
middle of the week and produce a few periods of moderate to
strong winds.

On Lake Erie, moderate southwest winds will continue tonight, then
increase into the 20-25 knot range on Tuesday as the pressure
gradient tightens over the lake. This will bring Small Craft
Advisory conditions Tuesday morning through Tuesday evening.

On Lake Ontario, moderate southwest winds tonight will become more
westerly late Tuesday through Wednesday. Winds will not be as strong
as Lake Erie, with winds and waves expected to remain just below
Small Craft Advisory criteria. Nonetheless, choppy conditions will
be found at the east end of the lake Tuesday through Wednesday.

Lighter winds are then expected Thursday and Friday as the pressure
gradient relaxes over the eastern Great Lakes.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Beach Hazards Statement from 8 AM EDT Tuesday through Tuesday
     evening for NYZ010-019-085.
MARINE...Small Craft Advisory from 8 AM to 11 PM EDT Tuesday for LEZ040-
         041.
         Small Craft Advisory from 10 AM to 8 PM EDT Tuesday for
         LEZ020.

&&

$$

SYNOPSIS...HITCHCOCK/WOOD
NEAR TERM...HITCHCOCK/RSH/WOOD
SHORT TERM...SMITH
LONG TERM...CHURCH/RSH
AVIATION...RSH
MARINE...HITCHCOCK



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