Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 211855

Area Forecast Discussion
National Weather Service Buffalo NY
255 PM EDT SUN AUG 21 2016

Rain showers will taper off across the North Country this afternoon
as a strong cold front pushes east across the area. Much cooler air
behind this front will bring a brief shot of lake effect rain to
areas east of Lake Erie tonight along with the coolest temperatures
we have seen since mid-June. The relief will last through Tuesday
before heat begins to build ahead midweek ahead of another cold
front, currently expected to cross the region by the end of the
week. Otherwise, expect dry conditions to return at least until
Wednesday evening as high pressure moves overhead.


Regional radar indicates that the bulk of the rainfall associated
with a cold front crossing the forecast area is now confined to the
North Country and Leatherstocking regions of New York. This rain
will continue push off to the east through the remainder of the
afternoon hours ahead of the parent cold front, itself tied to a
surface low centered near James Bay. Widespread cu and scattered
lake effect rain showers visible upstream across Michigan on
regional radar and satellite imagery is indicative of how cool the
airmass upstream is, and this cool air will continue to surge
southeast across our region this evening.

Mesoscale guidance continues to indicate the development of lake
effect rain showers off of Erie across the Buffalo metro early this
evening as increasingly cool WSW flow backs to the west, and
eventually the NW overnight. Any rain showers across Buffalo should
quickly shift into the western Southern Tier this evening as flow
veers to the NW and sfc-850mb delta-t values increase to around 15C.
Flow will be somewhat sheared in this flow however, which should
impede shower intensity, nonetheless an additional quarter to half
inch of rainfall cannot be ruled out across the Chautauqua Ridge
tonight. The cooler waters of Lake Ontario will limit lake
instability, and while lake effect clouds should be found in
abundance, showers appear to be much less likely at this time. The
cool shot will bring much needed refreshment to many tonight as lows
drop into the 50s across virtually all of the forecast area, with
the exception of areas immediately along the lakeshores, where
readings will bottom out around 60.

WNW flow will persist on Monday, though winds will slacken
considerably and lake effect clouds should diminish as high pressure
builds across the region. Lingering upper level troughing should
keep skies at least partly cloudy through much of the day,
particularly inland from the lakes, however conditions should remain
dry. Highs will be distinctively cooler, with readings only topping
out in the low to mid 70s - a welcome respite from the oppressive
heat of late.


High pressure will slowly cross the region through this period,
providing for fair weather, light winds and mostly clear skies. There
will likely be some river valley fog, especially across the Boston
Hills, Genesee Valley and Southern Tier Monday night, and possibly
Tuesday night under these clear skies and light winds. Overnight lows
will again be chilly in this fresh airmass Monday night,
with temperatures falling into the upper 40s to upper 50s. As this
airmass moderates, Tuesday night will drop back in the mid 50s
to lower 60s overnight, while Wednesday night will be mild in the
mid 60s to lower 70s.

High temperatures will be seasonable Tuesday in the upper 70s to
lower 80s, then Wednesday a southerly flow develops on the back side
of this area of high pressure allowing for low to mid 80s to return
to the region with a touch more of humidity.


The main weather event this period will be found within a series of
fronts crossing the region Thursday night and again late Friday night
and Saturday. Very warm temperatures and a muggy airmass will be
replaced by a cooler and drier airmass to close out the period.

The details...this Sunday afternoon a shortwave is dropping
southward along the British Columbia coastline, and this feature
will be slowly making its way to the Northern Plains and western
Great Lakes by the start of Thursday. Ahead of the shortwave trough
of low pressure a south to southwesterly flow will be increasing
both warmth aloft, as well as moisture. Air temperatures at 850 hPa
will rise to +16 to +17C, while PWATS climb through the one-inch
range and on their way up to around 2 inches by Thursday night.

The best chance for any showers or thunderstorms Thursday will come
through the afternoon hours when peak heating of the day sends MUCAPE
values upward to 1000 to 1500 J/KG over the Southern Tier, and
Genesee Valley and northern Finger Lakes region. With little forcing
activity will likely be isolated to scattered at best and will
continue with just the chance Pops in the forecast. A southwest wind
off Lake Erie will likely keep metro Buffalo dry through the
afternoon hours.

Thursday night a prefrontal trough will cross the region, with this
feature providing for better widespread lift across the region. This
period will be most likely for showers and thunderstorms, and will
continue with the likely pops. In addition to the trough, a 35 to 40
knot LLJ between 925 and 850 hPa will bring extra low level
convergence. The warm lakes will likely provide extra instability
through the night for the generation of convective showers.

This trough will cross the region Thursday night, with a few
lingering showers early Friday. There will be a minor
change in the airmass Friday, as dewpoints will remain well into the
60s, though air temperatures will be a bit cooler, climbing into the
upper 70s and lower 80s. It will not be until late Friday night and
early Saturday morning that a cold front drops southward across the
region, with this feature lowering both air and dewpoint
temperatures. This cold front may come across the region dry as there
will be much less available moisture to work with (PWATS now down to
an inch or less). If there were any activity it may be across the
North Country and SLV Friday night, and then Saturday morning as 850
hPa temperatures become just cool enough (+10 to +12C) that maybe a
little lake effect response will generate off Lake Ontario. Again
with the drier airmass will have just slight chance PoP in the
forecast for now.

Later Saturday and into Sunday our region will likely remain dry as
high pressure settles across the region. This area of high pressure
will exit east later Sunday, allowing for slight warming aloft and
high clouds likely to re-enter our region from the west. Air
temperatures Saturday behind the cold front will be in the upper 70s
to lower 80s, while Sunday should see a few more widespread 80s.


Regional radar currently shows a broad band of rain extending across
the North Country and central NY in advance of a cold front that has
moved into far western NY this afternoon. This front will continue
to advance to the east through the rest of this afternoon with
MVFR/IFR conditions moving out of the North Country over the next 2
hours. Behind this initial rainband, look for rapid improvement to
VFR cigs as broken cigs associated with cu linger along and behind
the front.

In addition, gusty WSW winds will be found behind the
front as it crosses the forecast area through the rest of this
afternoon and into the early evening hours, with gusts of around
25kts possible. As these winds continue to veer to the west this
evening, the westerly flow combined with strong cold advection will
yield lake effect clouds and showers off of Lake Erie that should
end up bringing MVFR conditions to areas south of KBUF. A brief
period of MVFR conditions may also be possible at KBUF between 23-
03Z this evening, though confidence in the exact location of any LE
precip remains uncertain, as flow will be rapidly transitioning to
the WNW through this period. Given colder waters over Lake Ontario,
widespread lake effect showers are not expected, though BKN cu of
around 3kft should linger through the overnight hours.

Moving into Monday, WNW flow will keep lake effect clouds in place
SE of the lakes at least during the early morning hours before
increasing surface ridging and diurnal heating quash any lingering
lake effect clouds. However, with troughing and generally cool
temperatures aloft, we will likely see sct/bkn cu redevelop during
the afternoon, particularly across higher terrain inland form the

Outlook... Monday Night...Mainly VFR except localized IFR in
fog in Southern Tier valleys.
Tuesday and Wednesday...VFR.
Thursday and Friday...Mainly VFR with a chance of showers and


Gusty WSW winds in the wake of a cold frontal passage will continue
to bring small craft advisory conditions to the majority of forecast
zones this afternoon and tonight. Much cooler air surging across the
lakes will result in the development of lake effect rain showers,
particularly off of Lake Erie, and the sharp temperature gradient
will also generate the potential for waterspouts tonight into Monday
morning, particularly on Lake Erie, where the temperature
differential will be maximized.

NW winds will gradually diminish through the morning hours on Monday
as high pressure builds across the region. Otherwise generally quiet
conditions will return to the lakes into Wednesday, at which point
high pressure moves off the East Coast and southerly flow freshens
across the region.


NY...Beach Hazards Statement until 11 PM EDT this evening for
MARINE...Small Craft Advisory until 5 AM EDT Monday for LEZ040-041.
         Small Craft Advisory until 8 PM EDT this evening for
         Small Craft Advisory until 11 AM EDT Monday for



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