Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 231852
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
252 PM EDT FRI SEP 23 2016

.SYNOPSIS...
A cold front move southeast and away from the area through this
evening with widely scattered showers ending from north to south.
This cold front will usher in a much cooler airmass for the weekend
with high pressure bringing a return to sunshine. Another cold front
will cross the region late Monday through Tuesday and bring the next
chance of rain.

&&

.NEAR TERM /THROUGH SATURDAY/...
Surface analysis early this afternoon showing the cold front pushing
southeast through PA and away from our region. This front has
anabatic characteristics, with the majority of the deeper moisture
and forcing for ascent on the cold side of the boundary. The last
band of scattered showers from Lake Ontario into the eastern Lake
Ontario region will drift southeast and across the region through
the rest of the afternoon. Temperatures are still in the 70s near
the PA state line, but elsewhere temperatures are falling in
moderate cold advection behind the cold front. Extensive stratus
supported by some contribution from lake effect moisture and
northerly upslope flow will maintain cloudy skies in most areas
through the rest of the afternoon.

A few scattered light showers may linger across the higher terrain
of the western Southern Tier and western Finger Lakes this evening,
otherwise the remainder of the night will be dry as mid level drying
advances south out of Canada. Despite the chilly airmass, a short
northerly fetch, extensive mid level dry air, and a stout inversion
near 5K feet will prevent any lake effect rain showers. The lakes
will be able to generate some cloud cover however, with north to
northeast low level flow favoring areas from the western Finger
Lakes westward across western NY for some lingering cloud cover
overnight, aided by upslope flow. The North Country and Central NY
will see at least partial clearing with no off-lake component.

Steady cold advection will bring much cooler temperatures overnight.
Expect lows in the upper 40s across most of the area, with lower 40s
east of Lake Ontario with no lake modification to the airmass. North
to northeast flow will keep areas within a few miles of the
lakeshores in the lower to mid 50s.

On Saturday surface high pressure over northwest Ontario province
will begin to nose into the Lower Great Lakes. Subsidence and drying
associated with the surface high will help to scour out any
remaining lake effect clouds south of the lakes by midday. A few
scattered diurnal cumulus will develop across the higher terrain of
the Southern Tier and Finger Lakes, with any clouds mixing out as
drier air continues to move in. The coolest airmass of the season
will settle into the area on Saturday. Expect highs in the mid 60s
in most locations, with lower 60s on the hills. The North Country
will be deeper into the cool air, with lower 60s at lower
elevations and mid 50s across the higher terrain.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
High pressure will settle upon the region Saturday night, bringing
clear skies and light winds. A pool of cold air will be centered
near northern New England Saturday night, where sub-zero 850 hPa
temperatures will reside. We will still be on the western edge of
this pool of cold air through the night, with the cooler air aloft
over our eastern zones.

The combination of clear skies, light winds and cool air overhead
will bring favorable radiational cooling conditions, with many areas
dipping down into the 40s, and interior regions dropping down into
the mid to upper 30s. This will likely allow for frost formation,
across the interior So Tier, and North Country, with greater
confidence across the North Country which will lie closer to the
colder air aloft. Frost in these regions is near the norm, with the
average first frost here around the third week in September. Closer
to the rivers in the valleys frost will not be likely, but some
patches of fog will be possible.

A crisp, but sunny start to Sunday. As the surface high pressure
scoots eastward, and upper level ridge of high pressure bears upon
us, we should see afternoon temperatures warm nicely into the 60s
which is near normal. It will remain dry Sunday night though mid and
high level clouds will likely keep overnight lows a few degrees
warmer than the preceding night. There may still be additional frost
across North Country Sunday night, but not as great in coverage
area.

Our next system will be forming across the plains Sunday, as a deep
upper level shortwave trough of low pressure drops from the Northern
Rockies towards the Northern Plains. This system will be advancing a
Pacific based cold front across the lower 48-states. Meanwhile, a
steady flow of moisture from the Gulf of Mexico will be circulating
around a southeastern area of high pressure, with this plume of
moisture advecting northward up the lower Mississippi Valley and
eventually along and ahead of the cold front.

This system will bring a chance for rain Monday afternoon across the
western counties of NYS, with rain possibly reaching as far east as
the North Country. The likely period for rain showers will be Monday
night as a cold front crosses the region. Reasons for increasing the
Pops for Monday night will be upper level height falls, and
convergence along a low level jet, with the jet nose within a nearly
saturated layer from the surface up through 10K feet. The nocturnal
passage of the cold front and limited instability will reduce
chances for thunder, and for now will not include it in the
forecast.

There is still some timing differences on the passage of the surface
cold front, and will continue with chance pops Tuesday morning
across our eastern zones where shower along the cold front may still
reside, while allowing for a dry period Tuesday morning across WNY
where a dry slot behind the cold front will likely be found.

Scattered showers will again increase across the region Tuesday
afternoon as daytime heating combined with the passage of the upper
level trough axis and return of ambient moisture may bring a few
showers.

Highs on Monday will reach into the upper 60s to mid 70s. Warmest
areas will likely be along the Lake Erie shore, and the western lake
plain where southeast winds will downslope. Cooler Tuesday with
widespread 60s found.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
It will be somewhat unsettled for the bulk of this period...although
none of the days are expected to be a washout. That being said...

Confidence during this long range period has increased...as the
medium range ensembles have come into closer agreement in the
handling of a long wave trough over the Great Lakes. The discussed
Rex block that will develop as a result of the digging trough will
have its col/reflection point near James Bay rather than over
Southern Ontario...so this will mean that we can anticipate a higher
chance for scattered showers. Interestingly enough...the more
northward location of the Rex block will translate into lower
temperatures across our region in the vcnty of the cold core within
the heart of the trough...or persistent closed low (as per some of
the GFS ensemble members).

The scattered showers will be supported by a chilly cyclonic flow
over the Lower Great Lakes...but again...there will be stretches of
rain free weather that should dominate the period.

As we work through Wednesday into Thursday...ridging over the Upper
Great Lakes will build east to diminish the potential for showers.

Looking further ahead...the approaching ridge should provide our
region with fair dry weather along with above normal temperatures
for the end of the week into the first weekend of October.

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
A cold front will move southeast and away from the region through
the rest of the afternoon and evening with scattered light showers
ending from north to south. A widespread area of IFR and MVFR CIGS
in low stratus behind the front will continue through this evening,
supported by northeast upslope flow and some contribution from lake
effect moisture. CIGS will improve to MVFR across lower elevations
this evening, with IFR lasting longer across the higher terrain of
the western Southern Tier and western Finger Lakes. Overnight some
lake effect clouds may persist south of Lake Ontario with areas of
MVFR, with partial clearing and VFR elsewhere.

On Saturday any remaining lake effect clouds with local MVFR CIGS
will scatter out by mid to late morning. This will leave some
diurnal cumulus across higher terrain inland from the lakes
during the afternoon with mainly VFR for the afternoon.

Outlook...

Sunday through Monday...VFR...save for some patchy overnight/
early morning valley fog with local IFR across the Southern Tier.
Monday Night and Tuesday...Areas of MVFR with a chance of showers.
Wednesday...VFR/MVFR with a chance of showers.

&&

.MARINE...
Moderate northeasterlies will continue on Lake Ontario through the
rest of the afternoon and tonight. This will continue to support
Small Craft Advisory conditions along the south shore of the lake.
Northeast winds will also increase on Lake Erie, with winds and
waves approaching Small Craft Advisory levels from Dunkirk to
Ripley. For now we have held off on a headline with the expectation
of conditions remaining just below Advisory levels.

High pressure begins to nose into the Lower Great Lakes Saturday
with winds starting to diminish. Winds and waves will subside
further Saturday night and Sunday as the surface high builds into
western Quebec and the Lower Great Lakes.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory until 11 AM EDT Saturday for LOZ042>044.

&&

$$

SYNOPSIS...HITCHCOCK
NEAR TERM...HITCHCOCK
SHORT TERM...THOMAS
LONG TERM...RSH
AVIATION...HITCHCOCK
MARINE...HITCHCOCK


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