Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 202157

Area Forecast Discussion
National Weather Service Buffalo NY
557 PM EDT Thu Oct 20 2016

An area of low pressure will track across the Southern Tier and
Finger Lakes region tonight into Friday...producing some moderate
to heavy rainfall across the entire region in the process. A few
thunderstorms may pass across the interior Southern Tie to the
Finger Lakes region this evening. This system will slowly edge
eastward Friday night...with rain of diminishing intensity
continuing through Saturday before tapering off as scattered
showers and higher elevation snow Saturday night.


Late this afternoon an area of low pressure is found across
Western PA, with another area of low pressure, of tropical origin
near the Bahamas. Regional radars show this first area of rain now
exiting the North Country this afternoon, with much of WNY mainly
dry. Clearing of the clouds within the warm sector of this storm
system has occurred over central PA, with some sunny breaks even
making their way into SE Cattaraugus County and Allegany County.

Upstream this afternoon, convection is forming along a baroclinic
frontal boundary across Southern OH. IR imagery displays this
convection with cooling cloud tops, with  Water Vapor imagery also
showing this next wave, along with a digging mid level trough
across the Mississippi Valley.

For tonight this upstream activity will enter our region late this
afternoon and evening. Surface low pressure will track northeastward
along the axis of an inverted trough that is oriented from Western
PA to Western New York, and within the mean SW to NE flow ahead of
the digging upper level low. Within this flow is also a strong 250
hPa jet, with our region lying within the favorable for lift right
entrance region of a 140 knot jet. Also within the SE to NE flow is
increasing amounts of moisture, with PWATs rising to near 1.50
inches which is +3SD above October normal. As this area of low
pressure nears NYS, it will bring enhanced low level convergence,
which when coupled with low level convergence along a strengthening
baroclinic frontal boundary over WNY, moderate to heavy rainfall
will be produced.

The baroclinic frontal boundary will be draped from roughly the
interior Southern Tier, through the southern Genesee Valley and into
the Finger Lakes region, and then the North Country. Here is where
we expect the heaviest of rainfall, with a narrow ribbon of upwards
to 3 inches of rainfall tonight and tomorrow along this boundary.
Farther westward over the Niagara Frontier rainfall totals will
likely be in the 1 to 2 inch range tonight and tomorrow. Have
issued a flash flood watch for portions of the Western Southern
Tier...Finger Lakes and eastern Lake Ontario regions to cover the
threat for the higher end of the rainfall range.

There will also be a risk of thunderstorms tonight. Clearing just to
our south is starting to produce SBCAPE values over 1000 J/KG and
this instability will eventually carry over the state line into our
region. MUCAPE values of 500 or so J/KG are possible in an area very
close and to the SE of the baroclinic frontal boundary, and this
region is where a chance for thunderstorms will be possible this
evening. With a 35 to 40 knot LLJ at 925 hPa, there will be small
possibility that some of these thunderstorms could produce strong to
damaging wind gusts, especially in the vicinity of the baroclinic
frontal boundary.

As moisture continues to saturate the atmosphere patchy fog will
develop and expand across a good portion of the region tonight.
While higher terrain is most likely, a northeast flow off Lake
Ontario will likely bring fog across the northern Niagara Frontier,
and northern Genesee Valley.

Friday...the surface low will merge with the tropical low, near
the mid-Atlantic coastline. Behind the now rapidly deepening
surface low a cool northwest flow will advance across the region.
With the upper level trough still overhead rain showers will
likely continue through the day, though likely not as intense as
tonight owing to a weakening low level convergence in the uniform
northwest flow. Clouds will remain thick within the northwest
flow, and with CAA there may be a few light wind gusts 20 to 30
mph across WNY.

With thick clouds there will be a narrow temperature fluctuation
through the night and tomorrow. Lows tonight will drop back into
the upper 40s and lower 50s, with highs tomorrow only climbing back
into the lower to mid 50s.


Friday night and Saturday the mid level trough will continue to
sharpen and move from the Great Lakes to western New England and
Quebec, closing off into a deep mid level closed low. A secondary
surface low will develop over the Gulf of Maine near the triple
point as the mid level low closes off, with a rapidly deepening low
over Maine or eastern Quebec. Abundant wrap around moisture and
ascent from the slow moving mid level closed low will continue to
support periods of rain showers across the entire region Friday
night, with the most widespread showers found east and southeast of
Lake Ontario by Saturday as the system moves slowly east. Most of
the rain will be light by this time as the stronger forcing and
plume of deep moisture re-organize off the New England coast. That
said, there may be a relatively small embedded area of moderate rain
moving from west to east across the area Friday night and Saturday
in the comma head of the deepening cyclone as a weak TROWAL

Saturday night the system begins to move east down the Saint
Lawrence Valley, with deeper wrap around moisture focusing on the
eastern Lake Ontario region. Precip will remain more widespread
there, while Western NY slowly dries out from west to east as a
drier airmass begins to build into the region.

The airmass will grow cold enough for lake enhancement as lake
induced equilibrium levels rise to around 8k feet. Off Lake Ontario,
this will manifest in the form of some lake enhancement within the
slowly departing comma head of the low. Off Lake Erie, some limited
northwest flow lake effect may develop later Friday night and
Saturday across the Chautauqua Ridge, but short fetch will limit the
coverage and intensity.

Temperatures aloft and in the boundary layer will remain warm enough
for all rain through late Friday night. By Saturday morning the
boundary layer should cool just enough to allow a few wet snowflakes
to mix in across the highest terrain of the Southern Tier and Tug
Hill region. A better chance of a mix and change to wet snow will
come Saturday night east of Lake Ontario, as colder air continues to
wrap around the deepening low. The column should cool enough for a
change to all wet snow overnight across the Tug Hill and western
Adirondacks above about 1200 feet in elevation, where some minor
accumulations are possible. Some wet snow may also mix in across
lower elevations with little or no accumulation.

On Sunday the deep surface low and associated mid level low will
move quickly northeast into the Canadian Maritimes. Any lingering
lake effect and upslope rain/snow showers early Sunday morning east
of Lake Ontario will end, leaving mainly dry conditions areawide
through the rest of the day. A fast moving weak wave of low pressure
over the central Great Lakes will approach later in the day, with
clouds increasing in the warm advection pattern ahead of the low.

Temperatures will bottom out on Saturday, with highs only in the
upper 40s on the lake plains and low to mid 40s across higher
terrain. Expect some recovery by Sunday with highs in the mid to
upper 50s on the lake plains of Western NY, and low to mid 50s
across the higher terrain and east of Lake Ontario.


Sunday night into Monday morning a shortwave trough will cross the
region in the northwesterly flow aloft. This will bring a few
showers across the forecast area, while reinforcing the cooler
Canadian source air into the region. Temperatures will remain near
to slightly below normal for the first half of the work week, as
we remain influenced by the troughing over New England and southern
Quebec. After the departing shortwave on Monday, heights aloft
slowly rise through Wednesday brining a mainly dry stretch of
weather. By Wednesday night into Thursday another shortwave trough
should approach from the Midwest and bring the next chance of


IFR to LIFR CIGS will be found across the bulk of western and north
central New York several waves of low pressure will
push by to our south along a stalled frontal boundary. The low cloud
cover will be accompanied by widespread rain...which will be heavy
at times for sites south and east of a line from ROC to Warsaw to
Jamestown where there could also be some evening thunderstorms. The
steady rain will combine with areas of fog to produce IFR to MVFR
VSBYS. Local delays will be likely.

On Friday...CIGS will generally remain at IFR to LIFR levels with
periods of rain persisting. Again...there will be the chance for

Friday night...MVFR to IFR in occasional rain and fog.
Saturday...Improving conditions far west but remaining IFR to MVFR
from KROC to the Eastern Lake Ontario Region.
Sunday...MVFR/VFR. A chance for rain showers SE of the lakes.
Monday...Mainly VFR. A slight chance for a rain/ North Country snow
Tuesday...Mainly VFR with a slight chance for a shower SE of Lake


An area of low pressure will cross just to the south and east of the
Eastern Great Lakes region tonight. Behind this surface low a
northwest, cool flow will cross the Great Lakes through the end of
the week, and this set-up will bring an extended period of Small
Craft Advisories to the lower Great Lakes.

Through the afternoon and evening will start the period easterly,
and then veer to northerly tonight. Friday, and into Saturday
northwest to west winds will maintain strength in the SCA level,
with winds possibly nearing gale force on Lake Ontario Saturday


NY...Flash Flood Watch through Friday morning for NYZ004>008-013-
MARINE...Small Craft Advisory from 7 PM Friday to 2 AM EDT Monday for
         Small Craft Advisory until 8 PM EDT Saturday for LEZ040.
         Small Craft Advisory until 8 PM EDT Saturday for
         Small Craft Advisory from 2 AM Friday to 2 AM EDT Monday
         for LOZ043.
         Small Craft Advisory until 11 PM EDT Sunday for LOZ042.
         Small Craft Advisory from 8 PM Friday to 11 PM EDT Sunday
         for LOZ045.
         Small Craft Advisory from 11 AM Friday to 2 AM EDT Monday
         for LOZ044.



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