Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 192341

Area Forecast Discussion
National Weather Service Buffalo NY
741 PM EDT Wed Oct 19 2016

Our brief reprieve from unsettled weather will come to an end late
tonight and Thursday as a series of low pressure systems will pass
by just to our south and east. This will result in a 36 hour period
where our region will receive a soaking rainfall. While everyone
should pick up at least an inch and a half of rain through Friday...
areas east of a line from Rochester to Warsaw to Jamestown could
pick up as much as three inches.


Weak high pressure over the region will provide us with a beautiful
evening with star filled skies...but conditions will quickly
deteriorate during the overnight. Clouds will increase and thicken
from the south after midnight as the first of several low pressure
waves will move from the Upper Ohio Valley to Pennsylvania. A low
level jet ahead of the first wave will help to push the moisture
northward...increasing PWAT values to well over an inch...which will
be 2 STD abv typical mid October levels.

Convergence along the leading edge of the LLJ...combined with deep
isentropic upglide motion will encourage the leading edge of the
steady rain to advance northward across the Pennsylvania border
during the wee hours of the overnight. This rain will quickly spread
north and eastward across the region Thursday morning. As an inverted
surface trough develops over the CWA through the day Thursday...
convergence along the trough will maintain a swath of rain.

A second wave of low pressure along the inverted surface trough will
near SW NYS late Thursday. This feature bringing enhanced low level
convergence will enhance the rainfall over the interior Southern
Tier and towards the Finger Lakes region. While a general half to
one inch of rain is likely across the region on Thursday...a
narrow strip of an inch to an inch and a half is possible across the
enhanced area outlined above.

Within the saturated lower levels, low clouds and fog are likely
late tonight and for much of Thursday. A developing northeast
flow Thursday may bring low clouds and patchy fog along the western-
southern Lake Ontario shoreline in the afternoon.

Temperatures tonight will drop down into the lower 50s to upper
40s...with little diurnal increase Thursday...with highs climbing
back into the upper 50s.


A complex frontal zone will move slowly east across the area
Thursday night and Friday, producing widespread steady rainfall. A
mid level trough will move slowly east into the Great Lakes and Ohio
Valley, deepening and sharpening with time. The deep layer southerly
flow ahead of the trough will transport abundant moisture northward,
with PWAT values of around 1.5 inches in central NY, which is 2-3
standard deviations above average for mid October. Dynamics will be
impressive, with a very sharp baroclinic zone developing from
central PA to central NY, focusing a ribbon of strong frontogenesis
and deformation in the 900-700mb layer. Convergence and moisture
transport into the boundary will be enhanced by a 30-35 knot low
level jet that will persist on the warm side of the boundary.
Finally, a very strong 140 knot upper level jet from the central
Great Lakes to New England will provide strong upper level
divergence, and phase with the low level frontogenetic forcing to
produce a wide band of deep layer ascent.

Rain will be ongoing across the entire region Thursday evening, and
continue through the night and through all of Friday. The heaviest
rain will fall in a band from Cattaraugus and Allegany counties
northeast across the Finger Lakes to the eastern Lake Ontario region
Thursday night, with the heaviest rain then tapering off early
Friday morning. To the west of this axis, and through the rest of
Friday, rain will be lighter in nature.

The multi-model consensus has shifted the axis of the heaviest
rainfall slightly east over the past few runs, with the highest
amounts now likely targeting the interior Southern Tier into the
Finger Lakes and Central NY to the Tug Hill region. This is the most
likely area for 2 to 3 inches over the 2 day period from Thursday
through Friday, with local amounts of up to 4 inches in some upslope
areas and also where any narrow corridors of enhanced rainfall
occurs near mesoscale banding. Amounts look somewhat lower near Lake
Erie and across the Niagara Frontier, but even here a solid 1 to 2
inches still looks reasonable. Given the very dry antecedent
conditions, these rainfall amounts will mainly be beneficial with
just some minor poor drainage flooding possible in a few spots.
Hourly rainfall rates are not expected to be high enough for any
flash flood concerns.

Friday night and Saturday the mid level trough will close off into a
closed low over Quebec and New England, forcing a stronger surface
low to develop over Maine. The heaviest rain axis will re-develop
off the eastern seaboard as this occurs, while abundant wrap around
moisture persists across our region. A broad area of relatively weak
large scale ascent on the western flank of the deepening low over
New England will combine with some lake instability and upslope flow
to keep showers going through Friday night, and even into Saturday
southeast of the lakes. The airmass will grow just cold enough to
support some wet snow mixing in very late Friday night into Saturday
across the higher terrain of the Southern Tier, and the Tug Hill
and western Adirondacks.

Temperatures will steadily drop through the period, with highs only
in the low to mid 50s Friday, then mid to upper 40s in most
locations Saturday as 850mb temps bottom out around -5C.


Rising heights on Sunday behind the departing low pressure system
should contribute to a drying and clearing trend outside of lake
cloudiness, but with slighly below normal temperatures lingering
across the region. By Sunday night through Monday, models continue
to advertise a clipper tracking across the region in the
northwesterly flow aloft. However, opinions continue to vary between
the global models on the timing, strength and exact track. Will
maintain a chance of rain showers in the forecast for Sunday night
through Monday for a lack of any better information on timing and

By Tuesday into Wednesday, general troughing over New England with
ridging building into the central plains will keep a northwesterly
flow across western NY. This will keep cool air nearby, with the
coldest portion of the airmass from the Hudson Bay to New England.
Western NY will remain on the fringes, yet solidly in, the cooler
airmass, supporting slightly below normal temperatures. While this
will be a largely dry period, any subtle shortwaves tracking along
the baroclinic zone could produce some showers across the region,
but there is little agreement on specific details from the models at
this range.


Weak high pressure over the region will keep VFR conditions in place
through at least 06z...then clouds will lower and thicken from the
south as a wave of low pressure will approach from the Upper Ohio
Valley. The leading edge of an expanding area of rain associated
with the surface wave will make its way north across the
Pennsylvania border after 08z...with CIGS rapidly deteriorating to
IFR across the Southern Tier (KJHW, KELZ) by daybreak.

The widespread steady rain will continue to spread north across all
of western and north central New York between 12 and 18z...with CIGS
lowering to at least IFR levels for all sites but KART where MVFR
conditions will be in place. LIFR CIGS are expected across the bulk
of western New York by late Thursday morning. Delays will be possible.

Widespread rain with IFR conditions will continue across all of the
region Thursday night. Some delays will be likely.

Friday through Saturday...Occasional rain with continued IFR flight
Sunday...MVFR/VFR. A chance for rain showers SE of the lakes.
Monday...Mainly VFR. A slight chance for a rain/ North Country snow


An area of high pressure will cross the Eastern Great Lakes region
tonight, with light winds and producing flat wave action. This area
of high pressure will slide to the east, while an area of low
pressure advances from the South to the Ohio Valley. A strengthening
easterly wind through the day tomorrow will develop. This will
likely bring small craft advisory conditions to the western end of
Lake Ontario, and also Lake Erie from roughly Dunkirk and points
southward. A complex front will then cross the lakes Thursday night
and Friday, with a cold northwest flow following over the lakes.
This flow will then bring an extended period of SCA to the Eastern
Great Lakes region through the remainder of the weekend.





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