Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 182116

Area Forecast Discussion
National Weather Service Buffalo NY
516 PM EDT Tue Oct 18 2016

A cold front will drop across the region through this evening which
will bring a short period of showers...and possibly a few
thunderstorms. Though cooler air will flow over the Eastern Great
Lakes region on Tuesday behind the cold front...temperatures will
still remain above normal. Our next significant weather event will
comer Thursday into Friday when several waves of low pressure
passing by to our south will produce a soaking rainfall.


While a deepening sub 985mb low continues to push north across the
northern reaches of Quebec late this afternoon...the strongest low
level jet from this system has largely pushed through the western
portion of our forecast area. Given that we are firmly entrenched
in a significant warm sector prevented the bulk of the 50kt low
level jet from being mixed to the sfc. Also working against high
winds was the fact that the storm tracked from south to north
from Wisconsin...climatologically NOT favorable for high winds.
That being said...winds across the advised counties of Wrn NY were
gusting to 30-40 mph as of the writing of this
plan on dropping the advisory for those counties by 21z and
letting the forecast speak for itself.

Further east...will hold onto the advisory into the evening as a
projected 50kt H9 (3k ft) jet has yet to move through. Otherwise...

A cold front will arrive from the northwest this evening...with
widespread rainfall and possibly some isolated thunderstorms. The
forecast still maintains likely to categorical POPs, with the
highest POPS/QPF inland and southeast of the lakes.

High pressure will build toward the region late tonight with
diminishing winds and cooler temperatures. Overnight low
temperatures will be in the 50s, with some patchy fog possible
across the Western Southern Tier.

High pressure will build across the region on Wednesday, providing
another pleasant day. Skies will be mostly sunny, with above
normal temperatures with highs mainly in the mid to upper 60s.


Weak surface high pressure from the Lower Great Lakes to New England
Wednesday evening will drift east off the New England coast by
Thursday morning. This high will initially provide dry weather and
at least partly clear skies through the first half of Wednesday
night. Increasing warm advection and mid level moisture ahead of the
next system will then bring thickening clouds from southwest to
northeast overnight, and a few showers may develop late across the
western Southern Tier as isentropic upglide increases.

A complex forecast scenario will then unfold for Thursday through
Friday, with a widespread moderate to heavy rain event looking more
and more likely. A mid level trough will move slowly east across the
Midwest and deepen with time, reaching the central Great Lakes by
Friday. A well defined baroclinic zone stretching from the Ohio
Valley to NY/PA will sharpen significantly and pivot with time as
the mid level trough approaches. The strong baroclinic zone will act
as a focus for a band of strong frontogenesis, deformation, and
moisture convergence. Meanwhile, a persistent and strong 140+ knot
upper level jet will remain in place from the central Great Lakes to
Quebec, placing our region in the favorable right entrance region
and allowing for steady upper level divergence atop the frontal

All of this will be aided by a persistent 30-40 knot low level jet
on the warm side of the boundary, pumping a continuous feed of deep
moisture into the frontal zone. PWAT values will range from 1.2 to
1.4 inches, which is 2-3 standard deviations above normal and a
significant amount of moisture considering the very strong dynamics
coming into play. The organized forcing should line up to produce a
wide band of deep layer ascent, with mesoscale waves and boundaries
providing embedded narrow regions of strong and focused ascent,
supporting periods of heavier rainfall.

The rain will develop across the Southern Tier shortly before
daybreak Thursday, with rain quickly overspreading the rest of the
area Thursday morning. Steady rain will then persist through the
rest of Thursday, Thursday night, and Friday. The heaviest rain is
likely to fall from Thursday afternoon through early Friday morning,
when a series of frontal waves run along the boundary and bring
periods of enhanced convergence and ascent. There remains some model
differences on the placement of the heaviest rain axis, but even
with the differences most, if not all, of the forecast area looks to
be in line for significant rainfall.

Early estimates are for 2-3 inches of rain over the two day period,
with locally higher amounts possible. Given the very dry antecedent
conditions, these rainfall amounts should not result in any notable
hydro issues, although some minor poor drainage flooding is possible
especially where leaves are blocking drainage systems. Hourly
rainfall rates are not expected to be high enough to create any
flash flood concern, unless narrow mesoscale bands develop with
slantwise or upright convection and locally enhanced rain rates.

Friday night the mid level trough will close off over eastern
Quebec, and allow a deep surface low to develop. The deeper plume of
moisture will move quickly east and off the east coast, while
abundant wrap around moisture wraps around the deepening system.
This will keep a few showers going Friday night, especially across
higher terrain and southeast of the lakes as upslope and lake
enhancement develops. 850mb temps drop to around -5C by Saturday
morning, which may allow for some wet snow to mix in across the
higher terrain of the Southern Tier and Tug Hill region. Expect lows
to be in the upper 30s to lower 40s at lower elevations, with mid
30s across higher terrain.


By Saturday the large upper-level trough will be centered over
southern Quebec with moist cyclonic northwesterly flow in place
across western NY. Ensemble guidance is in good agreement on the
placement of this trough, with some varying opinions of exactly how
cold of an airmass will follow in the wake of this low pressure
system. Generally expect 850 mb temperatures will drop below 0C,
with the GFS as cold as -6C, and the EC closer to -4C over the lower
Great Lakes. Nevertheless, expect a lake response coupled with
synoptic moisture and likely some vorticity max rotating around the
back side of the upper low. Thus lake effect rain will become likely
southeast of the lakes Saturday, with some possible snow mixing in
across the higher elevations early Saturday, should 850 mb
temperatures be closer to -6C than -4C. Afternoon temperatures will
reach the mid to upper 40s, warmest in locations outside of any lake
effect response, which should also support all rain through the

By Saturday night, drier air and rising heights start to build in
across the region as the upper level low tracks northeastward toward
east-central Quebec. The lake response will be tempered by
decreasing synoptic moisture and suppressed by increasing subsidence
and lowering capping inversion. Thus showers will diminish giving
way to just trapped low-level moisture resulting a cloudy night
southeast of the lakes. Overnight temperatures will be moderated
somewhat from this cloud cover and lingering northwest wind, despite
the cool airmass, resulting in lows in the low to upper 30s.

For Sunday through the beginning of the next work week, northwesterly
flow will remain in place aloft, keeping a supply of slightly below
normal temperatures in place across the northeast. High temperatures
will be mainly in the lower 50s with nighttime lows in the 30s. A
freeze is possible Monday night and Tuesday night in the Southern
Tier valleys and the North Country. Conditions will remain mostly
dry during this time period, with likely some lingering cloudiness.
The main uncertainty with respect to precipitation is the strength
of a shortwave trough that moves through Sunday afternoon into
Sunday night. The EC is more robust with this wave than the GFS and
if this verifies would result in a quick shot of cold rain across
the region.


For the 18Z TAFs VFR flight conditions continued for all five TAF
sites. A line of showers and embedded thunder upstream will cross
the TAF sites between 21Z and 04Z...and will produce MVFR flight
conditions...and IFR flight conditions across the Southern Tier as
activity passes.

Post front clearing will occur...though across the Southern Tier low
cloud formation...and areas of fog will likely bring a period of
late night IFR or lower flight conditions. These conditions should
improve between 09Z and 12Z as drier air associated with an area of
high pressure arrives.

Expect then VFR flight conditions on Wednesday with much lighter
winds with high pressure near by.


Wednesday night...VFR.
Thursday through Saturday...widespread rain with IFR flight
Sunday...mvfr/vfr in a chance for rain showers SE of the lakes.


Gusty southwest winds will continue through late afternoon or
early evening. A Small Craft Advisory remains in effect for Lake
Erie, Upper Niagara River, Lake Ontario and the Saint Lawrence
River through the day. Winds will decrease behind the front
tonight, along with subsiding waves as the surface gradient
relaxes and high pressure build over the lower Great Lakes.

Northeasterly winds will increase Thursday, then shift to the
northwest on Friday as low pressure tracks into New England. These
may require more small craft headlines, depending on the strength
of the low.


NY...Wind Advisory until 8 PM EDT this evening for NYZ003-007.
MARINE...Small Craft Advisory until 8 PM EDT this evening for LEZ020-
         Small Craft Advisory until 8 PM EDT this evening for
         Small Craft Advisory until 11 PM EDT this evening for
         Small Craft Advisory until 8 PM EDT this evening for



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