Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 190617

Area Forecast Discussion
National Weather Service Buffalo NY
217 AM EDT Wed Oct 19 2016

While it will be notably cooler in the wake of a cold front
today...the mercury will remain above normal mid October levels.
Weak high pressure will accompany the lower temperatures...but the
associated fair weather will be short lived. Our next significant
weather event will move in Thursday into Friday when several waves
of low pressure passing by to our south will produce a soaking


A cold front has shifted east of the forecast area early this
morning with all showers now east of Syracuse. Infrared satellite
imagery shows a band of clouds oriented along the front. Dry air on
northwest flow behind the front is working to erode cloud cover on
the back edge and as of 2am skies are now clear across much of the
Niagara Frontier and Lake Ontario east across Watertown. This
clearing trend will continue through the morning hours as weak high
pressure over the Upper Mississippi Valley builds across the Lower
Great Lakes. Cooler air in the wake of the front will send our
temperatures down through the 50s. While these readings will be some
10 deg f lower than those from last (Mon) night...they will still be
more than 10 deg f above typical mid Oct values.

After sunrise, the aforementioned area of weak high pressure will
support a fairly nice day across the region. We can anticipate ample
sunshine and fairly comfortable temperatures in the 60s to near
70... but the fair weather will be short lived. A change to much
rainier conditions can be expected as we move into the short term
forecast period.


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.


A cold front has shifted east of SYR this morning with all showers
also to the east of this site. A band of clouds along this front is
shifting east with skies clearing across the forecast area from
northwest of southeast. All TAF sites are VFR as of 06z and should
stay this way through the rest of the morning with a dry northwest

After sunrise VFR conditions will be in place as weak high pressure
will build across the Lower Great Lakes. These conditions will
persist through much of tonight before a period of wet and unsettled
weather will return Thursday.

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


Weak high pressure will build across the Lower Great Lakes during
the remainder of the overnight...and will remain in place today and
tonight. This will result in gentle to moderate breezes and
negligible waves on the lakes and associated waterways.

A stalled frontal boundary well to our south will then serve as a
pathway for multiple waves of low pressure Thursday and Friday. This
will lead to freshening northeasterlies that will very likely require
the next round of small craft advisories.





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