Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 012007

Area Forecast Discussion
National Weather Service Buffalo NY
407 PM EDT SAT OCT 1 2016

An upper level low over the Ohio Valley will slowly move into the
Great Lakes tonight and cross our region Sunday before exiting into
New England and weakening on Monday. This will keep the weather
unsettled through Monday with periods of rain showers. High
pressure will then bring a return to dry and warm weather Tuesday
through Thursday.


A very slow moving mid/upper level low and associated vertically
stacked surface low over the Ohio Valley will move slowly northeast
into the Central Great Lakes tonight and early Sunday, with the
center of circulation reaching Western NY by Sunday evening. This
will keep unsettled weather across the region through the remainder
of the weekend, with several additional rounds of showers expected.

Radar imagery showing dry conditions across most of the region late
this afternoon, with a concentrated area of rain over the Genesee
Valley and western Finger Lakes. This area of rain is in association
with a subtle, elongated area of mid level vorticity and an
associated low level speed max of around 30 knots. Low level
moisture convergence on the nose of this low level jet combined with
weak large scale ascent from the vorticity maxima is enough in this
moisture rich environment to support the concentrated area of rain.

During the evening, the rain associated with the mid level
vorticity maxima and low level jet will shift steadily east into
the eastern Lake Ontario region as the forcing shifts northeast
and weakens. Behind this area of rain, expect western NY to dry
out during the evening and remain dry through most of the night as
a mid level dry slot rotates around the upper level low. This
drying trend will also move eastward into the Genesee Valley and
western Finger Lakes overnight, with dry conditions reaching
Central NY by daybreak Sunday. The North Country will see a few
scattered showers linger overnight, although the more concentrated
rain should end as forcing and convergence weaken.

Toward Sunday morning large scale ascent and deeper moisture will
spread northeast across Lake Erie in advance of the mid/upper level
low. The increasing DPVA ahead of the system will bring showers to
areas near the Lake Erie shore by around daybreak Sunday. Through
the course of the day, the DPVA and deeper moisture will spread
steadily east across the area, with showers increasing in coverage
again from west to east. The strongest area of DPVA will combine
with low level convergence driven by terrain and local effects to
bring an expanding area of showers by midday across the higher
terrain just east of Lake Erie. This area of rain will continue to
expand and spread east across the Genesee Valley and western Finger
Lakes during the afternoon, reaching Central NY by early evening. In
addition, the airmass grows cold enough to support a lake response
as well, with lake induced equilibrium levels rising to around 20k
feet off Lake Erie in the afternoon with the approach of the upper
level low and associated cold pool. This should support a plume of
lake enhanced rain showers across the Niagara Frontier.

SBCAPE will rise into the 500-800J/kg range from both daytime
heating over the land and also from lake instability, supporting a
few scattered thunderstorms during the afternoon. Steep low/mid
level lapse rates and low wetbulb zero heights suggest some of these
storms may produce small hail. Modest shear in the lowest 10k feet
of the atmosphere will prevent any severe weather, although a few of
the storms may also contain gusts winds and brief, heavy downpours.


The upper-level low that has been pinwheeling across the Ohio Valley
for the last few days will finally make its departure during the
early part of the week, giving way to drier, sunnier and warmer
weather by mid-week.

First Sunday night, the upper-level low will be in the process of
crossing Lake Ontario and heading into eastern New York for the day
Monday. Picking up Sunday evening, strong QG forcing ahead of the
low center along with a limited pool of instability due to the
steeper mid-level lapse rates under the low, will support scattered
to numerous showers and few thunderstorms tracking eastward across
the forecast area toward central NY. Any stronger showers and
associated rumbles of thunder should wayne toward midnight with the
loss of surface heating after sunset. The bulk of the upper level
forcing will then settle across the North Country after midnight,
with developing upslope flow on the back side of the center of
circulation helping to increase shower persistence on the north side
of the Tug Hill / Adirondacks. Across western NY, the cooler air and
steeper lapse rates spilling across the anomalously warm Lake Erie
will support lake effect rain showers initially near Buffalo early
Sunday evening, and then quickly settling southward across the
western Southern Tier as the flow turns more northwesterly and
supports a Lake Huron connection.

By Monday morning, trapped low-level moisture, enhanced by the lower
Great Lakes warm surface temperatures, and developing northerly
upslope flow behind the departing low pressure system will support
low overcast, and scattered showers/sprinkles across the region.
These may be locally enhanced by the terrain and near the lake
shores. The low will continue sliding eastward through the day with
some limited drying and increasing subsidence across the forecast
area. This should act to slowly erode any stray showers and start
to break apart the clouds cover from west to east. With the cool
pool associated with the upper low remaining in control and low
cloud cover, expect daytime temperatures to top out in the mid 60s.

Monday night through Wednesday will finally see a prolonged period
of guaranteed dry weather, moderating temperatures and more sunshine
across the region as a bubble of high pressure builds in abruptly
behind the departing low pressure system. Developing southerly return
flow, downslope winds, and warmer air advecting in aloft will
finally scour out the cool pool and low-level moisture left behind
by the upper-level. This will result in day-to-day warming and more
abundant sunshine by mid-week. High temperatures will to near 70 on
Tuesday, and to the low 70s on Wednesday.


A strong sub tropical ridge centered off the Mid Atlantic coast will
control much of our weather during this period. The heart of its
associated surface high pressure will initially be anchored near
Nova Scotia and will extend back across the Lower Great Lakes...but
as we head into the weekend...a vigorous shortwave crossing the
Upper Mississippi Valley will help to dislodge the expansive fair
weather feature.

The result of this will be two fairly nice days of weather across
our forecast area with abundant sunshine and temperatures that will
average well above normal. Max temps will generally be in the 70s...
which is about 10 deg F above early October norms.

Things will start to get interesting as we push into the weekend...
particularly along the East Coast where Hurricane Matthew will be
chugging its way to the north. The good news for our forecast area
is that none of the guidance packages are suggesting a DIRECT impact
from the tropical system for our region. The bad news...if you want
to call it that a fairly vigorous shortwave moving across
the Upper Great Lakes will push a slow moving cold front across our
region. It is fairly reasonable to assume that at least some of the
tropical moisture from Matthew will be entrained into the airmass
ahead of the cold front. This will enhance the potential for some
moderate to heavy showers with the frontal we will
have to keep an eye on this.


Showers will increase during the mid to late afternoon mainly across
the Genesee Valley and western Finger Lakes, with this area of rain
then moving east across Central NY and the eastern Lake Ontario
region this evening, before tapering off overnight. The heavier
showers will contain areas of MVFR and brief IFR VSBY. Areas of MVFR
CIGS will continue through the rest of the afternoon and evening in
most areas, with IFR across the higher terrain of the Southern Tier
becoming less widespread. Developing southeast downslope flow will
keep the Niagara Frontier including KBUF mainly VFR this afternoon.

Any showers taper off from west to east this evening with mainly dry
conditions in most areas, except for the North Country overnight.
Low level moisture supported by a southeast flow of Atlantic
moisture will produce widespread IFR CIGS across higher terrain
overnight, with some of the stratus intersecting the hills to
produce patchy fog.

On Sunday a strong mid level low will move into the central Great
Lakes, with showers developing from west to east across the region.
Some of the heavier showers will produce areas of MVFR and local IFR
VSBY. CIGS will deteriorate to MVFR across lower elevations, while
the higher terrain IFR stratus improves to MVFR.


Monday...Areas of MVFR with scattered showers.
Tuesday through Thursday...Mainly VFR.


A surface low over the Ohio Valley will move slowly into the central
Great Lakes overnight. This will finally allow easterly winds on
Lake Ontario to weaken and become southeast, ending Small Craft
Advisory conditions on the west half of the lake overnight. Winds
will become southwest on Lake Erie and increase on Sunday, and
Sunday evening on Lake Ontario, but should remain just below Small
Craft Advisory conditions. Winds will diminish on Monday as the
surface low drifts towards New England and dissipates. High pressure
will then bring light winds Tuesday through Thursday.

Conditions will become favorable for waterspouts Sunday and continue
through Monday morning on Lakes Erie and Ontario as the upper level
low approaches and air cools aloft. The new run of the Szilagyi
waterspout forecast suggests a good chance of waterspouts Sunday and
Sunday night on Lake Erie, and by Sunday afternoon and evening for
Lake Ontario.


MARINE...Small Craft Advisory until 11 PM EDT this evening for LOZ042.



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