Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 290829

Area Forecast Discussion
National Weather Service Buffalo NY
429 AM EDT THU SEP 29 2016

An upper level low, cut off from the main jet stream, will meander
over the Midwest through week and the weekend while periodically
sending rain showers across the region.


The cut off upper level low that we will be talking about through at
least the end of the weekend is now over Indiana and will slowly
spiral towards northern Kentucky the next 24 hours.

IR satellite imagery displays a wealth of Atlantic moisture
stretching from the Carolinas towards the southern Mid-Atlantic
region this morning. This moisture will continue to push northward
today as the upper level low slowly drops southward.

A southeasterly LLJ will transport this moisture northwestward
across WNY today, with both early morning isentropic lift, and
convergence along the LLJ bringing lift through the deepening
moisture to produce rain showers. These rain showers will mainly
fall across WNY, with the longest duration over western areas that
are closer to the upper level low, and low level jet axis.

Tonight moisture will contract to near the upper level low, with
rain showers ending from NE to SW across WNY. Lingering showers may
clip far western Chautauqua through the night.

Rainfall totals today and tonight are expected to range from a few
tenths of an inch across Ontario/Wayne/Cayuga to around a half an
inch across the Northern Niagara Frontier, to an inch or more across
the So. Tier.

Though 850 hPa temperatures will be similar today as of Wednesday,
the thicker cloud cover will hold afternoon highs 5-10 degrees
cooler. Highs today will range through the 60s across WNY, but
possibly near 70F east of Lake Ontario where some sunshine this
morning is likely. Tonight lows will drop back to around 50F east of
Lake Ontario, to the low to mid 50s south of Lake Ontario.


On Friday an upper level low is forecast to lift from Kentucky into
Indiana, while high pressure retreats into Northern New England.
This will result in an increasing southeasterly mid-level flow which
will tap into Atlantic moisture. 00Z model consensus is a bit
slower, but there is broad model agreement that showers will lift
into the Western Southern Tier on Friday. This band should weaken as
the upper low stalls across Indiana with showers spreading across
the rest of Western New York late Friday. The Eastern Lake Ontario
region should remain dry on Friday since is is closer to the
departing surface high.

After this, the upper low should remain nearly stationary across
Indiana through Saturday. This will maintain a moist flow across our
region, but showers will be driven by subtle features such as
vorticity maxima pivoting around the upper low. These features are
difficult to forecast this far out, with this uncertainly reflected
by an extended period of mid-range POPs (40 to 60 percent) for
Friday night and Saturday. Model consensus lifts the upper low into
Eastern Michigan Saturday night. This will shift the diffluent flow
aloft northward into the Eastern Lake Ontario region with more
spotty showers elsewhere. Although there is a persistent chance for
showers, expect periods of dry weather too between disturbances.

Rainfall amounts should average between a quarter and half inch
across the Western Southern Tier on Friday. After this, consensus
QPF is on the light side with less than a quarter inch expected in
most locations during the Friday night through Saturday night

Due to the cloud cover temperatures should have a narrow
diurnal range with highs in the 60s and overnight lows in the 50s.
This is near to slightly above normal for this time of year.


The cut-off upper level low is expected to begin tracking from
Michigan eastward across Lake Ontario through Sunday. This track
will continue the threat for some showers across western and north-
central NY as lift produced by the low continues to interact with
Atlantic moisture wrapping into and around the circulation. Model
consensus finally transitions the closed low to an open wave on
Monday. The axis of this trough will cross our forecast area from
northwest to southeast along with residual moisture to continue
chances of scattered showers to start of the work week. During this
48-hour period we are not expecting any significant rainfall
accumulations due to the scattered nature of the showers.
Model consensus QPF during this time is around a quarter inch.

A return to drier weather is then expected by Monday night through
Wednesday as the remnants of the upper low shift off the coast of
southern New England and an amplified 500mb ridge builds over the
eastern States all in response to a deep trough pushing across the
western states. Subsidence beneath this ridge will help scatter out
much of the lingering moisture leading to partly to mainly sunny
skies. Temperatures through the entire long term period will top out
in the mid 60s to low 70s during the day and upper 40s to low 50s
each night.


A southeast flow aloft, and surface easterly flow will spread deeper
Atlantic moisture over the region and bring an area of showers over
the western three TAF sites.

The region remains VFR (So. Tier MVFR) to start the 06Z TAFS, but we
should see additional low clouds within the MVFR flight range (So.
Tier IFR) spread northward through the night with the deepening
Atlantic moisture. In addition to lowering cloud bases, we should
also see an increase in shower activity from the So. Tier at 06Z to
near KROC around 07Z and then KBUF/KIAG between 10Z and 14Z.

With the upper level low remaining to our west over the TAF cycle,
the bulk of the showers will fall along and west Finger Lakes
region. Greatest duration of shower chances will be across KJHW,
with lower duration across KROC. KART airfield shall remain dry and
VFR through the TAF cycle.

Moisture will retreat westward tonight, with shower activity
focusing more upon KJHW for the overnight period. Tonight will
mainly be VFR, with perhaps some MVFR over KJHW and vicinity in
lingering deeper moisture.

Friday...Areas of MVFR with periods of showers.
Saturday through Monday...VFR/MVFR with scattered showers.


High pressure over eastern Quebec this early morning will push
westward towards New England, strengthening a pressure gradient over
the Eastern Great Lakes region between a surface/upper level low to
our west. This will continue a strong easterly flow over the Lakes
today, with small craft advisories continuing for the western half
of Lake Ontario.

There will be enough of a NE component to the wind on Lake Erie that
we could see winds in excess of 20 knots along the southern
shoreline today. Will therefore issue a SCA for Lake Erie today and
into the evening hours.

This northeast flow through the SLV may also top 15 knots on the
river today, and though low confidence, will issue a SCA for the St.
Lawrence River today.

SCA will persist the longest on Lake Ontario where easterly winds
may exceed SCA through Friday night.


MARINE...Small Craft Advisory until 2 AM EDT Friday for LEZ040-041.
         Small Craft Advisory until 2 AM EDT Saturday for
         Small Craft Advisory from 11 AM this morning to 11 PM
         EDT this evening for SLZ022-024.



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