Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 272023

Area Forecast Discussion
National Weather Service Buffalo NY
423 PM EDT TUE SEP 27 2016

An upper-level low over the upper Great Lakes will drift south
toward the Ohio Valley tonight and Wednesday. Cooler air across the
region will spark a few scattered lake effect rain showers northeast
of Lake Erie this evening, with otherwise mainly clear and breezy
conditions. After a mainly dry day Wednesday, this slow moving upper-
level low will then bring unsettled weather to our region for the
rest of the week and next weekend.


Water vapor satellite imagery shows a large upper-level low spinning
over the upper Great Lakes with several small scale spokes of
enhanced vorticity with associated deeper moisture and ascent
pivoting from western Lake Erie toward western NY. Upstream radars
show little in the way of rainfall associated with these small scale
vorticity maxima, but they will act to create a somewhat more
favorable environment for lake effect rain showers during the
evening. The enhanced moisture and ascent will briefly raise lake
induced equilibrium levels to over 10k feet between 00Z-03Z Wed over
eastern Lake Erie. The low levels remain quite dry, but may moisten
enough to allow a few scattered showers to develop for a few hours.
Mean boundary layer flow direction from the SSW would favor Niagara
County and Grand Island if these showers were to develop. Inversion
heights lower, and moisture diminishes overnight so if any lake
effect showers develop, they will end by shortly after midnight.

Otherwise, most of forecast area including Rochester, the northern
Finger Lakes and the North Country will see a mostly to partly clear
evening. The southwest winds supported by the surface low will also
remain gusty through the early evening mainly from the Lake Erie
shore and Niagara Frontier east to Rochester, and will diminish with
the loss of solar insolation tonight. Temperatures tonight will fall
into the mid 40s to lower 50s.

A dry day is in store for all on Wednesday as the upper-level low
settles over northern Indiana. Initially limited moisture and
forcing staying clear of our area will allow for a dry day, however
as Atlantic sourced air is pulled northwestward by the low, we will
see increasing cloud cover from south to north across the region.
Temperatures will also moderate with the developing easterly flow
from the Atlantic, as 850 mb temperatures climb to near +10C. This
will result in a pleasant day, with high temperatures mainly in the
low 70s. Bottom line, Wednesday will be a great day to get any
outside work done before a long stretch of unsettled weather through
the end of the work week (more on that below).


An upper level low will meander from Indiana down into Kentucky and
back into Indiana during this period as it encounters a stout
blocking ridge over the Western Atlantic. This will result in mild
and showery weather across much of Western and North-Central New
York for the latter half of the week as the area comes under the
influence of a easterly conveyor belt of maritime air advecting in
off the Atlantic around the northeastern flank of the broad low to
our southwest over the upper Ohio valley.

Shower chances will gradually increase as we move from Wednesday
evening into Wednesday night as east-southeast flow begins to become
better aligned across the Mid-Atlantic states. The easterly surface
flow down the axis of Lake Ontario combined with relatively cool
temperatures aloft, around +9C, should yield a decent lake response,
producing considerable rainfall across the Golden Horseshoe in
Ontario province, however lake effect showers should largely spare
the New York side of the border, though showers may begin to affect
areas along the Lake Ontario shoreline as we move into Thursday
morning and flow begins to back to the northeast. Temperatures
overnight will reflect the mild airmass advecting into the region
and increasing cloud cloud cover, with temperatures only falling
into the mid to upper 50s.

The period of most significant rainfall across the forecast area
will likely be on Thursday, when the core of the easterly low level
jet arrives over the area, representing the maximum of the moisture
advection and isentropic lift across the region. Expect widespread
rain showers with periods of moderate rainfall, with general
rainfall around a half inch to an inch, with localized heavier
amounts. Lowest pops and QPF will be found across the North Country,
where the northeasterly flow will limit moisture advection. Higher
amounts will be found in the Niagara Frontier near the Lake Ontario
shoreline, where lake enhancement will come into play.

While the heaviest rains are expected on Thursday, when
southeasterly flow across the area will be maximized, the persistent
proximity of the low and general southeasterly orientation of flow
across the area will keep showers in play through the end of the
week. Regarding temperatures, expect readings to remain within a
couple of degrees of climatology during the day, with highs in the
mid to upper 60s, while overnight readings will remain above
average thanks to the abundant cloud cover, with lows in the 50s.


A slow improvement can be expected in our weather during the course
of the weekend and particularly as we push into the new work week.
The mid latitude blocking pattern that will have plagued our region
for several days is forecast by the majority of the medium range
ensemble members to gradually fill and lift out across the Lower
Great Lakes and eventually the St Lawrence Valley during this time
frame. The general northward drift to the previous stalled system
will short circuit the feed of Atlantic moisture that will have
become common...while drier air will gradually work its way into our
region from the Ohio Valley and Mid Atlantic region. This will lead
to a day to day diminishing of the amount...and areal coverage of...
the scattered shower activity.

Meanwhile...temperatures will average just a little above normal.
This will largely come as a result of overnight lows being in the
50s. Afternoon temperatures will generally be in the mid to upper

Looking further head towards the middle of the week...there is
moderately high confidence that a burgeoning ridge will amplify
across the eastern half of the country in the wake of the departing
mid level closed low. This should allow for fair dry weather to
return in earnest Tuesday and Wednesday with day to day warming.


Widely VFR conditions will prevail today and tonight, with gusty
southwest winds to around 25 knots through early evening (highest in
the Niagara Frontier KBUF/KIAG with up to 30 knots). The only
exception to the mainly VFR conditions will be a few scattered lake-
effect rain showers that may redevelop near KIAG this evening, and
could result in some temporary local MVFR/IFR restrictions.

Wednesday...VFR...with just a chance of showers late near KJHW.
Wednesday night through Sunday...VFR/MVFR with periodic rounds of
scattered to numerous showers.


A brisk southwesterly flow of cooler air will produce continued
advisory-worthy winds and waves on Lake Erie through this
evening...before slackening through the remainder of the night.
Conditions on Lake Ontario will continue to improve this evening
with diminishing winds and waves.

After a brief respite overnight and Wednesday morning...a brisk
easterly flow will develop across the Lower Lakes region between
later Wednesday and Thursday morning...then will persist through
the end of the work week. This will likely require the issuance of
another round of small craft advisories sometime tonight. Chance for
waterspouts will return Wednesday night on both Lakes Erie and


MARINE...Small Craft Advisory until 2 AM EDT Wednesday for LEZ040-041.
         Small Craft Advisory until 8 PM EDT this evening for



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