Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 232359

Area Forecast Discussion
National Weather Service Buffalo NY
759 PM EDT Tue May 23 2017

A weak ridge of high pressure will provide for mostly dry conditions
tonight. An weak mid level disturbance may bring a few showers to
the western Southern Tier and possibly an isolated shower to the
North Country on Wednesday. A stronger low will then produce more
widespread rain across the entire region later Wednesday night and
Thursday, with unsettled conditions lasting through Friday.


The diurnal cumulus from earlier this afternoon have mainly
dissipated this evening as the boundary layer begins to cool and
stabilize. High/thin cirrus will continue to slowly increase from
south to north as upper level moisture streams northward out of PA,
but these should remain thin enough to call the sky condition partly
cloudy in most areas through the bulk of tonight.

Most of the night will remain dry, however attention will be upon a
weak mid level shortwave which should reach the southwest corner of
NY by late tonight or early Wednesday morning. This feature,
combined with increasing atmospheric moisture will bring a chance
for a rain shower very late tonight and Wednesday morning across the
western Southern Tier, with the greatest chances across Chautauqua
County. Later in the day this shortwave, combined with minor
afternoon instability of 500 J/KG of CAPE will bring a chance for a
shower or two across the higher terrain east of Lake Ontario as
well. Otherwise the rest of the area should remain dry on Wednesday
with a mix of clouds and limited sun.

Tonight clouds will begin to increase somewhat, which will limit the
cooling. Overnight lows within a southeast wind will range from the
upper 40s to mid 50s, with the coolest readings in the interior
Southern Tier valleys and east of Lake Ontario, and the warmest
readings along the lake plains. Wednesday southeast winds across WNY
will bring mid to upper 70s on the lake plains with an added boost
from downslope flow, while a light east wind across the north
country within a similar airmass will promote highs in the low to
mid 70s. Northeast winds will keep the south shore of Lake Ontario


The deep closed low over the middle Mississippi Valley Wednesday
evening will track slowly across the Central Appalachians Thursday
to the Gulf of Maine by Friday afternoon. A complex surface low
occlusion over the Ohio Valley Wednesday night will lift northeast
as secondary development takes place from the Mid Atlantic to the
New England coast by Friday. Despite some model differences in
track/placement of these feature there is agreement that the
Wednesday night into Thursday night time frame will be a wet one.
Plenty of deep layer moisture and forcing in the front flank of the
of the system will generate a solid period of soaking rain, with
most areas receiving a general half inch to an inch of rainfall.
While forcing with the incoming system is impressive, instability is
not. Therefore, thunder chances remain rather subdued.

Precipitation will transition to showers Thursday night into Friday,
as the low moves overhead and past the forecast area, though
scattered to numerous showers should linger thorugh much of the day
on Friday, thanks to continued troughing across the area, coupled
with wrap-around moisture. Shortwave ridging moving into the region
in the wake of the departing low pressure system Friday night should
put an end to the showers.

This will be a cool period as plenty of cloud cover and rainy
conditions will help to suppress temperatures with highs both
Thursday and Friday likely not getting out of the 60s, with lows in
the 50s during the nights.


Upper level ridging crossing the region should result in generally
dry conditions on Saturday, though moisture moving through the top
of the low-amplitude ridge just might generate a shower or two, so
have low slight chance pops in place for now. A northern stream wave
diving across the upper Midwest and Great Lakes out of Canada will
bring the next likely round of showers to the forecast area on

The location and timing of the various vorticity maxima
rotating around the upper low, in addition to additional upper level
energy moving thorugh the longwave trough that will be re-
established across the east will determine the specific timing of
rounds of showers as we move into next week, and it is too far out
to pinpoint these kinds of details. However, given aforementioned
longwave troughing becoming re-established across the Great Lakes
and Northeast, suffice it to say that the coming week will trend
towards the cool and showery.


VFR conditions will prevail tonight and Wednesday. High cirrus level
cloudiness will cross the region tonight, with an increase in
somewhat lower VFR level cloudiness late tonight and early Wednesday
across the western Southern Tier. A few scattered showers may cross
the Southern Tier Wednesday, especially in the morning. An isolated
shower also cannot be ruled out across the eastern Lake Ontario
region in the afternoon. Otherwise the rest of the area will remain
dry, with cirrus and mid level VFR cloudiness slowly increasing.


Wednesday night...VFR/MVFR with rain developing.
Thursday...VFR/MVFR within rain. Some IFR conditions late across
the So. Tier.
Friday...IFR to VFR with a chance of showers.
Saturday...Mainly VFR.
Sunday...MVFR/VFR in likely showers.


High pressure will maintain light winds and minimal wave action
tonight. Tomorrow winds will become southeasterly across Lake Erie,
and ENE across Lake Ontario, with wave action limited to around 2
feet at the west end of Lake Ontario later Wednesday and Wednesday

Thursday ENE winds will become a bit stronger as a storm system
tracks through the Ohio Valley and towards western Lake Erie. This
flow may generate higher waves on Lake Ontario with Small Craft
conditions probable on the western half of the lake, with lesser
wave action on the east end of Lake Ontario and Lake Erie.


ENE winds will increase somewhat Wednesday and Wednesday evening
on Lake Ontario into the 12-15 knot range, generating waves
averaging about 2 feet on the west end of the lake.

Low pressure will then move from the Ohio Valley to western Lake
Erie later Wednesday night and Thursday. Meanwhile weak high
pressure will remain across Quebec and northern New England. The
ageostrophic component between the two systems will support
increasing ENE winds on Thursday for Lake Ontario, with winds
possibly reaching 20 knots for a good part of the day. The
ageostrophic component also tends to force the winds to have a
little more NE component than model forecasts. With this in
mind, it appears another higher impact day of lakeshore flooding
and shoreline erosion is probable along the south shore of Lake
Ontario west of the Genesee River. A lakeshore flood watch has
been issued for Thursday for the Lake Ontario shore of Niagara,
Orleans, and Monroe counties.


NY...Lakeshore Flood Watch from Thursday morning through Thursday
     evening for NYZ001>003.



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