Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 241840

Area Forecast Discussion
National Weather Service Buffalo NY
240 PM EDT Mon Oct 24 2016

Cold northwesterly flow will result in cloudy skies and below
average temperatures into Wednesday along with some scattered lake
effect rain showers. A low pressure system tracking out of the
Midwest is then expected to cross the lower Great Lakes Thursday,
bringing widespread rainfall. Another round of rainfall will be
possible this weekend, as another low pressure system drops across
the region.


IR/WV satellite imagery shows a subtle wave and area of enhanced
moisture over Lake Ontario. As this feature moves east of Lake
Ontario this afternoon, expect scattered lake effect rain showers
downwind of the lakes to increase in coverage into this evening.
Cooler air arrives aloft behind the wave, with 850 mb temps down to -
4C or colder overnight. Equilibrium levels will rise to around 10kft
as the cooler air aloft arrives, and added synoptic moisture from
the wave combined with an upstream lake connect should be enough to
sustain some lake showers. Lake effect showers are near the
Rochester Metro off Lake Ontario, and near the Chautauqua ridge off
Lake Erie this afternoon and evening. Behind the subtle wave passage
tonight, winds will bring the scattered showers back westward toward
the Niagara Frontier an northwestern PA before diminishing into the
day Tuesday. By tonight, temperatures overnight toward early Tuesday
morning may finally support some wet snowflakes in any showers over
higher terrain, however little if any accumulation is expected.
During the day Tuesday, drier air will build into the region,
combined with diurnal heating will help disrupt and break apart any
lingering lake effect.

Temperature-wise, he cold advection will be more noticeable tonight,
as readings fall into the 30s, with lower 30s across the North
County. Temperatures will remain crisp on Tuesday, with highs only
in the low to mid 40s.


Any lingering northwest flow lake effect rain/wet snow showers
will gradually come to an end Tuesday night as high pressure
centered over northern Ontario province ridges south across the
eastern Great Lakes. This high pressure will linger across the
eastern Great Lakes Wednesday supporting mainly fair, dry weather
with temperatures within a few degrees of normal.

Upper level energy off the West coast will track through the Rockies
and into Midwest by Wednesday night, with consolidating upper level
PV leading to cyclogenesis/deepening surface low, with the low then
tracking along or close to the southern Great Lakes. This will
develop widespread precipitation into the area from the west through
the night.

Using a general model consensus (Canadian/GFS/ECMWF), an initially
dry and cold airmass in place to start Wednesday night, thermal
profiles with the lead isentropic ascent/moisture advection closely
supporting the idea of a rain/snow mix east of the Genesee Valley
and all snow east of the Finger Lakes. Some wet snow accumulations
are expected across the higher terrain of the Finger Lakes and
North Country late Wednesday night/Thursday morning.

The low will continue to track east Thursday crossing just to the
north of the region continuing widespread shower activity. Strong
warm air advection pattern on a 50 knot low level jet will change
any snow to rain.

The system will then transfer its energy to a coastal low over the
Gulf of Maine by Thursday night. Wrap around moisture and continuing
cyclonic flow will keep chances of rain showers in play on the back
side of the system. Temperatures will run 10-15 degrees colder than
normal which may allow wet snow to mix with rain showers across the
Tug Hill region Thursday night.


A negatively tilted midlevel trough will deepen enough to generate a
stacked low in the vcnty of northern New England/Maine on Friday.
This will continue a cyclonic/northwest flow of moist chilly air
over our region on the back side of the low with chance POPs for
scattered showers. A minimal lake response should enhance coverage
and possibly the intensity of some of these showers southeast of
Lake Ontario. Weak ridging is forecast to quickly push east across
the Lower Great Lakes Friday night with a short window of dry time

00z guidance is in better agreement with EC and GFS showing another
compact fast moving shortwave trough quickly dropping across the
Great Lakes. This should drive another low and round of widespread
showers for Saturday. Have kept chance POPs due to uncertainty in
the exact timing.

On Sunday weak ridging will shift across our region from the
central/northern plains states with any lingering showers tapering
off. A wavy zonal midlevel flow will help return temperatures back
toward normal late October levels through the weekend.


Persistent cold cyclonic northwesterly flow across the Great
Lakes will continue to generate plenty of VFR cigs across the
forecast area through the TAF period, and a few lake effect rain
showers will be possible at times across the far western Southern
Tier, as well across areas south of Lake Ontario. Cigs may drop to
MVFR in these showers, but otherwise cigs will remain VFR
elsewhere through the TAF period.


Tuesday and Tuesday Night...Mainly VFR.
Thursday...MVFR/IFR with rain showers likely.
Friday and Saturday...MVFR with a chance of lake effect showers.


Cold air advection in the northwesterly flow will keep a stiff
breeze in place on the lakes into Tuesday. Small craft advisories
remain in effect, as northwesterly winds 15 to 25 knots will keep
waves along the south shores of the lakes.

The brisk northwesterly flow is expected to persist into Tuesday
evening, at which point a broad surface ridge extending from a high
centered over James Bay progresses across the lower Great Lakes,
bringing another short-lived respite from small-craft advisory
conditions. Expect easterly flow to develop Wednesday and freshen
into Thursday, as another low pressure system tracks out of the
Midwest and across the lower Great Lakes.

High pressure will briefly ridge across the lake on later Tuesday
but another fast moving storm system will arrive Wednesday night
into Thursday.


MARINE...Small Craft Advisory until 9 AM EDT Tuesday for LEZ040-041.
         Small Craft Advisory until 6 PM EDT Tuesday for
         Small Craft Advisory until 9 AM EDT Tuesday for LOZ045.



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