Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 241229

Area Forecast Discussion
National Weather Service Buffalo NY
829 AM 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.


Cold cyclonic flow across the Great Lakes is generating plenty of
cloud cover downwind of the lakes this morning, as evidenced by
regional satellite imagery. Upstream, lake effect rain showers have
begun off of Lake Superior and Lake Michigan across the Michigan
Upper Peninsula and northern Michigan, where 850 mb temps have
already fallen below -4C. IR satellite imagery shows a subtle wave
and area of enhanced moisture nearing northern Lake Huron and the
Georgian Bay. As this feature approaches Lake Ontario by mid-day,
expect to see an increase in scattered lake effect rain showers
downwind from the Georgian Bay into the Niagara Frontier initially,
and downwind of Lake Huron into northwest PA. 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. As this
subtle wave tracks through the region, expect all the lake effect
showers to shift eastward toward the Rochester Metro off Lake
Ontario, and toward 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.

Temperature-wise, the ongoing cold air advection across the forecast
area means that temperatures will climb little from present readings
today, with temperatures remaining in the upper 40s to lower 50s
throughout the day. The cold advection will be more noticeable
tonight, as readings fall into the 30s, with lower 30s across the
North County.


High pressure centered over northern Ontario province will ridge
south across the eastern Great Lakes Tuesday and Tuesday night. This
will effectively bring an end to any scattered lake effect southeast
of the lakes as lake-induced ELs fall from 10-15kft Tuesday morning
to less the 5kft by Wednesday morning. P-type should be mainly rain
showers with a slight chance of some wet snow flakes mixing in
across the higher terrain where overnight temps fall toward
freezing. Breezy winds under a cool northwest flow is also forecast.
This high pressure will linger across the eastern Great Lakes
Wednesday supporting mainly fair dry weather with temperatures
within a few degrees of normal.

A deepening storm system over the Midwest states on Wednesday will
shift across OH Wednesday night. This will bring an increase in
cloud cover and chances of rain showers over and west of the Genesee
Valley. While showers that arrive should mainly be in the form of
rain, there is a slight chance for some wet snow mixing in across
the higher terrain of the Southern Tier into the Bristol Hills.

The storm system will track right over Buffalo on Thursday with a
sharp shortwave trough aloft and strong 50kt low level jet driving a
likely probability of widespread rain showers. The storm will then
transfer its energy to a coastal low over the Gulf of Maine 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...MVFR with a chance of lake effect showers.


After a brief relative lull overnight, northwesterly flow will
freshen across the lower Great Lakes today as cold advection
strengthens and the gradient tightens between low pressure drifting
into the Gulf of Saint Lawrence and high pressure over the central
Great Lakes. Small craft advisories remain in effect, as
northwesterly winds will freshen to 15 to 25 knots, building 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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