Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 241132

Area Forecast Discussion
National Weather Service Buffalo NY
632 AM EST Fri Nov 24 2017

High pressure will bring a mostly sunny, breezy and dry day today,
before clouds increase tonight ahead of a cold front that will bring
chances for showers late tonight and Saturday. Cooler air behind the
front will change rain to snow showers Saturday night, with limited
lake effect snow southeast of the lakes Sunday.


High pressure is located over the eastern U.S. this morning,
centered across the mid-Appalachian region. Drier air associated
with the surface high is eroding the flat stratus clouds. Clearing
has reached SW NYS and this clearing will expand across WNY this
early morning, and east of Lake Ontario late morning.

We will be slowly warming aloft today and tonight. This warming
coupled with southerly flow will bring afternoon temperatures into
the lower 50s across the lake plains, and upper 40s across the
higher terrain. A 40 to 45 knot LLJ around 2K feet over WNY will mix
to the surface this afternoon, bringing wind gusts 25 to 40 mph with
highest gusts near Lake Erie.

High level clouds will begin to increase tonight, but remain thin
enough to allow evening temperatures to fall into the low to mid
40s. A cold front will advance across the Great Lakes region Friday
night, reaching near Lake Erie by 12Z Saturday. Southerly flow
remaining across the region will bring a mild overnight with
temperatures possibly rising a few degrees over the second half of
the night across the western areas as clouds thicken. Rain showers
ahead of the cold front are possible very late tonight, especially
near the lakes. Moisture may struggle to push into our region with a
deep dry layer established today...and thus will continue with
chance PoPs for showers.


On Saturday a mid level trough and a weak cold front will move
across the region. There will be some light showers along the
leading edge of this shortwave Saturday morning, but after this
forecast soundings suggest dry mid-level air behind this shortwave.
Although the cold front and upsloping will generate some low level
lift, cloud tops may not be cold enough to support anything more
than drizzle Saturday afternoon. This will result in light amounts,
probably less than model QPF guidance. Highs on Saturday will be in
the 40s.

There has been a subtle shift in model guidance after this with most
guidance dropping two weak cold fronts into the area rather than one
stronger one. This will result in a lake response behind each cold
front, first on Saturday night and again late Sunday into Sunday
night. In each case, a sharp north to south thermal gradient will
support more organized lake effect activity off Lake Ontario than
Lake Erie.

Temperatures aloft will cool to around -9C at 850mb Saturday night,
with an increase in lake effect activity and a gradual change over
from rain to snow. Snow showers will taper off Sunday morning with
the departure of the shortwave and associated mid-level moisture.
Any snow accumulations will be light, generally in the 1-2 inch
range southeast of Lake Ontario and across higher terrain in the
Western Southern Tier.

Following a brief lull mid-day Sunday, another shortwave will
approach late in the day with the flow shifting from NW to WSW ahead
of an approaching surface front. Another round of lake effect should
develop east of the lakes, with temperatures marginal but mainly
cold enough to support snow showers. More light accumulations are
possible east of Lake Ontario on the Tug Hill with rain mixing in
along the immediate lakeshore. Precipitation will taper off late
Sunday night with the departure of the shortwave. While
accumulations are expected to be on the lighter side, it still could
make untreated roadways more difficult to navigate.


Surface and mid-level ridging will build across western and central
New York Monday. Outside of a slight chance for a lingering shower
east of Lake Ontario, expect dry weather with low clouds breaking
for some sun. Temps with the ridging aloft will make a run into the
low 40s across WNY but likely linger in the 30s east of Lake Ontario.

The surface and mid-level ridge axis shift overhead Monday night
with a warm front also lifting north of Lake Ontario. The front
looks too far north to bring any risk of showers Monday night. A
southerly flow will bring warmer air into the region with highs
reaching into the 50s in many locations. The models do show a strong
50 knot low level jet crossing our region Tuesday which could lead
to some gusty winds with diurnal mixing.

A weak cold front associated with low pressure near James Bay will
approach the region Tuesday night. Model guidance differs on the
strength of the boundary with the ECMWF largely washing out the front
while GFS/GGEM guidance keep it together a bit longer. The forecast
maintains low chance PoPs for the front Tuesday night into
Wednesday. Surface temps on Wednesday have some bust potential with
the spread in the timing and location of the cold front. Have leaned
toward a blend of guidance for now yielding mid to upper 40s for

Generally expect Thursday to be dry with models forecasting a quick
moving surface high pressure behind the front/trough. Have included
slight chance POPs as the GFS shows enhanced moisture shifting north
form the Mid Atlantic north of a mid-level cut off low. Temps should
be close to seasonal averages with highs in the low to mid 40s
unless cloud cover/showers do work out as the GFS suggests.


For the 12Z TAFS, flight conditions are mainly VFR, with a few
pockets of MVFR in diminishing lake effect clouds.

Clouds will thin through the morning hours, with a period of VFR
flight conditions through the remainder of the day and tonight. It
will be breezy this afternoon...and a developing LLJ of 40-45 knots
at 2K feet will yield some LLWS this evening after winds decouple.

Clouds will increase tonight ahead of the next weather system, with
cirrus thickening and mid level clouds approaching. A spot rain
shower is possible very late tonight.


Saturday...VFR/MVFR with rain showers likely.
Sunday...Mainly MVFR, localized IFR in -SHSN SE of the lakes.
Monday and Tuesday...VFR.


Small craft advisories will remain in place today on the lakes and
upper Niagara River...with some of these advisories remaining in
place through Monday morning. Southerly winds ahead of a storm
system cutting through the Great Lakes will be strongest on Lake
Erie, as well as the far ends of Lake Ontario today. Towards central
Lake Ontario a slightly lighter wind field will allow for a brief
period of non-SCA conditions.

This low will cross Ontario and Quebec through Saturday with a
trailing cold front crossing the Eastern Great Lakes region
Saturday, and a secondary cold front Saturday night that will bring
a prolonged period of SCA conditions to Lake Erie, and the far
western and eastern sections of Lake Ontario.

It will not be until a ridge of surface high pressure crosses the
lakes later Monday that winds and waves will fall under advisory
levels on both lakes.


MARINE...Small Craft Advisory until 4 AM EST Monday for LEZ040-041.
         Small Craft Advisory until 10 AM EST Saturday for LEZ020.
         Small Craft Advisory until 10 AM EST this morning for
         Small Craft Advisory until 4 AM EST Monday for LOZ042-045.



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