Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 250027
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
727 PM EST Fri Nov 24 2017

.SYNOPSIS...
Low pressure near James Bay will track across northern Quebec
tonight and Saturday. After a dry night tonight...the low will push
a weak cold front across the region on Saturday along with a few
showers. Cooler air filtering in behind the front will then change
rain to snow showers Saturday night, with limited lake effect snow
showers then expected southeast of the lakes later Saturday night
and Sunday.

&&

.NEAR TERM /THROUGH SATURDAY/...
Tonight high pressure draped across the Mid Atlantic states will
slide east and off the Atlantic coastline...while a 985 mb low near
James Bay pushes into northern Quebec and drags its trailing cold
front into Southern Ontario. With our area thus remaining firmly
within the deep southwesterly flow of mild air between these two
systems...we can expect a quiet and dry night with just some increase
in mid and high cloud cover as the night progresses. Temperatures
will also remain on the mild side for late November...with the
ongoing warm advection pattern and expected increase in mid and
high cloud cover also leading to a non-diurnal temperature trend
in many locations.

On Saturday the cold front will push across the area during the
morning, with the boundary passing off to our east by midday/early
afternoon. While the front will supply a brief period of decent
forcing as it passes...moisture depth along the boundary looks
to be at least somewhat lacking...thus any frontally-driven showers
should remain largely scattered in nature. Behind the boundary...
steady cold air advection will lead to steady or slowly falling
temperatures during the course of the afternoon...and will also
lead to some additional lake and/or orographically-driven rain
showers east and southeast of the lakes as some degree of low
level moisture will remain.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
A weakening arctic frontal boundary will push south across the
forecast area Saturday night. While there will be scattered light
snow showers ahead of and along the front...the most concentrated
areas of snow will be found southeast of both lakes where some lake
enhancement will come into play. Despite the lake effect...snow
accumulations are not expected to exceed two inches.

Surface based ridging centered over the Ohio Valley on Sunday will
nose northeast across the Lower Great Lakes. The onset of the
corresponding warm advection will weaken the already unimpressive
lake snows while the remainder of the region will enjoy fair
weather.

The lake snows east of Lake Ontario will re-intensify Sunday
night...as westerly winds will become better aligned and the cap
rises a few thousand feet ahead of the next cold frontal boundary.
Given that the cap will still be under 10k ft...do not expect snow
accums on the Tug to exceed a couple inches.

Broad ridging over the Upper Great Lakes Monday morning will drift
east across the Ohio Valley and Lower Great Lakes Monday afternoon
and night. While this will keep uneventful weather in place...the
moderately strong warm advection with the ridge will set the stage
for above normal temperatures for the ensuing couple of days.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
There is high confidence that temperatures will average above normal
for our region during this period. While this will not be unusual in
itself...it will be given the forecast hemispheric pattern. A rather
strong Greenland block will be in place...but rather than having a
closed upstream low over eastern Canada...the flow will be
progressive and pacific in nature. This will keep true cold air
locked north of 50N...with only brief...transitory visits of chilly
air. It also does not help that the coldest air in the northern
hemisphere is on the other side of the pole. On a day to day
basis...

A broad southwest flow ahead of the next Pacific cold front will
boost H85 temps into the upper single digits C...and this will allow
max temperatures to climb into the 50s F for all but the North
Country. As the Pacific cold front pushes through the region Tuesday
night...there will be the chance for some mixed precipitation...but
nothing that should result in any problems.

Being in a fast...low amplitude pattern...systems will change out
fairly quickly. This will certainly be the case Wednesday as ridging
will waste no time in building across our region in the wake of the
front. This will provide our area with another fairly nice day with
temperatures reaching into the 40s.

The weather will get a little more interesting on Thursday...as a
robust Pacific shortwave crossing the Upper Great Lakes will steer a
deepening storm system by to our north and west. This will place our
region on the warm side of the storm system...with only some rain
showers to contend with.

&&

.AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
Dry VFR conditions will prevail across the region tonight...under
gradually increasing mid and high clouds out ahead of the next weather
system. This said...a 45-50 knot southwesterly low level jet will
also help to produce LLWS concerns at all TAF sites...with this
not subsiding until after sunrise Saturday morning.

On Saturday low pressure tracking across northern Ontario will push
its trailing cold front across the area during the morning. Scattered
rain showers will accompany the passage of the front...with additional
scattered to numerous rain showers then expected east and southeast
of the lakes in the afternoon as lake effect and orographic influences
come into play. Otherwise...increasing amounts of low level moisture
along and behind the front will result in flight conditions lowering
to MVFR/IFR during and immediately following its passage...before
conditions tend to improve back to VFR/MVFR later in the day.

Outlook...
Saturday night...Localized MVFR/IFR in lake effect snow showers
southeast of the lakes...otherwise VFR/MVFR.
Sunday...Mainly MVFR, localized IFR in -SHSN SE of the lakes.
Monday through Wednesday...VFR.

&&

.MARINE...
Brisk south-southwesterly winds ahead of a storm system tracking
from James Bay into northern Quebec will remain in place across Lake
Erie and the far ends of Lake Ontario tonight...for which Small Craft
Advisories remain in place. Meanwhile toward central Lake Ontario...a
slightly lighter wind field will allow for a brief period of non-SCA
conditions.

The low will then cross northern Quebec on Saturday...and will swing
an initial cold front across the Lower Great Lakes Saturday...followed
by a secondary cold front Saturday night. The tightening pressure
gradient associated with these latter features will result in a prolonged
period of fairly widespread advisory-level conditions on both lakes...
with conditions not really improving until high pressure builds across
the region on Monday.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
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 4 AM EST Monday for LOZ042-
         045.

&&

$$

SYNOPSIS...JJR/TMA
NEAR TERM...JJR/TMA
SHORT TERM...RSH
LONG TERM...RSH
AVIATION...JJR/TMA
MARINE...JJR/TMA



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