Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 031124
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
624 AM EST Sat Dec 3 2016

.SYNOPSIS...
Nuisance lake effect rain and snow showers southeast of Lakes Erie
and Ontario will gradually fall apart today and tonight as high
pressure builds across New York State. A few periods of rain and
snow will then follow through the middle of next week...before
much colder air arrives late in the week and brings an increasing
potential for significant lake effect snow downwind of the lakes.

&&

.NEAR TERM /THROUGH TONIGHT/...
During the near term period...scattered lake effect rain and
snow showers southeast of the lakes will gradually diminish as
high pressure builds eastward across New York State...and brings
about a lowering subsidence inversion and significant drying within
the prime dendritic snow growth zone. Marginal temperature profiles
will again mean that ptype within the weakening activity will be
heavily dependent upon elevation and to some degree the diurnal
cycle...with rain predominating across the lower elevations and
wet snow more favored across the higher terrain...before possibly
ending as some spotty drizzle due to the aforementioned loss
of moisture from the dendritic snow growth zone. Given the light/
scattered nature of the activity...any additional localized slushy
accumulations across the higher terrain should be under an inch.
Outside of the main lake effect areas...mainly dry and mostly cloudy
conditions should prevail as lingering low level moisture becomes
increasingly trapped under the sharpening subsidence inversion.

With respect to temperatures...925 mb temps will be on the order
of -1C to -4C today...and will be supportive of afternoon highs
ranging from the mid 30s across the higher terrain to around 40
across the lake plains. Lows tonight will then range from the
lower to mid 20s across the North Country to the upper 20s and
lower 30s elsewhere...with the warmest readings found right along
the immediate lakeshores.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/...
While no major weather concerns are anticipated during this
period...we will have to contend with a pair of mixed pcpn events.
This will be accompanied by above normal temperatures...but don`t
expect the Fall like weather to continue much longer as a
significant pattern change is on the horizon.

As we open this three day stretch on Sunday...leftover lake effect
showers southeast of both lakes will be grudgingly coming to an end.
This prolonged event has never been more than a nuisance as it has
been plagued by limited synoptic moisture...marginal instability and
a relatively low cap. As we progress through the first half of
Sunday...ridging crossing the Lower Great Lakes will essentially
squash the remaining mesoscale activity as the cap will drop to less
than 5 k ft. Meanwhile...surface high pressure will provide the bulk
of the region with at least partial sunshine. The fair weather will
be short lived though...as moisture will start to stream back across
the region during the afternoon. There could even be a few light
showers across the southern tier by dinner time.

Conditions will deteriorate Sunday night as a negatively tilted
trough...in the process of shearing out...will sweep northeast
across all of the Great Lakes region. While there will be some
lift provided by a diffluent upper level flow...the overall dynamics
with this feature do not look very impressive. Nonetheless...expect
light precipitation to overspread the region...mainly in the form of
snow. A light coating is possible across the lake plains...mainly on
grassy surfaces due to marginal surface temperatures...while an inch
or 2 will be possible across the higher terrain where surface
temperatures will remain below freezing.

As the shearing trough exits to our northeast on Monday...drier mid
level air will arrive in its wake while ridging will become re-
established over the region. This will encourage the light snow from
the previous night to taper off and end as a mix of rain and wet
snow showers by midday. While not significant...the mixed showers
will linger a bit longer east of Lake Ontario due to a little lake
enhancement. Daytime snow accumulations will be insignificant...
although an inch or two will be possible across the Easter Lake
Ontario region and particularly on the Tug. Temperatures Monday
afternoon will climb to within a couple degrees of 40.

High pressure passing over the region Monday night will promote fair
dry weather across our forecast area...with only a slight chance
for some flurries or light snow showers southeast of Lake Ontario.

As the axis of the surface high pushes east across New England on
Tuesday...a storm system within the southern branch of a split flow
will track northeast from the Tennessee Valley. While the strongest
dynamics with this feature will stay to our south...moisture will
stream northward across our region. This will result in thickening
cloud cover during the course of the day with the northern periphery
of the associated pcpn shield likely advancing to the Western
Southern Tier. The pcpn should start off in the form of light
rain...however a little wet snow is not out of the question.

Tuesday night...a weakening sfc low will make its way northeast
across our forecast area. While the dynamics will be unimpressive...
there will be enough forcing to generate some light mixed
precipitation. A small slushy snow accumulation will be possible
across the elevated terrain.

&&

.LONG TERM /WEDNESDAY THROUGH FRIDAY/...
A major pattern change will take place across the continent during
this period...as a pair of robust shortwaves ejecting out of a deep
storm system over the Gulf of Alaska will carve out a deep longwave
trough over the Lower 48. This progressive trough will initially
take shape over the Inter-mountain West. As we advance through the
second half of the week though...reinforcing shortwaves rotating
around the periphery of the parent closed low will deepen the trough
while helping to push it across the Great Lakes region. This will
coincide with a ridge that will dominate the Pacific Northwest and
Canadian Rockies. The combination of the two synoptic features will
produce an extended northerly flow that will tap an airmass that
will have been allowed to take on arctic like qualities over Alaska
and the Yukon.

H925 temps of -24 to -28c will thus be directed southward along the
foothills of the Canadian Rockies to the northern plains...and
eventually to the Ohio Valley. While this airmass will most
certainly lose a lot of its bite by the time it will impact our
region late in the week...it could still pack a punch in terms of
supporting significant lake snows towards the end of this forecast
period. To be fair...the various medium range ensembles have been
anything but consistent between themselves and even from run to run.
This will seriously work against providing much detail from this
range...although there is fairly high confidence in the general
trend to notably colder weather and the likelihood that significant
lake snows will be found across the Lower Great Lakes by late in
the forecast period.

In the meantime...a weak shortwave will exit our region on
Wednesday. This will bring an end to the steadier light snow with
only some nuisance mixed rain and wet snow showers left for the
midday and afternoon. Temperatures Wednesday are expected to reach
into the 40s.

Conditions will then significantly deteriorate late Wednesday night
and Thursday...as the strong cyclogenesis that will mark the phasing
of the overlying pattern will result in a deepening storm system
that will track from the Ohio Valley across our forecast area.
Again...the timing and exact track of this winter storm has yet to
be pin pointed so low confidence will be given to pcpn type. There
is fairly high confidence though that Thursday will be quite
unsettled.

Friday should be notably colder with lake snows likely impacting a
portion of our forecast area. The details will be ironed out in the
coming days.

Looking further down the road towards the middle of the month...
there are some ensemble members of both the GEFS and ECMWF that
suggest a displacement of the polar vortex. Rather than this ever
present feature remaining in the vcnty of the Pole...where it has
been the past couple weeks...some ensembles place at least a portion
of this mid level circulation just northwest of Hudson Bay. This
would be a change of more than a 1000 miles and could be supportive
of more persistent colder weather over our region during the coming
weeks.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
During the TAF period...scattered lake effect rain and snow showers
southeast of the lakes will gradually diminish as high pressure builds
across New York State. Conditions will largely be MVFR within the
diminishing lake effect activity...outside of it conditions will be
VFR with some temporary fluctuations to MVFR possible at times.

Outlook...
Sunday...Mainly VFR.
Sunday night...IFR/MVFR with a period of light snow likely.
Monday...MVFR with a chance of rain and snow showers.
Tuesday and Wednesday...VFR deteriorating to MVFR with some
rain becoming likely.

&&

.MARINE...
Lingering brisk northwesterlies will gradually diminish today and
tonight as high pressure builds eastward across New York State.
To cover wind and wave conditions still exceeding advisory levels...
small craft advisories remain in effect as outlined below.

After that relatively quiet boating conditions will be in place
from Sunday on through midweek...before winds and waves likely
build to advisory levels again late in the week following the
passage of another low pressure system.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory until 7 PM EST this evening for LEZ040-
         041.
         Small Craft Advisory until 4 AM EST Sunday for
         LOZ043>045.
         Small Craft Advisory until 7 PM EST this evening for
         LOZ042.

&&

$$

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



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