Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 211934

Area Forecast Discussion
National Weather Service Buffalo NY
234 PM EST Wed Feb 21 2018

In the wake of a strong cold front...lingering light rain will
steadily diminish this afternoon...while much cooler air finishes
overspreading our region. A weak system passing by to our south will
then bring some limited mixed precipitation...then an accumulating
snowfall to the Southern Tier and interior portions of the Finger
Lakes later tonight and Thursday. Yet another low pressure system
will then bring another round of mainly rain to our area on Friday.
Otherwise...temperatures will still remain near to above normal
through the end of the week.


As of mid afternoon the cold front has completely cleared our area...
with most locations (aside from far southeastern sections) having
already seen temperatures drop into the upper 30s and lower 40s.
Expect those areas still experiencing warmer readings to see the
same within the next couple of hours...with fairly steady or slowly
falling temps then expected for the balance of the day. With respect
to precipitation...the previously large area of rain behind the front
continues to disintegrate into some remnant patchy light rain...and
this trend will also continue through the rest of the day with the
precip pretty much tapering off altogether by sunset.

Tonight and Thursday...strong Canadian high pressure will build
eastward across the Great Lakes and into Southern Quebec...while a
wave of low pressure passes by to our south across the Ohio Valley
and Virginias. While some model disagreement still persists on the
exact track and northward extent of this latter general
the 12z guidance has come into better overall agreement on the above...
with the latest GFS still a bit weaker/further south...but also
trending notably toward the wetter and further north NAM and GEM
solutions. In addition...most guidance is also coming around to a
colder overall solution that would support an initial brief wintry
mix of freezing rain and sleet later tonight and early Thursday
across the Southern Tier...followed by a quick shot of light to
moderate accumulating snowfall across our southernmost two
tiers of zones during the day Thursday...while areas further to
the north only see the chance for a little light snow during
Thursday given what should be a rather sharp northern edge to
the steadier precipitation.

With the model consensus improving and converging toward the above
solution...forecast confidence in a short-lived round of light icing
across the Southern Tier has increased for later tonight and Thursday...
with this then likely to be followed by a general snowfall of 2-4"/
3-5" through mid Thursday afternoon. With this in mind...a Winter
Weather Advisory will be hoisted for our three western Southern Tier
counties for the second half of tonight and much of Thursday. Snowfall
amounts and probabilities on Thursday should then quickly diminish
with increasing northward extent across the remainder of the region...
with some lighter snowfall accumulations of 1-3" likely from Southern
Erie and Wyoming counties eastward across interior portions of the
Finger Lakes...and just a chance for some light snow/spotty light
rain and little if any accumulation found further to the north.

With respect to temperatures...continued steady cold air advection
tonight will allow temperatures to drop back to the lower to mid
20s areawide...with highs on Thursday then ranging through the 30s.
In spite of the much colder airmass...such readings will still
actually be a little above average for this time of year.


The prevailing flow aloft Thursday night through Saturday night will
feature a SW-NE oriented jet stream generally stretching from the
Desert Southwest into the Central Great Lakes region.  The result at
the surface will be a number of relatively weak troughs/lows.

The first feature will already be east of the region by Thursday
night while surface high pressure moves from the Northern Great
Lakes region east across Southern Ontario and Quebec.  This will
result in a temporary break in any precipitation across Western and
Central NY for Thursday night with weak subsidence in place.

The break will be short-lived however as another feature moves in.
Although the surface pattern looks relatively weak, moisture will
will be tapped from the Gulf of Mexico, with the potential for
another decent precipitation event at least toward the NY/PA line.
Although the details will likely change, overall it looks like some
areas could briefly start out with snow or a very brief period of
freezing precipitation before quickly changing over to rain on

Another surface high pressure system follows with a dry period
expected for most of Friday night and Saturday.  A more significant
synoptic low should have developed by this time over the plains.
This low, a result of the upper level disturbance currently moving
down the BC coast, should deepen as it moves toward the Northern
Great Lakes Saturday night.  The result will be increasing chances
for rain, with widespread rain expected Saturday night.


An active weather pattern will continue this weekend with mild
temperatures and chances for precipitation. The large scale weather
pattern will remain relatively unchanged with a stubborn ridge over
the southeast CONUS and large scale troughing over the intermountain
west. This pattern will continue to supply above normal temperatures
and increased precipitation chances with the flow of Gulf of Mexico
moisture wide open.

In particular, a low pressure system will eject from the four
corners region Saturday across the Great Lakes by Sunday. The result
should be a chance of widespread rainfall Sunday ahead of the
approaching low pressure system. As the low passes by to our
northwest, expect decent southwest winds to pick up behind in the
cold advection behind the front. Models vary on the strength of the
surface low, but there at least low potential for a high wind event
if surface low deepens sufficiently.

Quiet and drier weather returns Monday with surface high pressure
building over the Ohio Valley. Otherwise, highs will remain above
climo (+5F - +10F) with the daytime highs in the mid and upper 40s
likely for most locations. Sunday will likely be the warmest day, so
long as we briefly break into the warm sector, with at least 50s


For the balance of the day...lingering areas of light rain in the
wake of a cold front will continue to break down and taper off as
high pressure and drier air begins building into the region...with
the rain expected to pretty much come to an end before sunset.
Concurrent with this...predominantly IFR to MVFR flight conditions
will improve back to MVFR and then VFR through late afternoon and
early this evening...with this improvement arriving across the
lake plains first...and the higher terrain of the Southern Tier/
North Country last.

After that...high pressure will build eastward across the Great Lakes
and into Southern Quebec tonight through Thursday...while a wave
of low pressure passes by to our south across the Ohio Valley and
Virginias. After a period of widespread VFR conditions this evening...
this latter system will bring a brief wintry mix of precipitation
to the Southern Tier overnight and early Thursday...followed by an
accumulating snowfall to areas south of KBUF/KROC during Thursday...
with all of this accompanied by another round of IFR to MVFR conditions
in the aforementioned areas. To the north of the steadier precip...
there will just be a chance of a little spotty light rain or snow
during the day Thursday...with VFR conditions continuing to prevail.

Thursday night...VFR/MVFR with a chance of snow or rain.
Friday...Deterioration to MVFR with rain developing...with a very
brief wintry mix possible at the onset.
Saturday and Sunday...VFR/MVFR with additional periods of rain
developing...which may be mixed with a little snow across the
North Country.
Monday...Mainly VFR.


In the wake of a strong cold front, a brisk westerly to northwesterly
flow will continue across Lake Ontario through early this evening...
before diminishing and veering to northerly/northeasterly tonight as
high pressure builds into the region. This will bring a round of
advisory-worthy conditions to southeastern portions of Lake Ontario
through the first half of tonight...for which Small Craft Advisories
remain in place. Moderate northeasterlies to easterlies will then
persist across Lake Ontario through Thursday...before increasing
and potentially leading to another round of advisory-worthy conditions
across the western half of the lake Thursday night.


With much colder air arriving and only very light rain expected
to come to an end by the end of the day...the flood risk across
the North Country appears minimal through the rest of the day...
and this is reflected in River point forecasts which now barely
bring the Black River at Watertown to action stage...and keep
all other forecast points below action levels. While we will
still leave the Flood Watch up through early this evening to
cover any lingering potential for ice jams and related flooding
along waterways...the chances for such appear fairly low as of
this writing.


NY...Flood Watch until 7 PM EST this evening for NYZ006>008.
     Winter Weather Advisory from 1 AM to 4 PM EST Thursday for
MARINE...Small Craft Advisory until 1 AM EST Thursday for LOZ043-044.



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