Area Forecast Discussion
Issued by NWS Buffalo, NY

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551
FXUS61 KBUF 230556
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1256 AM EST Mon Jan 23 2017

.SYNOPSIS...
Warm and moist conditions will remain through the night with
above normal temperatures, and areas of fog or drizzle. Then low
pressure developing across the Southeastern states will move to
the mid-Atlantic on Monday and then into Southern New England on
Tuesday. This will bring rain and wet snow into our region with
potentially significant snow accumulations in some areas.

&&

.NEAR TERM /THROUGH TODAY/...
Through the remainder of the night the low stratus and fog will
remain the issue through the night. Northeast flow will continue
through the night, this between an area of high pressure over
eastern Canada, and two storm systems...one off the Atlantic
coastline, and a second system over the southern Tennessee Valley.
This northeast flow is a bit stronger than previous nights.

The northeast flow will continue to advect cool, moist air over the
warm lakes that will generate low stratus and fog along the southern
Lake Ontario shoreline. The stronger flow has carried this fog
inland to the NYS Thruway, with the fog expanding across the hills
and valleys of the Genesee Valley. Additional fog is also forming
along the immediate Lake Erie shoreline, with this fog reaching
Route 5 and the NYS Thruway as well.

Expect the fog to continue through the night, and into tomorrow
morning.

Low pressure from the Southeast will creep closer to our region,
with a chance of showers across the Southern Tier tonight. A
consensus of 12Z guidance is slower than previous runs, so timing
has been delayed to account for this.

There still remains high confidence in precipitation with synoptic
scale lift from a deep moist easterly mid-level flow and divergence
aloft. By late Monday afternoon even slower model guidance has
precipitation to the south shores of Lake Ontario, with steady
precipitation expected across the Southern Tier and Upper Genesee
Valley expected during this time.

Thermal profiles will start off too warm for snow, but will cool
with dynamic cooling as the system taps into slightly cooler air from
the ENE. Even though model guidance is in generally good agreement,
thermal profiles are so close that even a small error in forecast
soundings will be the difference between rain and snow. Based on
model consensus, preciopitaiton is expected to change over to snow
first across the upper Genesee basin and Finger Lakes region, with
modest accumulations of a 1 to 3 inches possible by sunset Monday.
Elsewhere, expect mainly wet rain, with perhaps some wet flakes
mixing in through late Monday afternoon.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/...
The main focus through the short term period remains on the strong
and complex storm system moving up the east coast in the Monday
night through Tuesday time frame. High pressure positioned off to
our north and approaching milder air ahead of the approaching
surface low from the DelMarVa will set up a complex thermal profile
across western and north central New York.

Precipiation associated with the approaching low will have already
reached at least southern portions of the area Monday evening, with
higher elevations already have transitioned over to all snow. This
transition over to snow should take place for all areas as heavier
precipitation makes it way into the region. Latest ensembles showing
a high likelihood of more than an inch of liquid equivalent over
much of western and north central New York Monday night into Tuesday.

Later Monday night and into Tuesday, NAM and GFS forecast soundings
showing a warm layer, mainly between 800mb and 700 mb arriving on a
strengthening easterly flow, as strong as 75 knots in some of the
guidance. This will result in a period of sleet mixing in at times.

Better confidence has been gained this cycle, not only with a period
of heavy precipitation, but with thermal profiles as well.
Therefore, will issue a winter storm watch for the Genesee Valley
eastward. The placement of the heaviest snow totals within the watch
area still remains quite uncertain, but current thinking is there
will be a swath of 5 to 10+ inches over the higher elevations from
Allegany/Wyoming counties through the Bristol Hills, then up through
the Tug Hill.

On Wednesday morning, a narrow ridge axis will extend up the Eastern
Seaboard while low pressure tracks across the Central Great Lakes
Region. A warm front associated with this low will likely bring some
precipitation which may start off as rain or wet snow but trend to
all rain as temperatures warm. This will be followed by an ill-
defined cold front and surface trough which will move across the
region Wednesday night and bring more rain, which will mix with wet
snow overnight as weak cold advection begins. Outside of the
showers, Wednesday should be a breezy day with highs in the
upper 30s to lower 40s.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
Welcome to the coldest time of the year...or at least in
climatological terms...what SHOULD be the coldest time of the year.
In the days leading up to this period...it has felt anything but
wintry though...as a split flow over the country has been dominated
by a Pacific maritime airmass. This rather warm regime will come to
an end during this time frame as a temporary block in the mid
level progressive flow will become established.

A closed low will stall in the vicinity of the Labrador Sea while a
fragile ridge will take shape along the west coast of the continent.
A more robust ridge would normally exhibit signs of being able to
withstand the battering of Pacific based shortwaves...but guidance
is suggesting that it could be more susceptible to breaking down.
This would limit the depth and strength of the northwest flow out
of the Canadian Archipelago...thereby limiting the impact/
intensity of any cold air intrusion.

That being said...the ensembles are in good agreement that enough
cold air will be siphoned southward from Hudson Bay to finally push
our mercury to at least normal levels for the weekend (end of this
forecast period). There are some signs that the cold air could
intensify as we push into the following week...but this is
certainly not anything that the ensembles agree upon.

The airmass during this period will gradually become cold enough to
support a lake response...but with lake temps in the mid 30s over
Lake Erie...we will need H85 temps to lower to at least -10c. As
is nearly always the case at this point in winter...the Lake
Ontario sfc temps are several degrees higher than those of Erie`s.
Currently...they are generally in the low to mid 40s (as per
GLERL)...so use the water temp at ROC with caution. Single point
readings can often be misleading.

The colder air that will lead to accumulating lake snows will
gradually work its across the Lower Great Lakes in the wake of a
very moist cold frontal passage on Thursday. The front is expected
to generate fairly widespread rain and wet snow showers...especially
during the second half of the day. Have raised pops to categorical
to cover this fropa.

As the cold air deepens Thursday night...some upslope will help to
produce some wet snow showers over parts of the Southern Tier while
true lake effect snow is likely to become established southeast of
Lake Ontario.

The passage of a shortwave within the chilly cyclonic flow on Friday
should then promote scattered snow showers over the entire forecast
area...but accumulating snows should be focused east of both lakes
where mesoscale processes will dominate. Temps Friday will peak
within a couple degrees from freezing.

The cyclonic flow will continue to generate flurries and light snow
showers over the region both Saturday and Sunday...with more
persistent lake snows persisting in the snow belts east of both
lakes.

&&

.AVIATION /06Z MONDAY THROUGH FRIDAY/...
Northeast flow off Lake Ontario with plentiful low level moisture
will maintain low IFR stratus around 300 feet at KBUF/KIAG/KROC
through sunrise Monday before improvement with daytime mixing.
Visibilities may also decrease at these sites overnight, with IFR or
lower possible at times. This low stratus will also impact the hill
tops of the southern Tier bringing low IFR conditions to JHW. KART
will see mainly MVFR conditions prevail with offshore flow
overnight.

Monday a storm system will bring a period of rain to the region.
Expect rain to reach the Southern Tier around daybreak, KIAG, KBUF,
KROC just after noontime, and KART by late afternoon. Though
conditions may improve to MVFR/VFR briefly before the rain, within
the rain, expect a deterioration back to IFR and MVFR flight
conditions. Rain will turn to a wintry mix late in the TAF cycle.

Outlook...

Monday night...Areas of MVFR/IFR with rain changing to wet snow.
Tuesday...Areas of MVFR/IFR with wet snow mixed with rain.
Wednesday and Thursday...VFR/MVFR with a chance of rain and snow.
Friday...VFR/MVFR with a chance of snow showers.

&&

.MARINE...
Easterly winds will increase across Lake Ontario and Erie through
tonight as we get caught between high pressure over Quebec and a
deepening low pressure system moving into the Mid Atlantic. Small
craft advisories have been issued for the western half of Lake
Ontario as the east- northeasterly winds strengthen to 20 to 25
knots. Winds and waves will remain elevated until the low pressure
system passes on Tuesday. Lake Erie remains less of a concern as
wave action will directed away from the eastern end of the lake.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Winter Storm Watch from this evening through Tuesday afternoon
     for NYZ003>008.
     Winter Storm Watch from this afternoon through Tuesday
     afternoon for NYZ012>014-021.
MARINE...Small Craft Advisory until 1 PM EST Tuesday for LOZ042-043.

&&

$$

SYNOPSIS...APFFEL/THOMAS
NEAR TERM...APFFEL/THOMAS
SHORT TERM...TMA
LONG TERM...RSH
AVIATION...CHURCH
MARINE...APFFEL



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