Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 251421
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
921 AM EST Sat Feb 25 2017

.SYNOPSIS...
A strong cold front will move from west to east across the area
today with a period of rain and scattered thunderstorms.
Temperatures will fall sharply on gusty winds behind the cold front
with scattered snow showers developing by late this afternoon and
this evening. Lake effect snow will bring minor accumulations east
of Lakes Erie and Ontario tonight into early Sunday before tapering
off later in the day. Temperatures will warm to well above normal
again by the middle of next week before winter cold returns by the
end of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Radar imagery shows a band of moderate rain over Western NY from
Buffalo to Rochester with this rain gradually moving east.
Farther east, it will remain dry east of Lake Ontario through
late morning. The mid-morning forecast update speeds up the
timing of the front by an hour or two based on the latest
observations. Otherwise, few changes were made to the existing
forecast.

A strong mid level trough will move from the central Great Lakes to
western Quebec through tonight, taking on a negative tilt with time.
Meanwhile at the surface, strong low pressure will take a similar
track from just north of Georgian Bay this morning to western Quebec
by this evening, deepening with time. A strong trailing cold front
will cross the area from west to east this morning through mid
afternoon.

Rain and Thunderstorms...
Expect mainly showers with just isolated thunderstorms west of
Rochester through the remainder of this morning. After this, the
leading edge of an upper level trough and strong DPVA catch up
to the surface boundary, which will destabilize the atmosphere
and enhance lift. Decent instability by late winter standards
will develop with an axis of around 500J/kg MUCAPE and LI of -2C
just ahead of the front from the Genesee Valley eastward.
Latest mesoscale model guidance remains consistent with runs
over the past day or so in strengthening the band of frontal
thunderstorms across Central and Eastern NY by early afternoon.

This is where the best chance of damaging wind gusts will
occur, and where SPC has included a slight risk. Farther west, a
few isolated damaging wind gusts cannot be ruled out across the
eastern half of our area, but the risk is very marginal with
storms strengthening just as they move east of our cwa.

Strong low level convergence along the advancing cold front
will focus the rainfall, with moisture convergence further
enhanced by a 50 knot low level jet. PWAT values will exceed 1
inch just ahead of the front, about 3 standard deviations above
normal for late February. The strong dynamics and deep moisture
will continue to support a solid band of rain as the front moves
east across the area, with rain lasting for 3-5 hours at any
one location. Rain amounts will generally be a half to three
quarters of an inch, with an inch to an inch an a quarter across
the Tug Hill region.

Following the band of frontal rainfall, a mid level dry slot will
bring a quick end to the rain from west to east this afternoon. A
few scattered rain and wet snow showers may develop again toward
evening across far western NY as wrap around moisture arrives.

Strong Winds...

Beyond the convective wind risk outlined above, this system will
also produce gusty synoptic scale winds this afternoon and evening
as cold air comes rushing back into Western NY. The track of the
surface low is very favorable for strong winds across Western NY,
with a deepening surface low tracking to the north and west of our
region. Strong pressure rises and cold advection behind the cold
front will support subsidence and downward momentum transfer of
stronger winds from aloft. A tropopause fold within the mid level
trough will move into Western NY later this afternoon with the 1.5
PVU surface decending to around 500mb, supporting enhanced
subsidence.

There are some negatives to this setup however. Winds aloft are not
particularly strong with around 50 knots on the GFS at 3K feet and
40-45 knots on the NAM. The strongest isallobaric fall/rise couplet
and deepest tropopause fold are both now forecast to miss our region
to the northwest, tracking across Lake Huron. Balancing out the
negatives and positives of the setup, it still appears to be a mid
range advisory event for areas along and northeast of Lake Erie
where funnelling down the lake enhances the wind. Expect peak gusts
of around 50mph in this area, with the strongest gusts only lasting
for a few hours from mid afternoon through early evening.

Also, mesoscale guidance and BUFKIT show the potential for
brief period of gusty west east of Lake Ontario early afternoon
with the passage of the front. These gusts are likely to be
sub- advisory unless convection enhances these gusts.

Lake Effect Snow...

Much colder air and wrap around moisture will sweep across the Lower
Great Lakes tonight. The passage of the mid level trough will
produce a few scattered snow showers outside of lake effect areas.
The airmass will briefly become favorable for a lake response, with
lake induced equilibrium levels rising to around 8K feet.

Off Lake Erie...expect lake effect snow showers to rapidly increase
this evening across the Chautauqua Ridge and higher terrain of
southern Erie and western Wyoming counties. The snow should reach
peak coverage and intensity during the mid to late evening, then
gradually weaken overnight as inversion heights begin to lower.
Expect total accumulations of 2-3 inches across the higher terrain
inland from the lake.

Off Lake Ontario...expect a plume of lake effect snow showers to
develop quickly on the heels of the synoptic rainfall by early this
evening. The band will then intensify by late evening across the Tug
Hill region, then move south across Oswego County during the wee
hours of Sunday morning. Snowfall rates may reach 1 inch per hour
briefly before weakening by daybreak Sunday. Expect amounts of 2-5
inches with the greatest amounts isolated to the higher terrain of
the Tug Hill Plateau.

Temperatures...

Temperatures ahead of the front will range from the upper 50s to
mid 60s, but will fall abruptly behind the boundary. Strong
cold advection will force temperatures to fall into the low to
mid 30s by 6PM across Western NY, and upper 30s across the
eastern Lake Ontario region by 6PM. Lows tonight will return to
typical late winter values, with mid 20s on the lake plains and
lower 20s across higher terrain.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
Lake effect snows will continue Sunday morning east and southeast of
Lakes Erie and Ontario, as -14C 850 mb air streams across the lower
Great Lakes. The best moisture will be found across Lake Ontario,
along with a long fetch of the lake and some upstream contribution
from the Georgian Bay and Lake Huron. Given these parameters, expect
a single plume of lake effect snow across southern Oswego and
northern Cayuga Counties. As the band shift toward the south shore
of Lake Ontario, expect some of the band to clip across shoreline
portions of Niagara, Orleans and Monroe counties for a few hours in
the morning. In terms of snowfall amounts, the least impressive
totals will be off Lake Erie, where mainly 1-3 inches across the
higher terrain, as the short fetch produces weaker multibands. East
of Lake Ontario, expect 24-36 hour total accumulations of 2-5 inches
east of Lake Ontario, with the higher amounts restricted to the Tug
Hill Plateau. Also expect a light coating up to an inch across
portions northern portions of Niagara and Orleans counties. In
addition to any snow chances, winds will remain quite gusty through
Sunday as the tail end of an 850mb jet lingers over the eastern
Great Lakes. Gusts 25 to 30 will be common. Temperatures will only
rebound to the low 30s on Sunday.

Sunday night a shortwave trough will move through southern Ontario
and Quebec, with a low-level jet developing as warmer air advects
into the region for Monday. This will bring early overnight lows
around 30 before warming to the mid 30s across the lake plains. It
will also get quite gusty again overnight across the lake plains as
the jet moves through, with gusts up to 35 mph possible. Interior
portions of the Southern Tier, Finger Lakes and North Country will
remain cooler and not nearly as windy overnight. A few snow showers
cannot be ruled out overnight in the North Country as the wave moves
by to the north with added moisture and upslope into the Tug and
western Adirondacks.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
After our brief shot of seasonal temperatures and weather early in
the week, we return to a very mild pattern again by mid-week.
Another low pressure system will develop in the central plains and
track toward the Great Lakes, bringing much above normal
temperatures to the east coast again. This will also bring more rain
to the region Tuesday night through Wednesday night as the low
tracks just to our west. 00Z model guidance has come into better
alignment on the timing and track of the low. Given this, have
increased high temperature forecasts for Tuesday and especially
Wednesday when we should become established in the warm sector ahead
of the low. Expect highs could once again push into the upper 50s,
and even the 60s for some on Wednesday.

In the wake of this low pressure system, we remain on track to
return to normal winter conditions to end the week. Model consensus
supports deep troughing across the northeast for the end of the
week, with 850 mb temperatures down to around -12C Thursday, and
perhaps as cold as -20C by Friday night. This would result in normal
to even below normal temperatures by Friday. Expect the return of
some lake effect snows during this period, with the potential for a
couple of clippers which could bring some light general snowfall to
the region.

&&

.AVIATION /14Z SATURDAY THROUGH WEDNESDAY/...
A cold front will sweep from west to east across the area during the
morning and early afternoon, producing a 3-5 hour period of showers
with an embedded area of heavier rain and a few scattered
thunderstorms right along the cold front from the Genesee Valley
eastward as the airmass destabilizes by midday. Expect a drop to
MVFR CIGS/VSBY for a few hours with the period of rainfall, with a
few brief periods of IFR in areas of heavier rain. IFR CIGS may also
develop for a few hours along and behind the cold front at
JHW/BUF. Some of the thunderstorms may also produce gusty
winds.

Following the cold front, the rain will end from west to east this
afternoon with a return to mainly VFR conditions. Winds will become
gusty, especially northeast of Lake Erie with gusts of over 40 knots
for a few hours from mid afternoon through early evening including
KBUF and KIAG.

Tonight a few scattered snow showers will develop as a mid level
trough crosses the region, producing spotty MVFR. Lake effect snow
will also develop east of both lakes with local IFR. Off Lake Erie
this will mainly impact the higher terrain of the Western Southern
Tier including KJHW. Off Lake Ontario this will mainly focus across
the Tug Hill and Oswego County.

Outlook...

Sunday...VFR, but IFR to MVFR in lake effect snow SE of both lakes.
Monday...VFR, possible MVFR with chance of -SHRA/-SHSN.
Tuesday...VFR/MVFR with a chance of showers.
Wednesday...MVFR/IFR with showers likely.

&&

.MARINE...
A strong cold front will sweep from west to east across the Lower
Great Lakes this morning and early afternoon. West winds will
increase in the wake of the cold front and peak during the late
afternoon on Lake Erie, and this evening on Lake Ontario. Both lakes
appear to peak just below gale force, with sustained winds reaching
30 knots for a few hours. This will bring high end Small Craft
Advisory conditions to both lakes. Stronger winds will continue
through Sunday night before the pressure gradient relaxes on Monday.

&&

.HYDROLOGY...
There is a potential for localized areal and small stream
flooding across the entire Eastern Lake Ontario Region today
through Sunday. River flood warnings have been issued for
forecast points along the Black River and Moose River. Also, an
areal flood warning is in effect for areas where there is
significant snow pack.

While the snow pack has largely melted across Western New York,
a significant snow pack remains east of Lake Ontario, including
the Black River basin. Snow water equivalent values are about
130% of normal, with this snow pack ripe due to the warm
weather.

Today, a strong system will pass to our north with a prolonged
period of warm (50+ degree) temperatures until the passage of a
cold front drops temperatures below freezing tonight. This will
be combine with gusty winds and high dewpoints to rapidly melt
a significant portion of the snow pack in place. This system
will also bring a period of rain today, with amounts expected to
average around an inch.

This may result in multiple issues east of Lake Ontario. The
combination of rainfall and snowmelt may cause flooding in low-
lying areas and faster responding creeks and rivers later today.
Some ice jams are also possible. After this, runoff will cause
the Black River and its tributaries that drain the Tug Hill
Plateau and the western Adirondacks to respond tonight and
Sunday and lasting into next week. Flooding is also possible on
the Salmon River and other rivers in northern Oswego County that
drain the western slopes of the Tug Hill.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Flood Watch through Sunday evening for NYZ006>008.
     Wind Advisory until 10 PM EST this evening for NYZ001>003-
     010>012-019-085.
MARINE...Small Craft Advisory until 1 AM EST Sunday for LEZ020.
         Small Craft Advisory until 7 AM EST Monday for LEZ040-041.
         Small Craft Advisory until 1 AM EST Sunday for LOZ030.
         Small Craft Advisory until 1 PM EST Monday for LOZ043>045.
         Small Craft Advisory until 10 AM EST Monday for LOZ042.

&&

$$

SYNOPSIS...HITCHCOCK
NEAR TERM...APFFEL/HITCHCOCK
SHORT TERM...CHURCH
LONG TERM...CHURCH
AVIATION...APFFEL/HITCHCOCK
MARINE...HITCHCOCK
HYDROLOGY...HITCHCOCK/APFFEL


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