Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 252010
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
310 PM EST Tue Feb 25 2020

.SYNOPSIS...
Rather active weather will prevail through the rest of this week.
Initially low pressure over the Ohio Valley will bring another round
of mixed rain and wet snow to the region tonight...with this then
changing to rain and temporarily breaking off for a time during
Wednesday. The low will then rapidly strengthen and track across our
area later Wednesday and Wednesday night while bringing a round of
moderate to heavy rain that will eventually change over to snow...
which will likely produce at least some moderate general snowfall
accumulations across far western New York from later Wednesday night
into Thursday morning. Much colder air pouring in behind this system
will then bring the likelihood of heavy lake effect snow to areas
east of the lakes Thursday through Friday...with somewhat weaker
lake snows then migrating to areas southeast of the lakes on
Saturday.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
Tonight and Wednesday morning the west-to-east oriented baroclinic
zone across our region will tighten a little more while slowly
pivoting northwestward in response to digging upper-level troughing
across the Mississippi Valley and Upper Great Lakes. As this
occurs...another shot of weak to modest isentropic upglide across
the baroclinic zone will generate another band of light precip that
will first pivot northward across our region tonight and thenceforth
into Southern Ontario Wednesday morning...for which categorical PoPs
remain in play. With respect to ptype...mainly rain at the onset
this evening will once again tend to go over to a mix of rain and
wet snow as the lower levels of the atmosphere cool...with snow
generally becoming more predominant overnight. Wednesday morning the
precip will then tend to temporarily taper off from southeast to
northwest while also changing back over mainly rain as the low
levels warm again. As for potential snow amounts...the light nature
of the precip and the very marginal temperature profiles will help
to keep these on the light side...with 1 to 3 inches of slushy
accumulation possible across the higher terrain and northern
portions of the Niagara Frontier and North Country...and a general
inch or less expected elsewhere.

Wednesday afternoon and night the digging upper level trough will
make its way eastward across the Lower Great Lakes and Ohio Valley...
while also taking on a considerable negative tilt. Strong height
falls and DCVA on the eastern flank of this very dynamic feature
will help encourage the previously broad and poorly organized
surface low to markedly deepen and lift northward across our area
between late Wednesday and especially Wednesday night...along with
an attendant swath of moderate to heavy precipitation given the
increasingly impressive dynamics and deep moisture.

Initially...thermal profiles across our region will still be warm
enough for predominantly rain as the moderate to heavy precipitation
begins overspreading our region later Wednesday afternoon and early
Wednesday evening. After that time though...colder air wrapping in
behind the backside of this system will then drive a southwest-
northeast changeover to snow during the course of Wednesday night
and very early Thursday morning.

What`s concerning about this is that compared to 24 hours ago...the
track of the surface low has trended notably further to the
southeast in almost all of the available guidance...which is a
marked reversal of the further northwestward track seen over the
previous few days. This change has important implications for far
western New York...where thermal profiles now appear to turn colder
faster and allow for a faster changeover from rain to snow Wednesday
night...thereby raising the specter of a period of accumulating
moderate to heavy snow from later Wednesday night into Thursday
morning. While there is still a fair amount of disagreement amongst
the various model packages on potential snowfall amounts stemming
from this...at least some advisory-type accumulations are starting
to appear likely across far western New York...with warning-criteria
snowfall amounts possible given some of the more impressive model
solutions (most notably the ECMWF). With this and the abrupt shift
in the guidance both in mind...we have elected to hoist a new Winter
Storm Watch for the Niagara Frontier for Wednesday night and
Thursday morning...and have also moved up the start time of the
existing Watch for the Southern Tier to cover this potential initial
synoptic snowfall...in addition to the lake enhancement that is
still expected to begin there later Wednesday night.

Meanwhile from about the Genesee Valley eastward...warmer air will
linger in place longer and should help to severely limit the
potential for accumulating snows until very late Wednesday night or
early Thursday morning...with any accumulations through daybreak
Thursday likely to remain on the order of a few tenths of an inch to
2 inches.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY/...
Low pressure will become increasingly vertically stacked on
Thursday, with the system moving into southern Quebec and then
stalling by late in the day. Strong cold advection in the wake of
the departing low will allow much colder air to pour back into the
region from west to east in the morning, setting the stage for what
will be an extended period of lake effect and lake enhanced
snowfall.

The heavy snow potential from Wednesday night will rapidly
exit Thursday morning. Abundant wrap around moisture will produce
areas of light snow Thursday across much of the region, especially
Western NY and the eastern Lake Ontario region, with a relative
minima in snow by afternoon for the Genesee Valley and western
Finger Lakes. Lake enhanced snow will be embedded within the general
area of synoptic snow as cold air rapidly deepens and lake induced
equilibrium levels rise to near 10K feet.

Off Lake Erie, lake enhanced and orographically enhanced snow will
focus on the higher terrain of the Chautauqua Ridge, Boston Hills,
and western Wyoming County. The deepest moisture and best synoptic
scale support will be in the morning, and this should support a
steady moderate, to marginally heavy snow in the upslope areas east
of Lake Erie. The deeper moisture and better synoptic ascent will
move away by afternoon, resulting in a lowering of snowfall rates
across upslope areas.

Off Lake Ontario, westerly flow will become established by late
morning or midday, with a strong band of lake effect/lake enhanced
snow targeting the Tug Hill region by afternoon. This will be
embedded within a broader area of light synoptic snow. The snowfall
rates will continue to get heavier as the afternoon progresses and
cold air deepens, and boundary layer flow becomes better aligned.

Thursday night through Saturday the vertically stacked low will
cutoff from the westerlies and drift slowly east across southern
Quebec. Model guidance has remained fairly consistent with this idea
since yesterday, although the latest models have a little more in
the way of widespread light synoptic snow through the period. The
synoptically forced snow will increase Friday afternoon and continue
Friday night through Saturday morning as the western tail of the mid
level trough moves southeast across the eastern Great Lakes, and the
deepest synoptic scale moisture crosses the area. This will produce
light to borderline moderate snow accumulations across much of the
region, with a relative minima across the valleys of Livingston and
Allegany counties where downsloping will minimize snowfall.

The synoptic scale pattern continues to support the idea of a
significant and long lasting lake effect/lake enhanced snow event.
CIPS analogs continue to return impressive analog means in terms of
snowfall, and also return some notable dates of analog events. The
large scale pattern also fits the climatology from our local analog
research for major lake effect events for east of Lakes Erie and
Ontario.

Off Lake Erie...

Persistent westerly flow will support lake enhanced upslope snow
across the higher terrain east of the lake Thursday night through
Saturday, with boundary layer flow slowly veering more northwesterly
late Friday night and Saturday. The highest snowfall rates will
likely occur Friday afternoon and Friday night when deeper synoptic
scale moisture and support move back over Western NY. The lake
enhanced snow will then decrease quickly in areal coverage and
intensity through the day Saturday as deeper moisture pulls away,
and inversion heights begin to lower.

As far as snowfall amounts go, storm totals are likely to reach 1-2
feet across the higher terrain inland from Lake Erie along the
Chautauqua Ridge, Boston Hills, and western Wyoming County. Some
localized amounts of over 2 feet are possible. Note, this does not
include the synoptic snow that precedes the main lake effect event.

Off Lake Ontario...

The heaviest snow will likely occur Thursday night with well aligned
westerly flow down the long axis of the lake, interacting
cooperatively with orographic enhancement on the Tug Hill Plateau.
Snowfall rates may reach 2+ inches per hour and this one 12 hour
period could produce well over a foot of accumulation for the Tug
Hill. On Friday boundary layer flow will begin to veer slightly, and
the position of the upstream mid level trough may also force lake
effect snow to move a little farther south, and re-orient itself
with less potential for one single, strong band, and more potential
for a broad area of lake enhanced snow east and southeast of the
lake. Boundary layer flow will continue to slowly veer more
northwest Friday night and Saturday, spreading lake enhanced snow to
much of the area southeast of the lake. Snowfall rates will decrease
during this time frame, but the footprint of the snow will spread
out over a much wider area. The snow will continue through Saturday
morning before decreasing in areal coverage and intensity Saturday
afternoon and evening as the deeper moisture pulls away.

As far as amounts go, storm totals are likely to reach 2-3 feet on
the Tug Hill with locally higher amounts possible if the band of
heaviest snow stalls in one location long enough. 6-10 inches of
snow is possible for areas southeast of the lake from Orleans to
western Oswego County, including the Rochester area. Much of this
will fall later Friday through Saturday as boundary layer flow veers
more northwesterly. Snowfall rates will not be as high in this phase
of the event. Note, these totals do not include the synoptic snow
that will precede the main lake effect event.

Finally, it will be very windy during the first phase of this lake
effect event Thursday and Thursday night. Wind gusts of 35 to 40 mph
will be common at times, producing significant blowing and drifting
snow. The strongest winds will be on the lake plains where the least
amount of snow will fall. There may be a period with wind gusts up
to or exceeding 45 mph Thursday afternoon and evening. Winds will
become somewhat lighter Friday through Saturday, although there will
still be enough wind to produce at least some limited blowing and
drifting snow in open areas.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
The vertically stacked low will continue to slowly fill and move
east into the Canadian Maritimes Saturday night. Synoptic scale
moisture and forcing will diminish from west to east overnight, with
inversion heights lowering steadily. Lake effect snow showers will
continue southeast of the lakes with boundary layer flow becoming
more northwest with time. The best coverage of snow will be in the
evening, with lessening coverage and intensity through the
overnight. Any remaining lake effect snow showers southeast of the
lakes Sunday morning will end as surface high pressure builds over
the eastern Great Lakes, further lowering inversion heights and
drying the column. Temperatures will remain cold through Sunday
under the influence of the departing deep trough and associated cold
air aloft.

Early next week the trough will advance steadily into the North
Atlantic. Rising heights and a westerly flow of Pacific origin air
will build east across the nation Monday and Tuesday. This will
allow temperatures to trend quickly above normal following our 3-4
day period of active winter weather and cold. Monday will be dry as
high pressure drifts off the east coast. Low pressure moving out of
the Ohio Valley will bring an increasing chance of rain showers by
Tuesday.

&&

.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
Cool, moist northeasterly upslope flow off of Lake Ontario is
keeping terminals across the lake plains (KBUF/KIAG/KROC) socked in
with IFR/LIFR CIGS this afternoon. Predominantly MVFR CIGS are found
across the western Southern Tier, with Low VFR CIGS at KART away
from the influences of the moist lake. Aside from a few widely
scattered light rain showers, expect mainly rain free conditions
through the remainder of the afternoon. There is the possibility
that CIGS may briefly become MVFR across the lake plains late this
afternoon and evening, with just the opposite occurring across the
western Southern Tier as CIGS will likely deteriorate to IFR during
this same timeframe as deeper low level moisture approaches from the
south.

CIGS/VSBY will deteriorate to IFR across all areas again overnight
tonight through the end of the TAF period in a mix of rain and/or
wet snow showers. The only exception with regard to CIGS will be
around KART, where MVFR CIGS will be predominant.

Outlook...

Wednesday...MVFR/IFR with morning rain and snow giving way to
periods of rain Wednesday afternoon...then changing back to all snow
Wednesday night.
Thursday and Friday...LIFR/IFR in potentially heavy lake effect snow
east of the lakes...with MVFR/VFR and scattered snow showers
elsewhere.
Saturday...IFR/MVFR with lake effect snow southeast of the lakes...
and scattered to numerous snow showers elsewhere.
Sunday...IFR/MVFR in snow showers...becoming VFR.

&&

.MARINE...
Low pressure tracking up the Ohio Valley will bring a period of
brisk northeasterlies to the Lower Great Lakes through tonight and a
good deal of Wednesday...for which Small Craft Advisories are in
effect as outlined below.

Later Wednesday and Wednesday night the surface low will strengthen
markedly and lift northeastward across New York State. Following the
passage of the low...winds will rapidly freshen out of the west
later Wednesday night and Thursday and may lead to a period of gales
on both lakes that would last through Thursday night...for which
Gale Watches are in effect as outlined below.

&&

.TIDES/COASTAL FLOODING...
A period of strong west-southwesterly winds in wake of strong
low pressure could bring a round of lakeshore flooding to Lake
Erie and Lake Ontario late Wednesday night and Thursday.

For Lake Erie, the setup looks increasingly favorable for a seiche
from late Wednesday night through early Thursday afternoon, as
east to southeast winds quickly turn west-southwesterly and increase
to 30 knots or possibly even gale force. The ramp up in winds
may cause the lake level to approach 8 feet above low water datum
at Buffalo with some flooding possible of the Buffalo Harbor,
Canalside, and Dunkirk Harbor.

For Lake Ontario, the combination of high lake levels, strong
onshore westerly winds, and high waves may produce some lakeshore
flooding in bays and inlets at the east end of the lake.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Lakeshore Flood Watch from Thursday afternoon through Friday
     morning for NYZ006-007.
     Winter Storm Watch from late Wednesday night through Saturday
     afternoon for NYZ006>008.
     Winter Storm Watch from Wednesday evening through Thursday
     afternoon for NYZ001-002-010-011.
     Lakeshore Flood Watch from late Wednesday night through
     Thursday afternoon for NYZ010-019-085.
     Winter Storm Watch from Wednesday evening through Saturday
     afternoon for NYZ012-019-020-085.
MARINE...Gale Watch from Thursday morning through Friday morning for
         LEZ040-041.
         Small Craft Advisory until 4 PM EST Wednesday for LEZ040-
         041.
         Gale Watch from Thursday morning through Friday
         morning for LOZ042>045-062>065.
         Small Craft Advisory from 7 PM this evening to 1 AM EST
         Thursday for LOZ043-044.
         Small Craft Advisory from 7 PM this evening to 7 AM EST
         Thursday for LOZ042.

&&

$$

SYNOPSIS...JJR
NEAR TERM...JJR
SHORT TERM...Hitchcock
LONG TERM...Hitchcock
AVIATION...JM
MARINE...JJR
TIDES/COASTAL FLOODING...JJR/TMA


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