Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 201533

Area Forecast Discussion
National Weather Service Buffalo NY
1033 AM EST Tue Feb 20 2018

Low pressure will move into the Upper Great Lakes today and into
Quebec Wednesday. This will result in periods of rain along with
springlike warmth through early Wednesday morning...with temperatures
peaking in the 60s to lower 70s today. While colder weather will
return following the passage of a cold front on Wednesday...our
temperatures will still remain above normal through the end of the


As of 15Z...surface low pressure was located across Upper Michigan...
with an attendant warm front extending east-southeastward to Lake
Ontario and the North Country. Area radars continue to show surges
of mainly light to moderate rain sliding eastward along and north
of the warm front...while activity south of the front has begun
the process of diminishing to some scattered leftover rain showers
across the Niagara Frontier and portions of the Finger Lakes.
Meanwhile...dry conditions prevail across interior portions of
the Finger Lakes and the Southern Tier...which lie deeper within
the burgeoning warm sector.

Through the rest of today the surface low will track northeastward
into Ontario Province...while slowly pushing the warm front northward
to the upper Saint Lawrence Valley by early this evening. As a result
the steadiest rains will continue to shift northward and diminish over
time...with these largely confined to northern Jefferson and Lewis
counties by early this evening. Behind the departing steadier rains
largely dry weather will tend to prevail through this afternoon
along with some breaks of sunshine...through we still cannot totally
rule out a few additional scattered showers with daytime warming of
our unusually warm and moist airmass.

As has been previously will be an unseasonably
warm day across our region...with afternoon highs still expected
to range from the upper 50s/lower 60s across the North Country to
the mid 60s to lower 70s south of Lake Ontario...with the warmest
readings expected across interior portions of the Niagara Frontier
and the Genesee Valley/western Finger Lakes. Within the warm sector
southwesterly winds will also increase today...with enough mixing
likely to warrant some 35-40 mph wind gusts across portions of
western New York in spite of a lingering temperature inversion.
Further north and east...progressively more stable conditions will
result in weaker winds.

A large sub-tropical ridge will continue to move northward across
the east coast tonight. This along with the warm front moving into
Ontario/Quebec will keep the region mostly dry overnight. A
southerly flow continues and temperatures will hold steady in the
60s. Due to the cold lakes, fog is likely near the shore lines
through tonight.


The slow progression of the cold front will keep the rainfall
potential going through much of the day Wednesday. The front will
eventually push through the area by late afternoon and bring an end
to the rainfall as dry air and cooler temperatures move in. Expect
high temperatures to be well into the 60s east of Rochester, with
slightly cooler highs likely to the west. Highs will come early in
the day with temperatures falling back into the upper 30s and 40s by
late afternoon.

High pressure will build into the upper Great Lakes behind the front
Wednesday night. There is some uncertainty how far south of the area
the boundary will push, and whether a wave of low pressure which
develops along this boundary will clip southern portions of the area
late Wednesday night into Thursday. Model consensus supports at
least a chance of precipitation across the Southern Tier with
diminishing chances to the north which will be closer to surface
high pressure. Temperatures will get marginally cold enough to
support snow, with rain, snow, or mixed precipitation possible.

High pressure will pass just to the north of the region Thursday
night, supporting mainly dry weather. Lows will be mainly in the
20s. There is a small chance for rain or snow late across the
Western Southern Tier depending on the speed of the next system.


Active weather pattern to continue during this period with several
chances for precipitation.

Low pressure over the Central Plains will be in the process of
moving into the Mississippi and Ohio River Valley on Friday.
Meanwhile, high pressure over New England will slowly exit to the
Northeast. A warm front associated with this approaching system will
cross the Lower Great lakes early Friday. Initially, it will be cold
enough for a mixture of a little snow mixed with rain before turning
over to all rain as southwesterly flow brings in a much warmer air
mass to the region. The surface low will then track just to the west
of the lower lakes late during the day Friday and then push its cold
front through the region. Latest Guidance packages suggest that the
cold front will stall over Pennsylvania Friday night. Several weak
waves of low pressure will then ride along this boundary bringing a
chance of showers to the region on Saturday.

The last in a series of low pressures will quickly develop over the
Central Plains which will bring the best chance for widespread rain
Sunday. The low pressure system will depart the region late Sunday
with precipitation ending from west to east. 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


A warm front draped across Lake Ontario and the North Country will
slowly push northward to the Upper Saint Lawrence Valley by early
this evening. Along and north of the front periods of light to
moderate rain will produce MVFR to IFR conditions at times...while
to the south of the front conditions will tend to improve to VFR
from south to north...with mainly dry conditions expected save for
some widely scattered showers. Largely dry and mainly VFR conditions
are then expected for the majority of tonight...with just a low
chance of a few showers reading extreme far western New York late
in association with an approaching cold front.

Otherwise low level wind shear will remain an issue through much of
the TAF period, with a persistent 45 knot low level jet lingering at
about 2kft. The exception to this will be across far western New York
this afternoon...where increasing mixing will help to temporarily
alleviate the wind shear and may lead to surface gusts to 35 knots
or so.


Wednesday...MVFR with -SHRA.
Friday and Saturday...VFR/MVFR. A chance of rain or snow showers.


Southerly, mostly offshore winds will continue this afternoon as a low
pressure system tracks by to our northwest. Winds will be mainly in
the 15-25kt range on Lake Erie. A Small Craft Advisory is in effect
for Lake Erie through tonight. This pattern will continue through
Wednesday morning. A cold front will then move through Wednesday
with WNW flow behind the front, with likely SCA conditions
developing on Lake Ontario.


There remains a significant risk for flooding in the Black River
Basin. The combination of rain and a prolonged period of warm
temperatures will result in significant run-off in the basin. There
is still a basin average of 4-5 inches (water equivalent) with up to
10 inches across higher terrain. The majority of this will melt over
the next two days.

Although there is high confidence in warm temperatures and
associated snow melt, it is uncertain exactly how much rain will
fall. Model consensus has the axis of heaviest rainfall along the
Saint Lawrence Valley, with less rain expected south of Watertown.
Total rainfall amounts of 1-2 inches are likely in the Black River
Basin through Wednesday. There is a chance there will be more if
this axis shifts slightly south.

The greatest risk for flooding is as the Watertown forecast point
due to the widespread nature of the event and higher rainfall
amounts across the Black River basin north of Lowville. MMEFS
ensembles continue to show a likelihood of at least minor flooding
at Watertown, with significant chances of moderate and possibly even
major flooding. This depends on how much rain falls with the
ensembles capturing some model runs which place this axis across the
Black River basin. The risk for flooding is slightly lower at the
Boonville and McKeever forecast points since less rain will fall in
these portions of the basin. Even so, snowmelt and even some rain
may cause at least minor flooding.

In addition to river flooding, the combination of rain and snow melt
may cause localized flooding in the Watertown area. Ponding of water
may close roadways and cause basement flooding, especially if the
axis of heaviest rainfall shifts even slightly south. Also smaller
creeks and rivers are at risk across Northern Jefferson county where
rainfall amounts will be the greatest. Ice jams also may be an issue
with some ice still in place in and along some waterways in the

Elsewhere, there is much less snow pack in place due to recent warm
temperatures. Rainfall amounts in excess of an inch may cause some
creeks in the Buffalo area and lower Genesee basin to approach flood
stage, but model consensus keeps the steadier rains to the north of
these basins with rainfall amounts of an inch or less expected in
these basins. High flows can still be expected, with some locations
likely to reach action stage.


NY...Flood Watch through Wednesday evening for NYZ006>008.
MARINE...Small Craft Advisory until 10 AM EST Wednesday for LEZ020-040-



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