Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 200909
AFDBUF

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

.SYNOPSIS...
Low pressure will move into the Upper Great Lakes today and into
Quebec Wednesday. This will result in periods of rain along with a
dramatic warm up for the first half of the week as temperatures soar
into the 60s and low 70s in parts of the Genesee Valley.  This will
be the warmest weather across the region since last October. A cold
front will move through on Wednesday, but temperatures will still
remain a little above February normals during the end of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Low pressure is located in southern Wisconsin while an associated
warm front is stretched across the Great Lakes and into Western New
York this morning. A cold front is stretched south into the Mid-
West/Central Plains. Unseasonably wet and warm weather will continue
today and tonight.

A plume of high PWAT air will continue to stream northward into the
eastern Great Lakes today as a 50-60kt LLJ connects the region with
the Gulf of Mexico. Rain has been ongoing along the warm front this
morning as this conveyor belt of moisture overrides the boundary.
The warm front will slowly move northward today and tonight. The
steady rain will follow suit and lift northward across Lake Ontario
and the North Country by this afternoon. Moderate, steady rain
currently extends across the southern Great Lakes. This region of
rain will track northeastward along the warm front and move across
the Niagara Frontier, Lake Ontario and the North Country. The
Southern Tier is expected to stay mainly dry today as most of the
activity stays to the north. Rainfall amounts will range from a few
hundredths across the Southern Tier to a half inch along the Lake
Shore of Lake Ontario to three quarters of an inch across the North
Country. The North Country will see the most rainfall today with
slightly higher amounts across the Tug Hill. High dewpoints
especially across snowpack will lead to fog outside of the rain
today. Brief breaks in the rain has resulted in sudden drops in
visibilities.

Today will be very warm for late February across Western New York
and the North Country. Temperatures are still on tap to reach the
60s to the low 70s away from the lakes and in low lying areas such
as the Genesee Valley. As the warm front and rain shifts northward
across much of Western NY by the afternoon, some breaks in the
clouds are possible today. With warmth comes gusty winds in the
colder months. Southwest winds will increase this afternoon. A low
level inversion will be present through the day but there should be
enough mixing to mix down 30-40 mph gusts mainly across the Niagara
Frontier. Stable conditions expected across the North Country and
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.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
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.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
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
locations.

&&

.AVIATION /09Z TUESDAY THROUGH SATURDAY/...
Widespread MVFR conditions with widespread rain will continue this
morning, with local IFR conditions across the higher terrain of the
Southern Tier. Rain will move slowly northward today, with rain
ending from south to north. KJHW will be mostly dry where as KART
will see rain through today. Low level wind shear will remain an
issue through much of the TAF period, with a 45 knot low level jet
at about 2kft. Gusty southwest winds are expected Tuesday afternoon
across the Niagara Frontier, with gusts 35 to 40 knots possible. Low
level wind shear reappears tonight as an inversion becomes stronger
tonight. SHRA will re-enter the terminals from west to east late
tonight resulting in MVFR conditions with the potential for IFR
vsbys.

Outlook...

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

&&

.MARINE...
Southerly, mostly offshore winds will continue today 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.

&&

.HYDROLOGY...
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
basin.

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.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Flood Watch through Wednesday evening for NYZ006>008.
MARINE...Small Craft Advisory until 10 AM EST Wednesday for LEZ020-040-
         041.

&&

$$

SYNOPSIS...HSK
NEAR TERM...HSK
SHORT TERM...TMA
LONG TERM...AR
AVIATION...HSK
MARINE...HSK
HYDROLOGY...APFFEL/HSK



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