Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 281501

Area Forecast Discussion
National Weather Service Buffalo NY
1001 AM EST Tue Feb 28 2017

Unseasonably mild air will surge into the region today through
Wednesday, with highs topping out around 70 for some on Wednesday.
A few widely scattered light showers are possible today and this
evening, then an approaching low pressure system and cold front
will bring widespread showers and scattered thunderstorms Wednesday.
In the wake of the cold front...more typical late winter temperatures
and some limited lake snows will return for the end of the week...
before another warmup arrives for Sunday and early next week.


Developing low pressure over the central Plains will continue to
gradually get better organized today while slowly pushing toward the
Upper Mississippi Valley. In the process...this feature will push
its attendant warm front northeastward into our region. Warm
advective forcing along and out ahead of this front continues to
look relatively weak...which will translate into only some lower-
end probabilities for some scattered light showers as the front
works across our region...with the bulk of the day more than likely
to just be dry with increasing amounts of cloud cover. Temperature-
wise...the continued warm air advective regime will result in temps
climbing even higher today...with afternoon highs ranging from the
lower to mid 50s east of Lake Ontario to the mid and upper 50s
elsewhere. With a general southerly downslope flow in place...we
could even see areas along the immediate Lake Erie shoreline reach
the 60 degree mark.

Tonight, a secondary, and stronger, wave of low pressure tracks into
the central plains, creating an elongated area of low pressure
across the upper mid-west into the upper Great Lakes by Wednesday
morning. This stronger wave will bring an added surge of warm air
and moisture advection to the region overnight tonight. Expect some
increasing south-southeasterly winds overnight, which will promote
further downsloping, along with dew points rising into the 50s.
Overnight lows will likely occur early in the evening in the low
50s, then rise overnight with some locations seeing 60s by daybreak
Wednesday. In terms of precipitation, we will be largely in the warm
sector, and thus for much of the night expect just an increasing
chance of scattered showers. However, by later in the night, toward
Wednesday morning, expect ongoing thunderstorms tracking out of Ohio
Valley and southern Ontario will approach the region. More on this
thunderstorm potential below.


The midweek period will be active as a strong system moves through
the Great Lakes region. A longwave mid level trough will advance
eastward into the Great Lakes Wednesday and Wednesday night, with a
strong shortwave on the leading edge of the trough. This feature
will support strong cyclogenesis today in the Central Plains, with a
cutter low then moving through the Great Lakes Wednesday and
reaching Quebec Wednesday night.

Rain and Severe Potential...

A leading mid level shortwave and broad warm advection regime
supported by 50+ knot low level flow will likely produce one round
of showers and a few scattered thunderstorms Wednesday morning
across the area. This first round of scattered storms will likely
remain somewhat elevated with heavy downpours possible but little
risk of severe weather.

Following the first round of showers and scattered storms, there
will likely be a few hours break with just scattered showers and
even some sunny breaks. Showers and scattered storms should then
become more widespread again in the afternoon with diurnal
destabilization and stronger ascent from the approach of the strong
mid level shortwave. Mesoscale model guidance suggests most of the
storms are likely to form along a pre-frontal trough and possibly
lake breeze boundaries during the afternoon.

The severe potential is not very clear at this point, with
uncertainty with regard to the degree of destabilization following
the morning showers and scattered storms, and timing and placement
of better forcing in the afternoon. Mesoscale model guidance and SPC
outlooks agree in placing a greater chance of organized strong
convection south of our area. That said, strong 60+ knot low level
flow in the warm sector may support a few damaging wind gusts with
any stronger storms that area able to develop farther north over New

Unseasonable PWAT values will also support locally heavy downpours
with any stronger storms. This could potentially lead to an isolated
flood risk with any storms that train along the lake breeze
boundary, but strong flow will keep storm motion fast and possibly
mitigate flood risk.

Wind Potential...

Beyond the convective wind potential, the strong surface low passing
just to the north and west of the area is climatologically favored
for strong winds northeast of Lakes Erie and Ontario. Model guidance
is in very poor agreement with the details however. The NAM and
Canadian GEM show a more elongated surface low with several waves of
low pressure eventually yielding to a consolidating surface low over
southern Quebec by early Wednesday evening. This scenario would keep
the strongest winds aloft confined to the warm sector of the system,
with winds aloft then rapidly decreasing as cold advection begins
and steeper lapse rates arrive. If this verifies wind gusts would be
well below advisory criteria. The GFS on the other hand emphasizes
the western portion of the elongated low, with a consolidating
surface low just north of Toronto by late Wednesday afternoon. This
scenario yields much stronger winds in the cold advection behind the
system, and would suggest warning criteria wind gusts northeast of
Lakes Erie and Ontario. The ECMWF solution is somewhat of a
compromise between the two, suggesting advisory gusts behind the
front Wednesday evening.

The GFS performed very poorly with wind gust potential on the last
system over the weekend, over-forecasting the potential. Given the
recent history and the outlier nature of the GFS solution, have
strongly favored the compromise solution of the ECMWF with a period
of advisory gusts Wednesday evening. Given the very poor model
agreement so far on this system, will continue with mention of this
potential in the HWO and allow for at least another model run before
any wind headlines are considered.


It will be another very warm day on Wednesday, especially if the
break in convection around midday is realized. Latest guidance
suggests a good chance of lower 70s for highs across the Niagara
Frontier (inland from Lake Erie) eastward across the Genesee Valley
and Finger Lakes. A southwest wind will keep the Buffalo area cooler
with flow off Lake Erie.

Wednesday night the surface low will move quickly across Southern
Quebec with the cold front clearing east of our area during the
evening. There should be a brief break in precip behind the cold
front in a mid level dry slot. Overnight deeper wrap around moisture
and a period of ascent will cross the area in association with the
mid level trough axis. Strong cold advection will quickly cool the
column and support snow by the time the wrap around moisture
arrives. This may produce a coating to an inch of accumulation in
many areas later Wednesday night and early Thursday morning, with up
to 2 inches across the higher terrain of the western Southern Tier
and Tug Hill with an added boost of upslope flow and lake

The airmass will quickly dry out on Thursday, with snow showers
southeast of the lakes rapidly diminishing and ending as drier air
builds into the Lower Great Lakes. It will be dramatically colder
than Wednesday, with highs around 30 on the lake plains and mid to
upper 20s across higher terrain and the North Country.


Winter will return at least for a few days on Friday and Saturday as
a deep trough becomes established from the Great Lakes to the
Northeast. A clipper system will move through the area later
Thursday night and Friday with a few snow showers and some limited
lake effect snow southeast of the lakes. The dry nature of the
airmass will likely prevent any significant lake effect snow during
this time period, with accumulations remaining modest.

Warm advection will then increase Sunday and Monday as the mid level
trough moves east into the Canadian Maritimes and a ridge progresses
east into the Ohio Valley and Great Lakes. A weak warm front may
bring a few wet snow or rain showers Sunday, with another stronger
warm front bringing a better chance of rain showers by later Monday.
Temperatures will warm to above normal again for Sunday afternoon
through Monday.


A warm front will bring increasing clouds and a few widely scattered
light showers as it crosses the region this afternoon and early this
evening...however these will be unlikely to produce any restrictions.
Thus...expect VFR conditions to continue to prevail through the rest
of today and into this evening.

Tonight widespread MVFR CIGs will develop as a warm and moist
airmass moves into the region. With this, shower chances will
increase as well, and have included VCSH in the TAFs overnight
tonight. Low-level wind shear will also increase across western NY
overnight as this airmass surges into the region, have thus included
about 50kts of LLWS at BUF/IAG/ROC/JHW later tonight. Toward
daybreak Wednesday, thunderstorms will approach western and north
Central NY, which could bring heavy rainfall, gusty winds, an
localized IFR conditions.

Wednesday...MVFR/IFR in widespread showers and possible
thunderstorms. LLWS remaining possible.
Thursday and Friday...Scattered snow showers with areas of MVFR.


Light winds and waves will continue today. Stronger winds will then
return tonight and Wednesday as a deepening area of low pressure
moves across the Great Lakes...then will continue through Wednesday
night and Thursday as the low deepens further while tracking across
the Saint Lawrence Valley and Canadian Maritimes.


The Black River will maintain high levels through the weekend. It
has crested upstream of Lowville, but is still rising slowly at
Watertown. Forecasts keep it just below flood stage with its crest
at Watertown tonight. Even after it crests, the river will maintain
high levels, with minor flooding in the typically vulnerable flats.

After this, low pressure will again track to the north and bring
more much above normal temperatures and a period of rain. Although
the previous system melted a lot of the snow pack, there is still a
significant snow pack in place across the Tug Hill and the Western
Adirondacks. Run-off from snow melt will combine with rain from this
system to cause the Black River and its tributaries to rise again
late this week. The Boonville and Watertown forecast points are of
greatest concern, where there is a potential for flooding in the
Thursday and Friday timeframe. There is still uncertainty in the
timing of the cold front, so there is not enough forecast confidence
to issue a Flood Watch yet. Elsewhere, the risk for flooding is
limited given the lack of snow pack.





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