Area Forecast Discussion
Issued by NWS Buffalo, NY

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384
FXUS61 KBUF 272043
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
343 PM EST Mon Feb 27 2017

.SYNOPSIS...
Weak high pressure will keep mainly dry weather across our region
through tonight. A warm front will then bring an increasing risk for
some showers on Tuesday...before more widespread showers and possible
thunderstorms develop later Tuesday night and Wednesday as low pressure
moves through the Great Lakes. Temperatures will remain well above
normal through Wednesday...before colder air returns late in the
week.

&&

.NEAR TERM /THROUGH TUESDAY/...
Tonight a weak mid level wave over the Upper Ohio Valley will quickly
slide east and off the mid Atlantic coastline...while weak low-mid level
warm air advection continues across Pennsylvania and New York. The weak
warm advective regime will drive a south-north increase in cloud cover
across the region tonight...with perhaps just enough moisture and lift
available to generate a few sprinkles and/or flurries across interior
portions of the Southern Tier...Finger Lakes...and North Country.
Otherwise the night will be dry...with the increasing cloud cover
helping to keep temps from dropping below the lower to mid 30s south
of Lake Ontario...and the upper 20s across the North Country.

On Tuesday expect a dry start to the day...before strengthening warm
air advection and an approaching warm frontal boundary bring about the
likelihood of a few light showers for a portion of the afternoon.
Otherwise temperatures will continue to trend higher under the continued
warm advection...with our region seeing afternoon highs ranging from
the upper 40s and lower 50s across the North Country to the mid and
upper 50s south of Lake Ontario.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/...
Low pressure will strengthen as it tracks from Eastern Michigan to
Northern Maine during the Tuesday night to Wednesday night period.
This bring another round of unseasonably warm temperatures to the
region and some showers and thunderstorms. Then a cold front will
drop across the region behind this system, bringing in colder
temperatures and some snow showers Wednesday night into Thursday.

Model consensus is in good agreement concerning this general
pattern, but there are more subtle differences which will have a
significant impact on our forecast. It appears there will be a pre-
frontal trough followed by a strong cold front on Wednesday. The
timing and location of these features is uncertain because of
differences in the strength of of a secondary low which will develop
along an elongated surface trough.

The most active period will be from late Tuesday night through
Wednesday night when there will be multiple issues to deal with.
This includes a potential for strong winds, severe weather, and
flooding. The flooding potential will be discussed in the hydrology
section, while the other threats are outlined below.

...Wind potential...

Winds aloft will increase ahead of the initial wave late Tuesday
night into Wednesday morning with 925mb winds around 50kts and 850mb
at 60kts. The strongest winds will slide to our east with the pre-
frontal trough, but will pick up again ahead of the surface front
late Wednesday. The GFS and NAM differ considerably in the position
of the front with the GFS keeping the entire CWA in a southwesterly
flow while the NAM drops the cold front across Lake Ontario
Wednesday afternoon. Model consensus favors the later GFS timing,
but with uncertainty in wind fields aloft it is difficult to be too
specific concerning the high wind potential. This said, there
appears to be several opportunities for winds to reach at least wind
advisory criteria, with a chance for SSW winds to downslope late
Tuesday night, followed by a southwesterly flow across the lake
planes behind the pre-frontal trough and again in all areas with the
cold front. For the most part, expect peak gusts in the 40 to 50 mph
range, or in the wind advisory realm. While higher gusts cannot be
ruled out, there is not enough forecast confidence to issue a high
wind watch yet.

...Severe Weather...

There will be significant wind shear in place from late Tuesday
night through early Wednesday evening, with instability the limiting
factor. It appears the best instability will be ahead of the pre-
frontal trough on Wednesday morning with guidance showing SB CAPES
to around 500 J/kg across southern portions of the cwa. This is also
when model guidance brings the most organized convection across the
region, supported by a shortwave and jet dynamics. The timing is
unfavorable during the morning hours, but there may be enough
dynamics to overcome this. In fact, SPC has included the area in a
marginal risk for severe weather on Wednesday, in the latest day 3
outlook. Based on this, have added a mention of gusty wind to
southern portions of the cwa, though it`s possible this will need to
be expanded later as model guidance comes into better agreement.
There a smaller, but non-zero, risk for severe weather along the
cold frontal boundary. Will continue to mention this in HWO.

Outside of these main threats, a weak wave may bring some showers
and embedded thunderstorms across the region Tuesday evening though
most guidance keeps our region dry. Temperatures will be well above
normal with overnight lows in the upper 40s to lower 50s. Model
consensus shows the best chance for showers with the pre-frontal
trough late Tuesday night and into Wednesday morning. Will carry
categorical POPs with this feature, then trend down to likely until
the cold front passes later in the day. Wednesday should be
unseasonably warm, with highs mainly in the 60s. Record highs for
March 1st are in jeopardy with forecast highs near or above the
records which are: Buffalo 64, Rochester 62, and Watertown 60.

Temperatures will cool abruptly behind the cold front which will
likely move through the region Wednesday evening though this timing
could change with future model runs. Temperatures will quickly fall
to near freezing, changing precipitation over to snow as the 500 mb
shortwave moves across the region. There also will be some modest
lake enhancement with 850mb temps falling to around -13C by Thursday
morning. Expect only modest accumulation from this south and
southeast of the lakes before this tapers off Thursday afternoon.
Then expect Thursday night to be mainly dry with the exception of the
Southern Tier where a clipper low may bring a brief period of light
snow.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
Winter conditions will return for the end of week into the weekend
as a deep progressive trough brings a surge of colder air across the
northeast CONUS. There will be enough cold air will slide into the
area for increasing northwest/west-northwest flow lake effect snows
Friday into Friday night as 850 mb temperatures drop to around
-18C. Lake induced equilibrium levels rise to between 10k and
15k for about a 9 hour period off both lakes and this may be
enough time for some modest accumulations to the south and
southeast of the lakes, but do not see any signals in the
soundings to suggest that this will be a significant event.

A stronger Pacific shortwave and surface low moving into the
upper Great lakes will bring a developing southwesterly flow
Saturday along with increasing warm air advection. This will
eventually lift the lake snows northward as the flow backs to the
southwest, but with equilibrium levels crashing down within the
warm air advection, see little of this activity left as it
crosses the Buffalo and Watertown areas.

Sunday into Monday there is some uncertainty in how things will
unfold with the deterministic models suggesting another storm system
will eject out of the Rockies. The big question will be what track
the system will take. The GFS suggests the system will develop
across the northern Rockies and the Canadian is much further south
across the southern and central Rockies, with the ECMWF falling in
between the two solutions. Nonetheless, it will remain on the mild
side within a persistent warm air advection regime with most high
temperatures both Sunday and Monday in the 40s to perhaps as warm
as the mid 50s.

&&

.AVIATION /21Z MONDAY THROUGH SATURDAY/...
Tonight a weak mid level wave will pass by to the south of the area...
with continued weak warm air advection bringing a south to north increase
in cloud cover...and perhaps a few sprinkles or flurries to interior
portions of the Southern Tier...Finger Lakes...and North Country. While
conditions should remain VFR in most areas...there could be enough low
level moisture to allow for a period of MVFR ceilings to develop across
the Southern Tier.

On Tuesday...expect mostly dry conditions to prevail during the morning...
before an approaching warm front brings a period of a few light showers
during the afternoon. Expect conditions to be largely VFR...with some
MVFR possible across far western New York later in the afternoon as low
level moisture increases.

Outlook...
Tuesday night...Deterioration to MVFR/IFR with more widespread showers
and possible thunderstorms developing. Some LLWS also developing.
Wednesday...MVFR/IFR in widespread showers and possible thunderstorms.
LLWS remaining possible.
Thursday and Friday...Scattered snow showers with areas of MVFR.
Saturday...VFR/MVFR.

&&

.MARINE...
Winds and waves have diminished enough on Lake Ontario to allow the
remaining small craft advisories to be dropped a little early. These
will continue to subside through early this evening...with generally
light to modest winds and relatively minimal waves expected for the
rest of tonight and most of Tuesday.

Stronger winds will then return Tuesday night 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.

&&

.HYDROLOGY...
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.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...None.

&&

$$

SYNOPSIS...JJR
NEAR TERM...JJR
SHORT TERM...APFFEL
LONG TERM...TMA
AVIATION...JJR
MARINE...JJR
HYDROLOGY...APFFEL



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