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Area forecast discussion 
National Weather Service Buffalo New York
1006 PM EDT Monday Sep 1 2014

Synopsis...
showers and a few isolated thunderstorms will likely reach western
New York around midnight...and advance eastward overnight while diminishing
in intensity and coverage area towards The Finger lakes and areas
east of Lake Ontario. A cold front will then cross the region on
Tuesday with more widespread showers and thunderstorms...some of
which could produce strong gusty winds across portions of the
southern tier and Finger Lakes. In the wake of the front...high
pressure will build into the lower Great Lakes and bring a return to
drier and less humid weather Wednesday and Thursday.

&&

Near term /through Tuesday/...
this late evening regional radars display a few widely scattered
showers along the Southern Lake Ontario shoreline and northeastward
towards Cape Vincent. This activity will continue to progress
eastward through the night. Farther westward a line of showers and
thunderstorms continues as a prefrontal trough nears western New
York. This activity...feeding off a narrow ribbon of 1000 j/kg of
100 mb mixed layer cape and an increasing low level jet will continue to
advance eastward. The northern portion of this line is showing some
weakening trends to its structure...while the segment closer to Lake
Erie continues to exhibit decent showers and thunderstorms. Will
place likely probability of precipitation across far wny...with the highest probability of precipitation towards the
lake and south...with low end likely probability of precipitation near Lake Ontario.
Instability is expect to diminish some as the night carries on and
this line of showers and thunderstorms will likely also weaken
some. However the low level jet of 30 knots at 850 hpa should maintain at
least a chance of showers towards the Genesee Valley and points
eastward through the overnight time period.

Lows tonight will remain on the mild side for early September with
lows in the middle 60s to lower 70s...warmest across the lake plain.

On Tuesday...the axis of broad middle and upper level troughing will
slide east from the upper Great Lakes to the lower lakes region...
with an associated weak cold front easing eastward across the
forecast area during the course of the afternoon. In advance of this
front...a very warm and humid airmass will remain in place with
precipitable water values approaching two inches...while large-scale
lift will be on the increase owing to a combination of increasing
convergence along the front/the nose of a 30-40 knots low-middle level
jet...supporting synoptic-scale DCVA/height falls...and increasing
upper level diffluence in the right entrance region of a 120+ knot
upper level jet. Coupled with daytime heating...all of this should
result in fairly numerous showers and thunderstorms developing
along/ahead of the front as it crosses our region...for which some
likely to low-end categorical probability of precipitation will be in play.

While there will be a fair amount of wind in place aloft to keep
things moving along...given the very moist airmass there still will
be at least some threat of locally heavy rainfall on Tuesday...
especially if any stronger/heavier cells manage to train repeatedly
over a particular area. The overall severe potential is somewhat
less clear given lingering uncertainty with respect to how much
heating/destabilization will occur prior to the arrival of the
front...however with 35-45 knots Worth of 0-6 km bulk shear in
place...the potential for some stronger storms capable of attendant
strong to severe wind gusts certainly exists provided enough
instability can ultimately be realized. At this point...a rough
model consensus suggests that the greatest potential for this will
exist from interior portions of the southern tier northeastward
across The Finger lakes region...where the best instability and
large-scale dynamics will be superimposed upon each other. Not
coincidentally... this agrees quite well with spc's latest day 2
convective outlook...which portrays a slight risk of severe storms
across this particular region.

&&

Short term /Tuesday night through Thursday/...
the cold front will slide south and east of the forecast area
Tuesday night. Most 12z guidance has the trailing edge of showers
and thunderstorms with this front along the southeast border of the County Warning Area at
00z. Once this exits...expect dry weather late Tuesday evening which
will last through most of the week.

Surface high pressure across the Ohio Valley on Tuesday night will
gradually shift into southern New England through Thursday. This
will bring fair weather and mostly clear skies Wednesday and
Wednesday night. Temperatures will only be modestly cooler behind
the front...with mostly skies temperatures rise into the upper 70s
on Wednesday.

On Thursday...there will be a zonal flow aloft...with the jet stream
well to our north in Canada. Low pressure will lift across
Minnesota Thursday...with middle-level warm air advection forecast to
lift across our region. This may produce a stray sprinkle or shower
in northeastern portions of the County Warning Area...while the vast majority of the
region stays dry. A NAM/GFS consensus warms 850mb temperatures in
far western New York to +18c by 00z Friday. Depending on timing of
the front...highs on Thursday should rise into the lower 80s in most
locations.

&&

Long term /Thursday night through Monday/...
high pressure will slide off the New England coast Thursday
night...meanwhile a cold front will approach from the west. This
frontal passage will be the most significant weather factor for the
long term period...with 12z guidance still differing on the fronts
timing and how much cold air will be behind it. The forecast will
follow a consensus of this guidance which is notably slower than the
12z ggem in terms of timing...and warmer than the 12z GFS with
Post-frontal temperatures.

Friday should Summer-like...with highs in the 80s. The front is
likely to move across the region Friday night...with a chance for
showers and thunderstorms Friday afternoon through Saturday. With a
nighttime passage...expect only a broken line of showers with the
front...and possibly behind it with some anafrontal precipitation.

The front will push south of the region Saturday night...with dry
weather expected on Sunday and Monday. A consensus of this guidance
drops 850mb temperatures down to +5c...which should result in
lingering lake effect clouds for at least part of the day on Sunday.
High pressure will build across the region on Monday...with a bit
more sunshine. Temperatures behind the front will be much
cooler...with highs in the upper 60s to lower 70s Sunday and Monday.

&&

Aviation /02z Tuesday through Saturday/...
VFR flight conditions at 00z will persist for another 6 hours or
so...before some patches of MVFR ceilings...and southern tier IFR ceilings
form across the region just before dawn.

A pre frontal surface trough may bring a few showers across wny just
past midnight...with activity diminishing across the County Warning Area overnight.
This activity will likely diminish before reaching the kart
airfield...so will only place vcsh in taf sites to the west of
Watertown.

On Tuesday...a weak cold front will slowly ease eastward across the
region through the course of the day. Coupled with increasing
daytime instability...expect more widespread showers and storms to
develop along and ahead of this front as it crosses the area...with
some of these potentially bringing brief periods of MVFR/IFR. A few
of these storms could even become strong to severe across interior
portions of the southern tier and Finger Lakes...where overall
instability appears as if it will be the strongest.

Outlook...
Tuesday night...showers and thunderstorms ending across southern and
eastern sections...with conditions mostly returning to VFR.
Wednesday and Thursday...VFR.
Friday and Saturday...a chance of showers and thunderstorms with
associated brief MVFR/IFR...otherwise VFR.

&&

Marine...
a cold front will work across the upper Great Lakes tonight...before
crossing the lower lakes region on Tuesday. In advance of the
front...southwesterly winds will increase later tonight and Tuesday
morning...particularly on on Lake Erie where winds and waves will
climb to near advisory levels. Will issue a Small Craft Advisory for Lake Erie
through midday tomorrow to account for some winds nearing 18-20
knots overnight and through the morning hours. The front itself will
also produce a round of scattered to numerous thunderstorms on
Tuesday... a few of which could produce strong gusty winds.

In the wake of the frontal passage...high pressure will build across
the region Tuesday night through Thursday while bringing a return to
fair weather and lighter winds.

&&

Buf watches/warnings/advisories...
New York...none.
Marine...Small Craft Advisory until 2 PM EDT Tuesday for lez040-041.

&&

$$

Synopsis...jjr/Thomas
near term...jjr/Thomas
short term...apffel
long term...apffel
aviation...Thomas
marine...Thomas

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