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Area forecast discussion 
National Weather Service Buffalo New York
351 PM EDT Tuesday Sep 2 2014

Synopsis...
a cold front will slowly cross the region this evening with
widespread showers and thunderstorms...some of which could
produce strong gusty winds and heavy rainfall. 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. The next chance of rain will be on Friday with the next
frontal passage.

&&

Near term /through Wednesday/...
a broad middle-level trough is crossing Michigan this afternoon with a
surface cold front extending from low pressure over northern Quebec
southwest to Toronto then Cleveland. Regional radars are showing two
main areas of showers and thunderstorms. The first extends from just
east of Buffalo south across the western southern tier. This is a
pre-frontal band of showers associated with a 30-35 knot low-level
jet ahead of the front. The second and more organized area of showers
and thunderstorms is oriented along the cold front focused mainly
across the western end of Lake Ontario and Niagara Frontier. Satellite
imagery shows a wealth of clouds along and ahead of the front which
is likely keeping a lid on what could be stronger and more organized
storm structures.

Expect the front to shift east through the rest of this afternoon
with the best potential for showers and thunderstorms being found
along its leading edge. This will merge with the southern tier
region of showers per near-term guidance. A slight risk of severe
storms remains outlined from Storm Prediction Center extending from the interior southern
tier across The Finger lakes into central New York. In this area
better surface heating occurred earlier helping to boost instability.
Effective bulk shear at 0-6km of 45-55kts will keep strong gusty
winds the main severe threat with storms along the cold front while
limited lapse rates due to cloud cover should keep a low hail
threat. High precipitable water values of 1.7"-1.8" out ahead of the
front will offer the risk for heavy downpours with any thunderstorm.
Temperatures and humidity will remain on the warm and muggy side
right into the evening hours.

The cold front will slide east of the forecast area
tonight...tapering off last across central New York just after
midnight. High pressure will expand north behind the front across
New York overnight. BUFKIT profiles indicating some low level
moisture will remain near the surface keeping low stratus hanging
around much of the night so have went more pessimistic than
guidance. This may interact with the higher terrain to produce areas
of fog. Lows will be generally only fall to around 60 as the airmass
behind the front is Pacific sourced.

On Wednesday high pressure will expand north from the Tennessee
Valley across New York with a zonal flow aloft. Dry weather is
expected with morning clouds slowly breaking up and lifting for some
afternoon sunshine. Temperatures will rise into the upper 70s to around 80.

&&

Short term /Wednesday night through Friday night/...
a broad ridge of high pressure across the northeastern states will
be firmly in control of our weather Wednesday night with fair
weather and clear skies.

Low pressure will lift north of Lake Superior on Thursday...with an
associated warm front forecast to move across the Great Lakes
region. For our region...this is most apparent in temperatures aloft
where model consensus increases 850mb temperatures to +18c by 00z
Friday. There may some clouds associated with this middle-level warm
air advection...but expect most of the day to be sunny which will
allow temperatures to climb into the lower to middle 80s.

South-southwest winds will increase ahead of an approaching cold front on
Thursday night...which should limit radiational cooling and also
downslope a bit north of I-90. As a result temperatures will not
drop very much overnight...with lows expected to range from the middle
and upper 60s inland to lower 70s near the lakeshores. Any showers
should hold off...with the cold front still well to our northwest.

Things get a bit more interesting on Friday...with a vigorous
shortwave forecast to lift toward Hudson Bay while an associated
surface low takes a similar track and pushes a cold front toward our
region. Showers and thunderstorms should hold off until the
afternoon and ahead of the showers temperatures should easily climb
well into the 80s. There will be a gusty southwest flow in
place...which should limit temperatures downwind of Lake Erie across
the Niagara Frontier. But this flow downslopes east of
Rochester...where highs should be around 90.

Expect a broken line of showers and thunderstorms to develop out
ahead of the cold front during the afternoon hours. This may
initially struggle to make it across the brisk southwest flow up the
lakes...but should eventually push into the Niagara Frontier. The
12z NAM appears too moist with its surface dew points...with most
other guidance forecasting dew points in the upper 60s with ml convective available potential energy
building to around 1000 j/kg. Even so this may be enough for some
storms to develop inland of the lakes late Friday afternoon.

Model guidance continues is in good agreement in bringing the cold
front across the region Friday night. In addition to the
front...an upper trough just behind the front will bring another
opportunity for showers. Although the initial round of showers and
thunderstorms with the front may be broken...trailing showers and
increased confidence in timing still supports low likely probability of precipitation for
Friday night.

&&

Long term /Saturday through Tuesday/...
a cold front will push south of our region...ushering in cooler air
for the weekend. Broad high pressure across the middle-western states
will expand eastward and into our region for the weekend. Some
guidance (notably the ggem) stalls the front across the southern
tier Saturday...while most other guidance suggests a more decisive
passage. Given the timeframe...can still see a chance of showers
lingering through Saturday. After this...high pressure gains control
and should provide dry weather Saturday night through Tuesday.

Temperatures will be notably cooler for the weekend...with highs in
the upper 60s to lower 70s. Temperatures aloft appear cool enough
for lake effect clouds to linger southeast of the lakes...which
should at least partially limit sunshine. There should be more sun
on Monday and Tuesday...with temperatures warming to the middle to
upper 70s by Tuesday.

&&

Aviation /20z Tuesday through Sunday/...
VFR found near 20z ahead of a cold front crossing southwest Ontario
province toward western New York. Showers and isolated thunderstorms
are shifting east along the front. Weak instability has kept
lightning activity limited to just the stronger cores near cyyz and
north of kart. Expect showers and isolated thunderstorms along the
front to cross western and central New York into this evening. Have
kept thunderstorms in the vicinity to cover for passing storms but the main issue will be
brief periods of MVFR/IFR in heavy downpours. A few of these storms
could even become strong to severe across the forecast area with
strong gusty winds. Outside of any showers and
thunderstorms...expect VFR flight conditions.

All precipitation will exit south and east of the region this
evening...with most areas seeing VFR flight conditions returning for
most of the night. Across the southern tier it appears that IFR low
ceilings will develop behind the cold front and linger through much of
the night. High pressure will build in across the region on
Wednesday helping to bring a slow lifting and then clearing trend
into the afternoon.

Outlook...
Wednesday and Thursday...VFR.
Friday and Saturday...a chance of showers and thunderstorms with
associated brief MVFR/IFR...otherwise VFR.
Sunday...a chance of MVFR/IFR across the southern tier in the morning
otherwise VFR.

&&

Marine...
a cold front will cross the lower lakes region through this evening.
On Lake Erie winds and waves have averaged below advisory levels
this afternoon so have dropped the Small Craft Advisory. The front
itself is bringing widespread showers and thunderstorms shifting
east across the lakes. A few of these storms could produce strong
gusty winds and locally higher waves.

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...none.

&&

$$

Synopsis...Smith
near term...Smith
short term...apffel
long term...apffel
aviation...Smith
marine...Smith

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