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Area forecast discussion 
National Weather Service Buffalo New York
757 PM EDT Wednesday may 27 2015

a weak cold front will move across the region early tonight.
High pressure will move in behind the front Thursday...then move
off the New England coast Friday. A sharp cold front is expected
to push through the region over the weekend.


Near term /through Thursday/...
a middle level trough will be swinging through the Great Lakes tonight
while a surface low over Ontario pulls a cold front across western
New York late tonight. This will finally provide some surface based
forcing to a warm and humid airmass thats been in place for the past
several days.

Radar imagery this evening showing an area of showers and scattered
storms crossing western New York along a pre-frontal trough and just ahead
of a middle level trough moving through the Central Lakes. Large scale
ascent ahead of the middle level trough and low level convergence along
the pre-frontal trough will continue to support scattered convection
through the early overnight as the pre-frontal trough and composite
outflow boundary moves east across the area. The actual surface cold
front is lagging behind across the Central Lakes...and will cross
the area late tonight possibly producing a few more showers and
scattered thunderstorms.

A few of the stronger storms may produce gusty winds and heavy
rainfall through this evening. SBCAPE is around 1000j/kg with 0-6km
shear on the order of 30-35 knots...both very marginal to support
any severe potential. In far the composite outflow
boundary ahead of the area of convection which has limited
intensity. New storms developing over the Genesee Valley are near
the leading edge of the outflow...and will have some isolated severe
risk in the near term. Overnight boundary layer stabilization will
end any severe risk.

Once the front pushes through the threat for convection will
diminish. Cooler and drier air will move in overnight with lows in
the middle 50s to lower 60s.

Rising heights will continue to push across the Great Lakes region
during the day on Thursday. Plenty of dry air and subsidence will
provide a fair weather day. High mainly in the lower to middle
70s...but likely remaining the the upper 60s across the north


Short term /Thursday night through Saturday night/...
a progressive flow found over North America will offer two fairly
significant cold frontal passages over the Great Lakes during this
period....but the bulk of the time will be dominated by a strong
East Coast ridge. This will translate into mainly dry...uneventful
weather. The good news for agriculturalists is that the stretch
of dry weather will likely end with a 'wet' frontal passage as
this time frame comes to a close.

A strong shortwave crossing the upper Great Lakes today will drive
a cold front across our region late tonight and early Thursday.
The main front should be through most of our forecast area by
daybreak with middle level drying already becoming established over
the western counties. A secondary frontal boundary will sweep
across the north country by midday though...and this should delay
the onset of fair weather for that area by some 3 to 6 hours.
Otherwise...high pressure centered in the vicinity of James Bay will
nose south across the lower Great Lakes during the course of the
day....with subsidence and continued drying leading to increasing
amounts of sunshine. It will be cooler and noticeably less humid
as dewpoints that had been in the 60s will drop back
through the 50s. Afternoon maximum temperatures will generally be in the 70s.

Thursday night will feature moonlit skies as a burgeoning 500 mb ridge
will slide across the lower Great Lakes. It will be a comfortable
night with temperatures generally settling into the 50s. Sites in
the cooler southern tier valleys and in the foothills of the Adirondacks
could conceivably experience mins in the upper 40s.

Warmer weather will return to our forecast area on a
strengthening ridge will take shape along the East Coast. The
deepening southerly flow found between the associated offshore surface
high and a cold front over the upper Great Lakes will pump 850 mb
temperatures back into the middle teens celsius...which will easily support
afternoon maximum temperatures in the middle 80s for all but the Lake Shores
and higher terrain. The only fly ion the ointment for Friday will
be the potential for a late afternoon thunderstorm in the vicinity
of a lake breeze boundary over the southern tier. From this Vantage
Point though...the airmass looks like it will still be dry enough
to keep this threat from being too widespread.

After a very mild and uneventful Friday night when min
temperatures will hold in the middle to upper will likely
turn quite unsettled for Saturday. A sharp cold frontal boundary
stretching from Georgian Bay and lower Michigan to about Chicago
at daybreak Saturday will slowly press southeast to lakes Erie
and Ontario by evening. A warm unstable airmass in advance of the
front will support the development of numerous showers and
thunderstorms by afternoon...with a strong 130kt h25 jet over
Quebec reinforcing deep synoptic lift through the entire boundary
layer. This should result in some areas of significant downpours
with rainfall amounts of over an inch possible.

High pressure over Ontario will slowly push the front across
western and north central New York Saturday night. The anabatic
nature of the slow moving cold front will likely keep showers in
place Saturday night when another half inch or more of rain
could fall. This frontal passage certainly has the potential to
produce the most widespread soaking rainfall in quite some time.


Long term /Sunday through Wednesday/...
anomalously strong high pressure will drift across eastern Canada
Sunday and Monday...and this will shove a moisture rich cold front
further south across the Middle Atlantic States. Leftover showers over
much of our region on Sunday will finally come to an end as a
result...but a fair amount of clouds will likely persist. This will
especially be the case closer to the Pennsylvania border.

850 mb temperatures in the wake of the front are forecast to be in the upper
single digits (celsius) Sunday and Monday will feature below
normal temperatures with maximum temperatures generally in the 60s.

As the aforementioned surface high moves off the New England coast
Monday night and Tuesday...its clockwise circulation will open
the door for somewhat milder air to return to the region from the
upper Ohio Valley. Temperatures on Tuesday are thus forecast to
climb back into the low to middle 70s.


Aviation /00z Thursday through Monday/...
a band of showers and scattered thunderstorms across western New York this
evening will continue to move east overnight along a middle level
disturbance and pre-frontal trough. The actual cold front will cross
the area overnight and may produce a few more showers and scattered
thunderstorms. VFR will prevail most of the time through 06z with
only the heavier showers and storms producing brief/local MVFR to
IFR conditions. A few storms may also produce gusty winds.

Late tonight the showers and scattered storms will taper off from
west to east. In the wake of the showers several hours of MVFR to
IFR ceilings may develop across the higher terrain of the western
southern tier...Finger Lakes...and east of Lake Ontario as moisture
becomes trapped beneath a shallow frontal inversion and upslopes
into the higher terrain.

On Thursday any early showers east of Lake Ontario will end. This
will leave clearing skies with any MVFR/IFR ceilings across higher
terrain scattering out by middle morning. VFR will then prevail through
the rest of the day.

Friday...mainly VFR with a chance of showers and
thunderstorms across the southern tier and interior portions of The
Finger lakes.
Saturday...mainly VFR though showers and thunderstorms may bring
brief flight restrictions.
Sunday and Monday...mainly VFR.


southwest winds are diminishing this evening across the Niagara
River and Saint Lawrence River with the loss of daytime mixing.
There will be a veering to the winds to westerly tonight following a
cold frontal passage. Showers and a few thunderstorms will be
possible as this feature moves through with the potential for
locally higher wind and waves.

There is very little cold air behind the front and we do not
expect much increase in either winds or wave height later tonight
and into Thursday.

Expect another period of non Small Craft Advisory conditions on the area water bodies
into the beginning of the weekend. Later Saturday southwest winds
will increase ahead of a stronger cold front...possibly
necessitating the hoisting of additional small craft flags.


Buf watches/warnings/advisories...
New York...none.



near term...Hitchcock/tma
short term...Levan
long term...Levan/rsh

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