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Area forecast discussion
National Weather Service Buffalo New York
242 PM EDT Mon Aug 19 2019

Synopsis...
summery conditions will continue through midweek as high
pressure builds into the region for the early part of the week.
This will mean generally clear nights and days with abundant
sunshine until the approach of a system on Wednesday. This will
spread showers and thunderstorms across the region ahead of a
cold front that will slice through the area and bring cooler and
drier air into the area on the heels of gusty northwest winds
the second half of the week.

&&

Near term /through Tuesday/...
the departure of a cold front to the east has allowed for
nominally lower dewpoints to begin their spread into the area
from the west. This will continue for a few more hours as the
apex of a surface high pressure ridge begins to bridge toward
the lower Great Lakes from the middle Ohio Valley through the
evening hours. This will be the main influence over our weather
for the next 36 hours or so, which means gradually fading flow
over the area and strong inversions forming tonight. As a result,
fair weather cumulus will be common through the remainder of
the afternoon with fairly apparent lake breeze formation. This
will reverse tonight with land breezes forming and isolated
boundary layers in the valleys. As such, fog formation is almost
a foregone conclusion in the valleys of the southern tier. Based
upon river to atmosphere Delta t's, this could be locally dense.

High pressure will gradually slink east of the region on Tuesday,
which will turn flow from the southwest again. This will allow
for warm advection to resume, which will bring temperatures back
up into the mid 80s on a widespread basis after fog mix out.
Likewise, flow from the southwest will again bring dewpoints back
up into the rather disgusting territory near 70f.

&&

Short term /Tuesday night through Friday night/...
..a 'change of seasons' on the horizon...

The amplification of the upper level pattern will not only lead to a
change in the weather across our region...but it will feel like
we've changed seasons. The buckling of the current near zonal flow
will come as a result of a strong shortwave that will rotate across
British Columbia in the hours leading up to this period. This will
force an anomalously strong ridge to build over central Canada...
while a deep but progressive trough will dig over our region. The
result of this scenario will be a change from mid July weather to
early autumn as temperatures will plunge to below normal levels. As
is almost always the case...this transition could be marked by
significant weather. The details.

High pressure will move off the New England coast Tuesday night...
while a strong cold front will approach from the upper Great Lakes.
The deepening southerly flow found between these systems will not
only help to hold up our temperatures...but it will also transport
increased low level moisture into our region. This could lead to
some nuisance showers across the southern tier...although the bulk
of the region will just be warm and muggy with no precipitation.

Wednesday will then be quite active across our region. A pre-frontal
trough in the morning will combine with an already unstable
environment (mlcapes averaging 500 j/kg) to encourage an increasing
coverage of showers and possible thunderstorms. As we push into the
afternoon...a strong cold front will settle to the south across
lakes Erie and Ontario. While there will be a fair amount of cloud
cover around...there should be enough insolation to push sbcapes to
between 1000-1500 j/kg. The increasingly unstable airmass ahead of
the approaching front will then combine with the forcing form a
modest 30kt low level jet to support widespread showers and
thunderstorms...which should include locally heavy rain and possibly
some strong convective wind gusts. Have already raised pops to
categorical for the afternoon.

The showers and thunderstorms will taper off from north to south
early Wednesday night as the cold front pushes into Pennsylvania.
While somewhat drier air will work into the region late...the real
airmass change in the wake of the front will be delayed until
Thursday.

Speaking of which...Thursday will be cooler and much more
comfortable as dew points will gradually drop through the 50s.
Meanwhile 850 mb temps falling into the single digits will only support
afternoon temperatures in the low to mid 70s. Otherwise the day will
feature some 'self destruct sunshine'...as steep lapse rates of 9-10
deg c/km beneath a staunch substance inversion will combine with a
chilly cyclonic flow to encourage midday and afternoon strato-cu.
Despite the low level instability...the vast majority of the region
will experience rain free conditions. Will include slgt chc pops
away from the lakes with low chc pops found over the north country
where an upslope flow and a passing shortwave could allow for a
couple showers.

Thursday night through Friday night will have an autumnal feel...as
overnight mins will range from the mid 50s near the lakes to the 40s
in the cooler southern tier valleys and possibly the foothills of
the Adirondacks. Outside of some lake induced cloud cover southeast
of Lake Ontario late Thursday night...this three period stretch
should be mainly clear. Enjoy!

&&

Long term /Saturday through Sunday/...
there is fairly strong consensus between the gefs and operational
European model (ecmwf) that general ridging will be found over the region through
this period. The resulting fair dry weather will be accompanied by
subtle day to day warming...so that near to below normal
temperatures at the start of the period will climb above normal by
the start of the new work week.

&&

Aviation /19z Monday through Saturday/...
generally VFR conditions will continue through the afternoon
with fair weather cumulus prevailing. These will fade with
sunset, and clear skies will reign supreme. Fog development is
likely in the valleys around jhw tonight, with some locally
below 1/4sm. This will mix out for another VFR day Tuesday.

Outlook...

Tuesday...VFR.
Wednesday...VFR with areas of IFR in thunderstorms. Some storms
may be strong with gusty winds and hail.
Thursday through Saturday...mainly VFR.

&&

Marine...
while winds and waves will remain below Small Craft Advisory
criteria throughout the lower Great Lakes today...they will freshen
somewhat. This will especially be the case on the eastern half of
Lake Ontario where moderate westerlies will generate choppy
conditions for the open waters and the nearshore waters north of
Oswego.

Winds will weaken this evening and become light and variable
overnight through most of Tuesday...as high pressure will drift
across the region.

A cold front will cross the lower Great Lakes late Wednesday and
Wednesday evening. This will generate numerous showers and
thunderstorms...with some storms likely producing strong gusty
winds.

Strengthening northwesterlies in the wake of the cold front will
lead to solid small craft advisories for the Lake Ontario nearshore
waters Wednesday night and Thursday. Meanwhile...a shorter fetch and
lower wind speeds may allow conditions to remain below Small Craft
Advisory criteria on Lake Erie.

&&

Tides/coastal flooding...
a strong cold front will cross the lower Great Lakes late
Wednesday and Wednesday evening. Strengthening northwesterlies
in the wake of the front may combine with increased wave action
and already High Lake levels to produce more significant
shoreline erosion and flooding Wednesday night into Thursday
evening. A Lake Shore Flood Watch has been issued from Niagara
County to Oswego County to address this increased risk.

&&

Buf watches/warnings/advisories...
New York...Lakeshore Flood Watch from Wednesday evening through Thursday
evening for nyz004>006.
Lakeshore Flood Watch from Wednesday evening through Thursday
afternoon for nyz001>003.
Marine...none.

&&

$$

Synopsis...Fries
near term...Fries
short term...rsh

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