Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 240808

Area Forecast Discussion
National Weather Service Buffalo NY
408 AM EDT WED AUG 24 2016

High pressure will slowly drift east and off the Mid Atlantic coast
through tonight. This feature will provide our region with fair
and dry weather today, with a developing southwesterly flow of
warmer air pushing temperatures back to above normal. A weak cold
front will then cross the region Thursday with a few rounds of
scattered showers and thunderstorms before fair weather returns in
time for the weekend.


Surface high pressure will move to the eastern seaboard where it
will remain a dominant weather feature across the forecast area
today. This will result in another mostly sunny day across the
region today, with a few diurnal cumulus and some mid level
clouds approaching western New York this afternoon. As the high
slides further off the coast increasing southwesterly return flow
will allow a steady increase of heat and humidity. 850 mb
temperatures will surge to around +17C, supporting high
temperatures in the mid 80s to around 90 on the lake plains, and
lower 80s elsewhere. The southwest wind will keep the Lake Erie
shore a little cooler, and the gradient flow will be weak enough
to allow a lake breeze circulation to develop along the Lake
Ontario shore with locally cooler temps within a few miles of the

Our weather turns a bit more unsettled tonight. Models remain in
agreement on a convectively enhanced shortwave ejecting out of the
southwest US. This shortwave will lift to the northeast, transiting
mainly northern portions of the region. Increasing chances for
showers and perhaps some embedded thunderstorms will accompany the
warm conveyor belt into area as the night progresses.


After a couple of days of outstanding weather across our
region...Mother Nature will slap us back into reality with an all
too familiar sultry airmass. A strong sub-tropical ridge anchored
over the Southeastern states will pump a wealth of GOMEX moisture
across the Lower Great Lakes...and this will set the stage for what
should be 12-24 hours of potentially very unsettled weather.

As we open this period early Thursday morning...a shortwave
currently over the Upper Mid West will be in the process of crossing
Lake Ontario. While there may be some associated convection leftover
from the preceding overnight hours...subsidence will build across
the region in the wake of the exiting shortwave. This should offer
us with a few hours of benign weather during the remainder of the
morning. As we push through the midday and into the afternoon
though...the muggy unstable airmass will interact with several
potential boundaries to generate scattered thunderstorms. These
could include some leftover outflow boundaries from the previous
night...and at least a lake breeze boundary...with the potential for
a pre-frontal trough by late afternoon. Have high chc pops in place
for all but the lake shadowed area northeast of Lake Erie...and also
the mention for heavy rain with convection as PWAT values will be in
the vcnty of 2 inches with relatively short MBE vectors (as per NAM
based BUFKIT profiles). All this being said...the bulk of the day
will just be warm and sultry with highs in the mid to upper 80s.

A pre frontal trough will likely push southeast across our forecast
area during the first half of Thursday night. While this initial
front will not usher in a change of will clash with the
muggy sub-tropical air in place to generate more thunderstorms with
localized heavy rain. The coverage and intensity of the convection
will drop off rather substantially during the course of the night
though as the deep moisture field will be pushed away to the
southeast. The real cold front will make its way to the waters of
Lakes Erie and Ontario by around daybreak. Since a true airmass
change will not take place overnight...temps will be close to those
of the previous night with lows in most areas not far from 70.

The main cold front will drop south across our forecast area on
Friday morning. The bulk of instability will have been stripped from
our region during the previous night...and with mid level drying
already underway...will only carry low chc pops for the morning for
sites south and east of a line from KART and KDSV to KELZ.
Otherwise...high pressure over the Upper Great lakes will gain
control of our region with continued drying leading to a partly to
mostly sunny afternoon. Steadily lowering dew points will make it
feel increasingly more comfortable as we push towards evening.

The large surface high will drift across the Lower Great Lakes
Friday night. Light winds and clear starlit skies will support
decent radiational cooling so that it will be a much more
comfortable night for sleeping. Overnight lows will be in the 50s to
near 60...roughly 10 degrees lower than the previous two nights.

We can then look forward to a beautiful day across the region
Saturday as Canadian high pressure will pass by to our north. Sun
filled skies will be accompanied by a fairly comfortable airmass...
which will include max temps in the lower 80s (up 70s North Country)
and tolerable humidity levels (Tds up 50s/nr 60).


Persistent ridging based over the Southeastern states will provide
our forecast area with above normal temperatures and moderately high
humidity through this period. This will be accompanied by a little
unsettled weather...mainly Sunday night and Monday. The details...

Sunday should be the most uncomfortable day of this long term
period. A shortwave pushing across the Upper Mississippi Valley will
combine with the sub tropical ridge to our south to establish a deep
southerly flow across the Lower Great Lakes. Both the deterministic
GFS and ECMWF are suggesting that H85 temps will climb to as high as
20c over our region on Sunday...and that if it were well mixed...
would easily support afternoon highs close to 90F for the lake
plains and valleys. Given that we are on the backside of the thermal
solstice and have had a little rain the past week or so...will be
conservative with highs in the upper 80s for the favored warm areas.
These values could be nudged higher as the time period draws closer.

A pre frontal trough could cross our forecast area Sunday night
ahead of a more pronounced cool front that is expected to move
through during the day Monday. In both cases...the features could
touch off scattered showers and thunderstorms. The greatest chance
for this activity would come on Monday.

By Tuesday...the front is expected to be stalled to our south with
weak high pressure moving by to our north. While confidence with
this solution is relatively low from this vantage point...such a
scenario would keep at least slgt chc pops in place for the Southern
Tier and Finger Lakes regions. Max temps on Tuesday are forecast to
be in the lower 80s for most areas. Meanwhile...overnight lows
through the period will be in the low to mid 60s.


High pressure drifting off the Mid Atlantic coast will keep mainly
clear skies and VFR for most areas early this morning. Some
typical river valley fog will form across the western Southern
Tier with local IFR through 12Z. This fog should remain in the
valleys and not impact the hilltop KJHW airfield.

Any valley fog will burn off by mid morning, leaving VFR to
prevail with just a few sct diurnal cumulus inland from the lakes
and some increase in mid level clouds late in the day across
Western NY.

Thursday...VFR with scattered showers and thunderstorms
becoming more numerous Thursday night...when some MVFR will also
become possible.
Friday thru Sunday...Mainly VFR.


High pressure will drift from Maryland off the Mid Atlantic
coastline through tonight...while maintaining light to modest winds
and lower waves. The gradient flow will be light enough to allow for
local lake breezes to develop this afternoon, with winds becoming
onshore and waves building to up to 2 feet locally.

Thursday and Thursday night a cold front will ease its way across the
Lower Lakes. This feature will bring some showers and thunderstorms
to the region...with freshening southwesterlies out in advance of the
front veering to westerly following its passage Thursday night...
then gradually diminishing on Friday as high pressure builds into
the region. Depending upon how much winds and waves increase...small
craft advisories may eventually be needed for some areas Thursday
and Thursday night.





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