Area Forecast Discussion
Issued by NWS Buffalo, NY

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503
FXUS61 KBUF 201516
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1116 AM EDT WED JUL 20 2016

.SYNOPSIS...
High pressure will drift across the region today and tonight
bringing comfortable summer weather with low humidity. The surface
high will settle off the east coast Thursday allowing heat and
humidity to build across the region through the weekend. Scattered
strong thunderstorms are possible across the region Friday ahead of
an approaching shortwave.

&&

.NEAR TERM /THROUGH TONIGHT/...
High pressure centered over Lake Erie will drift across the region
through tonight before settling off the east coast on Thursday.
Mostly sunny skies will persist across the region today, with just
some passing high thin cirrus and a few diurnal cumulus inland from
the lakes. The dry airmass, with dewpoints largely in the upper 40s
and low 50s, will combine with air temperatures in the upper 70s to
lower 80s to make for a fantastic summer afternoon across western
and north central NY.

Tonight, the lack of cloud cover, mostly light winds, and dry
airmass under the surface high will promote radiational cooling
overnight. Temperatures dip into the mid to lower 50s overnight,
with some readings near 60 along the immediate lakeshores. The
relatively low dew points should limit the southern tier valley fog,
but some isolated to patchy fog cannot be ruled out there.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/...
A massive +597dm H5 ridge will completely dominate the bulk of the
country during this period...with our forecast area being found on
its eastern fringes...thereby experiencing a sampling of its
effects. While the ridge with +2 std hgts over the center of the
country will generate an unusually extensive area of heat related
headlines for the Plains and Mississippi Valley...our region will
have to tolerate another extended stretch (3-4 days) where daytime
highs will climb to within a couple degrees of 90.

The hot afternoons through the upcoming weekend will be accompanied
by overnight lows that will be in the 70s across the more densely
populated lake plains. This means that our temperatures will average
5 to as much as 10 deg f above normal throughout the period...which
is made even more impressive knowing that we are in the midst of our
thermal solstice. It is also interesting that the above normal
temperatures and current moderate to severe drought will feed upon
each other...with the alarmingly dry antecedent soil conditions
adding several degrees to daytime highs while the higher temps will
further exacerbate the problems associated with the drought.

As we head into the upcoming weekend though...a Pacific based
shortwave pushing across the Northern Rockies will basically flatten
the impressive ridge. Meanwhile...lowering hgts near Hawaii will
encourage the heart of the newly flattened ridge to retrograde back
across the Desert Southwest to the California Coast. This will leave
a seasonally biased area of high pressure that will monopolize the
weather between 20-35 N from Hawaii to the Southeast Coast...while
downstream troughing over the St Lawrence Valley will eventually
allow a legitimate cold front to push thorugh to cut off our source
of heat. More on that in the long term discussion.

As for the day to day details...
High pressure off the East Coast on Thursday will combine with high
hgts over the Lower Great Lakes to support fair weather across our
forecast area. The deepening southerly flow found around the pseudo-
Bermuda High will not only advect warmer air across our region...but
will allow GOMEX moisture to finally return. The result will be a
day where both temperatures and dew points will be some 10 deg
higher than the previous two days. Plenty of sunshine and H85 temps
in the upper teens will easily support afternoon max temps in the
upper 80s to lower 90s across the lake plains and valleys. The only
potential fly in the ointment on Thursday will be the amount of
cirrus blowoff that makes its way into the region from upstream
convection found over the Upper Great Lakes and Southern Ontario.

It will then become interesting Thursday night as a cold frontal
boundary will push south across Southern Ontario. Convection that
will had previously blown up well ahead of the front could sustain
itself as it pushes south across Lake Ontario early in the night...
and if it can...it should encounter an increasingly unstable airmass
over Western and North Central New York. Given the northwesterly
flow aloft...there will also be favorable kinematics to induce bulk
shear values in excess of 40 knots. This would be favorable for
strong to severe convection with an emphasis being placed on
damaging straight line winds. The most favorable area for such
activity should be west of the Finger Lakes where organized
convection would likely build southeast into the most unstable air.
While there is relatively low confidence in this forecast...it is
certainly worth addressing and needs to be further examined as the
time frame nears. Temperatures Thursday night will likely remain
above 70 for the majority of the region.

On Friday...any strong storms from the previous night should have
since weakened and pushed south...while another area of convection
associated with a cold front will take aim on the region. Between
the two batches of storms...there will be a 3-6 hour window of
uneventful weather...but this will be nearly impossible to narrow
down from this vantage point given the timing and strength of the
original convection. In any case...the cold front will push south
across the forecast area during the midday and afternoon. As the
atmosphere heats back up and `re-loads`...the stage could be set for
another round of strong storms. Northwest winds will still be in
place aloft...so this will once again help to produce favorable
conditions for potentially hazardous weather. Otherwise it will be
very warm and humid with H85 temps in the upper teens supporting
afternoon temperatures in the upper 80s to near 90 for the lake
plains and most valleys.

The cold front will push south of our region Friday night while
drier air will make its way across the Lower Great Lakes. Any
lingering showers or storms will end early with skies clearing from
the northwest during the course of the night. Unfortunately...there
is not expected to be a real change in airmasses...so temperatures
will be similar to those from the previous night.

On Saturday...high pressure will build back across our region while
a reinforcing push of oppressive warmth will make its way across the
Lower Great Lakes. H85 temps should again be in the upper teens to
near 20...so our afternoon temps will climb back towards 90 away
from the lakes and higher terrain.

While fair weather can be anticipated for Saturday night with high
pressure still over the region...the next area of convection will be
approaching from the west. These storms will be associated with a
possible MCS that will be riding along the top of the flattened H5
ridge. Temps Saturday night will again hold well above normal.

&&

.LONG TERM /SUNDAY THROUGH TUESDAY/...
While more comfortable weather will gradually work its way across
the Lower Great Lakes during this period...there should be no doubt
that our temperatures will average above normal. This will be due to
a subtle pattern change that was briefly discussed above.

In the days leading up to this point...an anomalously strong ridge
based over the Southern Plains and Desert Southwest helped to pump
very warm air across all of the Great lakes region. During this time
frame though...the upper level pattern will have reoriented itself
to consist of an elongated ridge from the Southeast Coast to the
central Pacific while an undulating low amplitude flow will be found
along the Canadian border. This will serve to suppress the real heat
to the southern and western portions of the country.

Interestingly enough...one of the key features in the pattern change
will be the Pacific shortwave that initially flattened the dominant
ridge several days earlier. This bundle of mid level energy will
cross the Upper Great Lakes Sunday night and Monday while driving a
legitimate cold front across our forecast area. It will not be until
this frontal passage that we start to experience some relief from
the heat and humidity. Lets take a closer look at the details.

Sunday should be our last day of real heat and humidity as ridging
will cross our region. While there will be the potential for some
storms over the western counties during the afternoon...the bulk of
the day will be partly sunny and sultry with high temperatures
ranging from around 90 across the lake plains and valleys to the mid
80s across the highest terrain.

Showers and thunderstorms will become more widespread Sunday night
and Monday when the aforementioned cold front will pres through the
region. Given the consistency between the ECMWF and GFS ensembles...
have raised pops to high chc for this 24 hour period.

High pressure over the Upper Great Lakes Monday night will then
start to build across our forecast area on Tuesday. This will be
accompanied by an airmass change with dew points in the lower 60s
and H85 temps averaging 12C providing pleasant conditions for
outdoor activities.

&&

.AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
High pressure crossing the region through the TAF period will bring
light winds and VFR flight conditions.

Later today lake breeze circulations will develop with winds
veering to northwesterly at the KROC airfield between 18 and 20Z.

Outlook...
Thursday...VFR.
Friday...Mainly VFR with a chance of showers and thunderstorms.
Saturday...VFR.
Sunday...Mainly VFR with a chance of showers and thunderstorms.

&&

.MARINE...
High pressure will cross the region today, with little wind and wave
action on the Eastern Great Lakes. A few disturbances will cross the
lake waters later this week, increasing the waves a bit on the
lakes, though likely remaining below 4 foot. Entering the weekend
fine boating conditions will again occur.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...None.

&&

$$

SYNOPSIS...THOMAS
NEAR TERM...CHURCH
SHORT TERM...RSH
LONG TERM...RSH
AVIATION...CHURCH/THOMAS
MARINE...CHURCH/THOMAS



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