Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 210802
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
402 AM EDT THU JUL 21 2016

.SYNOPSIS...
An area of high pressure will continue to slip eastward today, while
providing for one more sunny and pleasant weather day. Tonight
southerly winds will increase, along with the level of humidity.
This moisture will feed thunderstorms across the region late tonight
and through the course of Friday, with some storms potentially
becoming strong.

&&

.NEAR TERM /THROUGH TONIGHT/...
IR satellite imagery displays the region virtually cloud free this
early morning. High pressure centered just to our east is producing
plenty of subsidence...with this sinking air continuing the clear
skies through the morning hours.

This afternoon as this surface high slips farther to the east we
will begin to see an increase in cirrus clouds...these ahead of a
cold front and convection over the Upper Great Lakes region.

We will return to the sultry conditions this afternoon as 850 hPa
temperatures increase to near +18 to +20c by this evening. This
warming aloft, combined with the southerly wind flow and still high
summer sun angle will allow for air temperatures to peak in the 80s
to lower 90s today.  Dew point temperatures will remain tolerable
with values in the upper 40s to mid 50s through the day. It will not
be until this evening when we see a rapid increase in the humidity.

Tonight humidity will continue to increase ahead of a cold front
that will be dropping across the central Great Lakes region. Our
region should see a increase in dewpoints up into the 60s, to
possibly around 70 across far WNY. This increase will be the result
of a strengthening nocturnal LLJ that will peak around 35 to 40
knots at 850 hPa.

The increase in moisture and air temperatures will create an
unstable atmosphere overnight. Upstream convection should blossom
over Michigan this afternoon, with such convection then traveling
SEward along the 1000-500 hPa thickness lines. While there will be
some weakening to the overnight convection, we should remain
unstable enough to allow for storms to expand eastward, clipping WNY
after the midnight hour.

Greatest chances for storms will lie mainly across the Niagara
Frontier and the western Southern Tier. A convective shortwave
producing lift for such storms will drop across WNY late tonight.
Will continue with likely pops here, and also across the SLV where
afternoon convection north of Lake Ontario may spread eastward
across the North Country overnight.

There will continue to be a chance for a few of these storms across
mainly WNY to become severe. MUCAPE values will remain 1000-1500
J/KG overnight and 0-6 km bulk shear values of 35 knots or so will
continue to support thunderstorms upstream reaching our CWA after
midnight. Greatest mid level lapse rates will be across WNY Thursday
night, and any thunderstorm could rush the stronger LLJ downward
with straight line winds the primary threat for strong to severe
storms.

With the cold front remaining well to our west overnight, and an
airmass that is increasing in moisture, our overnight lows will be
much warmer than this morning. Temperatures will likely linger in
the 70s overnight, with a few mid 60s found farther inland across
the interior Southern Tier and over the Tug Hill region.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/...
While temperatures across our region will certainly average well
above normal during this period...it is now starting to look like
the well advertised stretch of near 90 degree weather will be short
circuited. The actions behind this may prove to be a double edged
sword though. On one hand we will likely pick up some desperately
needed rainfall and eventual `protection`/relief from the oppressive
heat...but on the other...there will be a very real threat for
severe weather.

Starting with the big picture...the imposing 598dm ridge that had
been landlocked over the nations mid section for the past few days
will break down somewhat during this period. As the dominant mid
level anticyclone loses its amplitude...extreme heat that had been
confined to the Plains and Mississippi Valley will partially
`escape` to the east. Luckily for our region...we will only be side
swiped by the nose of the most oppressive air...as a weakness in the
hgt field from the dampening ridge will allow a cold front to
eventually settle south and essentially cut off the nose of the
heat.

As for the day to day details...
The first round of convection will exit our region early Friday
morning...then a few hours of temporary clearing with dew points
steadily climbing to near 70 will set the stage for significant
destabilization for more thunderstorms. This second round of
convection will be focused ahead of a pre-frontal trough that will
be found well ahead of the REAL cold front that will be temporarily
stalled north of Georgian Bay. Thermodynamically...while the NAM
looks over done with its forecast CAPE values (2500-3000 j/kg)...it
is quite reasonable that MLCAPES reach as high as 2000 j/kg if any
one area can experience a few hours of partial sunshine. This will
combine with a west to northwest flow aloft (climatologically
favorable for severe weather) to generate bulk shear values in the
vcnty of 40kts. Along with the nose of the most oppressive air
trying poke into our region...so too will an EML.

Mid level lapse rates of at least 7 deg c/km can be expected on
Friday...helping to create a `fat` CAPE profile that would not only
support damaging wind gusts but also the threat for large hail. Will
include some enhanced wording for the storms...including the mention
of gusty winds and hail. Otherwise...it will be a very warm and
humid day with H85 temps near 20c supporting max temps near 90
across the lake plains and in the valleys.

Strong to severe convection will likely still be found over at least
the Western Southern Tier and portions of the Finger Lakes Friday
evening as very unstable air and a favorable kinematic field will be
in place ahead of the approaching cold front. The lingering
convection should die off by midnight or so...as mid level
moisture is forecast to be stripped away several hours ahead of the
actual cold frontal passage. Speaking of which...without a change of
airmasses...it will once again be a `soupy` night across the region
with temperatures Friday night struggling to fall below 70.

On Saturday...high pressure centered over James Bay will nose south
across the Lower Great Lakes. This will help to push the weakening
cold front across Pennsylvania so that slightly lower dew points can
make their way south across our forecast area. While plenty of
sunshine will help to boost afternoon temperatures back into the mid
to upper 80s across the lower elevations...the possibility of
another shortwave passing through within the northwest flow will
keep the slight chc for a shower over the North Country and Thousand
Islands Region.

The axis of the sfc high will pass over our forecast area Saturday
night. While it will be a warm airmass...dew points will be lower
than the days...so some radiational cooling will make this night
somewhat comfortable for sleeping.

As the high moves east of our region on Sunday...the door will once
again open for warmer air to advance into our region from the Upper
Mid west. H85 temps will return to the upper teens...so afternoon
max temps should top out between 85 and 90.

A cold front will approach our region Sunday night. This will offer
the chance for our next round of showers and thunderstorms...
especially west of the Finger Lakes. Low temperatures this night
will generally be within a couple degrees of 70.

&&

.LONG TERM /MONDAY THROUGH WEDNESDAY/...
While temperatures will continue to average above normal during this
period...they will be closer to 30 year averages than during the
previous week. This will be due to a suppressed sub tropical ridge
that will extend from the Hawaiian Islands across the southern Conus
to the Southeast Coast...while an undulating low amplitude flow will
straddle the Canadian border. Weak troughing will be favored over
the Great Lakes in this pattern...so a trend towards less humid
conditions can be expected as well.

In terms of rainfall...a cold front will offer the opportunity for
some showers and thunderstorms on Monday...then ridging will take
charge over the Great Lakes Region through the middle of the week.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
VFR flight conditions are found across the region for the start of
the 06z TAFs and these flight conditions should prevail through
much, if not all of the TAF cycle.

Winds will become south to southwesterly today, while still
remaining light as high pressure slips eastward away from the
region.

A few showers and thunderstorms will drop southeastward within a
northwest flow overnight tonight. Much of this activity will arrive
after midnight, with the most likely time period for activity being
between 06Z and 12Z. A few of these storms could contain gusty to
strong winds. Flight conditions may drop to MVFR/brief IFR within
such activity.

Outlook...
Friday...Mainly VFR with a chance of showers and thunderstorms and
associated brief MVFR/IFR.
Saturday and Sunday...VFR.
Sunday night and Monday... Mainly VFR with a chance of showers and
thunderstorms and associated brief MVFR/IFR.

&&

.MARINE...
High pressure will remain over the Northeast region through the
weekend and then through at least the middle of next week. There
will be several cold fronts that will extend into the region of high
pressure, with such cold fronts increasing the winds and waves some
over the Eastern Great Lakes Friday, and again early next week. Both
fronts will bring winds and waves up towards small craft advisories
on Lake Erie, though likely remaining just below SCA criteria.

&&

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

&&

$$

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


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