Area Forecast Discussion
Issued by NWS Buffalo, NY

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000
FXUS61 KBUF 250901
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
501 AM EDT Sun Jun 25 2017

.SYNOPSIS...
Temperatures will continue to run cooler than average into early
next week, as an upper level trough moves across the region. The
cooler temperatures will be accompanied by showers at times, as a
series of upper level disturbances cross the area. The trough will
move east by Wednesday, with warmer temperatures expected by mid-
week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Expect dry conditions with mainly clear skies through the rest of the
pre-dawn hours. The cooler temperatures aloft, combined with
diminished cloud cover will translate to cooler overnight readings
than we have seen of late, with lows dipping into the upper 50s
along the lake plains, with mid 50s across the higher elevations
inland.

A broad mid-level longwave trough extends from the Northern Plains
across the Great Lakes and into the Northeast region this morning.
Water vapor imagery showing an embedded vigorous vorticity max over
northern lower Michigan that is expected to cross western and
central New York today. A weak surface low is forming beneath the
shortwave with a trailing cold front. Synoptic scale lift from the
shortwave with low-level forcing from the surface low and a 30 knot
low level jet will work with steepening lapse rates in cool air
advection to produce scattered to numerous showers and isolated
thunderstorms. The most widespread coverage will be during the
afternoon corresponding to peak heating and closer approach of the
cold front. Gusty southwest winds 25-30kts downwind of the lakes
should provide a lake shadow to keep shower/storm mainly south and
east of a Buffalo to Rochester to Watertown line. Any enhanced
showers or storms could bring a risk of some small hail/graupel as
WBZ heights are down to around 6kft. Temperatures will top out
around 10 degrees below normal due to the influence of the longwave
trough and associated pool of cool air aloft. Highs are forecast to
only reach into the mid to upper 60s with the best chance of 70+
being across the Finger Lakes and Genesee Valley. Dewpoints in the
50s will make for very comfortable humidity levels.

In the wake of the surface cold front this evening, 850mb temps will
become cool enough to bring a potenial for some rare June lake
effect/enhancement east of the lakes. 850mb temps bottoming out
around +6C with lake temps of +22C on Lake Erie and +19C on Lake
Ontario will bring very steep low level lapse rates of 8C/km or
better. This will support the development of lake effect clouds and
showers through the overnight. A 270 degree flow over the lakes will
direct the highest probabilities for showers across the western
Southern Tier off Lake Erie and Oswego county into Southern Lewis
off Lake Ontario. Lake induced equilibrium levels of 20kft+ yields a
chance of thunder along with a graupel within the more organized
bands. Overnight lows will again dip into the low-mid 50s and even
upper 40s in the cooler interior western Southern Tier and Tug Hill.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
Through the course of this period a long wave trough will pass
across the Great Lakes region, reaching its greatest depth Monday
night as a strong shortwave passes through. Within this trough
temperatures at 850 hPa will bottom out around +5 to +6C, and at 500
hPa temperatures of -20C within this trough will be around 4SD below
normal for this time of year centered across the Ohio Valley.

Any lake enhanced showers will become more scattered during the
late morning hours during increased daytime mixing. The
approach of an upper level shortwave later Monday will again
increase the coverage area of showers and thunderstorms over the
region. The deep 500 hPa trough and its associated cool pool
will encourage some thunderstorm development, and with low
freezing levels and WBZ heights around 6- 8K feet some graupel
or small hail will be possible. However the skinny CAPE profiles
suggest that larger hail will be unlikely.

Showers and thunderstorms will diminish Monday night with the
passage of the shortwave within the base of the long wave trough.
There may linger a few lake enhanced rain showers deeper into the
night, especially across the North Country which will lie under the
cooler air aloft.

Tuesday we will remain within the influences of the upper level
trough, through now behind the robust shortwave, and slowly rising
heights aloft the rain shower coverage/intensity should be less than
Monday. The still cool pool aloft will continue the chances for a
few thunderstorms. By Tuesday night the upper level trough will be
pushing away from our region with any linger rain showers largely
ending by the late evening hours. A few lake effect rain showers may
develop off Lake Ontario as low level convergence increases on a
westerly flow. However we will also begin to warm a degree or two at
850 hPa, so lake instability will not be as great as previous
nights.

Temperatures will be well below normal Monday and Tuesday with both
days only pushing mid to upper 60s for highs. Overnight lows will
drop back into the upper 40s to mid 50s closer to the lakes.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
While humidity will increase to uncomfortable levels during this
period...temperatures will not stray very far from normal. This will
be due to an eastward displacement of the sub tropical ridge that
during the summer typically supplies our region with very warm
and sultry weather. The heart of this ridge will be centered well
off the coast of the Carolinas between 60-70W longitude rather than
70-80W...so this will allow a very broad low amplitude trough to
become established over the center of the country. The overall
result will be to keep the true heat out of area...although we
will have our fair share of humid conditions.

Unfortunately...the position of the low amplitude trough to our west
will also mean that the core of the sub tropical jet will undulate
back and forth across the Great Lakes region. This will keep active
weather over our forecast area...as several significant waves/sfc
lows will track east along a frontal boundary that will essentially
mimic the position of the overlying jet. Given the time of year...
this will enhance/focus diurnally enhanced convection. As for the
day to day details...

Wednesday should be the `nicest` weather day of the period...as a
shortwave ridge will work its way across the Lower Great Lakes.
While there could be some disorganized lake effect rain showers east
of Lake Ontario to start the day...any lake effect will quickly be
broken apart by strong diurnal mixing. Otherwise...we can expect at
least partial sunshine with a comfortable afternoon as temperatures
in the 70s will be accompanied by relatively low humidity.

Conditions will start to deteriorate Wednesday night as a warm front
will extend east across our region from the Upper Great Lakes. While
the strongest isentropic lift along and head of this boundary should
be to our north and west...there will be the potential for some late
night showers and storms.

While the warm front will push north of our region during the day
Thursday...we will become firmly entrenched within the more unstable
warm sector of the parent system. This will allow any boundaries to
touch off some showers and thunderstorms...which appears to be a
favored solution by many of the ensembles. Will thus raise pops to
likely. Otherwise it will be a warmer and more humid day with
temperatures climbing into the lower 80s for the bulk of western New
York...while readings will be in the 70s east of Lake Ontario and
across the higher elevations. The increased humidity will be more
noticeable as dew points will be some 10 deg higher...reaching into
the low to mid 60s.

As low pressure moves east and weakens across the st Lawrence Valley
Thursday night...its trailing cold front will settle south and
essentially stall over our forecast area. This will keep unsettled
conditions in place with fairly frequent showers and thunderstorms
expected into the start of the weekend. In fact...with dew points
forecast to climb into the upper 60s for most areas on Friday...
storms will likely contain heavier than normal downpours resulting
in an elevated risk for flash flooding. Stay tuned.

&&

.AVIATION /09Z SUNDAY THROUGH THURSDAY/...
VFR conditions will largely last through today with showers and a
few thunderstorms expected to develop mainly during the afternoon
hours. Lower VIS is possible in any passing scattered to numerous
showers/isolated storm.

Tonight, a much cooler airmass will move over western and central
New York. This will promote some lake effect showers east of the
lakes with lake effect clouds also developing and lowering to MVFR
east of the lakes. MVFR is most possible at KJHW.

Outlook...
Monday through Tuesday...Mainly VFR with scattered to
numerous showers and thunderstorms...mainly in the afternoons.
Wednesday...Mainly VFR.
Thursday...VFR/MVFR with a chance of showers and thunderstorms.

&&

.MARINE...
Southwesterly winds will increase again today. Waves will rise
higher particularly on the eastern half of Lake Erie, as winds
strengthen further as a strong upper level disturbance moves
through. Small craft advisory conditions will develop on the eastern
end of Lake Erie this afternoon and perhaps on the eastern end of
Lake Ontario tonight.

After a brief respite Monday morning, another passing upper level
disturbance will likely bring another period of small craft advisory
conditions to Lake Erie Monday night.

&&

.EQUIPMENT...
The Buffalo radar is inoperable at this time. Technicians have
been notified and are troubleshooting the problem. A return to
service is unknown until the problem is identified.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Beach Hazards Statement from noon EDT today through this
     evening for NYZ010-019-085.
MARINE...Small Craft Advisory from noon today to 2 AM EDT Monday for
         LEZ040-041.
         Small Craft Advisory from noon today to 8 PM EDT this
         evening for LEZ020.

&&

$$

SYNOPSIS...SMITH
NEAR TERM...SMITH
SHORT TERM...THOMAS
LONG TERM...RSH
AVIATION...SMITH
MARINE...SMITH/TMA
EQUIPMENT...



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