Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 251714
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
114 PM 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/...
A broad mid-level longwave trough extends from the Northern Plains
across the Great Lakes and into the Northeast region. Water vapor
imagery showing an embedded vigorous vorticity max over Lake Huron
which will cross western and central New York this afternoon. A weak
surface low is 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, combined with peak
heating will work with steepening lapse rates in cool air
advection to produce scattered to numerous showers and isolated
thunderstorms this afternoon.

Gusty southwest winds of 25-30 knots 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. Temperatures this afternoon are only expected to reach into
the upper 60s with the best chance of 70+ readings 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/...
June is not typically a month that one associates with lake effect,
but here we are in late June, talking about just that. The culprit
is an anomalously cold upper level trough that will be crossing the
Great Lakes during the period. The combination of above-average lake
temperatures, particular on Lake Erie, and 850mb temps that will be
plunging as low as +4C are sure to generate a robust lake response,
creating the potential for heavy rains and potential flooding across
portions of the Niagara Frontier and western Southern Tier,
particularly given recent rains.

Digging into the details, as we move from the weekend into Monday,
the combination of DPVA and cool temperatures aloft will encourage
the development of showers and thunderstorms during the day on
Monday. As we move through the day Monday and into Monday night, we
should see lake effect rains ramp up as well aligned west-southwest
flow takes hold across the lakes. With sfc-850mb delta-t values
running as much as +16C and equilibrium levels climbing as high as
25-30kft, it seems increasingly likely that lake effect rain
showers, with embedded thunderstorms are set to line up across the
Buffalo on a 240-250 degree flow. Given that freezing heights will
only be around 7kft, some of these storms may well drop small
hail/graupel as well. With this southwest flow holding into Tuesday
morning, as a slow moving shortwave pivots across the area, rainfall
amounts could end up being quite robust, with localized amounts of 2-
3" possible through Tuesday morning. This could raise the specter of
flooding on area creeks and low-lying areas, and will need to be
monitored closely.

Moving through Monday night, we should also see lake effect showers
ramping up northeast of lake Ontario, with activity keying in north
of Watertown into the Thousand Islands, though with Lake Ontario
running colder than Erie, intensity should be reduced relative to
Lake Erie. With the upper level trough crossing the area on Tuesday,
we should once again see fairly widespread showers and thunderstorms
firing during the afternoon across the forecast area. Showers will
taper off fairly rapidly Tuesday evening with the departure of the
upper level trough and the arrival of surface ridging across the
lower Great Lakes.

Regarding temperatures, as can be surmised from the above
discussion, the presence of an anomalously cold trough aloft will be
reflected in the surface temperatures. Readings Monday and Tuesday
are not likely to climb out of the 60s, with higher elevations
staying in the lower 60s, making it feel more like September than
mid-summer. Lows will run in the low to mid 50s, once again, a solid
10 degrees below normal for late June.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Wednesday will more likely than not be a quiet day, as surface
ridging will continue to transit the region. Temperatures will begin
to recover towards normal though, particularly once the axis of the
ridge shifts to our east, paving the way for the return of more warm
and moist southerly flow. Highs will return to the 70s on Wednesday,
with 50s to low 60s Wednesday night.

Precipitation chances will increase markedly from late Wednesday
night into Thursday, as isentropic uplift increases ahead of a
surface low tracking across the Great Lakes. Current guidance
suggest another widespread soaking for the forecast area on
Thursday, as this area of widespread synoptic lift crosses the
region ahead of the surface low, which is currently progged to track
rapidly north of Lake Ontario en route to New England by Friday
morning. Yet another system follows rapidly in the steps of this
system, keeping rain in the forecast Friday into Saturday, as the
longwave troughing across the region maintains its grip.
Temperatures during the latter half of next week will at least run
near to slightly above normal, thanks to the position of the
forecast area ahead of the longwave trough axis, with highs
generally in the mid to upper 70s, and lows in the 60s.

&&

.AVIATION /17Z SUNDAY THROUGH FRIDAY/...
Showers and a few thunderstorms will continue through the rest
of the afternoon. The greatest coverage will be away from the
lakes. Restrictions are possible in any of this activity. Some
of the storms could produce gusty winds to 35 knots and small
hail. Lake shadowing will protect KBUF and KART this afternoon.

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 and KBUF.

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

&&

.MARINE...
An increase in winds will occur on the lower Great Lakes as the
pressure gradient tightens between a trough of low pressure tracking
through the Great Lakes and high pressure building into the
Tennessee Valley. The strengthening southwesterly winds will be
sufficient for small craft advisory conditions 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.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Beach Hazards Statement until 10 PM EDT this evening for
     NYZ010-019-085.
MARINE...Small Craft Advisory until 2 AM EDT Monday for LEZ040-041.
         Small Craft Advisory until 8 PM EDT this evening for
         LEZ020.

&&

$$

SYNOPSIS...SMITH/TMA
NEAR TERM...SMITH/TMA
SHORT TERM...WOOD
LONG TERM...WOOD
AVIATION...TMA
MARINE...SMITH/TMA



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