Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 251102

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

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-


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.


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.


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.


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 and KBUF.

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.


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.


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.


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
         Small Craft Advisory from noon today to 8 PM EDT this
         evening for LEZ020.



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