Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 220845

Area Forecast Discussion
National Weather Service Buffalo NY
445 AM EDT Thu Jun 22 2017

High pressure will bring clear skies through the morning hours. A
warm front lifting across the region ahead of an area of low
pressure moving across central and eastern Canada will usher in
warmer temperatures, along with a chance for showers and
thunderstorms Thursday afternoon. Activity will become more
widespread Thursday night into Friday, as tropical moisture surges
across the region ahead of an approaching cold front. Cooler
temperatures, along with scattered showers return for the weekend,
as upper level troughing returns to the Great Lakes.


Clear skies prevail across much of the state this morning, thanks to
high pressure currently in place over western New York. Aside from
patchy valley fog, expect a sunny start to the day across the
forecast area. The morning sunshine will give way to increasing
clouds this afternoon however, as the high moves off to the east and
a warm front shifts north across the region this afternoon. A few
showers and thunderstorms may accompany this front, though a fresh
southwesterly lake breeze and associated lake-shadowing should spare
much of metro Buffalo from storms this afternoon.

In fact, the bulk of the activity should be focused across Canada
and the North Country, as guidance suggests that western New York
and the Finger Lakes should rapidly transition into the warm sector
of a developing low over the central Great Lakes. Nonetheless,
should the front set up a little farther south, areas south of Lake
Ontario may have a better chance of seeing convective activity,
especially tonight, and as such, have left a chance of showers and
thunderstorms in the forecast, especially given abundant upstream
moisture that will be surging northwards towards the area later

The aforementioned warm frontal passage today will boost temperatures
above average this afternoon. As 850mb temps climb above +17C,
expect highs to reach the low to mid 80s, with cooler readings found
northeast of the lakes, thanks to a fresh southwesterly lake
breeze. As the forecast area transitions into the warm sector, and
moisture-rich air surges northwards across the region out of the
Mississippi and Ohio valleys, pushing dewpoints well into the 60s,
expect a muggy summer night, with lows not dropping below 70 across
the lake plains, and only dropping into the upper 60s across higher


Thursday night a broad warm advection regime will remain in place
across the Lower Great Lakes, with another warm frontal segment and
associated subtle mid level shortwave moving ENE across the area.
The associated weak DPVA and isentropic ascent will maintain a
chance of a few showers and thunderstorms overnight, although the
weak/broad nature of the forcing will make the timing and placement
of better rain chances difficult at best. In a general sense expect
rain chances to increase through late evening and overnight as the
warm frontal segment arrives, then move northeast across Lake
Ontario and the North Country overnight. Clouds and warm advection
will keep temperatures very warm, with lows in the lower 70s on the
lake plains of Western NY and upper 60s for the interior Southern
Tier and east of Lake Ontario.

On Friday the warm sector will become established across the area.
It will not be a clean warm sector however, with a good deal of
cloud cover and scattered showers still around through the first
half of Friday. The best chance for breaks in the clouds will be
found from the Genesee Valley to Central NY from mid morning through
early afternoon. Later Friday afternoon and evening the cold front
will approach, with the associated mid level trough bringing
increasing DPVA and mid level height falls. At least some
instability will develop with a few breaks in the clouds, and
combine with increasing forcing and moisture convergence to produce
more widespread showers and thunderstorms during the afternoon and
evening. Southwest flow off the lakes may try to limit convection
across the Niagara Frontier and near Watertown, with the greatest
coverage likely from the western Southern Tier into the Finger Lakes
and southern Tug Hill region. It will become humid with dewpoints
rising into the 65-70 degree range. Expect highs in the lower to mid
80s at lower elevations away from lake influences, with mid to upper
70s across higher terrain and northeast of the lakes.

The somewhat limited instability and poor mid level lapse rates
should limit the overall severe potential, although an isolated
storm or two with strong winds cannot be ruled out. PWAT reaches
about 1.75 inches just ahead of the front, supporting heavy
downpours with a few storms.

Friday night the cold front will sweep east across the area, with
showers and thunderstorms ending from northwest to southeast. There
is enough of a mid level dry push to allow for partial clearing
overnight. Moderate cold advection and the arrival of a drier
airmass will allow temperatures to fall into the lower 60s on the
lake plains and upper 50s across the higher terrain.

On Saturday a broad longwave trough will be in place across the
Great Lakes, while a mid level shortwave moves across Southern
Ontario in the afternoon and brushes our region with some weak DPVA
and ascent. The airmass is fairly dry, so at first glance Saturday
appears to be mainly dry. Upon closer inspection, cool air aloft
will support steep lapse rates with daytime heating. The synoptic
pattern will support the development of a mesoscale convergence band
from Niagara County eastward along the south shore of Lake Ontario
all the way to Oswego County, as the enhanced WSW flow off Lake Erie
meets the WNW flow over Lake Ontario. This band of convergence
combined with the steep lapse rates may support a few scattered
showers and isolated thunderstorms Saturday afternoon, similar to
what we say Tuesday afternoon. Expect highs in the low to mid 70s in
most locations.

Any scattered showers will end Saturday evening as the convergence
zone breaks down and the boundary layer cools. This will leave
partial clearing overnight. Expect cool and comfortable lows in the
mid 50s on the lake plains and around 50 across the interior
Southern Tier and Lewis County.


Long range models are in good agreement on a overall broad troughing
pattern over the Hudson Bay over the weekend into early next week.
200hPa NAEFS height anomalies suggest a 99th percentile for the time
of year upper-level trough moving across the lower Great Lakes.
While the 850hPa temperature anomalies aren`t extreme, they are
certainly below normal as this trough crosses the region Monday into
Tuesday. More impressive are the 500hPa temperature anomalies,
suggesting steep mid-level lapse rates under the cyclonic flow
aloft. Typically in this pattern for this time of year we will see
an impressive diurnal cumulus field inland from the lake breezes
with showers and low topped thunderstorms developing each mid-day
through the afternoon. These showers and thunderstorms will be
further focused by any shortwaves rotating around the mean trough.
If this environment can be coupled with a stout shortwave, would
not rule out some small-hail producing storms given the lower
freezing level heights and steep lapse rates aloft, especially if
storms focus along a lake breeze boundary. Otherwise, this will
result in fairly cool and less humid conditions across the forecast
area with daytime highs perhaps not reaching the 70 degree mark
Monday and/or Tuesday as the trough axis swings through the area.


High pressure and clear skies overnight will persist through the
morning hours, potentially allowing for localized valley fog in the
Southern Tier. Mid/high clouds will increase during the afternoon
hours, as a warm front lifts north across the region. A few showers
and thunderstorms will be possible in the afternoon, as the front
moves across the region, mainly inland from the lakes. Overall
though, conditions should remain VFR. A strengthening low level jet
aloft may result in LLWS towards the end of the forecast period,
particularly across far western New York.

Friday...VFR/MVFR with widespread showers and thunderstorms.
Friday Night...VFR/MVFR with rain showers and a chance of thunderstorms.
Saturday and Sunday...Mainly VFR with a chance of showers and thunderstorms.
Monday...Mainly VFR with a chance of showers.


High pressure will keep conditions tranquil on the lakes for much of
the day, with the exception of southwesterly lake breezes to around
15kts on the northeastern ends of the lakes this afternoon.
Southerly winds will freshen tonight as a warm front crosses the
region and low pressure develops over the central Great Lakes. This
will largely keep wave action confined to Canadian waters however,
and the only serious threat for small craft advisory conditions will
not be until Friday night, when a cold front crossing the region
will bring cooler temperatures and fresh westerly flow that will
raise waves above 4-5 feet on the eastern end of Lake Ontario. The
fresh westerly flow and subsequent SCA conditions will likely
continue through the weekend, thanks to persistent upper level
troughing in place across the region.





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