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Area forecast discussion
National Weather Service Buffalo New York
1015 PM EDT sun Jun 25 2017

Synopsis...
temperatures will continue to run cooler than average through
Tuesday, 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 Monday/...
broad mid-level longwave trough remains across the Great Lakes and
into the northeast Continental U.S.. water vapor imagery showing an embedded
robust vorticity Max moving into southern Quebec with a spoke
dropping southward across central New York state co-located with a surface
cold front. Scattered showers and thunderstorms associated with
this feature will quickly move through central New York with a short
break for much of wny.

Later this evening, additional showers are expected with
continued cold air advection and additional upstream short wave
troughs poised to move in overnight.

Behind the front, a chilly airmass will spread into the region
and will be cool enough to bring a potenial for some lake
effect/enhancement east of the lakes. 850 mb temperatures
dropping to around +6c with lake temperatures of +22c on Lake
Erie and +19c on Lake Ontario will bring steep low level lapse
rates. This will support the development of scattered lake
effect showers through the overnight. Shear profiles do not look
ideal for well organized bands. An overall 260-270 degree flow
will direct the highest probabilities for showers across the
western southern tier/southern Erie County 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 graupel possible if some degree of organized bands can
develop. Overnight lows will again dip into the low-mid 50s and
even upper 40s in the cooler interior western southern tier and
Tug Hill.

Monday, anomalously cold upper level trough will continue to cross
the Great Lakes. Another short wave looks to rotate through the base
of the trough improving overall dynamics. This feature along with
the combination of above-average lake temperatures, and 850 mb
temperatures nearing +4c are almost certain to generate a robust lake
response, creating the potential for bands of rains downwind of the
lakes. Cool air aloft, clouds and rain will keep most temperatures
in the 60s.

&&

Short term /Monday night through Wednesday night/...
Monday night and Tuesday The Heart of a much cooler than normal
airmass will cross the area as a potent mid level shortwave moves
through the mean longwave trough over the Great Lakes and New
England. DPVA associated with the sharp mid level vorticity maxima
will produce a few scattered showers across the region. The main
concern will be lake effect rain potential, a rarity for late June.
850mb temps will bottom out around +4c Tuesday morning. With the
lake at around 21c on average that yields more than enough lake
induced instability to support lake effect rain. These temperatures
will generate around 1800j/kg of lake induced cape and equilibrium
levels around 30k feet.

Off Lake Erie...expect lake effect rain showers to slowly become
better organized during the late evening and early overnight Monday
night, with lingering diurnal mixing initially hurting the chances
of organized development. By late Monday night and early Tuesday
morning expect a broken line of nearly steady state convection to
focus on the Buffalo southtowns on west-southwest flow, and likely hugging the
shoreline of southern Erie County and possibly into the Dunkirk
area. Given the strong instability, expect scattered thunderstorms
to be supported within this band of lake effect rain, and locally
heavy rainfall. If the band stays stationary long enough, rainfall
amounts could easily exceed 1 inch. Tuesday morning boundary layer
flow will become more westerly following the passage of the mid
level trough, forcing the lake effect rain inland across the western
southern tier where it will transition to diurnally driven scattered
showers by early afternoon.

Off Lake Ontario...the airmass is not quite as cold or supportive of
lake effect rain at the east end of Lake Ontario, and the lake
itself is not as warm yet. This will yield less of a lake response
compared to Lake Erie. Expect scattered lake effect rain showers
across Jefferson County later Monday night, likely peaking Tuesday
morning with an added boost of lift from the passing mid level
shortwave. By Tuesday afternoon most of the showers will move inland
and transition to diurnally driven showers




Precipitation chances will increase markedly 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., Most numerous across the
higher terrain of the Tug Hill and western Adirondacks.

Otherwise Tuesday afternoon scattered showers will continue, driven
by some limited moisture and steep low/mid level lapse rates beneath
the cold air aloft. These will gradually end Tuesday evening with
the loss of daytime heating, with the possible exception of the
Eastern Lake Ontario region where some weak lake induced instability
and more synoptic scale moisture may still support a few showers.

By Wednesday the base of the mid level trough will swing northeast
across Quebec. This will leave the bulk of the area in a drier, and
somewhat warmer airmass as high pressure builds from the Ohio Valley
to the mid Atlantic states. This will bring a return to dry weather
for most, with diurnal cumulus still developing with daytime heating
inland from the lakes. There may still be a few scattered showers
east of Lake Ontario in closer proximity to the departing mid level
trough.

Wednesday evening any lingering scattered showers east of Lake
Ontario will end as the trough moves farther away. Overnight clouds
will increase from west to east as fairly strong warm advection and
isentropic upglide develop ahead of low pressure moving through the
upper Midwest. This may produce a few showers towards Thursday
morning across western New York.

Temperature-wise, Tuesday will be well below normal with highs only
in the upper 60s on the lake plains and lower 60s on the hills,
about 10 degrees below normal. Lows Monday night and Tuesday night
will be in the mid 50s on the lake plains, with some upper 40s in
the cooler interior southern tier valleys and Lewis County.
Temperatures will begin to warm back closer to average by Wednesday,
with low to mid 70s across western New York and upper 60s to lower 70s
east of Lake Ontario.

&&

Long term /Thursday through Sunday/...
this will be a very unsettled period across our forecast area...as
we can anticipate numerous showers and thunderstorms...including the
likelihood for some localized heavy rain. Temperatures will average
a little above normal...largely due to warm nights...while humidity
levels will climb to uncomfortable levels.

The unsettled conditions will be supported by an oscillating frontal
boundary that will straddle the lower Great Lakes. Two distinct
surface waves will eject out of a broad...low amplitude trough over
the center of the country during this time period...with each
pushing the boundary back and forth across our region to
force/enhance the convection. The most widespread shower and
thunderstorm activity will be on Thursday in advance of the first
wave...then Friday night and Saturday as the second feature passes.

Max temperatures all four of these days will generally range from
the upper 70s to lower 80s...while overnight lows will mainly be in
the mid 60s.

&&

Aviation /02z Monday through Friday/...
most areas should remain VFR tonight with only isolated showers.
The exception may be toward kjhw where some lake effect showers
will likely develop toward morning before moving inland as a
lake effect modifies to a lake breeze. Associated convection
should move inland during the day as a result. Some MVFR will be
possible with those showers (and thunderstorms).

Outlook...
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...
although winds may drop off a little overnight, expect winds to
quickly pick up again on Monday with renewed west to southwest
winds near 20 knots, lasting through Monday evening. Waves will
generally range from 3 to 6 feet on the eastern end of Lake
Erie, sufficient for Small Craft Advisory conditions through
Monday evening. Smaller waves are expected on Lake Ontario.

&&

Buf watches/warnings/advisories...
New York...none.
Marine...Small Craft Advisory until 10 PM EDT Monday for lez020-040-041.

&&

$$

Synopsis...tma
near term...tma/zaff

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