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Area forecast discussion
National Weather Service Buffalo New York
1037 PM EDT sun may 28 2017

Synopsis...
widespread showers and scattered thunderstorms will shift across
western and north-central New York overnight as a warm front crosses
the region. Showers will taper off from west to east on Monday. More
showers will be possible Monday night into Tuesday, as a weakening
cold front crosses the region. In fact, mild temperatures and
afternoon showers will be possible through the coming week, as a
broad upper level trough will linger across the region.

&&

Near term /through Monday/...
Buffalo radar at 1030pm shows widespread showers and scattered
thunderstorms oriented ahead of and along a warm front lifting north
across western New York. This will continue to shift over western New York
through the overnight in two rounds. The first round along the warm
front and the second round now crossing The Thumb of Michigan
oriented along the cold front. Both front are expected to occlude
overnight while shifting east into central New York. Severe storms
are not expected as instability has weakened with the loss of
daytime heating but heavy showers and embedded thunderstorms can
certainly be expected with some pockets of frequent lightning.

Shower and thunderstorm activity is expected to taper off from west
to east during the day on Monday as an upper level shortwave driving
the frontal system and precipitation moves overhead, with negative vorticity advection and
associated subsidence behind the wave drying things out. While much
of the precipitation will be convective in nature at least through
the evening hours allowing for locally higher qpfs, a general
quarter to half inch can be expected across the forecast area though
tonight and Monday morning.

Regarding temperatures, given the moisture-rich high dewpoint air
that will be advecting into the region tonight, temperatures will
only bottom out in the upper 50s to lower 60s. Drier, but still
relatively warm air will move in behind the departing mid/upper
level troughing on Tuesday, and temperatures should top out in the
low to mid 70s away from the lakes. However, with southwesterly
winds strengthening behind the trough, cooler readings will be found
downwind of the lakes, with upper 60s prevailing.

&&

Short term /Monday night through Wednesday night/...
an upper level closed low over the southern shore of Lake Winnipeg
this afternoon will drop across the Great Lakes and influence our
weather for the Monday night through Wednesday night time period.
Several shortwaves rotating around the upper level low will give
increase chances for showers and thunderstorms. Though this wet
month of may will close out with thunderstorms, much of the time
will be rainfree.

Monday night the first such shortwave, and associated low level wind
speed Max, will near our region. Convergence along this little speed
Max in the lower levels and around 100 to 250 j/kg of MUCAPE may
produce a shower or thunderstorm, with activity later in the
evening across wny, and in the predawn hours east of Lake Ontario.

Another shortwave impulse on Tuesday, combined with the upper level
low drawing closer will bring increasing chances for showers and
thunderstorms. The bulk of this activity will likely form on lake
breeze boundaries through the afternoon and evening hours. MLCAPE
values of 500 to 750 j/kg and precipitable water values around three quarters of
an inch will provide the instability and moisture that when
interacting with the lift along lake breeze boundaries, convection
is likely to form. A morning inversion will likely keep this
convection at Bay, but by noontime convection should be able to
overcome the decreasing capping inversion. Moisture is not overly
impressive, and activity may be just scattered in nature. Northeast
of the lakes, a southwest stabilizing wind flow will promote
sunshine and likely a dry day for areas such as Metro Buffalo, and
north of Watertown. Winds will also be gusty within the sunshine
northeast of the lakes, with gusts 30 to 35 mph.

Wednesday may be a bit more active as upper level heights fall in
response to the upper level low reaching the region, and its trough
axis crossing the lower lakes. Similar to Tuesday, much of the
activity will be upon lake breeze boundaries, with showers and
thunderstorms sprouting in the afternoon heating. Northeast of the
lakes, a stabilizing lake induced airmass will maintain Metro
Buffalo, and areas north of Watertown dry through the day, with a
gusty breeze. With the upper level trough axis passing through
chances for storms will be possible across the region through the
evening hours.

Temperatures will be held in check by the upper level low, with
highs in the 60s, (cooler Wednesday with the upper level low upon
us) and overnight temperatures back into the mid 50s to upper 40s.

&&

Long term /Thursday through Sunday/...
the region will be in a longwave cyclonic flow during the
period with frequent chances for precipitation and slightly
below normal temperatures. There will be periods of dry weather
too, however timing embedded shortwaves is difficult this far
out.

On Thursday the upper level low will be centered just south of
Hudson Bay with a ridge of high pressure at the surface across
the Appalachians. For the most part, this surface ridge should
keep the area dry, with a small chance for showers across the
north country Thursday afternoon with the passage of a weak
shortwave. Highs will be in the mid 60s to around 70.

Model consensus drops the upper level low into southern Quebec by
late Friday, which will eventually push a cold front southward
across the region. Model guidance differs on the timing, with a
chance of showers and possibly a thunderstorm along and ahead
of the cold front late Thursday night through Friday evening.

This front is likely to stall to the south of the area late
Friday night and Saturday. It will be close, but as long as it
remains to the south surface ridging will keep Saturday dry.
Highs on Friday and Saturday will be on the cool side behind
this front...mainly in the 60s.

The front should meander northward back into the area on Sunday.
Some guidance develops a wave along this front, with another chance
for showers and possibly a thunderstorm. The best chance will be
across southern portions of the cwa which will be closest to the
boundary.

&&

Aviation /03z Monday through Friday/...
widespread -shra and scattered -tsra are shifting north across western New York
along a warm front near 03z. Two rounds of showers/storms are
expected with the first round occuring now and a second round coming
from eastern lower Michigan along the occluding cold front. All of
this activity will shift into central New York early Monday while staying
below severe limits. Periods of MVFR will be possible in heavier -
rain showers/-tsra, with MVFR and isolated IFR cigs becoming more widespread
after 06z, with plenty of lingering moisture across the area.

Showers and thunderstorms will taper off from west to east after 12z
Monday, as the upper level disturbance moves through. VFR conditions
will prevail by Monday afternoon.



Outlook...
Monday night...mainly VFR, with a chance of showers and thunderstorms.
Tuesday through Friday...mainly VFR...with localized MVFR possible
in scattered (mainly afternoon) showers and thunderstorms.

&&

Marine...
southeasterly winds occuring ahead of warm front. This front will
move across the eastern Great Lakes through overnight, accompanied
by showers and thunderstorms. Skies will clear out behind the
occluding frontal system on Monday, with winds shifting to
southwesterly and freshening to around 15kts by Monday afternoon,
resulting in light to moderate chop on the northeastern ends of the
lakes.

The SW flow will strengthen further Tuesday, as a cold front moves
through, potentially generating small craft conditions on the east
end of Lake Erie. In fact, an upper level trough will linger through
much of the coming week, with SW flow continuing as a result. This
will serve to reinforce afternoon lake breezes northeast of the
lakes, resulting in at least near-Small Craft Advisory conditions each afternoon
through the rest of the week.

&&

Buf watches/warnings/advisories...
New York...none.
Marine...none.

&&

$$

Synopsis...Smith/wood
near term...Smith/wood

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