Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 191344

Area Forecast Discussion
National Weather Service Buffalo NY
944 AM EDT Mon Jun 19 2017

A cold front will cross the region today with showers and a few
thunderstorms, mainly across the Southern Tier, Finger Lakes, and
east of Lake Ontario. Behind the front, cooler and unsettled weather
will dominate the region through mid-week.


Radar imagery this morning showing rain showers over the eastern
edge of the CWA, from Allegany County through the western Finger
Lakes to the eastern Lake Ontario region. This rain is associated
with a weak wave of low pressure along a pre-frontal trough, and
will slowly exit eastern areas through early afternoon. Farther
west, the western end of the state is dry, with sunshine developing
across the Niagara Frontier.

This afternoon, leftover moisture and instability may be able to
fire some lake breeze convection, especially along the southern edge
of the Lake Erie lake breeze. This would impact areas from the
western Southern Tier into the western Finger Lakes. A southwest
flow off the lakes will produce stable lake shadows and keep the
corridor from Buffalo to Rochester, and Jefferson County rain free
with more sunshine.

Temperatures will be a little cooler and less humid today, with
highs in the 75 to 80 degree range. Southwest flow will keep the
Buffalo and Watertown areas a little cooler. Those southwest winds
may gust to 25 mph northeast of Lake Erie from Buffalo to the west
side of Rochester.

Broad troughing is expected to continue across the Great Lakes
tonight. Guidance continues to suggest another opportunity for
precipitation will come later tonight as a surface trough swings
through with weak mid level energy moving in aloft. Post cold
frontal airmass will be notably drier than the previous few
days, with dewpoints in the 50s, but still enough forcing to
produce a few showers.


While there will be some showers and thunderstorms around at the
beginning and end of this three day period...the most noteworthy
part of the weather will be a change to cooler more comfortable
conditions. This change will be brought about by a transitory
longwave trough that will work its way across the Lower Great Lakes
Tuesday and Wednesday...supplying our region with somewhat more
refreshing Canadian air in the process. This will include daytime
temperatures in the 70s and overnight lows in the 50s along with
notably lower dew points/humidity. As for the day to day details...

The first of a pair of shortwaves that will affect our region during
this period will be exiting to our east Tuesday morning. Showers
associated with this feature should end from west to east by
lunchtime...with subsidence in the wake of the first `bundle of
energy` promoting mainly dry weather during the bulk of the day
between 15 and 21z. The short lived period of fair weather will then
succumb to the second shortwave...which will already have our area
in its sights by the end of the day.

This next frisky feature will sweep across the Lower Great Lakes
during the first half of Tuesday night...pushing a secondary/
reinforcing cool front through the region in the process. While
diurnally based instability will be waning during its passage with
SBCAPE values averaging 500 j/kg...there may be favorable kinematics
in place to support a few robust thunderstorms. 0-6km bulk shear
values are forecast to be in the vcnty of 30-40 kts...largely due to
a 40-50kt low level jet. Will add the mention of gusty winds to the
package to cover the risk for any organized/robust convection. The
second half of the night should feature fair weather.

The base of the longwave trough will push east across New England
during the day Wednesday...while surface high pressure centered over
the Ohio Valley will nose northward into our forecast area. The
resulting hgt rises and increased subsidence will provide us with
mainly fair dry weather....although there could be one last mid
level disturbance within the northwest flow aloft that could spark a
shower near/east of Lake Ontario. It will remain comfortable as
well...with single digit H85 temps only supporting afternoon highs
in the 70s.

As our hgts continue to rise in advance of a shortwave ridge
Wednesday night...a burgeoning warm front will take shape over the
Upper Great Lakes. The bulk of the forcing associated with this
feature will remain well to our our area should be able to
enjoy one last night of comfortable weather with mins in the 50s.
Its not out of the question though that some of the cooler valleys
of the Srn Tier...or sites east of the Tug Hill briefly drop into
the 40s.

The question then arises as to whether our region experiences a
`clean` or `dirty` warm up during the day Thursday. While the
strongest dynamics with the aforementioned warm front will stay to
our north...the uncertainty will come as to how far this forcing can
extend to the southeast. The various guidance packages are at odds
over the amount of lift that will be provided for our
will have to hold onto chc pops from continuity until the scenario
comes more into focus. Either way you slice it though... H85 temps
will climb back into the mid we can anticipate a return
to warm and more humid conditions.


An expansive...low amplitude trough will cover the northern half of
the continent during this period. While this will virtually insure
that temperatures will not stray far from late June
would be a mistake to think that the lack of amplitude would equate
to an absence of meaningful weather. There will be two distinct
precipitation events during this period...both with the potential to
produce either soaking rains or include the risk of strong

The first of these systems will be a cold front that will plow
across the Lower Great Lakes on Friday. While it is too early to get
specific with the amount of instability or shear that will be is worth noting that the frontal passage should take
place within a west to northwest flow...and these inherently include
a higher than normal amount of directional shear. This could make
the event more `interesting`.  Given the consistency between the
medium range models...have raised pops to likely for this event.

Rapid clearing in the wake of the front is expected Friday night
when low temperatures will return to the 50s.

A wedge of high pressure over the Lower Great Lakes will promote
nice weather for the first day of the a fair amount of
sunshine will combine with H85 temps around 12c to support afternoon
highs in the upper 70s to around 80.

Low pressure organizing over the Ohio Valley Saturday night will
track northeast across our forecast area on Sunday. This will likely
result in some showers and thunderstorms...and in a worse case
scenario...a period of steady rain. Its fair to say at this point
though that Sunday will be the less favorable day for outdoor
activities. Stay tuned.


Remaining showers and associated MVFR conditions from the western
Southern Tier into the Finger Lakes, Genesee Valley, and eastern
Lake Ontario region will exit during the morning. This will leave
mainly VFR to prevail. A few thunderstorms may develop again later
in the afternoon from the western Southern Tier into the Finger
Lakes with local/brief MVFR to IFR. These storms will diminish later
this evening with the loss of daytime heating.


Tuesday and Wednesday...Chance of showers with mainly VFR.
Thursday through Friday...A chance of showers and thunderstorms
with local MVFR.


Moderate southwest winds will continue through the middle of the
week as low pressure stalls over northern Quebec. Winds and waves
will remain below Small Craft criteria most of the time. The one
exception may be Tuesday on Lake Erie, and Tuesday night on Lake
Ontario when winds may become just strong enough for waves to
approach Small Craft Advisory levels.





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