Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 191837

Area Forecast Discussion
National Weather Service Buffalo NY
237 PM EDT Mon Jun 19 2017

A mid level trough will slowly cross the region and produce a few
scattered showers and isolated thunderstorms this afternoon through
Wednesday. A better chance of more widespread showers and
thunderstorms will arrive Friday and Saturday as low pressure moves
through the Ohio Valley. Temperatures will be cooler through the
middle of the week before warmth and humidity briefly returns at the
end of the week.


Radar imagery showing showers and a few isolated thunderstorms
developing along the southern edge of the Lake Erie lake breeze from
Chautauqua to southern Wyoming counties. This convection will
continue to develop northeastward towards the western Finger Lakes
and also begin to move slowly eastward during the late afternoon and
early evening. Farther north, a few showers have also developed over
the Niagara Peninsula on the northern edge of the Lake Erie lake
breeze. A few of these showers may drift into central and northern
Niagara County. Farther east, the last area of rain associated with
a weak wave of low pressure along the pre-frontal trough will move
through the eastern Lake Ontario region through mid afternoon, with
the steadiest rain in Lewis County. This should weaken and move east
of the area by early evening.

Going into the evening, what remains of the Southern Tier convection
will move east across the western Finger Lakes and slowly dissipate
this evening, with the Niagara County showers ending even earlier as
the lake breeze weakens. Overnight the mid level trough over the
western Great Lakes will move slowly east, with a few embedded
shortwaves crossing the region. Weak ascent and deeper moisture
associated with the trough will support a few scattered showers
overnight. The weak nature of the forcing should keep the activity
scattered and difficult to time. Weak cold advection will allow for
a cooler night, with lows in the lower 60s on the lake plains and
mid 50s across the interior Southern Tier and Tug Hill region.

On Tuesday the mid level trough will flatten and broaden as another
shortwave dives into the western Great Lakes. Weak shortwaves moving
through the mean trough along with deeper moisture will continue to
support a few scattered showers during the morning and midday hours.
Going into the afternoon, most of the weak forcing and moisture will
focus on the eastern Lake Ontario region where a few more showers or
an isolated thunderstorm may occur. Across Western NY, the mid
levels dry and weak forcing moves away, which should leave a mainly
dry afternoon. Abundant low level moisture will continue to support
plenty of stratocumulus and congested cumulus on Tuesday with only
limited sunshine. The one exception may be northeast of Lake Erie in
the Buffalo area where a stable lake shadow may try to develop with
increasing sunshine in the afternoon. 850mb temps lower to around
+8C, which will support highs in the mid 70s on the lake plains and
upper 60s to around 70 on the hills.


The axis of a Great Lakes longwave trough is forecast to cross
western and central New York Tuesday night. Forecast models continue
to show a nice vort max at the base of the trough axis with
additional forcing support from a surface trough crossing our region
00-06z. This brings the potential for a broken line of showers and
possible thunderstorms Tuesday evening. Have gone with high chance
range POPs during this time period along with maintaining the
enhanced wording for gusty winds from continuity. SBCAPE should be
very weak but forecast bulk shear of 40-50 knots could support some
gusty showers or isolated storms. A lingering wing of low-mid level
moisture and upslope flow has kept a chance for showers east of Lake
Ontario through the second half of the night while western NY dries
out. Low temperatures are expected to dip into the low to mid 50s as
dewpoints fall behind the surface trough.

A cool airmass with 850mb temps down to +8C will arrive behind the
mid level trough axis and continue comfortable temperatures
averaging a few degrees below normal as astronomical summer begins
Wednesday. Surface highs are forecast to run in the low to mid 70s.
A fresh shot of Canadian air will also continue to filter across our
region with dewpoints slipping back into the low to mid 50s which
will provide very comfortable humidity for summer standards. This
drier airmass will allow overnight temperatures to slip back into
the low to mid 50s Wednesday night. Have included a slight chance
for an isolated shower or thunderstorm Wednesday which would be
mainly diurnal influenced as the cooler air aloft steepens lapse
rates during the afternoon. Highest POPs in the low chance range
will continue to be across the eastern Lake Ontario region where
best moisture and coolest air aloft will be found. Diurnal
influences showers/storms should end after sunset Wednesday with
mainly clear skies arriving overnight within weak high pressure.
This may bring some patchy Southern Tier river valley fog.

A warm front is then forecast to lift across western and central NY
on Thursday. This front will be associated with low pressure over
western Ontario province. The warm front will bring a return of
warmer temperatures and increasing humidity along with a potential
for some showers and thunderstorms along the front and within the
trailing warm sector into Thursday night. Instability and shear is
not forecast to be particularly high so only including a general
thunderstorm risk for now. An incoming cold front sometime late
Thursday night or Friday morning will keep elevated chances for
showers and storms into Thursday night. Highs Thursday are forecast
to reach into the mid 70s to around 80 with dewpoints climbing back
toward 60. The increased humidity and southerly flow will keep
warmer temps in place overnight Thursday with lows only forecast
down to the low to mid 60s.


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.


One more round of steadier showers will cross the eastern Lake
Ontario region through late afternoon with areas of MVFR. Farther
west, scattered showers and isolated thunderstorms will develop
along the edge of the Lake Erie breeze from the western Southern
Tier into the western Finger Lakes including KJHW. These will
continue through early evening before slowly ending later this
evening with the loss of daytime heating. A few showers along the
northern edge of the Lake Erie breeze may approach KIAG during the
late afternoon and early evening. Otherwise the rest of the area
will stay dry with VFR prevailing.

Overnight into Tuesday a mid level trough will cross the region with
widely scattered showers and an increase in cloud cover. CIGS should
remain VFR across lower elevations, with a period of MVFR across the
higher terrain late tonight and Tuesday morning. VSBY will be mainly
VFR, although brief MVFR is possible in any moderate showers.


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


Low pressure will stall across northern Quebec tonight through the
middle of the week and produce a few periods of moderate to
strong winds.

On Lake Erie, moderate southwest winds will continue tonight, then
increase into the 20-25 knot range on Tuesday as the pressure
gradient tightens over the lake. This will bring Small Craft
Advisory conditions Tuesday morning through Tuesday evening.

On Lake Ontario, moderate southwest winds tonight will become more
westerly late Tuesday through Wednesday. Winds will not be as strong
as Lake Erie, with winds and waves expected to remain just below
Small Craft Advisory criteria. Nonetheless, choppy conditions will
be found at the east end of the lake Tuesday through Wednesday.

Lighter winds are then expected Thursday and Friday as the pressure
gradient relaxes over the eastern Great Lakes.


MARINE...Small Craft Advisory from 8 AM to 11 PM EDT Tuesday for LEZ040-
         Small Craft Advisory from 10 AM to 8 PM EDT Tuesday for



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