Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 240256

Area Forecast Discussion
National Weather Service Buffalo NY
1056 PM EDT Sat Jun 23 2018

Low pressure will move slowly across the region through tonight,
with a cold front then moving slowly south across the area Sunday
and Sunday night. This will continue to support occasional showers
and scattered thunderstorms through the rest of the weekend, with
some rain free periods as well. High pressure will build into the
eastern Great Lakes and New England Monday and Tuesday, bringing a
return to dry weather.


Unorganized and light scattered showers tracking ENE across the
CWA will continue to weaken and diminish in coverage over the
course of the night. With the de-amplifying mid level trough
moving into western New England, it will leave little in the way
of forcing across our region. However, an east-west oriented
mid level frontal zone and abundant moisture will remain in
place, with the chance of one or two meso-beta scale
convectively generated perturbations supporting the possibility
of a few but brief showers. Otherwise, much of the time should
be rain free through most of the night. Expect lows in the low
to mid 60s in most areas.

Sunday another mid level trough over the central Great Lakes will
approach Western NY during the afternoon. Increasing large scale
ascent in the DPVA region ahead of the trough, and some limited
diurnal instability will support a gradual increase in showers and
scattered thunderstorms during the day. The initial development in
the morning will likely focus on a few subtle wind shift boundaries
forecast to drift across Western NY, with coverage improving and
moving east through the afternoon with the arrival of better large
scale support. PWAT values are high but not excessive, at around 1.5
inches. Flow from the boundary layer through the mid levels is
fairly weak, with short Corfidi propagation vectors and deep
moisture suggesting the potential for slow moving heavy rain
producing storms where convection develops. That said, the flash
flood risk does not appear organized enough to justify a watch at
this time.

The mid level trough axis and first cold frontal segment will move
southeast across the area Sunday evening, with fairly widespread
showers and scattered thunderstorms initially. A heavy rain risk
will last into the evening before the boundary layer begins to
stabilize and better forcing moves east of the area. Overnight the
rain will end from north to south with the passage of the cold
front. A secondary cold front will cross the area late Sunday night
and early Monday morning, with a re-enforcing push of cooler and
drier air. Lows will drop into the mid 50s in most areas by daybreak
Monday, with some lower 50s across the North Country.


Canadian high pressure will transit the forecast area Monday and
Tuesday bringing a return to fair weather with continued comfortable
temperatures and low humidity. By Wednesday and Wednesday night, a
potent wave will cross the Great Lakes bringing our next chance for
showers and thunderstorms, along with increasingly warm and humid

Monday and Monday night will remain on the cool side of normal with
the high to our north feeding in a cool, dry airmass. Highs will top
out in the low to mid 70s with abundant sunshine and dew points in
the 40s will make for quite low humidity. Monday night will be cool
and crisp under excellent radiational cooling conditions as the
surface high crests overhead. Inland locations across the Southern
Tier and Eastern Lake Ontario region will see overnight lows solidly
in the 40s, while the lake plains remain a bit milder in the low to
mid 50s.

Temperatures and moisture will start to rebound on Tuesday as return
flow develops with the surface high moving off the East Coast.
Temperatures and moisture will return to more typical June levels
with highs around the 80 degree mark and dew points back into the
50s. Mostly sunny skies early will become increasingly obscured by
thickening high clouds late in the day Tuesday ahead of the next
approaching weather system.

Wednesday and Wednesday night a robust wave will move through the
central Great Lakes while pushing a cold front across the area.
Several rounds of showers and possibly thunderstorms will move
across the region. Severe thunderstorm potential will be non-zero
during this time period, conditional on the timing of the wave and
how much destabilization occurs Wednesday. The temperature forecast
is a bit tricky given the likely ubiquitous cloud cover and
potential for a couple of rounds of showers. Thus while 850 mb
temperatures push +16 to +18C, have remained a bit conservative with
highs in the mid 80s for the lake plains and low 80s over the higher
terrain. Dew points will also soar into the mid to upper 60s making
for much muggier conditions. Shower and thunderstorm chances will
then diminish from west to east Wednesday night with continued warm
and muggy conditions overnight.


...Prolonged stretch of hot weather on the way...

A low amplitude split flow found over the Lower 48 leading into this
period will transition into a phased trough-ridge pattern that will
be dominated by a >595dm tropical ridge centered over New York and
New England.  This will lead to notably higher temperatures over our
region with afternoon mercury readings in the upper 80s to lower 90s
becoming common place. For some of the valleys across western New
York...several days in the mid 90s is a likely bet. While there will
be some leftover showers around as we get set to ramp up the heat...
the bulk of this period will be rain free. Breaking this down in a
little more detail...

A cold front will be in the process of exiting our forecast as we
open this period on Thursday. While this feature will still likely
be generating some showers over the Eastern Lake Ontario region
Thursday morning...the bulk of any scattered shower activity will be
driven by the trailing mid level shortwave. This will keep just a
chance for showers over the western counties during the morning
hours before significant clearing moves in from the west during the
midday and afternoon. All in the all though...the second half of the
day should not be too bad.

Ridging will quickly follow the front Thursday night. Without any
real change in airmasses though...Thursday night will be very
similar to that from Wednesday night as mins will be in the mid to
upper 60s.

Significant amplification of the ridge will then take place over the
Ohio Valley and Lower Great Lakes Friday and Saturday. H5 hgts will
build to >595dm over our region...while H85 temps will climb to at
LEAST 20c. At these levels...Friday and Saturday afternoons will
feature max temps in the upper 80s to lower 90s...while overnight
lows will range from the upper 60s in the mid 60s in the cooler
spots of the Southern Tier and North Country to the lower 70s across
the lake plains. No real thunderstorm relief from this heat is
expected either day being under the heart of the
burgeoning ridge will come with plenty of subsidence and H7 temps in
the vcnty 12c.


Weak and unorganized shower activity will continue to diminish in
coverage as the mid-level trough exits the eastern Great Lakes
tonight. This will leave plenty of rain free time, although an east-
west mid level frontal zone and plenty of moisture which may support
a few isolated showers overnight. Additionally, with recent rain and
abundant low level moisture widespread IFR CIGS will likely
develop and last through the first half of Sunday, with some
patchy fog (lower VSBYS) developing as well, especially across
the Southern Tier.

Sunday another mid level trough will cross the region, with a cold
front arriving by Sunday evening. This will support increasing
coverage of showers and scattered thunderstorms through the day,
first across Western NY and then spreading east across the rest of
the region through the afternoon. Any heavier showers will produce
local MVFR to IFR conditions.

Sunday night...Showers and scattered thunderstorms ending. MVFR/IFR
improving to VFR.
Monday and Tuesday...VFR.
Wednesday...Local/brief MVFR to IFR showers and thunderstorms likely.
Thursday...Mainly VFR with a chance of showers.


Low pressure will weaken and crossing Lake Ontario this evening.
East winds will produce choppy conditions at the west end of Lake
Ontario, although winds and waves are now expected to remain below
Small Craft Advisory criteria this evening.

A weak cold front will move south across the eastern Great Lakes
Sunday, with a secondary cold front moving south across the area
late Sunday night. North winds in the wake of these two cold fronts
will produce choppy conditions at times along the south shore of
Lakes Erie and Ontario, but winds and waves are expected to remain
below Small Craft Advisory criteria.





NEAR TERM...AR/Hitchcock
SHORT TERM...Church/Thomas
MARINE...AR/Hitchcock is the U.S. government's official web portal to all federal, state and local government web resources and services.