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875
FXUS61 KBUF 190220
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1020 PM EDT Sun Aug 18 2019

.SYNOPSIS...
Warm and muggy conditions will remain over the region through the
middle of the week. While the sub tropical airmass will fuel some
showers and thunderstorms during this period...the vast majority of the
time will be rain free. A strong cold front that will pass through the
region late Wednesday will then introduce a cooler and notably more
comfortable airmass to our region for the second half of the week.

&&

.NEAR TERM /THROUGH MONDAY/...
Radar imagery showing the entire area dry late this evening as the
earlier convection has weakened and moved well east of the area. It
will remain dry through the midnight hour before our attention turns
to a solid line of convection over southwest Ontario and western
Lake Erie.

A well defined shortwave over the Midwest will then take aim on our
region for the overnight period. A fairly solid line of convection
is moving east across southwest Ontario and western Lake Erie with
this feature, and is forecast to reach Western NY by around 06Z.
While there will initially be some upper level lift for the system
to work with...this will weaken with time. The upstream line of
convection will likely hold together and reach Western NY, then move
east across the Genesee Valley and western Finger Lakes very late
tonight. Increased the POPS to likely from the Genesee Valley
westward to account for this, and also added wording for gusty winds
and heavy rainfall. As forcing weakens and instability wanes, the
storms should decrease in coverage and intensity late tonight as the
system moves towards the eastern Lake Ontario region.

The aforementioned shortwaves will precede a weak cold front that
will gradually push south across our forecast area during the day
Monday. This front will help to focus yet another round of showers
and thunderstorms over the region...mainly during the midday and
afternoon when instability will be at its greatest. Once again
though...a lack of upper level jet support or notable low level jet
will leave the bulk of the forcing to convergence in the vcnty of
the front or other subtle boundaries within a conditionally unstable
airmass with MLCAPE values under 1000 j/kg. Bulk shear values are
not forecast to exceed 20-25 knots...so am not anticipating
widespread strong to severe convection.

Otherwise...the largely rain free day will feature muggy conditions
with dew points within a few degrees of 70. Max temps will range from
80 to 85.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/...
This period will feature a mainly dry and warm, but less humid day
on Tuesday, followed by showers and thunderstorms on Wednesday into
Wednesday evening as a strong cold front plows across the area.

Monday night into Tuesday will be mainly dry as a push of somewhat
drier air works in behind a weak, stalled out frontal boundary lying
across northern PA. With no discernible shortwaves moving over the
area, there will just a slight chance for a few showers toward the
PA line closest to the boundary. Dew points will drop off some
across the entire area, bringing some relief to the mugginess,
especially east of Lake Ontario where dewpoints could fall into the
upper 50s. Temperatures Monday night will be some ten degrees cooler
than the previous night, with lows in the upper 50s to lower 60s.
Highs on Tuesday will be mainly in the upper 70s to lower 80s,
however will a drier `feel` to the air.

Tuesday night, the frontal boundary over PA will start to make a
move back to the north as a weak warm front, while an upper level
shortwave approaches the Lower Great Lakes. While the night may
start out dry, deeper moisture to our south will make a push back to
the north ahead of the now northward advancing warm front. This will
increase the chance of some showers/isolated storms from south to
north across the area, especially during the second half of the
night due to added lift associated with the approaching shortwave.
Humidity levels will be a bit higher, as will overnight temperatures
as compared to Monday night, with lows mainly in the mid 60s. The
exception will be across the northcountry, where lows will bottom
out in the upper 50s to lower 60s.

A cold front will be poised to plow across the region later
Wednesday into early part of Wednesday night. A warm, humid airmass
will be found out ahead of the approaching cold front. As the upper
level trough sharpens just to the west over the central Great Lakes,
enhanced lift provided by this feature within an already unstable
environment will promote widespread showers and thunderstorms
Wednesday afternoon/early evening with the pre-frontal trough out
ahead of the main cold front. The main cold front will then plow
across the region later Wednesday evening into the early overnight,
with possibly another round of general showers and storms. Storms
Wednesday afternoon into the early evening hours could become strong
with both gusty winds and hail possible. Mid level lapse rates will
increase with height falls aloft, bulk wind shear values upwards of
35 to 40 knots and CAPE deepening through the mid levels on forecast
soundings will support these stronger storms.

Temperatures on Wednesday will be similar to Tuesday, however dew
points pushing back into the upper 60s to near 70 will make it feel
more uncomfortable outside. Cooler, less humid air will pour in
behind the cold front Wednesday night. Lows will generally be in the
upper 50s to lower 60s, with some mid 50s across the higher terrain
east of Lake Ontario.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
In the wake of a strong cold front...a much cooler and drier airmass
will continue to overspread our region Thursday and Thursday night...
with 850 mb temperatures falling to within a couple degrees either
side of +7C. The combination of lingering secondary surface troughing
and a digging upper level trough could lead to a few more isolated
to widely scattered showers on Thursday...with the cooler airmass
and loss of diurnal influences then potentially supporting a weak lake
response east and southeast of Lake Ontario Thursday night into early
Friday...with this limited by the rather dry nature of the airmass.
Otherwise...the Thursday-Friday time frame will be dry and notably
cooler as expansive surface-based ridging slowly builds southeastward
across the Great Lakes. Expect highs to mostly be in the lower half of
the 70s both days...though some of the higher terrain may see readings
confined to the upper 60s. Meanwhile lows will be mainly in the 50s...
with some upper 40s possible across interior portions of the Southern
Tier and North Country.

After that...the axis of the aforementioned surface ridge will crest
across our region on Saturday...then will drift to the Atlantic
coastline on Sunday. This will provide our region with continued
fair dry weather both days...with diurnal airmass modification
and eventually warm air advection allowing highs to climb back into
the mid to upper 70s on Saturday...and to the upper 70s to lower 80s
on Sunday.

&&

.AVIATION /03Z MONDAY THROUGH FRIDAY/...
Dry conditions will prevail through about 05Z with VFR. An upper
level disturbance to our west will continue to support a line of
convection over western Lake Erie and southwest Ontario. Some of
this may hold together overnight and move into Western NY by around
06Z. The best chance of organized convection will be across Western
NY, with a weakening trend expected thereafter as the system moves
towards the eastern Lake Ontario region late tonight. A few storms
may contain gusty winds in Western NY if the line holds together.
VFR will prevail tonight, with any MVFR and IFR limited to in and
near thunderstorms.

A few more scattered showers and storms will develop Monday,
especially during the afternoon along and inland of the lake breeze
boundaries. There may be some MVFR CIGS across the higher terrain of
the Southern Tier for a few hours in the morning. Otherwise VFR will
prevail except in and near thunderstorms, which may contain
local/brief MVFR to IFR conditions.

Outlook...

Monday night...Mainly VFR...but IFR vsbys possible across the Southern
Tier late.
Tuesday...VFR...with a chance of showers and thunderstorms across the
Southern Tier
Wednesday...Thunderstorms likely that could impact operations.
Thursday and friday...Mainly VFR.

&&

.MARINE...
West winds will increase to around 15 knots on average tonight and
Monday, which will produce choppy conditions on Lakes Erie and
Ontario. Waves will reach around 3 feet at times, but conditions are
expected to remain below Small Craft Advisory criteria. There will
be a few rounds of thunderstorms tonight and Monday, with locally
higher winds and waves near storms.

Looking further out into the middle of next week...a cold front
will cross the region on Wednesday along with more showers and
thunderstorms. In its wake...increasingly brisk northwesterly
winds will bring an increase in wave action and could eventually
require the issuance of Small Craft Advisories for Wednesday night
and Thursday.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...None.

&&

$$

SYNOPSIS...RSH
NEAR TERM...Hitchcock/RSH
SHORT TERM...JM
LONG TERM...JJR
AVIATION...Hitchcock
MARINE...Hitchcock/RSH