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000
FXUS61 KBUF 212029
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
429 PM EDT Wed Aug 21 2019

.SYNOPSIS...
A cold front will push through the region tonight. While this could
spark a few more showers or thunderstorms...it will bring an end to
a stretch of warm and muggy conditions. We will then experience
spectacular weather Thursday through the upcoming weekend with
little cloud cover...comfortable temperatures and low humidity.

&&

.NEAR TERM /THROUGH THURSDAY/...
During the remainder of the afternoon...our forecast area will find
itself within an unstable airmass well ahead of an approaching cold
front. A well established lake shadow downwind of Lake Erie will
keep the BUF metro area and much of the IAG Frontier free of any
rainfall...while there will be the risk for some widely separated
showers and storms most elsewhere.

Any convection that does fire up before 6 PM will likely do so along
and just ahead of a strengthening lake breeze boundary. As of
1730z...this line of enhanced Cu stretched from near Batavia
southwest along the Chautauqua ridge to about Ripley. As this
mesoscale forcing mechanism pushes east...it will encounter SBCAPEs
averaging 1500 j/kg. Fortunately bulk shear values will only range
from 20 to 25 knots...so there will not be a significant risk for
severe weather. PWAT values in the vcnty of 1.5" though could
encourage pockets of locally heavy rain...mainly over the Southern
Tier and Finger Lakes region. That being said...the coverage for the
possible convection should not be nearly as widespread as that from
early this morning.

Otherwise it will be warm and humid for the rest of the afternoon
with 70 degree dew points being accompanied by temperatures that
will largely range from the low to mid 80s.

A cold front will gradually push to the south across our forecast
area tonight. Other than a very modest 30kt low level jet and some
convergence near and ahead of this boundary...there really is not
much forcing to support WIDESPREAD pcpn. A strong H25 jet will pass
to our north...but it will be in the `wrong` place to give any
additional lift from the upper levels. It is interesting to note
though...that most if not all of the guidance packages are grossly
under estimating the strength of the UL jet. Aircraft measurements
from across Minnesota this morning measured winds >160kts with this
jet...but upper air soundings have only been able to `capture` winds
of 115 to 120kts. As mentioned though...the position of the jet is
more important and this is not favorable for significant weather
production. In any case...will use chc pops for showers and
thunderstorms.

Thursday will feature improving conditions...as a cooler and notably
drier airmass will gradually push across our region in the wake of
the overnight cold frontal passage. While a brief shower cannot be
ruled out across the Southern Tier...dry air advecting south in the
mid levels and a developing subsidence inversion should keep any
shower activity to a minimum. Otherwise...it will become
increasingly comfortable as dew points in the lower 60s during the
morning will drop through the 50s during the afternoon. Meanwhile...
afternoon highs will be in the low to mid 70s.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
The first taste of fall-like conditions will be felt across the
forecast area during this period. Cold air advection continuing
behind the front will keep in place a much cooler airmass for Friday
and also Saturday. How cool will it be? Well, H850T are forecast to
fall from +11C to +7C Thursday night, that`s chilly (single digits
at H850) for August standards.

Friday, with a cool NNW`erly flow filtering in across the region and
much warmer lakes, it will result in a conditionally unstable
airmass for any lake effect processes. However, with only a thin,
shallow layer of moisture left and strong subsidence any lake
response will be very limited, if anything at all. The most likely
scenario, with steep low level lapse rates, will be some diurnally
driven flat fair weather cu. With that said, look for dry weather
across all locations, with a mixture of afternoon clouds and
sunshine. With a much cooler air mass in place, look for highs in
the upper 60s to low 70s, which will roughly be 5-8F below normal
for this time of year.

Friday night, Canadian sourced high pressure will provide light
winds and clear skies overnight. In fact, it will be an excellent
night for star gazing, if you get a chance head outside and make use
of a telescope if you have one. The only thing weather wise will be
some interior valley fog across the Southern Tier and to a lesser
extent east of Lake Ontario in the Black River valley. With clear
skies and excellent radiational cooling look for lows to fall back
in the upper 40s to low 50s by daybreak.

Saturday, more of the same as cool NNE flow will reside across the
forecast area with highs only expected in the upper 60s to low 70s.
Saturday night, another spectacular night is on tap with clear skies
and light winds. Lows will generally be found in the low 50s, with a
few pockets of upper 40s across interior sections of the Southern
Tier and east of Lake Ontario. Sunday, a gradual warming trend
begins as the broad Canadian sourced high slowly slides east. This
will allow return southerly flow to develop across our region which
will encourage a return to near normal highs, mid and upper 70s.

Sunday night, the center of the surface high pressure slides further
east to New Brunswick and Prince Edward Island. However, it will
continue to maintain dry conditions as we head into the new work
week. Also, it won`t be as cool overnight with lows expected in the
50s to low 60s by sunrise Monday morning.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
A return to above normal temperatures is likely during the long
term period.

Otherwise, medium range guidance is not in good agreement and
diverge with respect to how quickly the ridge slides further
east and out to sea, and how quickly the next trough and
associated moisture approaches from the west. The GFS remains
fastest with this overall scenario and brings increasing chances
for convection into our region. Meanwhile, the ECMWF lies on
the other side of the guidance envelope and keeps the ridge
intact and our region totally dry through Tuesday. Keeping this
in mind, have held POPs to only a chance showers and
thunderstorms for the time being with all the uncertainty beyond
Monday.

With the above said, the combination of general airmass modification
and strengthening warm air advection will lead to a day-to-day
warming trend through this period with highs climbing into the low
to mid 80s.

&&

.AVIATION /21Z WEDNESDAY THROUGH MONDAY/...
VFR conditions will be found across the region this afternoon and
evening...although a developing lake breeze boundary should help to
re-ignite some thunderstorms well south and east of Buffalo and
Rochester.

Tonight...a cold front will gradually push across the region. While
this feature should generate more scattered convection...the vast
majority of the area should continue to experience VFR weather. The
exception will be across the Southern Tier and possibly the North
Country...where late night fog and stratus could lead to MVFR to IFR
conditions.

Thursday will feature VFR weather as high pressure over central
Canada will gradually build south across the Upper Great Lakes.

Outlook...

Thursday through Monday...Mainly VFR with nothing more than Southern
Tier valley fog producing local MVFR/IFR conditions each morning.

&&

.MARINE...
A southwesterly flow will be in place across the region this
afternoon ahead of a cold front with waves building to 2-4 feet on
Lake Erie. A cold front will swing across the Lower Lakes this
evening and early overnight, with waves and winds increasing within
the cold air advection environment.

WNW winds over the shorter fetch of Lake Erie will build waves 2-3
feet tonight and Thursday, while a longer fetch and slightly
stronger wind flow over Lake Ontario will bring waves up to 5 feet
or greater on the southern Lake Ontario shoreline. Small craft
advisories have been issued.

&&

.TIDES/COASTAL FLOODING...
A strong cold front will cross the Lower Great Lakes this evening.
Strengthening west to northwesterlies in the wake of the front will
increase wave action and combine with already high lake levels to
produce significant shoreline erosion and flooding late tonight
through late Thursday afternoon. A Lakeshore Flood Warning is
now in effect for Wayne, northern Cayuga and Oswego counties.
Since winds will be more westerly and not as much onshore, the
lakeshore flood watch was dropped for Niagara, Orleans and
Monroe counties.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Lakeshore Flood Warning from 5 AM to 5 PM EDT Thursday for
     NYZ004>006.
MARINE...Small Craft Advisory from 2 AM to 8 PM EDT Thursday for LOZ043-
         044.
         Small Craft Advisory from 2 AM to 2 PM EDT Thursday for
         LOZ042.
         Small Craft Advisory from 8 AM to 8 PM EDT Thursday for
         LOZ045.

&&

$$

SYNOPSIS...RSH
NEAR TERM...RSH
SHORT TERM...AR
LONG TERM...AR/JLA
AVIATION...RSH
MARINE...Hitchcock/JLA/RSH
TIDES/COASTAL FLOODING...RSH/JLA