Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 230635
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
235 AM EDT Fri Jun 23 2017

.SYNOPSIS...
A warm front will make its way northeastward across our region
through tonight...while bringing a general chance of showers and
thunderstorms and ushering in a much warmer and more humid
airmass. Showers and storms will then become more widespread on
Friday as tropical moisture surges across our area in advance of
an approaching cold front...which will then cross New York
State late Friday and Friday night. In the wake of the front...
cooler and somewhat unsettled weather will follow for this
weekend as broad upper level troughing digs across the Great
Lakes.

&&

.NEAR TERM /THROUGH TODAY/...
Regional radar shows that the bulk of the shower and thunderstorm
activity has shifted north across lake Ontario, and is riding a warm
frontal boundary into the North Country. Showers and embedded
thunderstorms will impact the North Country over the next few hours,
before shifting north across the St. Lawrence valley, as the front
continue to drift northwards into Canada. Expect dry, but muggy
conditions for the rest of the forecast area overnight, though
mesoscale guidance does indicate showers popping up along the PA
border towards daybreak. Given how moist the airmass is, this is
entirely reasonable.

The increasingly tropical nature of the incoming airmass will make
for a downright sultry night...with surface dewpoints surging well
into the mid and upper 60s...and overnight lows failing to drop
below the upper 60s and lower 70s...with the warmest readings found
across the lake plains.

On Friday tropical moisture will continue to stream northeastward across
our region in advance of an approaching cold front...which will begin to
impinge upon our area by the mid to late afternoon hours. Coupled with
renewed daytime heating and increasing large-scale lift associated with
the front/possible prefrontal trough and modest height falls aloft...this
should result in showers and thunderstorms becoming more
widespread during the day. With some potential for lake
shadowing to develop northeast of the lakes... it still appears
that the highest potential for showers and storms will lie from
interior sections of the Southern Tier northeastward across the
Finger Lakes and North Country...where categorical PoPs will
remain in play.

At this juncture...the biggest potential concern with Friday`s convection
remains the possibility of locally heavy rainfall...especially when given
precipitable water values in the vicinity of 2 inches. A secondary concern
will be the potential for gusty winds with any stronger convection given
favorable 0-6 km bulk shear values of 35-40 knots...however this will be
strongly dependent upon the amount of instability that develops...a factor
that remains highly uncertain and will be heavily dependent upon the amount
of morning cloud cover/precipitation that will be in place. Given the above...
for now have elected to keep our current enhanced wording of heavy rain and
gusty winds in the forecast.

Otherwise...Friday will be a warm and very humid day...with high temps
ranging from the mid 70s to lower 80s in most places...and surface
dewpoints ranging within a few degrees of 70.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...
The weekend will be a period of transition to overall below normal
temperatures by the start of next week, breezy conditions and
scattered showers and thunderstorms at times. This will occur as
broad troughing develops over the Hudson Bay Friday and shifts
eastward across New England through the weekend.

Friday night a cold front with numerous showers and thunderstorms
ahead of it will sweep eastward into central and eastern NY. Cold
air advection behind the front will bring in a cooler and drier
airmass with partial clearing developing from northwest to southeast
overnight. The drier airmass will allow temperatures to fall into
the lower 60s on the lake plains and upper 50s across the higher
terrain.

Saturday will see continued weak cold advection behind the front on
west to west-southwesterly flow as 850mb temperatures fall to around
+10C. Some steepening of the lapse rates behind the front will
support diurnal cumulus clouds developing inland from the lake
breezes. Speaking of which, the more westerly flow will support an
area of lake breeze convergence along the south shore of Lake
Ontario. This may act as a focus for some convection to develop and
train along the lake breeze as a subtle PV max in the cyclonic flow
aloft tracks up the lower Great Lakes. While a few isolated showers
or thunderstorms are possible inland from the lake breezes, the best
chance will again be for the south shore of Lake Ontario on the lake
breeze convergence zone. Highs on Saturday will be in the mid 70s.
By Saturday night the loss of heating and brief area of subsidence
behind the shortwave should end any shower activity. The clearing
skies and cooler airmass will support lows in the 50s.

Sunday will be similar to Saturday, expect that a more robust PV max
will track from southern Michigan across the axis of the lower Great
Lakes through the day. This wave will both usher in cooler
temperatures aloft steepening the lapse rates further, and also
supply more ascent for convection to develop Sunday afternoon. 850mb
temperatures fall to around +6 to +7C over the lower Great Lakes,
which will support cooler daytime highs in upper 60s to near 70.
This will also neutralize the afternoon lake breeze action some as
latest reported lake temperatures and satellite analysis suggest
Lake Erie is around 70 degrees, while Lake Ontario is in the mid
60s. This will support scattered showers and some thunderstorms
across the entire area (with very little lake breeze protection NE
of the lakes). This will also readily allow for momentum transfer to
the surface with steep low to mid level lapse rates, and little to
no inversion over the lakes themselves. A core of 30 knot winds near
925mb will be able to mix down to the lake surfaces under and in the
wake of the PV max passage directly over the lakes, helping to full
mix the winds to the surface. This will likely result in gusts to
around 35 mph across the Niagara Frontier and Saint Lawrence Valley,
but will also likely result in hazardous beach conditions on the
east end of both lakes, and increase lake shore flood potential on
the east end of Lake Ontario.

By Monday, another robust shortwave will track to near Lake Erie by
the afternoon. The combined steep lapse rates under the cyclonic
flow aloft and the increasing QG ascent ahead of the PV max will
support scattered to numerous showers and thunderstorms across the
region by the afternoon. Temperatures will again be quite cool with
850 mb temperatures similar to Sunday around +6 to +7C. High
temperatures will again be in the 60s with perhaps the typical warm
spots touching the 70 degree mark.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
An upper level trough will remain across the Great Lakes and
Northeast to start this period, bringing chances for showers and
daytime thunderstorms Monday night through Tuesday night. The
trough/cool pool reaches its depth Monday night and into Tuesday,
and these stronger lapse rates will maintain the thunder chances. By
Wednesday the upper level trough begins to slide eastward, with
chances for showers mainly confined to the Finger Lakes and Eastern
Lake Ontario region. Surface high pressure will cross the region
Wednesday and narrow ridging aloft will allow for the return of some
sunshine. By Thursday this high pressure will be to our east, with
southerly behind the surface high bringing increasing moisture and
warmth northward across the region. This moisture may fuel a few
showers and thunderstorms later in the day Thursday.

Under the influences of the upper level trough temperatures next
week will remain below normal, though on Thursday the increasing
southerly flow should bring back above normal warmth, with upper 70s
to lower 80s across the region.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
A broad area of showers with embedded thunderstorms is situated
along a warm frontal boundary that has largely moved north of the
forecast area, with the exception of the North Country. -TSRA will
affect KART over the next 2 to 4 hours, before the front drifts
farther north into Canada. Otherwise, the rest of the forecast area
should stay dry through the rest of the night, with the exception of
near the PA border, where a few popup showers may develop late.
Outside of any showers, look for VFR conditions to prevail, with the
exception of the higher terrain of the Southern Tier, where cigs may
drop into MVFR range as low level moisture deepens across the region.

A pre-frontal trough is expected to move across the region this
afternoon, triggering widespread -shra/tsra across much of the
forecast area, though the Niagara Frontier is expected to remain
lake-shadowed and thus dry for much of the afternoon. Another round
of -shra/tsra will move across the forecast area this evening, ahead
of an approaching cold front. Some of the afternoon storms will be
strong, and potentially severe. Given abundant moisture, expect MVFR
conditions within showers, with brief periods of IFR. IFR conditions
are also expected across higher terrain of the Southern Tier for
much of the day, given deep low level moisture streaming across the
region.

Outlook...

Saturday through Tuesday...Mainly VFR with a chance of mainly
afternoon showers and isolated thunderstorms.
Wednesday...Mainly VFR with a chance of showers.

&&

.MARINE...
Southerly winds will freshen overnight and Friday as the warm
front finishes crossing the region...before turning
southwesterly on Friday out ahead of an approaching cold
front...then westerly Friday night and Saturday following the
passage of the cold front. This stated... winds and waves are
still expected to remain largely below advisory levels tonight
through Saturday.

At this point... better chances for advisory-level winds and waves look
to hold off until Sunday...when a stronger westerly flow of cooler air
looks to overspread the Lower Great Lakes.

&&

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

&&

$$

SYNOPSIS...JJR
NEAR TERM...APFFEL/WOOD
SHORT TERM...CHURCH
LONG TERM...THOMAS
AVIATION...WOOD
MARINE...APFFEL/JJR



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