Area Forecast Discussion
Issued by NWS Buffalo, NY

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529
FXUS61 KBUF 222034
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
434 PM EDT Thu Jun 22 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 FRIDAY/...
As of 1845Z...an elongated warm frontal zone extends all the way from
low pressure over Manitoba to northwestern Pennsylvania. As previously
expected...the complex of showers and storms over Southern Ontario as
of mid to late morning rapidly degenerated into some scattered light
showers and a few leftover storms as it pushed into western New York...
with this sharp weakening trend due to the much drier and more stable
airmass found over our region. As of this writing...the remnants of
this activity extend from the Finger Lakes to interior portions of the
Southern Tier...with any thunder now confined to areas south of the
Pennsylvania border. All of this will continue to weaken and slide east-
southeastward along the warm front over the next 2-3 hours...with this
initial round of activity likely to be done by mid to late afternoon.

Otherwise...the surface warm front will continue to make its way
northeastward into our region this afternoon...with this boundary
reaching the lower Genesee Valley and western Finger Lakes by late
this afternoon or early this evening. Cannot rule out a few additional
showers or storms along and north of the front as it works into our
region this afternoon...particularly later on in the day as a weak
MCV-type feature (currently pushing across the southeastern shore of
Lake Huron) impinges across our region. For this reason...have retained
a general chance of showers and thunderstorms in the forecast.

Following the warm frontal passage...much warmer and more humid air
will also overspread far western New York during the mid to late afternoon
hours. With some heating...this could result in the development of enough
instability to pop a few additional scattered showers and storms late this
afternoon and/or early this evening across the Western Southern Tier. Should
these actually materialize (a factor that still remains in question as of
this writing)...available instability and shear profiles could be sufficient
for a couple of storms capable of producing locally gusty winds in this
latter area...something that we`ll need to keep an eye out for as we push
through this time frame.

Temperature-wise...continued steady warm air advection across our region
will push 850 mb temps up to between +13C and +17C by late this afternoon...
which should translate into high temps ranging from the mid and upper 70s
across the North Country to the lower to mid 80s across much of the area
south of Lake Ontario. Humidity levels will also be on the increase as
well...particularly across far western New York where surface dewpoints
will climb into the mid 60s by late this afternoon/early this evening.

Tonight the surface warm front will continue to make steady northward
progress...with this feature largely clearing our area by daybreak on
Friday. While the bulk of any associated convection should tend to
focus along and northward of the advancing front (i.e., across Lake
Ontario...the North Country...and Saint Lawrence Valley)...some additional
scattered convection will still be possible across the rest of the area
given the continued advection of an increasingly warm and moisture-rich
airmass across our region...for which some chance PoPs remain in play.
The increasingly tropical nature of the incoming airmass will also result
in 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 across
the region as the day progresses...particularly during the afternoon hours.
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 /FRIDAY NIGHT 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 /21Z THURSDAY THROUGH TUESDAY/...
This afternoon and tonight...a surface warm front will lift northeastward
across the forecast area. As a result...scattered showers and thunderstorms
will be possible just about anywhere across the region through tonight...
with the activity likely becoming a more numerous across Lake Ontario and
the North Country tonight. Overall...flight conditions should largely
remain VFR through a good chunk of tonight...with MVFR possible within any
convection. Later on tonight and early Friday...continued advection of a
very moist airmass into our region may result in the development of MVFR
ceilings from southwest to northeast...with the greatest potential for
these/lowest overall ceilings found across the higher terrain.

While a strengthening low level jet will be found across portions of our
region tonight...at this point it appears that surface winds will be just
strong enough to preclude the mention of LLWS in the TAFs for now. This
said...this is something that will need to be closely monitored as the
night progresses.

On Friday showers and thunderstorms will become more widespread across
our region as a cold front approaches...and interacts with the tropical
airmass that will be in place across New York State. This will result in
a mix of VFR/MVFR conditions deteriorating to MVFR...with IFR possible
within locally heavy downpours. In addition...a few storms may also
become strong enough to produce locally gusty winds...provided enough
instability actually develops.

Outlook...
Friday Night...VFR/MVFR with showers and thunderstorms diminishing from
northwest to southeast.
Saturday through Monday...VFR/MVFR with a chance of showers and
thunderstorms.
Tuesday...Mainly VFR with a chance of showers.

&&

.MARINE...
High pressure will keep conditions relatively tranquil on the lakes
this afternoon...with the exception of southwesterly winds to around
15 kts across Lake Erie late this afternoon...following the passage of
a warm front.

Southerly winds will then freshen some tonight 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...JJR
SHORT TERM...CHURCH
LONG TERM...THOMAS
AVIATION...JJR
MARINE...JJR



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