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Area forecast discussion
National Weather Service Buffalo New York
755 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/...
at 7 p.M. A warm front extended from Georgian Bay and across
west-central New York roughly from Rochester to Binghamton.
Radar showed sparse showers along this boundary, with more
widespread showers and thunderstorms to the south and west of
the region.

For the evening hours, expect mainly dry and warm conditions
across western New York. Temperatures will not drop much behind
the warm front, with evening temperatures remaining in the upper
70s in most locations. There is a small chance for a shower or
thunderstorm with the warm front, and across the western
southern tier from left- over diurnal instability. However,
mesoscale guidance has trended drier, with the guidance that is
wet not matching latest radar trends.

Moisture will increase later tonight, with most mesoscale
guidance capturing a large area of showers and thunderstorms
across Lake Huron and moving in across southern Ontario and into
the north country late tonight. This supports likely/categorical
pops given the model agreement and supportive radar trends. This
may clip other areas if it expands southward as some guidance
suggests, but confidence is lower across the rest of western New
York with only a chance of showers or thunderstorms overnight.

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 New York. 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 /00z Friday through Tuesday/...
expect mainly VFR conditions to last through 06z outside of
localized MVFR or lower conditions in showers or thunderstorms.
The chance for this appears low except for the north country
(including art) where showers and thunderstorms are likely
tonight.

Low moisture will continue to increase later tonight, with model
guidance suggesting that ceilings will lower to MVFR or IFR late
tonight and through Friday morning. This guidance appears a bit
pessimistic, but expect at least a period of MVFR conditions as
steadier rain moves in Friday morning. Areas of IFR cigs are
certainly possible, especially at jhw and northeast of Lake Erie
at buf/iag. Perhaps the bigger concern for Friday is the
embedded thunderstorms which will be slow moving so they may
impact any given location for several hours before moving away.
However, these are difficult to time this far out so tafs show a
prolonged thunderstorms in the vicinity until confidence in timing improves. Locally
heavy rain is possible in these storms.

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 low level wind shear in the tafs for now. This
said...this is something that will need to be closely monitored as the
night progresses.

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...
southerly winds will 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...
New York...none.
Marine...none.

&&

$$

Synopsis...jjr

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