Area Forecast Discussion
Issued by NWS Buffalo, NY

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000
FXUS61 KBUF 250851
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
451 AM EDT SUN SEP 25 2016

.SYNOPSIS...
A large area of high pressure centered over eastern Canada will push
east this afternoon and tonight...and this will guarantee another
sun filled day to end the first weekend of Fall. A strong cold front
will then plow across Western and North Central New York late Monday
and early Monday night...producing several hours of showers and
possibly some thunderstorms in the process. Colder air in the wake
of the front will generate some lake effect rain showers northeast
of both lakes on Tuesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Expansive high pressure stretching from Baffin Island and Quebec to
the Carolinas will assure us of another beautiful early Autumn day
across the region...as sun filled skies will accompany seasonable
temperatures in the 60s.

The only issue to deal with...and it is a minor one...is the
presence of some scattered lake effect cloud cover this morning.
While H85 (general cloud level) temps in the vcnty of 6 C are
supportive of lake induced instability...the overall environment is
notably drier than forecast. The 00z KBUF sounding has a much wider
T/Td spread in the lowest layers than what was suggested by early
BUFKIT soundings. This...along with a great deal of shear below 5k
ft...is limiting the associated lake response. The original thinking
was for some weak `tea kettling` along and just north of the Lake
Ontario shoreline...but the above variables have only allowed
scattered to occasional broken strato-cu to the south of the lake.
This cloud cover is transitory though...so should not pose a problem
for any one area during the early morning hours.

As we progress through the morning and into the midday...relatively
strong late season diurnal effects will break up any residual lake
induced cloud cover. This will only leave some streaks of cirrus and
alto-stratus that spills over the highly amplified mid level ridge
to our west. As mentioned...temperatures will climb to near seasonal
levels for the afternoon...a carbon copy from Saturday.

Tonight...the axis of the surface high will push east across New
England. This will allow for some weak warm advection to get
underway as high and mid level cloud cover will thicken over the
western counties during the course of the night. While this should
help to hold temperatures up several degrees higher over the western
counties than those from this morning...there will likely be another
round of frost tonight for Lewis Co where starlit skies will
prevail. Since there is already a frost advisory in effect for that
county for the remaining early morning hours...will refrain from
issuing another one until later this morning to avoid confusion.
Thanks BTV, ALY and BGM for collaboration with this.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/...
Monday and Monday night...our weather will deteriorate as surface-
based ridging over Eastern New York and New England at the start of
the day slides east into the Canadian Maritimes...and gives way to
a deep mid and upper level trough digging southeastward across Ontario
Province and the Great Lakes...with this feature eventually morphing
into a deep closed upper low over Central Ontario by Tuesday morning.
At the surface...an attendant surface wave will meander along a similar
path...and will swing its trailing cold front through our region
between late Monday afternoon and Monday night.

As the front passes through our region...it will be accompanied by
a narrow but impressive band of deep moisture (PWATs of 1.5 to 1.75
inches)...as well as an equally impressive swath of deep-layer lift
driven by the front itself...and strong height falls/DCVA/diffluent
flow aloft. All of this should lead to a narrow but fairly cohesive
band of showers traversing our region from west to east...for which
categorical PoPs look very reasonable and thus remain in play. Given
that some weak instability will also be in place...a few embedded
thunderstorms will also be possible across far WNY and western
portions of the Finger Lakes from Monday afternoon into early
Monday evening...before fading out with the loss of heating after
sunset.

Following the passage of the front...strong dry slotting aloft will
build into the region Monday night...while bringing a return to mainly
dry weather for many areas. This break will not last very long northeast
of Lake Erie though...as a sheared southwesterly flow of progressively
cooler air and a modest increase in low-mid level moisture should be
sufficient to drive the development of some scattered lake effect rain
showers overnight...with these initially forming a little south of
Buffalo...then lifting northward across the Niagara Frontier in
response to a subtle but steady backing of the low level flow.

With respect to temperatures during the first 24 hours of this period...
the strengthening southerly downslope flow and the overall warm air
advection regime out in advance of the cold front will allow temps to
rebound back into the lower to mid 70s across much of the region on
Monday...with only interior portions of the North Country likely
confined to the mid and upper 60s. The warmest overall temps will
be found across the lake plains of far Western New York where the
above mentioned downslope flow will be most favorable...and where
we have accordingly continued to aim a bit above current MET/MAV
guidance. Developing cool air advection in the wake of the cold
front will then send readings tumbling back into the upper 40s to
mid 50s Monday night.

Tuesday and Tuesday night...the large (and now closed-off) upper low
will slowly meander its way south-southeastward across the state of
Michigan...with our region remaining firmly under of the influence
of its accompanying cool pool (850 mb temps of +4C to +7C)...though
the best and deepest associated wraparound moisture will generally
remain to our west...with just an attending spoke of this sliding across
far Western New York and adjoining portions of Lake Erie/Lake Ontario.
Thus for most locations...Tuesday and Tuesday night should just be
mainly dry and cooler...with highs ranging through the 60s on Tuesday
and nighttime lows falling into the mid 40s to lower 50s Tuesday
night. The exceptions to this will of course be over and downwind
of Lakes Erie and Ontario... where the cool airmass aloft and warm
lakes will help to generate some lake effect rain showers.

Overall the best setup will be found over and downwind of Lake Erie
Tuesday morning...where a somewhat sheared southwesterly low level flow
and the aforementioned spoke of deeper moisture will be supportive of
more numerous showers across much of the Niagara Frontier...though
the combination of the shear and late September diurnal influences
will probably help keep these from evolving into a cohesive rain band...
especially as diurnal effects increase later on Tuesday morning.
After that time...the combination of diminishing background moisture...
a slow but steady backing of the low level flow...and a further increase
in shear will result in the showers weakening/becoming more scattered
and lifting northward into Niagara County Tuesday afternoon and
evening...before shifting west of the area and falling apart altogether
Tuesday night as our airmass becomes too dry and the low level
flow too southerly.

Meanwhile off our other lake...the overall setup appears less
impressive as background moisture will be less favorable...and the
low level flow will likely be a bit more sheared and south-
southwesterly overall. This should result in much more scattered
showers primarily across Jefferson County and the uppermost Saint
Lawrence Valley on Tuesday...with this activity then also shifting
further northwestward and falling apart altogether Tuesday night
as the airmass dries out and the low level flow backs to southerly.

During Wednesday and Wednesday night...the closed upper low and its
original surface reflection will continue to meander south-southeastward
into the Ohio Valley. For our region...an initial southerly flow of
drier air on the eastern flank of this system should result in a mainly
dry and slightly warmer day for most of Wednesday...before increasing
moisture and lift associated with the encroaching northern portion of
the low leads to a renewed potential for some scattered showers later
Wednesday afternoon and night. Temperature-wise...highs on Wednesday
should range between 65 and 70 in most places...with lows in the mid
40s to lower 50s then following for Wednesday night.

&&

.LONG TERM /THURSDAY THROUGH SATURDAY/...
Later on in the week forecast confidence decreases markedly...as much
disagreement remains amongst the medium range guidance packages with
respect to the eventual evolution/movement of the lingering closed low.
More specifically...the 00z/25 GFS/Global GEM both continue to meander
this feature eastward across the Mid-Atlantic and Northeastern States
Thursday and Friday...which would support a continued general chance
for some showers through the end of the work week...followed by a return
to dry weather for next Saturday as high pressure builds in behind the
departing system. Meanwhile the ECMWF continues to stick with its idea
of taking the closed low due southward into the Tennessee Valley on
Thursday...before lifting it back north toward the Central Great Lakes
Friday and Saturday...a solution that would favor drier weather for our
area Thursday...followed by increasing shower chances again for both
Friday and Saturday.

Given the poor model-to-model and run-to-run consistencies that thus
continue to plague this time frame...and our previous continuity of a
mainly dry forecast...for now will elect to lean more towards continuity
and only trend the forecast a little more pessimistic for the latter
portions of the week...with a low chance of showers Thursday (as per
the GFS/GEM) followed by slight chance PoPs for both Friday and Saturday...
along with continued near to slightly above normal temperatures.

&&

.AVIATION /09Z SUNDAY THROUGH THURSDAY/...
Expansive high pressure stretching from Hudson Bay to the Carolinas
will provide VFR conditions across our region through tonight. The
only possible exception will be across the Western Southern Tier
where there could be some valley fog between 09 and 13z to reduce
VSBYS to MVFR levels.

Outlook...

Monday...While VFR weather will prevail for most sites...showers and
possible thunderstorms will arrive in the far west after 18z to
produce localized MVFR conditions.
Monday Night...Areas of MVFR with showers likely.
Tuesday and Wednesday...VFR/MVFR with a chance of showers.
Thursday...Mainly VFR.

&&

.MARINE...
A large area of high pressure centered over Quebec will keep a
northeasterly flow of chilly air across the Lower Great Lakes today.
The flow will be strong enough to generate small craft advisory
conditions on the Lake Ontario nearshore waters west of Hamlin Beach
and also on the Lower Niagara River. Choppy...sub advisory
conditions will be found on Lake Ontario from Hamlin Beach to Sodus
Bay and also on Lake Erie southwest of Dunkirk.

The surface high will push east across New england the St Lawrence
Valley tonight. This will encourage winds to veer to the
southeast...thus removing the choppy conditions described above as
the highest waves will move into Canadian waters.

The southeast winds will freshen on Monday ahead of an approaching
cold front...with the winds coming around to southwest by late
Monday and Monday evening. Winds should freshen enough to warrant a
new round of small craft advisories by late Monday. SCA conditions
are then expected to persist through Tuesday as a stationary storm
system will be parked over the Upper Great Lakes.

&&

.CLIMATE...
Saturday marked the end of the longest stretch of 70+ degree days
in Buffalo and Rochester since records began in the early 1870s.
The high temperature Saturday topped out at 65 for Buffalo and 64
for Rochester...which marks 102 days since the last time (June
13th) that the high temperature did not reach the 70 degree mark.
Following is a top ten list of longest stretches of 70+ degrees
days for Buffalo and Rochester.

Buffalo
Rank Run Length Ending date
1      102       2016-09-23
2       95       2005-09-22
3       94       2012-09-08
4       80       1959-09-10
5       78       2006-08-28
6       77       1878-09-10
7       75       1993-08-20
-       75       1987-08-23
9       73       1980-09-11
10      71       1952-08-21

Rochester
Rank Run Length Ending Date
1      102      2016-09-23
2      101      2002-09-26
3       88      2005-09-15
4       84      1959-09-10
5       83      1939-09-04
6       82      2011-09-04
7       81      1975-08-29
8       79      1881-09-12
9       78      2006-08-29
10      75      2012-09-08

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Frost Advisory until 9 AM EDT this morning for NYZ007-008.
MARINE...Small Craft Advisory until 4 PM EDT this afternoon for LOZ030-
         042.

&&

$$

SYNOPSIS...RSH
NEAR TERM...RSH
SHORT TERM...JJR
LONG TERM...JJR
AVIATION...RSH
MARINE...RSH
CLIMATE...STAFF



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