Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 182308
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
708 PM EDT Tue Sep 18 2018

.SYNOPSIS...
High pressure will bring drier and cooler weather for Wednesday.
This will be followed by a warm front that could produce a few
showers across the forecast area Thursday into Thursday night. A
cold frontal passage late Friday will then lead a much cooler
airmass into our region for the weekend.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
A weak cool front will stagger to the south across our region this
evening. A cooler and notably less humid airmass will follow for the
overnight into Wednesday. Despite the cooler airmass...there should
still be enough low level moisture in the wake of the front to allow
for some stratus late tonight...and this will help to limit the
cooling. Mins by daybreak will generally range from 60 along the
immediate lake shores to the low 50s across the North Country.

On Wednesday...high pressure centered over eastern Ontario will
slowly drift by to our north. A building upper level ridge will also
shift east and be centered near the mid Mississippi Valley. With the
region sandwiched between these two areas, this will result in dry
conditions across the area. It will be a noticeably cooler day with
max temps generally within a couple degrees of 70.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
Wednesday night a weak high pressure ridge over eastern NY and
New England will continue to drift away from the area, allowing
for increasing warm advection and increasing mid/upper level
moisture ahead of a developing warm front over the western Great
Lakes. This will bring an increase in clouds from west to east
overnight, although any showers should hold off until Thursday.
Expect lows to range from the upper 50s near Lake Erie, to the
mid 50s from the Genesee Valley into the western Finger Lakes,
with upper 40s east of Lake Ontario.

Thursday and Thursday night a warm front will strengthen and move
northeast across the area in response to increasing southwest flow
across the Ohio Valley and Great Lakes, downstream of a digging
trough over the Upper Midwest. The strongest forcing, upper level
support, and deepest moisture will move across the Upper Great Lakes
into Ontario and southwest Quebec, with somewhat weaker forcing and
more shallow moisture along the southeastern extent of the warm
front which will cross our region. Nonetheless, expect enough
forcing and moisture to produce at least scattered showers as the
warm front moves northeast across our area. The rain chances will
arrive in Western NY by later Thursday morning, before reaching the
eastern Lake Ontario region by late afternoon. The shower chances
will then diminish from southwest to northeast later Thursday night
with the passage of the warm front. We have left out any mention of
thunder at this point, although model point soundings suggest some
marginal elevated instability that could produce a few rumbles of
thunder.

Warmer and more humid air will surge into the region late Thursday
and Thursday night behind the advancing warm front. Expect highs in
the upper 70s by late Thursday afternoon across Western NY, mid 70s
for the Genesee Valley and western Finger Lakes, and upper 60s to
lower 70s east of Lake Ontario. Lows Thursday night will be in the
upper 60s to around 70 on the lake plains, with mid 60s across the
interior Southern Tier and east of Lake Ontario.

Our region will be solidly in the warm sector for most, if not all
of Friday. Any warm frontal showers across the North Country will
end early, leaving the area dry through at least early to mid
afternoon. 850mb temps around +16C to +17C will support highs in the
mid or even upper 80s across the lower elevations away from lake
influences. Strong southwest flow will keep the Buffalo and
Watertown areas cooler. Speaking of wind, a strong 50+ knot low
level jet in the warm sector will cross the eastern Great Lakes. The
warm low/mid levels will keep lapse rates somewhat muted, with less
than full mixing of strong winds from aloft. Nonetheless, BUFKIT
momentum transfer schemes suggest potential for advisory level gusts
of around 50 mph in the normal spots northeast of the lakes,
including the Niagara Frontier to near Rochester, and in Jefferson
County. Elsewhere gusts of 30-40 mph are expected.

The cold front arrives by late afternoon or evening. Strong
convergence along the front and increasing upper level support from
the approaching trough will allow for a band of showers and possibly
a few thunderstorms to develop along or just ahead of the front. The
very strong wind fields and strongly forced front suggest the
possibility of a line of convective showers (with our without
thunder) that may produce very gusty winds.

The cold front will sweep east across the area Friday evening with
showers mostly ending with the frontal passage. Winds will drop off
fairly quickly following the passage of the cold front, since all
the strong winds aloft are found in the warm sector. Overnight,
strong cold advection and northwest flow may allow for a few light
lake effect/upslope showers to develop. These will then diminish
during Saturday morning with dry air advection and increasing
diurnal influences...leaving behind dry weather for Saturday
afternoon along with a return to some partial sunshine. Meanwhile
much cooler and drier air advecting into the region behind the cold
front will allow nighttime lows to drop back into the much more
comfortable 50s Friday night...with daytime highs on Saturday then
struggling to climb above the lower to mid 60s...which will be a
marked departure from the midsummer warmth and humidity of the
previous week...and right on cue for the arrival of astronomical
autumn.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
Canadian high pressure will be draped across the region as this
period opens Saturday night...with attendant subsidence and dry
air ensuring a quiet and dry night. With mainly clear to partly
cloudy skies and generally light winds also expected to be in
place...the cooler and drier airmass will support solid radiational
cooling...with overnight lows ranging from the lower 50s along
the immediate south shores of Lakes Erie and Ontario to the mid
to upper 40s elsewhere...with the coolest readings found across
the North Country.

Sunday and Sunday night the core of the surface ridge will exit
eastward across New England and the Canadian Maritimes. Lingering
weak ridging and associated drier air will still linger back
westward across our region on Sunday and should largely support
continued fair and dry weather across our region...before a
developing southerly return flow around the ridge possibly supports
a few isolated showers along our southeastern periphery Sunday
night. Meanwhile slow modification of our airmass should allow
daytime highs to warm back into the 65-70 range Sunday...and
nighttime lows to climb back into the upper 40s to lower 50s
Sunday night.

As we head into Monday and Monday night...the medium range models
offer increasingly disparate solutions...with the GFS pushing a weak
and relatively moisture-starved cold front southward through our
region...while the ECMWF and GEM both push a much stronger warm
frontal boundary northeastward and across our area. Given these
differing solutions...have just advertised broadbrush lower-end
chance PoPs for now...along with temperatures returning back to
right around seasonal normals.

After that...the guidance packages come back into better agreement
on a stronger warm advection regime developing across our region on
Tuesday...well out ahead of a strong cold front that will be slowly
making its way across the Upper Great Lakes. With this in mind...
have kept broadbrush mid-range shower chances in play...along with
highs in the lower to mid 70s to close out the period.

&&

.AVIATION /23Z TUESDAY THROUGH SUNDAY/...
Tonight, low-level moisture will increase behind the cold front as
cool, moist north to northeast upslope flow develops off of Lakes
Erie and Ontario. This will bring an increase in low stratus tonight
for areas to the south of both lakes. Later tonight, this will lead
to the formation of mainly MVFR CIGS across the lower elevations,
with IFR CIGS across the higher terrain of the western Southern Tier
and western Finger Lakes that will persist through the end of
the TAF period.

On Wednesday, low clouds will scatter out quickly as high
pressure builds into the region. This will giveway to widespread
VFR conditions which will last for the remainder of the day.

Outlook...

Wednesday night...VFR.
Thursday...Mainly VFR. A chance of showers.
Friday...VFR/MVFR. Showers likely with a chance of
thunderstorms. Windy.
Saturday and Sunday...Mainly VFR. A chance of showers.

&&

.MARINE...
Northwesterly winds will freshen to around 10-15 knots behind a cold
front, which will push south of the Great Lakes this evening. Winds
will then shift to the northeast late tonight and Wednesday. This
will produce some choppy conditions along the south shores of Lake
Ontario and Lake Erie, but winds and waves are expected to remain
below Small Craft Advisory criteria.

Southwest to westerly winds will increase sharply Thursday night
into Friday as deepening low pressure moves through the Upper Great
Lakes. High end Small Craft advisory conditions will develop on the
Lower Great Lakes with the potential for gale force wind gusts,
especially Friday morning into Friday afternoon.

&&

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

&&

$$

SYNOPSIS...RSH
NEAR TERM...RSH/SW
SHORT TERM...Hitchcock/JJR
LONG TERM...JJR
AVIATION...Apffel/RSH/SW
MARINE...Apffel


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