Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 010245
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1045 PM EDT FRI SEP 30 2016

.SYNOPSIS...
A slow moving upper level low over the Ohio Valley will move towards
the region. This will result in periodic rain showers through the
weekend. Along with plenty of clouds, temperatures will be a little
cooler than recent days. Improvement is expected by the early to
middle part of next week once the slow moving storm system moves
away from the region.

&&

.NEAR TERM /THROUGH SATURDAY/...
A mid latitude block will remain in place through Saturday...as a
stacked low will very slowly make its way from the Ohio Valley to
western Lake Erie. Meanwhile...strong high pressure will hold its
ground across the eastern provinces of Canada. This will keep an
anomalously strong and persistent easterly flow over our forecast
area with a wealth of Atlantic moisture keeping us shrouded under
cloudy skies.

While upslope flow in the low levels and a divergent flow aloft will
help with producing weak lift over the whole region...shower
activity through saturday will be highly dependent on forcing from
mid level shortwaves rotating northward around the front side of the
closed low and the proximity of upper level jets. In the case of
the showers over North Central New York early tonight...the driving
force will be a weakly coupled H25 jet. As a 110kt H25 jet over New
England pushes east overnight...the added lift will be removed and
showers will taper off from the south. This will leave several hours
of little if any pcpn over the forecast area before the next round
arrives during the wee hours of the morning.

Dopplers across the Mid Atlantic region are doing a fairly good job
early tonight of verifying what some guidance packages are depicting
as a spoke of vorticity pinwheeling to the north. This feature is
difficult to identify in WV imagery. Extrapolation of this feature
would suggest that the next round of showers would push north across
Western Pennsylvania during the overnight...then make its north of
the border before daybreak to affect our Western Southern Tier.

During the day Saturday...this ribbon of mid level forcing will
become co-located with a 90kt jet core around the east side of the
advancing closed storm system. This will support an increase in
coverage of showers across the region...with the activity as a whole
drifting north across all of our forecast area. As we work
through the mid and late afternoon...the focus for this lift will
make its up towards the North Country...while the showers should
start to taper off across the Southern Tier. This scenario will
support the raising of pops to likely for the bulk of the region.
Temperatures Saturday afternoon will generally be in the mid 60s.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH TUESDAY/...
By Saturday night an upper low will remain stalled across Eastern
Michigan, with the best forcing having lifted north of the forecast
area. Model guidance shows no significant waves embedded in the
cyclonic flow, and thus expect mainly a drying trend overnight from
south to north with most areas seeing plenty of dry time outside of
an isolated shower.

On Sunday this upper low will slowly track eastward, reaching the
Lower Great Lake and/or Western New York on Sunday night. The
steadiest showers are likely to be just to the north of the surface
low and underneath the upper low which may be slightly offset from
the surface reflection. Showers are likely across the western two-
thirds of the cwa by Sunday afternoon. Showers should then gradually
lift across Lake Ontario and into the Eastern Lake Ontario region
late Sunday night. Steeper lapse rates under the upper low may
support some thunderstorms Sunday afternoon and evening. Also worth
noting is the increasing chances for waterspouts on the lower Great
Lakes Sunday into Sunday night given the steeper lapse rates under
the upper level low and warm lake surface temperatures in the upper
60s.

Total precipitation amounts through this period won`t be very high,
likely ranging between a quarter and three quarters of an inch. The
greatest amounts are likely to be across the Niagara Frontier and
Lower Genesee Vally where this rainfall should be beneficial.
Temperatures should remain above normal for the weekend, especially
on Sunday when temperatures should rise into the upper 60s to lower
70s.

For Monday into Tuesday the upper-level low will finally depart the
region to our east and heights will rise across the forecast area
into Tuesday as a sharp upper-level ridge builds eastward. Monday
will be mainly dry outside of a few isolated/scattered showers in the
eastern Lake Ontario region. Low level moisture in the northerly
flow behind the departing low will however keep Monday mostly cloudy
across the area with high temperatures remaining in the mid to upper
60s. Temperatures will moderate some on Tuesday with decreasing
cloud cover compared to Monday, with high temperatures in the upper
60s to low 70s.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
High pressure will remain anchored over eastern New England Tuesday
night through Thursday. This will bring several days of dry weather
with a good deal of sunshine for Wednesday and Thursday as
subsidence and dry air dominate from the eastern Great Lakes to New
England. Temperatures will run above normal, with highs in the lower
to mid 70s both days on the lake plains. The dry airmass will allow
for a wide diurnal range, with cool nights in the 50s on the lake
plains and 40s well inland.

Later Thursday night and Friday the next system approaches. A deep
mid level trough will advance into the western Great Lakes, with a
cold front pushing east into our region. Model guidance begins to
diverge to some extent on timing, with the ECMWF faster in bringing
rain into Western NY late Thursday night, while the GFS and most of
the GEFS ensemble members hold the rain off until Friday. For now
have kept Thursday night dry, with a chance of showers introduced
into the new day 7 next Friday.

&&

.AVIATION /03Z SATURDAY THROUGH WEDNESDAY/...
An anomalously strong and persistent easterly flow of Atlantic
moisture will produce MVFR conditions across the majority of the
region overnight...with a few hours of IFR cigs anticipated for
KROC and also for portions of the Southern Tier. The cloud cover
will be accompanied by some showers east of Lake Ontario through
06z...then additional showers will push north from Pennsylvania to
the Southern Tier after 06z.

Saturday morning...cigs will range from IFR across the interior of
the Southern Tier to MVFR for most of Western New York to VFR across
the North Country. These cigs will only marginally improve during the
course of the afternoon as a swath of showers will push north across
the region.

Outlook...
Saturday night...MVFR to IFR cigs for the Southern Tier and parts of
the Finger Lakes region...with improvement to VFR elsewhere.
Sunday and Monday...Areas of MVFR with scattered showers.
Tuesday and Wednesday...Mainly VFR.

&&

.MARINE...
An upper level low will only shift slightly northward from the Ohio
Valley into tonight. This will maintain the easterly wind fetch
over the Eastern Great Lakes through tonight. On the western half
of Lake Ontario the easterly winds will remain strong enough to
maintain small craft advisory conditions for much of the night,
and possibly extending further into Saturday.

The upper-level low will track across the lower Great Lakes on
Sunday, and will bring increasing chances for waterspouts across the
lakes through Sunday night.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory until 2 AM EDT Saturday for LOZ043.
         Small Craft Advisory until 11 PM EDT Saturday for LOZ042.

&&

$$

SYNOPSIS...TMA
NEAR TERM...RSH
SHORT TERM...CHURCH
LONG TERM...HITCHCOCK
AVIATION...RSH
MARINE...TMA



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