Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 140003
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
803 PM EDT Fri Oct 13 2017

.SYNOPSIS...
A frontal zone will develop north of Lake Ontario this weekend. Some
showers may lurk both near the Lake Ontario shoreline and east of
Lake Ontario through Saturday night, but other areas should remain
dry with another bout of warm weather. Then on Sunday, a sharp cold
front will cross the region with possible thunderstorms and gusty
winds. Lake effect showers will develop southeast of the lakes
Monday, with high temperatures dropping about 25 degrees from
Sunday`s highs. Dry weather and gradually rising temperatures will
return later next week.

&&

.NEAR TERM /THROUGH SATURDAY/...
A broad Western US trough and eastern US ridge defines the weather
until late Sunday. As the upper level trough moves east, a low level
warm front will continue to strengthen over the Midwest, into the
central Great Lakes, and north of Lake Ontario with eventual surface
development over the midwest during Saturday.

For WNY, this means that the abundant low level moisture observed in
Satellite imagery lingering over our region will begin to focus to
the north over or just north of Lake Ontario overnight and into
Saturday. The cloud cover over the Southern Tier south into PA and
the Mid-Atlantic states is due to cold air damming and will be very
slow to erode overnight and Saturday. While most of the area should
remain dry, there may be some showers to the north or east of Lake
Ontario Saturday afternoon where the warm front will set up.
Otherwise expect continued cloud cover at times. This will act as a
blanket, keeping temperatures from falling too much overnight and
rising too much on Saturday. Overall, this will yield lows/highs
that are yet again above normal. Lows tonight will only dip into the
mid to upper 50s then highs tomorrow will reach into the low to mid
60s except upper 60s east of Lake Ontario.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
Saturday evening a stalled frontal boundary over Lake Ontario will
begin to move northward as a warm front in response to flow
adjustments ahead of a trough moving through the Upper Midwest.
Increasing warm advection and isentropic upglide will produce an
area of showers over Lake Ontario and southern Ontario province. The
most likely area for these showers to cross into NY will be across
the eastern Lake Ontario region, especially Jefferson County. A few
showers may also clip areas from the Niagara Frontier to Oswego
County along the south shore of Lake Ontario. Any showers will end
from southwest to northeast overnight as the warm front retreats
northward into Canada. Increasing SSW flow will keep temperatures
very mild, with lows in the mid 60s in most areas, and around 60 in
the interior Southern Tier and Lewis County. These lows will likely
occur late evening, with temperatures rising several degrees by
daybreak Sunday.

On Sunday the area will be solidly in the warm sector during the
morning and early afternoon. There may be a few breaks of sunshine
for a few hours before clouds increase ahead of the cold front.
Temperatures will soar again, with highs in the mid to upper 70s in
most areas, with 80 not out of the question from the Genesee Valley
to Central NY.

The main focus will be on a strong cold front crossing the region
during the late afternoon and evening. Strong convergence along the
advancing cold front, strong mid level DPVA from the approach of a
strong mid level trough, and strong upper level jet dynamics will
come together to produce a band of strong ascent along the cold
front. This should result in a fairly solid band of showers moving
from west to east across the area, entering Western NY by early to
mid afternoon, then racing to the eastern Lake Ontario region by
early evening. 12Z model guidance trended a few hours slower with
the cold front, so adjusted the timing of rain in the gridded
forecast accordingly.

Model guidance continues to develop 300-500J/kg of SBCAPE just ahead
of the cold front. This may allow a few scattered thunderstorms to
develop along the cold front. With or without thunder, there may be
a band of convective showers along the cold front. Given the very
strong wind fields aloft, downdrafts and precip loading in any line
of heavy showers may transport gusty winds to the surface at a
minimum, with damaging winds a low, but non-zero possibility.

In addition to the convective wind potential, it will be windy in
general on Sunday and Sunday evening. Winds aloft will be strongest
in the warm sector ahead of the cold front, but warm advection
patterns are not favorable for transporting strong gusts to the
surface in most situations ahead of cold fronts. With this in mind,
expect the strongest winds to be along and just behind the cold
front for an hour or two, when low level lapse rates steepen and
subsidence develops with the onset of strong cold advection. This
may produce a few wind gusts in the 45-50 mph range, mainly in the
typical areas along and northeast of Lake Erie from the Niagara
Frontier to Rochester, and also in Jefferson County. Winds aloft
quickly diminish Sunday evening, with any advisory level gusts being
short lived.

The cold frontal showers will end quickly from west to east Sunday
evening. A dry slot initially will give way to some limited wrap
around moisture late Sunday night. Increasing lake induced
instability will bring a chance of lake effect rain showers
overnight southeast of the lakes. It will turn sharply cooler, with
temperatures falling into the low to mid 40s by daybreak Monday.

On Monday lake effect rain showers will continue southeast of the
lakes. Despite the very chilly airmass, a relatively dry synoptic
scale background and short northwest fetch will keep coverage and
amounts limited. 850mb temps bottoming out around -4C will only
support highs in the lower 50s at lower elevations, with mid to
upper 40s across higher terrain. Lake effect rain showers will end
later Monday afternoon or evening, with a brief ridge of high
pressure bringing dry weather and chilly temperatures Monday night.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
The period will feature a rather pleasant fall pattern with mainly
dry weather and gradually warming temperatures. Model consensus
tracks a shortwave trough across Quebec on Tuesday which is likely
to keep any showers to our north with only a slight chance showers
will clip the Saint Lawrence Valley. This will result in a breezy
day on Tuesday with temperatures topping out in the upper 50s to
lower 60s.

After this high pressure across the mid-Atlantic states will ridge
into the region with dry weather and slightly warmer temperatures
for Wednesday. Model guidance diverges after this, with the 12Z GGEM
digging a trough across the region while the ECMWF/GFS guidance
strengthen a broad Atlantic ridge into the region. Given continuity
and model track record the forecast favors the latter solution which
would result in a return much above normal temperatures for the end
of the week. By Friday, temperatures should warm into the upper 60s
to lower 70s in most locations.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
Stubborn low clouds will linger much of the overnight as a frontal
boundary sets up across Lake Ontario into the Saint Lawrence River
Valley tonight into Saturday. MVFR and local IFR cigs should be
limited to the interior Southern Tier and KJHW overnight with low
end VFR at remaining TAF sites. Some showers may form over or north
of Lake Ontario east toward the Eastern Lake Ontario region Saturday
afternoon which may run close to all TAF sites except KJHW but most
likely at KART where VCSH has been added.

Outlook...

Saturday night...Showers across and east of Lake Ontario with local
MVFR.
Sunday...VFR/MVFR, chance -TSRA Sunday Afternoon, windy with
strong cold front.
Monday...MVFR/VFR. A chance -SHRA SE of the
lakes.
Tuesday and Wednesday.  VFR with local AM valley fog.

&&

.MARINE...
Southwest winds will build waves 3-5 feet on the northeast corner of
Lake Ontario and head of the Saint Lawrence River tonight. Have
issued a Small Craft Advisory through tonight.

Otherwise, fair winds and waves through Saturday with a lurking
frontal boundary near or north of Lake Ontario. A strong cold front
will move east on Sunday with possible westerly gale force winds
following the front. A Gale Watch has been issued. Winds will slowly
drop as winds veer to the NW on Monday.

&&

.TIDES/COASTAL FLOODING...
A strong cold front will cross Lake Ontario late Sunday
afternoon. Southwest winds will increase ahead of the front
through the day Sunday, then become west and increase further to
near gale force early Sunday evening, bringing significant wave
action to the entire NY shoreline. Winds will then become
northwest and quickly diminish late Sunday night and Monday
morning.

The Lake Ontario level is several feet lower than late spring,
and is about a foot above normal for the month of October. The
lower lake level reduces the risk of flooding along the
lakeshore even on windy days. However, the lakeshore is still
very fragile and unstable in many areas following the heavy
erosion from earlier this year. With this in mind, a Lakeshore
Flood Watch is still needed due to the potential for more
shoreline erosion Sunday night from the period of high wave
action.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Lakeshore Flood Watch from Sunday evening through Monday
     morning for NYZ004>007.
     Lakeshore Flood Watch from Sunday evening through late Sunday
     night for NYZ001>003.
MARINE...Gale Watch from Sunday evening through late Sunday night for
         LOZ043>045-063>065.
         Gale Watch from Sunday afternoon through Sunday evening
         for LOZ042-062.
         Small Craft Advisory until 8 AM EDT Saturday for LOZ045.

&&

$$

SYNOPSIS...ZAFF
NEAR TERM...SMITH/ZAFF
SHORT TERM...HITCHCOCK
LONG TERM...APFFEL
AVIATION...SMITH/ZAFF
MARINE...SMITH/ZAFF
TIDES/COASTAL FLOODING...HITCHCOCK



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