Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 151446
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1046 AM EDT Sun Oct 15 2017

.SYNOPSIS...
Very warm temperatures and dry weather will continue through early
this afternoon. A strong cold front will then sweep across the area
late this afternoon and early evening with a band of showers and
possibly a thunderstorm. Winds will become gusty along and behind
the front, especially for areas northeast of Lakes Erie and Ontario.
This front will usher in much cooler temperatures for Monday with a
few lake effect rain showers. High pressure will then bring a return
to dry weather Tuesday through the end of the week with temperatures
warming to above normal again.

&&

.NEAR TERM /THROUGH TONIGHT/...
The first half of today will be dry as the warm sector is well
established across the region. Breaks of sun will fill in with
thickening clouds early afternoon. Temperatures will rise into the
70s on strong SSW downslope flow, with a few areas possibly reaching
the lower 80s from the Genesee Valley to central NY.

Our focus then turns to a deepening surface low tracking from Lake
Huron to southern Quebec. A strong cold front trailing this low will
sweep across the area from mid afternoon through early evening.
Strong forcing in the form of DPVA, upper level jet dynamics, and
low level frontal convergence will support a focused, but relatively
narrow band of showers along the cold front. 200-400J/kg of SBCAPE
may be just enough to support a few isolated thunderstorms as well
given the strong forcing. While instability is meager, the strong
forcing and strong wind fields may allow a fine line of showers with
gusty winds along the cold front. There is a small chance of this
line producing a few instances of damaging winds if it becomes
focused enough. The SHERB High Shear/Low CAPE Parameter reaches 1
this afternoon just ahead of the front, suggesting this limited
potential.

In addition to the convective winds, it will become windy in
general. SSW winds will increase through the day ahead of the cold
front, with gusts of 30-40 mph becoming common. Warm advection and
poor lapse rates should prevent any advisory level gusts ahead of
the cold front. Along and just behind the cold front, strong cold
advection and subsidence will support better downward momentum
transfer. This should support a few hours of advisory gusts along
and northeast of Lake Erie from the Niagara Frontier to Rochester,
and also northeast of Lake Ontario in Jefferson County. The 00Z NAM
and GFS trended about 5-8 knots lower on surface and low level wind
fields. This should still be sufficient for a few advisory gusts in
the areas mentioned above, but has likely removed the risk of any
warning criteria gusts.

Tonight winds will steadily diminish as the stronger winds aloft
move off and the pressure gradient relaxes. A dry slot behind the
cold front will bring a quick end to the rain from west to east
during the evening. Increasing wrap around moisture and lake
instability will bring lake effect clouds and scattered showers
overnight as flow becomes westerly and then northwesterly. There
will also be some contribution from Lake Huron and Georgian Bay as
well. Temperatures will drop into the 40s by Monday morning.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/...
The difference in our weather will be like night and day...at least
to start this period...as a significantly cooler airmass will move
into our region to remind us that it really IS Autumn. Temperatures
Monday afternoon will be 25 to 30 degrees lower than those
experienced on Sunday...with the mercury going from levels more
typical of early August to those more characteristic of early
November. In other words...in twenty four hours we have advanced the
thermal calender by three months.

The dramatic change in the weather will be brought about by a pair
of strong shortwaves...the second of which will make its way across
our region on Monday. This trailing shortwave...highlighted in GOES
16 imagery over the Canadian prairies early this morning...will dive
southeast across the Upper Mississippi Valley today before making
its way across the Lower Great Lakes on Monday. This will complete
the transition in the pattern change to colder weather...but looking
upstream...we can tell that this will be short lived. An anomalously
strong East Asian jet over the North Atlantic will GUARANTEE that
the change to colder weather will be fleeting.

An extensive latitudinal belt of 175 kt H25 winds over the North
Atlantic during the first half of the week will eventually lead to
renewed troughing over the western portion of the country. This will
prompt significant height rises downstream over the eastern conus
which will lead to assured day to day warming after Monday. In
fact...our temperatures will return to above normal levels for the
second half of the week and stay there through next weekend. More on
this in the long term section below.

As for the day to day details...
A robust mid level trough will pass over the region on Monday...
while an expansive area of high pressure centered over the southern
plains will extend across the Ohio Valley to the Lower Great Lakes.
While notably cooler air associated with the trough will support
some lake driven instability...although the lake response will be
severely muted by the lack of synoptic moisture and a subsidence
inversion that will be based around 5-6k ft. This will result in
some nuisance lake effect rain showers southeast of both lakes
during the morning hours...then diurnal effects and some entrainment
of drier air from aloft should further weaken already unimpressive
lake showers. The bulk of the region though should be pcpn free with
only some lake effect strato-cu. The main characteristic of the day
will be the change to colder weather...as H85 temps between -2 and
-4c will only allow afternoon temperatures to climb into the upper
40s to lower 50s f. After a stretch of days with above normal
temperatures...these readings will be nearly 10 deg f below average.

The mid level trough will push off to our east Monday night while
the expansive area of high pressure will continue to nose northeast
across our forecast area. This will guarantee fair dry weather for
the vast majority of the region...with only some leftover sprinkles
possible immediately east-southeast of the lakes. Temperatures will
settle into the 30s away from the lake shores...so we can almost be
assured that there will be some frost. Since the growing season has
officially ended in the normally colder counties (Cattaraugus...
Allegany...Wyoming...Jefferson and Lewis) though...frost headlines
may not be needed. Stay tuned though...as the remainder of the
forecast area could still be susceptible to late season damage from
temps in the mid to upper 30s.

As heights continue to gradually build across the Lower Great Lakes
on Tuesday...the heart of the large surface high will drift to the
Middle Atlantic region. While this will establish a stronger warm
advective pattern...the tightest H925-85 thermal gradient and
subsequent isentropic upglide will be to our north. That will be
where the bulk of the associated alto-cu should be found and minimal
shower potential For our region...partly to mostly sunny skies are
anticipated with afternoon temperatures rebounding nearly 10 degrees
from the day before as highs will be in the mid 50s to lower 60s.

The strong surface high will become anchored along the mid Atlantic
coast Tuesday night and Wednesday...and this will further support
moderating temperatures as H85 readings will climb back into the
double digits. Along with continued fair weather...the mercury
Wednesday afternoon will warm into the mid to upper 60s (some 10 deg
f above normal).

&&

.LONG TERM /THURSDAY THROUGH SATURDAY/...
There is 100 percent confidence that this period will feature fair
dry weather with above normal temperatures...as a +590dm H5 ridge
will be centered over the Tennessee Valley. The stacked high
pressure system will keep our skies sunny each day...with H85
temperatures moderating into the teens c supporting the above
normal temperatures. Now for some details.

In the wake of a fairly strong shortwave that will pass WELL to our
north Wednesday night...significant height rises will take place
across the Ohio valley Thursday and Thursday night. This will
encourage the heart of the aforementioned surface high to retrograde
to about West Virginia while extending northward across the Lower
Great Lakes. While there will be a weak frontal boundary that will
sweep across our region...the dry frontal passage will temporarily
delay the upward push of our temperatures...as highs Thursday will
again range from 65 to 70.

The mid level ridge will amplify Friday and Saturday with its axis
gradually pushing east across our region in the process. Meanwhile
H85 temperatures will climb to as high as 14c...which would lead to
the third straight Saturday where temperatures will have been at
least in the 70s.

A peak ahead at the end of the weekend suggests that temperatures
will very likely remain well above normal.

&&

.AVIATION /15Z SUNDAY THROUGH THURSDAY/...
Mainly VFR and dry weather will prevail through early afternoon. A
strong cold front will then sweep east across the area during the
late afternoon and early evening, producing a brief period of gusty
rain showers and associated MVFR conditions. There may be just
enough instability for an isolated thunderstorm as well. It will
become windy today with gusts of 25 to 30 knots becoming common from
late morning through mid afternoon. Winds will increase further
along and just behind the front, with gusts of over 40 knots
possible for a brief time northeast of Lakes Erie and Ontario during
the late afternoon and early evening.

Tonight winds will quickly diminish and become northwest. Areas of
MVFR CIGS and scattered lake effect rain showers will develop as
much cooler air moves into the region.

Outlook...

Monday...Areas of MVFR with a chance -SHRA SE of the lakes.
Tuesday through Thursday...VFR except for local IFR in river valley
fog each late night and early morning.

&&

.MARINE...
SSW winds will steadily increase ahead of a deepening low moving
across the central Great Lakes. This low will deepen further as it
moves into southern Quebec by late today. A strong trailing cold
front will sweep across the eastern Great Lakes from mid afternoon
through early evening. Winds will increase to gale force on both
Lakes Erie and Ontario this afternoon and evening along and just
behind the cold front. Sustained winds will increase to around 35
knots on both lakes, although these gale force winds will likely
only last for a few hours. This will generate significant wave
height of up to 11 feet on Lake Erie and 13 feet on Lake Ontario for
a brief time.

Winds will then become northwest and slowly diminish late tonight
and Monday morning. Another period of stronger southwest winds will
develop Tuesday, though not as strong as today. This will likely
bring a round of Small Craft Advisory conditions to Lakes Erie and
Ontario.

&&

.TIDES/COASTAL FLOODING...
A strong cold front will cross Lake Ontario late this afternoon
and early evening. Southwest winds will increase ahead of the
front through the day today, then become west and increase
further to gale force by late afternoon and early evening,
bringing significant wave action to the entire NY shoreline.
Winds will then become northwest and quickly diminish 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 Warning has been issued, with the potential for more
significant shoreline erosion and associated damage.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Lakeshore Flood Warning from 8 PM this evening to 11 AM EDT
     Monday for NYZ004>007.
     Wind Advisory from 5 PM this afternoon to 2 AM EDT Monday for
     NYZ007.
     Lakeshore Flood Warning from 6 PM this evening to 8 AM EDT
     Monday for NYZ001>003.
     Wind Advisory from 2 PM this afternoon to 11 PM EDT this
     evening for NYZ001>003-010>012-019-085.
MARINE...Gale Warning from 2 PM this afternoon to 11 PM EDT this
         evening for LEZ020-040-041.
         Small Craft Advisory until 5 AM EDT Monday for LOZ030.
         Gale Warning from 6 PM this evening to 5 AM EDT Monday for
         LOZ043>045-063>065.
         Gale Warning from 4 PM this afternoon to 2 AM EDT Monday
         for LOZ042-062.
         Small Craft Advisory from 5 PM this afternoon to 5 AM
         EDT Monday for SLZ022-024.

&&

$$

SYNOPSIS...HITCHCOCK/TMA
NEAR TERM...HITCHCOCK/TMA
SHORT TERM...RSH
LONG TERM...RSH
AVIATION...HITCHCOCK/TMA
MARINE...HITCHCOCK/TMA
TIDES/COASTAL FLOODING...HITCHCOCK



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