Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 231444
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1044 AM EDT Mon Oct 23 2017

.SYNOPSIS...
The streak of unseasonably warmth and dry conditions that has
remained with us through much of the autumn season will come to an
end today...with temperatures topping out in the upper 60s and 70s
ahead of a strong cold front. This eastward bound cold front will
bring a period of gusty rain showers across our region tonight.
While it will turn progressively colder through Thursday...the
mercury will rebound for the latter portion of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Very unsettled weather is on the immediate horizon with moderately
heavy rain and strong winds expected tonight. Wind advisories are
in place for parts of the forecast area.

The summer-like warm that has been with us the past several weeks
will be coming to an end today...with temperatures peaking this
afternoon in the 70s across the lower elevations. Southerly flow
ahead of a storm system that is tracking northward across the Ohio
Valley, combined with 850 hPa temperatures 12-14C will bring
temperatures into the upper 60s across the So. Tier and Tug Hill
region, while downslope areas of the Lake Plain, and Saint Lawrence
Valley will likely reach into the mid 70s. A thicker cirrus cover
today will likely keep these highs today a few degrees cooler than
Sunday.

Water vapor imagery displays a cut off upper level low, that has a
deep 1.5 PV anomaly down to around 700 hPa, over the mid-Mississippi
Valley, while a northern branch of the jet stream is dipping across
the North Plains as a trough of low pressure moves through. Over the
course of today these two features will merge, and it will create a
slightly negatively tilted trough over the Great lakes region. This
PV anomaly will swing northward across Lake Erie this evening.

A surface low that is currently over the southern Ohio Valley will
undergo rapid cyclogenesis today and tonight, deepening from around
1010 mb this morning to around 980 mb over northern Michigan by 12Z
Tuesday. Aiding in the rapid deepening of the surface low will be
the strong PV anomaly, as well as a coupled jet with the central
Great Lakes under the right entrance region of a 140 knot upper
level jet over the western Great lakes, and the left exit region of
a 55 knot LLJ.

Dry weather will remain across the region through much of the day
with rain showers edging into Western New York late this afternoon.
The first concern will be strong winds ahead of the line of rain
showers. The strong SE LLJ will likely downslope across the
Chautauqua ridge late this afternoon and early evening...with gusts
upwards to 50 mph. The LLJ appears to have slightly backed with
recent model runs such that the flow will be more perpendicular to
the ridge axis. This will increase confidence of stronger wind gusts
along the Lake Erie shoreline, and a wind advisory will be issued
from 4 pm to 11 pm this evening for Chautauqua and Southern Erie
counties.

In addition to the northwest of the Tug Hill, SE downslope winds
will likely reach near 50 mph here too, with the base of the LLJ
just a 1k feet above the surface. Timing will be a bit later than
along the Lake Erie shoreline...with stronger wind gusts likely
after sunset. Will have a wind advisory here from 8 pm tonight
through the overnight to 8 am tomorrow morning for Jefferson and
Lewis counties.

Rain will then spread eastward across the region this evening as a
cold front swings across the region. PWATS near +2SD, along with
favorable upward lift ahead of the strong PV anomaly that will
rotate northward across Lake Erie and into southern Canada, along
with lift ahead of the cold front will support a line of rain
showers. Overall rain totals will likely range between a half to one
inch for much of the region. The SE downslope flow will likely keep
areas along the Lake Erie shoreline with slightly less rainfall, on
the order of a third to half an inch.

Behind the cold front, southwest synoptic winds will continue to
remain moderate tonight, with the deepening surface low cutting
northward to our west. While the best isallobaric couplet will be
over western Lake Erie and Michigan, we will still see pressure
falls/rises of 2 to 4 mb per three hours tonight, that when combined
with cold air advection could produce wind gusts upwards to 40 mph
near Lake Erie and the hill tops of SW NYS. Farther away from the
surface low gusts will not be as strong across the Finger Lakes and
southern Tug Hill region.

By the close of tonight the surface cold front will be along our
eastern zones. Rain will begin to end a few hours past midnight near
Chautauqua County and likely end across much of WNY by sunrise
tomorrow.

Temperatures will be mild until the front crosses, with areas across
the Finger Lakes and east of Lake Ontario holding onto low to mid
60s through much of the night. To the west temperatures will be
dropping into the 50s by the close of the night.

&&

.SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/...
By Tuesday morning, steady rain focused along a strong LLJ will be
confined to the Eastern Lake Ontario region with this tapering to
showers by Tuesday afternoon. 00Z model guidance has trended
slightly faster with this system, with mainly dry weather for the
rest of Western New York on Tuesday. Post frontal subsidence and
drying will result in some breaks of sunshine, perhaps sneaking in
one more fairly nice day before `Fall` arrives. Highs on Tuesday be
west to east dependent due to the front, ranging from the upper 50s
to mid 60s across far western New York to the upper 60s to around 70
east of Rochester.

Vertically stacked low pressure will remain across eastern Michigan
Tuesday night, which will maintain a moderate SSW surface flow.
Temperatures aloft will cool enough (-2C at 850mb) for lake effect
rain showers, however these will largely be on the Canadian side of
the border, perhaps just clipping Niagara county. Otherwise, the
cyclonic flow aloft may result in a stray shower or sprinkle but a
narrow surface ridge axis should keep the vast majority of the
region dry Tuesday night.

After this, the forecast focus shift primarily to lake effect rain
showers. The closed upper low driving our weather will be very slow
to move, and model guidance often struggles timing the ejection of
such a system. Using the latest model consensus, expect this will
transition to a sharp trough axis Wednesday with this axis moving
into western New York on Wednesday night. This will focus lake
effect rain showers across the Niagara Frontier on Wednesday, mainly
Buffalo north and west. These showers will drop across Buffalo
Wednesday afternoon and then to across the south towns and to the
Western Southern Tier Wednesday night. The same trend will play out
later northeast of lake Ontario, with showers focused mainly on
Jefferson and Lewis counties Wednesday night. Otherwise, the upper
level trough will allow scattered light showers to spread further
from the lakes.

By Thursday the upper level trough axis should be in southern Quebec
with winds shifting from the southwest to the south. Lingering lake
effect rain showers will weaken and shift northward with fair
weather elsewhere. Then a weak surface ridge will extend from Maine
to Alabama, with this providing dry weather for Thursday night.

Temperatures will be notably cooler with highs generally in the 50s
Wednesday and Thursday, with upper 40s across higher terrain on
Wednesday. Even so, this is only slightly below normal for late
October.

&&

.LONG TERM /FRIDAY THROUGH SUNDAY/...
The longwave trough over the center of the country will `reload`
Friday...as the next vigorous mid level disturbance will dive
southwards across the northern plains. This will re-establish the
longwave trough while the next (second) shot of colder air will pour
southwards into the Lower 48.

The leading edge of this next cold shot will follow a cold front
that will extend south form a sub-1000mb low over the Upper Great
Lakes. This front will make its way across the Lower Great Lakes on
Saturday...then is forecast to stall over our forecast area as it
will become parallel to the mean H925-70 flow. Following a nice day
of weather on Friday...this scenario will favor scattered showers
for both days of the weekend.

Looking further ahead towards the following week...a third shot of
cold air will charge southwards...and this one will have the best
chance of supporting our first flakes of the season across our
forecast area.

&&

.AVIATION /15Z MONDAY THROUGH FRIDAY/...
A deepening area of low pressure will track from the Ohio
Valley through the Central Great Lakes today, while swinging a
cold front across the region tonight.

This front will bring a steady area of showers, with flight
conditions deteriorating to MVFR (possible So. Tier IFR) late this
afternoon and through tonight. Rain will taper off between 05Z to
the west, and near 12Z to the east.

In addition a strong LLJ up to 50 knots at 2K feet may produce some
areas of LLWS across WNY tonight. Also the deepening area of low
pressure will bring some gusty winds to the region, upwards to 30
knots.

Outlook...

Tuesday...MVFR in occasional rain early east of Lake Ontario.
Otherwise MVFR/VFR.
Wednesday and Thursday...Areas of MVFR with a chance of showers.
Friday...VFR.

&&

.MARINE...
A southeast wind will increase over Lake Erie this afternoon,
accelerating off the Chautauqua Ridge. Though these winds will slow
some as they reach the lake waters...they should still remain strong
enough to warrant small craft advisories...with a SCA for Lake Erie,
and the Upper Niagara River later this afternoon and into the
overnight hours. Progressively cooler air through the week will
maintain these SCA for Lake Erie into Thursday.

Over Lake Ontario the southeast flow will largely maintain the
higher waves over the central and northern side of the Lake.
Southeast winds along the eastern shoreline will bring SCA late this
afternoon and through Tuesday morning.

After a cold front passes, a southwesterly wind will increase waves
on the entire Lake Ontario later Tuesday night, with SCA likely
through Thursday.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Wind Advisory from 8 PM this evening to 8 AM EDT Tuesday for
     NYZ007-008.
     Wind Advisory from 4 PM this afternoon to 11 PM EDT this
     evening for NYZ019-085.
MARINE...Small Craft Advisory from 4 PM this afternoon to 2 PM EDT
         Thursday for LEZ040-041.
         Small Craft Advisory from 5 PM this afternoon to 5 AM EDT
         Tuesday for LEZ020.
         Small Craft Advisory from 5 PM this afternoon to 11
         AM EDT Tuesday for LOZ045.

&&

$$

SYNOPSIS...RSH/THOMAS
NEAR TERM...RSH/THOMAS
SHORT TERM...APFFEL
LONG TERM...RSH
AVIATION...RSH/THOMAS
MARINE...THOMAS



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