Area Forecast Discussion
Issued by NWS Buffalo, NY

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000
FXUS61 KBUF 160850
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
350 AM EST Thu Nov 16 2017

.SYNOPSIS...
A cold front and its showers will finish crossing the region early
this morning. In its wake...lake effect rain showers east of the lakes
this morning will sink southward to areas southeast of the lakes this
afternoon and evening...where they will mix with and changeover to snow
before tapering off tonight. After a dry and quiet day Friday...a strong
storm system will then bring gusty winds and widespread rain Saturday...
with much colder weather then returning for Sunday along with lake effect
rain and snow showers southeast of the lakes.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 0845Z...the surface cold frontal boundary is now in the process
of working across far western New York...with a broken band of weakening
showers denoting the frontal position. Meanwhile well out ahead of
the front...a larger area of more widespread showers continues to
steadily translate eastward across the North Country. Through sunrise...
the front will continue to progress eastward through the rest of
the area...with occasional light to moderate synoptically-driven
showers diminishing following its passage.

In the wake of the front...a west-southwesterly to southwesterly flow
of progressively cooler air will overspread the region from west to
east this morning. With sufficient moisture in place...steady cool
air advection will reach levels sufficient to trigger a lake response
east-northeast of Lake Erie starting somewhere in the 4-5 am time
frame...and northeast of Lake Ontario (between Watertown and the
Saint Lawrence River) somewhere around 7-8 am.

After that point...gradual veering of the low level flow out ahead of
an approaching secondary cold front will force the more-developed Lake
Erie lake plume to sag southward to areas east of the lake through late
morning and early afternoon hours...while the initially more disorganized
Lake Ontario-driven activity sags southward to around Watertown while
gradually becoming better organized. The secondary cold front itself
will then push through the area during the early to mid afternoon
hours...with sharper veering of the flow to west-northwesterly in
its wake forcing the lake bands to settle southward to areas southeast
of the lakes through early this evening...during which time they will
also weaken due the disruptive effects of the wind shift and the
subsequent shortening of the fetch.

With respect to temps and ptypes...850 mb temps will cool to the -2C
to -4C range through early afternoon...before dropping off another
degree or two through the rest of the day following the passage of
the secondary cold front. Through early afternoon...this will translate
into surface temps mostly in the lower to mid 40s across the lower
elevations and the upper 30s to lower 40s across the higher terrain...
before readings pull back another category through the balance of
the day. Such temperatures should translate into the precipitation
remaining all rain across the lower elevations...and rain gradually
mixing with snow across the higher terrain of the Southern Tier...
where some slushy accumulations of an inch or less will be possible
by day`s end.

Outside of the main lake effect areas...precipitation across the
region will be much more scattered behind the initial cold front
today...and mainly tied to the secondary cold frontal passage and
areas of orographically-driven ascent. Otherwise it will be a mostly
cloudy and windy day...with fairly widespread sustained winds of
15-25 mph and gusts to 30-35 mph expected.

Tonight...high pressure and colder/drier air will quickly build into
the region in the wake of the secondary cold front. This will result
in any lingering lake effect precipitation changing over to snow...
with some additional minor accumulations of an inch or less possible
southeast of the lakes before steady drying of our airmass and a
crashing subsidence inversion help to squelch this activity from west
to east overnight. Otherwise conditions should generally be dry...
with fairly widespread cloud cover this evening giving way to some
partial clearing across the area overnight...and nighttime lows
settling into the 25-30 range under continued steady cold air
advection.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/...
This will be a very active period across our region...one that will
likely include wind and lake effect snow headlines. Welcome to `The
Season`.

The main culprit for our upcoming bout of stormy weather will be the
well defined storm system that is churning east from Queen Charlotte
Sound. To be more exact it will be a pair of robust shortwaves...
that with a trained eye...can be seen rotating through the base of
this closed low. While the whole system will bodily move onshore and
cross the Pacific Northwest...it will be the shortwaves ejecting
across the Inter-Mountain region that will initiate broad
cyclogenesis over the High Plains by Friday afternoon. The resulting
disorganized surface low over the plains will consolidate and push
northeast to the Upper Great Lakes as a classic `cutter storm`...as
so typically occurs when lee side cyclogenesis occurs within a
phased mid level flow. These storms are notorious for producing
significant weather throughout the Great lakes region...which for
our region at this time of year...includes the potential for high
winds and...and on the backside...accumulating lake snows. Now for
the details.

A broad mid level ridge and its corresponding surface high will work
to the east across the Lower Great Lakes on Friday. This will
provide us with the `calm before the storm`...as we can anticipate a
fair amount of sunshine and relatively light winds. While moderately
strong warm advection will boost H85 temps to nearly 4 deg c by the
end of the afternoon...it will be a pronounced 3 deg c subsidence
inversion and winds of less than 15 knots through 5k ft that will
prevent the warming from mixing to the surface. As a result...max
temps are forecast to barely reach 40 across the majority of western
New York...while highs close to freezing can be expected across the
North Country.

As the broad storm system over the center of the country starts to
consolidate and move northeast Friday night...the progressive ridge
over our region will exit across New England. This will strengthen
the warm advection over our forecast area while also allowing a
modest increase in moisture. There will certainly be enough mid and
high level moisture to cloud our skies...but there is some `debate`
among the shorter range guidance packages as to how much low level
moisture will be in place to support some showers. Will back off a
bit from continuity...with new pops ranging from likely over many of
the far western counties (Cat pops still for Chautauqua) to chc over
the Finger Lakes and slgt chc east of Lake Ontario. Will maintain a
non-diurnal temp trend for Fri night...especially over the western
counties. This should ensure that the expected pcpn will be
liquid...and not a wintry mix. Do NOT allow the overnight mins to
fool you...as they should occur before midnight and before the onset
of pcpn. In fact...a southerly downslope wind may keep mins above 40
for sites between Lake Erie and the Chautauqua ridge....and possibly
north of the IAG escarpment in Niagara county.

Saturday then promises to be a miserable day across all of our
forecast area. The deepening storm system over the mid western
states will continue to track northeast...crossing Lower Michigan to
southernmost Ontario while pushing a warm front across our area.
While there will be some lift contributed by the warm frontal
boundary in the low levels...the bulk of the heavy lifting will be
done by a classic example of a coupled upper level jet. At H25...a
110kt jet is forecast to cross central Quebec while a strong 140kt
jet will be found in the vcnty of the Lower Ohio Valley. The co-
located exit and entrance regions of these jets will track right
across our region...providing a 4-6 hour window of deep lift that
will interact with a GOMEX fed airmass with anomalously high PWAT
values in the neighborhood of one inch. Rainfall on Saturday is
forecast to range from a half to three quarters of an inch over the
Southern Tier and Finger Lakes region with lesser amounts over the
Eastern Lake Ontario region. Some sites south of Buffalo and
Rochester could even experience higher amounts if the suggested
elevated instability prompts some embedded thunderstorms. Will add a
slight chc for to cover this potential. Downsloping southerly winds
will probably account for a 25 percent reduction in rainfall in a 20
mile wide swath centered roughly along the New York state Thruway
from Buffalo to Syracuse. Otherwise will maintain 100 pops.
Meanwhile temperatures in the wake of the warm front are expected to
soar into the 50s over the western counties.

A dramatic turn in the weather can then be expected Saturday
night...as the still strengthening cyclone will pass by to our north
while slinging a powerful cold front through the region. There will
be a burst of moderately heavy rain as the front plows through
during the evening...then as we progress through the overnight...the
deepening cold air will support a significant lake response off both
Lakes Erie and Ontario. Temperatures will be marginally cold enough
for just snow...but several inches will be possible east of both
lakes...with upstream connections for both adding to potential
accumulations. The more concerning element at this point though will
be the strong winds. Normally when a deepening cyclone passes to the
west of Buffalo...very strong winds become established from Lake
Erie and the Niagara Frontier to the Roch metro area...partly due to
funnelling up the full length of Lake Erie.

In this particular case though...the sfc low will track just close
enough to Buffalo and Rochester that the near surface winds will not
have the opportunity to be enhanced off Lake Erie...rather they will
veer more quickly to the west and northwest. Another factor playing
into the this is the tilt of the supporting trough...which will not
go negative until several hours after fropa. Local research suggests
that the trough should be negative earlier...enhancing/promoting a
deeper southwest flow for a longer duration around the time of
fropa. Also working against true high winds is a lack of strong
subsidence in the wake of the front...and more importantly...a lack
of a significant (>60kt) low level jet. While winds between H925 and
85 are forecast to be in the vcnty of 60 kts ahead of the front
within the warm advection...the low level jet will weaken somewhat
to 55-60 knots in the cold advection. It will certainly still be
windy across the region with wind gusts to near 50 mph near the lake
shores...but the threat for widespread damaging winds does not seem
to be as high as earlier guidance suggested. This will have to be
closely watched during the next few days though...as a track further
to the west could greatly enhance the potential. One area that could
experience more substantial winds though will be across Oswego
County...where experience has shown that a very strong west to
northwest flow off Lake Ontario can be funneled down the Mohawk
Valley...allowing winds to accelerate as they head into the
topographic restriction. Wind headlines for at least part of the
forecast area will be likely with this event.

Sunday and Sunday night will then feature cold...gusty winds with
focused lake snows east of both lakes. While the deep storm system
will exit across eastern Quebec...a large surface high will drift
east from Texas to the Tennessee valley. This will keep a prolonged
(24 hrs) cyclonic flow of -8 to -10c H85 over the Lower Great
Lakes...with a 290-300 flow keeping lake snows aimed at the Southern
Tier and Oswego County. Several inches of accumulation will
certainly be possible during this period...with lake effect oriented
headlines a possibility. Temperatures Sunday will hit their peak
between midnight and 12 noon...with gradually falling mercury
readings during the course of the afternoon when temperatures will
not be far from freezing.

&&

.LONG TERM /MONDAY THROUGH WEDNESDAY/...
While lake snows will still be in place east of both lakes on
Monday...conditions will generally improve as a progressive...low
amplitude ridge will traverse across our region during the afternoon
and night. The associated warm advection will lead to a cap that
will initially weaken the lake snows...then Monday night as winds
back more to the south and H85 temps climb above zero c...the
environment will stabilize over the lakes and fair weather will
return to all of our forecast area.

The next vigorous shortwave is then forecast to dig across the Upper
Great Lakes on Tuesday while the flat ridge will push across new
England. This will establish a milder southerly flow that will
enable our temperatures to climb well into the 40s in most areas.
Without any pcpn in the forecast...this may be the best day to make
final preparations or travel for the Thanksgiving.

Things will become more interesting Tuesday night and Wednesday as
the shortwave will race by to our north while pushing another fairly
strong cold front across our region. This will generate some rain
and snow showers...with some accumulating lake snows possible east
of both lakes on Wednesday as H85 temps are expected to drop off to
at least -6c.

&&

.AVIATION /09Z THURSDAY THROUGH MONDAY/...
Through sunrise...a cold front will slowly press eastward across
the region...with occasional light showers along and out ahead of the
front generally tending to become more scattered following its passage.
The one exception to this will be near KBUF...where a west-southwesterly
flow of progressively cooler air behind the front will eventually become
cold enough to support the development of some lake effect rain showers.
As for flight conditions...these will continue to steadily deteriorate
from west to east...with conditions falling to MVFR across the lower
elevations and IFR across the higher terrain.

On Thursday...continued slow but steady cooling of our airmass
will support continued bands of lake effect precipitation downwind
of the lakes...with these initially found east of the lakes during
the morning...before sinking to areas southeast of the lakes
following the passage of a secondary cold front in the afternoon.
The above stated...our airmass should remain warm enough to support
mainly rain across the lower elevations...with a rain/snow mix
possibly developing across the higher terrain. Otherwise flight
conditions will generally remain in the MVFR range across the lower
elevations and in the IFR/MVFR ranges across the higher terrain.

Thursday night lingering areas of lake effect precipitation southeast
of the lakes will change over to snow while quickly diminishing
from west to east as high pressure builds into the region along
with colder/drier air. Expect lingering restrictions to IFR/MVFR
within the lake effect areas to gradually improve to MVFR...while
MVFR conditions elsewhere largely improve to VFR as the night
progresses.

Outlook...
Friday...Mainly VFR.
Friday night...Rain becoming likely with conditions deteriorating
to IFR/MVFR and LLWS becoming possible across far western New York...
otherwise VFR.
Saturday...Widespread rain and MVFR developing...also turning windy.
Sunday and Monday...Lake effect snow and IFR southeast of the lakes...
otherwise mainly VFR.

&&

.MARINE...
An initial cold front will finish crossing the region early this
morning...followed by a secondary cold front this afternoon. The
tight pressure gradient found around these boundaries will keep
rather brisk winds in place across the Lower Lakes Region into
this evening...while these gradually veer from southerly to
westerly...then to northwesterly. For this reason...Small Craft
Advisories remain in effect as outlined below...with these
gradually dropping off from west to east tonight and Friday
as high pressure builds into the region and brings diminishing
winds and waves.

After a brief period of calmer conditions Friday afternoon...another
period of strong gusty winds (possibly to gale force) still looks
to arrive this weekend as a stronger storm system tracks northeastward
across the Great Lakes.

&&

.TIDES/COASTAL FLOODING...
Northwest winds will develop behind a cold front passage today,
with wind speeds increasing through the afternoon and early
evening hours. This will build water levels and wave action
along much of the Lake Ontario shoreline this afternoon into
tonight. The combination of already higher lake levels and
added wave action will result in increased shoreline erosion,
especially where the lakeshore is already unstable from erosion
earlier in the year.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Lakeshore Flood Warning from 1 PM this afternoon to 7 AM EST
     Friday for NYZ001>007.
MARINE...Small Craft Advisory until 4 AM EST Friday for LEZ040-041.
         Small Craft Advisory until 7 PM EST this evening for
         LEZ020.
         Small Craft Advisory from 2 PM this afternoon to 4 AM
         EST Friday for LOZ030.
         Small Craft Advisory until 1 PM EST Friday for LOZ043>045.
         Small Craft Advisory until 10 AM EST Friday for LOZ042.

&&

$$

SYNOPSIS...JJR
NEAR TERM...JJR
SHORT TERM...RSH
LONG TERM...RSH
AVIATION...JJR
MARINE...JJR
TIDES/COASTAL FLOODING...THOMAS/JJR


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