NWS Area Forecast Discussion

000
FXUS61 KBUF 211442
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
942 AM EST Tue Nov 21 2017

.SYNOPSIS...
In advance of an approaching cold front...a brisk southwesterly
flow of mild air will dominate our region today...with temperatures
surging back into the lower to mid 50s in most areas. The cold
front will then push across our region tonight...with associated
rain showers mixing with or changing to snow before diminishing
overnight. In the wake of the front...building high pressure will
then bring a return to colder and mainly dry weather for Wednesday
and Thanksgiving Day...with just some nuisance-type lake effect
snow showers possible downwind of the lakes at times.

&&

.NEAR TERM /THROUGH TONIGHT/...
Today surface low pressure over Central Ontario Province will push
northeastward into western Quebec...while slowly dragging its trailing
cold front in our direction. With our area remaining well out ahead
of the front...we can expect a dry day with fairly plentiful sunshine
this morning merely giving way to some increasing clouds during the
afternoon hours. However it appears that much of the mid and high
level cloudiness off to the west will erode away as it approaches
our region and encounters a good deal of subsidence in the mid and
upper levels as seen on area forecast sounding profiles. Would
expect mainly some patchy cirrus during the daylight hours. As for
winds...the tightening pressure gradient developing out ahead of the
cold front will also guarantee the development of another round of
rather breezy to windy conditions...with the strongest winds found
across far WNY...which will lie under an axis of stronger (40-50
knot) flow in the 925-850 mb layer.

While the low level warm air advection regime will help to prevent
the strongest winds from completely mixing down to the surface...am
still concerned that at least some 40 knot or so gusts will be able
to make it to the surface between late this morning and early this
afternoon...particularly with both NAM/GFS BUFKIT profiles for KBUF/
KIAG indicating the presence of 40-45 knot winds as low as 1-2 kft
off the deck and increasingly well mixed lower levels. Given the
prevailing south-southwesterly to southwesterly low level flow...the
greatest overall potential for this will be found across Niagara and
Northern Erie counties...where a Wind Advisory has been issued to cover
this possibility. While conditions will also be breezy to windy across
the rest of the region...in general both sustained wind speeds and
gusts should tend to progressively lower with increasing eastward and
southward extent.

Otherwise we can expect a rather mild day today...with the aforementioned
breezy to windy conditions...expected sunshine...and 925 mb temps of +4C
to +7C all leading to widespread high temps in the lower to mid 50s.
The warmest overall readings will be found across the lower elevations
of the Genesee Valley and Finger Lakes where downsloping effects will
be maximized...and where a few spots might see highs reach the upper 50s.

As we move into tonight...the surface low will gradually push further
northeastward across Quebec...and in the process will drag its trailing
cold front across our region. While the main surface low will thus remain
far to our north...the boundary will still have the robust support of a
fairly sharp mid level trough to work with...and this combined with low
level convergence and moisture pooling along the boundary should be more
than sufficient to generate a fairly solid band of rain showers as the
front crosses our region...for which PoPs have been bumped up into the
categorical range areawide. In the wake of the frontal passage...modest
cold air advection will then lead to the synoptic precipitation briefly
mixing with or changing over to wet snow before diminishing overnight...
while some limited lake effect snow showers also develop southeast of
the lakes in the developing northwest flow regime. This changeover to
snow could potentially lead to some minor accums of an inch or less
across the higher terrain...with little or no accumulation expected
across the lower elevations. As for temps...the cold advection regime
behind the front will result in readings falling back to the upper 20s
to mid 30s by the end of the night.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/...
Not only will uneventful weather dominate this period...but we can
also look forward to gradual day to day warming. This...despite a
pattern that will feature ridging in the west and an oscillating
trough over the Great Lakes region. These are both favorable
ingredients for Thanksgiving travelers...but the good news will not
last through the upcoming weekend. More on this in the long term
section found below.

Notably colder air in the wake of a cold front will pour across our
region on Wednesday. Temperatures will be some 15 to 20 degrees
lower than the day before...with the mercury not climbing out of the
30s. The cold air will support some lake effect snow southeast of
both lakes...especially during the morning when synoptic moisture
will be the most plentiful and the cap will be at its highest for
the day...around 8k ft. Even so...the lake response will be minimal
with snowfall only forecast to be an inch or so for the Chautauqua
ridge and in the vcnty of the Tug Hill. Otherwise...clouds will
gradually thin out during the course of the day while winds gusting
between 25 and 30 mph will keep wind chill values in the 20s.

The axis of a large...elongated surface based ridge will cross our
forecast area Wednesday night. While this will provide our region
with fair dry weather...cirrus streaming in from the west should
temper an otherwise favorable environment for radiational cooling.
The only thing we will have to watch for will be some very minor
lake snow showers that could develop northeast of the lakes towards
daybreak. A low cap of about 5k ft will severely limit any real
development though.

On Thanksgiving...the surface high will push east and this will
initiate a warm advective pattern for our forecast area. While a
weak mid level shortwave will cross our region...the surface based
high should remain the dominant feature. Will thus keep the majority
of the region pcpn free for Thursday...with the exception again
coming northeast of the lakes where some nuisance light lake driven
snow showers will be possible. Will just use low chc pops for this.

A stronger shortwave will pass by further to our north Thursday
night. While this will push a weakening frontal boundary as far
south as Lake Ontario...while low level ridging will persist over
the western counties. Will thus back off on chc pops for the western
counties and only maintain the chc for snow showers over the eastern
Lake Ontario region.

As a flat shortwave ridge pushes across the Lower Great Lakes on
Friday...it will force the remnants of the stalled frontal boundary
back into Canada. This will also establish another brief warm up...
as a strengthening south-southwest flow ahead of an approaching
Pacific based cold front will boost H85 temps from the minus single
digits c to around 5c. Our temperatures will respond by climbing
into the 40s in most areas by Friday afternoon. The moderating
temperatures will be accompanied by at least partial sunshine.

Conditions will then deteriorate somewhat Friday night...as a
vigorous shortwave will push the first of two frontal boundaries
across our region. The first one...a Pacific based cold front...
will push through our region late Friday night. This feature should
generate some mixed rain and snow showers...mainly over the western
counties after midnight.

&&

.LONG TERM /SATURDAY THROUGH MONDAY/...
While temperatures will actually be on the plus side of normal to
start this period...a digging longwave trough over the Great Lakes
will unlock the door for a chunk of very cold air to settle over us
for Sunday and Monday. As one would expect for this time of year...
the plunging temperatures will support some lake snows as well. This
will likely present some problems for holiday travelers at the end
of the weekend. More on this in a moment.

Saturday will be somewhat unsettled across our region...but it will
be far from a wash out. In fact...there may be more hours of pcpn
free weather than those with mixed rain and snow showers. The
Pacific based cool front will pass to our east during the morning...
and this should leave a lull in the synoptic forcing for the
afternoon. As the cold air behind the first front deepens though...
any residual rain showers should mix with/change to wet snow
showers.

A fairly strong arctic cold front will then plow across the Lower
Great Lakes Saturday night. This will generate scattered snow showers
throughout our region...with lake snows becoming organized southeast
of the lakes after midnight. The stage will then be set for what
could be a miserable day for travel on Sunday.

Medium range ensembles are in good agreement that a cold cyclonic
northerly flow will be in place over our region on Sunday...while
fairly deep synoptic moisture will persist. Given that H85 temps are
forecast to be in the vcnty of -12 to -15c and that there should be
some added lift from the northerly upslope flow...it is likely that
fairly steady snow will be found southeast of both lakes...including
along the bulk of the New York State Thruway. This could make travel
a little more challenging for those heading home Sunday and Sunday
night. Stay tuned.

On Monday...a broad ridge over the Mid West and Upper Great Lakes
will begin to push across the Lower Great Lakes. The ensuing warm
advection and subsequent lowering subsidence inversion will bring an
end to the accumulating...problematic lake snows southeast of both
lakes...while fair weather will be found elsewhere.

&&

.AVIATION /15Z TUESDAY THROUGH SATURDAY/...
Widespread VFR conditions will continue right through today...with
patchy thin/high cirrus for much of day. It appears that much of the
mid and high level cloudiness approaching from off to the west will
erode away as it approaches our region and encounters a good deal of
subsidence in the mid and upper levels as seen on area forecast
sounding profiles. Expect thicker clouds to start making their way
across our area very late this afternoon/evening out ahead of a cold
front slowly pressing in our direction from the Upper Great Lakes.
Mixing is already occurring at many terminals which has eliminated
most of the wind shear concerns from earlier this morning...although
there are a few sites that still have relatively light winds. This
said...would expect mixing to commence at all terminals by late
this morning...thus eliminating all wind shear concerns. This mixing
will allow some of the stronger winds from aloft to mix to the
surface...resulting in breezy to windy surface conditions. The
windiest overall conditions today will be found in the vicinity of
KBUF/KIAG...where a period of surface wind gusts to around 40 knots
or so can be expected during the late morning and early afternoon
hours.

Tonight the aforementioned cold front will push across our region
from west to east along with a band of fairly widespread rain
showers...which will briefly mix with or changeover to snow showers
before diminishing overnight. This will result in flight conditions
lowering to MVFR...with embedded pockets of IFR possible.

Outlook...
Wednesday...Mainly VFR...with a chance of localized MVFR/IFR in
scattered snow showers southeast of the lakes.
Thursday...Mainly VFR...with a chance of localized MVFR in
scattered snow showers north-northeast of the lakes.
Thursday night...A chance of snow showers/MVFR across the North
Country...otherwise mainly VFR.
Friday...Mainly VFR.
Saturday...VFR/MVFR with rain showers likely.

&&

.MARINE...
Out ahead of an approaching cold front...rather brisk southwesterlies
will continue across the Lower Great Lakes today...before veering
to northwesterly tonight following the frontal passage...then slowly
diminishing from west to east during Wednesday as high pressure
builds across the region. As such...Small Craft Advisories remain
in effect as outlined below.

Looking a bit further out in time...some additional Small Craft
Advisories may be needed again for Thursday afternoon and night as the
pressure gradient tightens around a cold front passing by just to our
north...with more widespread advisories then possible this weekend as
a stronger low pressure system passes by to our north.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Wind Advisory until 5 PM EST this afternoon for NYZ001-010.
MARINE...Small Craft Advisory until 7 PM EST this evening for LEZ020.
         Small Craft Advisory until 1 PM EST Wednesday for LEZ040-
         041.
         Small Craft Advisory until 7 PM EST this evening for
         LOZ030.
         Small Craft Advisory until 7 PM EST Wednesday for
         LOZ042>045.

&&

$$

SYNOPSIS...JJR
NEAR TERM...JM/JJR
SHORT TERM...RSH
LONG TERM...RSH
AVIATION...JM/JJR
MARINE...JJR

NWS BUF Office Area Forecast Discussion