Area Forecast Discussion
Issued by NWS Buffalo, NY

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653
FXUS61 KBUF 170244
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
944 PM EST Sat Dec 16 2017

.SYNOPSIS...
High pressure will cross the region tonight and Sunday, with
dry weather for the second half of the weekend. Temperatures
will warm above freezing Monday as a warm front lifts across the
region, bringing a chance for rain and snow showers into
Tuesday before a cold front sweeps across the lower Great Lakes
Tuesday night, bringing a return to more wintry conditions by
Wednesday.

&&

.NEAR TERM /THROUGH SUNDAY/...
High pressure building into southern Ontario tonight will stop
the northward progression of a frontal boundary and keep our
region mainly dry overnight. Satellite imagery shows a sharp
cloud cut-off with clear skies north of Rochester and cloudy
skies to the south. Low temperatures will depend heavily on
cloud cover, with a similar trend likely to continue most of
the night. Cloud cover will limit radiational cooling with
temperatures dropping very little across the Southern Tier. It
is a different story east of Lake Ontario where the surface high
is likely to maintain clear skies with good radiational cooling
conditions. The forecast goes well below consensus guidance for
low temperatures in the North Country with lows expected to be
below zero in many locations.

Quiet weather is expected Sunday as the ridge of high pressure
continues to influence our weather. Highs on Sunday will
generally range from around 20 across the North County to the
lower 30s across western New York.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH WEDNESDAY NIGHT/...
Sunday night and Monday broad warm air advection will remain in
place across our region...while a surface warm front gradually pushes
northeastward across our area. This will result in plenty of cloud
cover throughout this 24 hour period...along with some scattered light
precipitation from later Sunday evening through Monday. While the latter
will start out in the form of snow showers Sunday night...slow but steady
warming of the atmospheric column will force the precip to mix with and
then change over to mainly rain...with this changeover first taking place
across the lake plains of far western New York Sunday night...before
spreading northeastward across the remainder of the area on Monday. With
respect to temperatures...lows Monday night will occur during the evening
and range from the teens across the North Country to the upper 20s and
lower 30s across most areas south of Lake Ontario...with rising temps
then following for the balance of the night. Highs on Monday will then
reach into the mid to upper 30s east of Lake Ontario and to around 40
elsewhere.

Monday night our region will remain under the influence of broad warm
air advection out ahead of a modest mid level trough/attendant surface
low pushing into the Upper Great Lakes. This will result in continued
plentiful cloud cover and at least some scattered shower potential...
with these possibly becoming a little more numerous across the North
Country...which will still lie relatively close to the advancing warm
front. Like yesterday...thermal profiles remain warm enough to support
mostly rain...with the possible exception of across the higher terrain
where a little wet snow will still be possible. Given the steady warm air
advection regime...nighttime lows will again occur during the evening and
will range from the lower to mid 30s east of Lake Ontario to the mid and
upper 30s elsewhere...before yielding to steady or slowly rising
temperatures overnight.

On Tuesday the aforementioned mid level trough/surface low will make their
way further eastward...and will eventually push their attendant cold front
across our area during the late afternoon and early evening hours. With
only limited to modest forcing available...expect any precip out ahead of
and along the front to remain largely scattered on Tuesday...though
orographic influences could still lead to areas of enhanced precipitation
coverage east of Lake Ontario at times. The antecedent mild airmass in
place out ahead of the front will result in milder temperatures and a
ptype of mostly rain...with area highs reaching into the lower to mid
40s areawide...and some portions of the Genesee Valley/Finger Lakes
possibly making a run at the upper 40s. While the tightening pressure
gradient out ahead of the front will also result in a breezier to windier
day...the poor to modest low level lapse rates that will be in place
will likely prevent wind gusts from reaching much above 30 knots or so.

In the wake of the front...a westerly to west-northwesterly flow of colder
air will overspread our region Tuesday night and Wednesday. Given current
lake surface temperatures of around +4C...this airmass will eventually
become cold enough to support a lake response by late Tuesday evening off
Lake Erie...and during the second half of Tuesday night off Lake Ontario.

Off Lake Erie...the overall lake response increasingly appears to remain
fairly muted by a general lack of deep background moisture through midweek...
as well as rather low inversion heights ranging between only 3 and 5 thousand
feet. This should keep any activity fairly scattered and light in nature...
and as such have pulled back considerably on PoPs downwind of Lake Erie
for Tuesday night and Wednesday...with any lake snows likely to end
altogether by Wednesday evening as high pressure and drier air builds
into the region.

Off Lake Ontario...conditions appear to be at least somewhat more favorable
with somewhat deeper moisture and higher inversion heights becoming available
for a time between later Tuesday night and early Wednesday...though even
here conditions still appear to be less that ideal for an overly significant
lake response. With this in mind...have elected to restrict PoPs for the
Lake Ontario activity to the likely range with this package...with the
lake snows likely winding down Wednesday evening thanks to the arrival
of the aforementioned ridging and drier air.

Outside of the lake effect areas...the Tuesday night-Wednesday night time
frame should be largely dry...with all areas seeing a return to colder
temperatures for midweek. Speaking more specifically...lows on Tuesday
night will settle back to between 25 and 30 areawide in the wake of the
cold front. Highs on Wednesday will then struggle to get much above the
lower to mid 30s...with readings then falling back to the teens and lower
20s to close out the period Wednesday night.

&&

.LONG TERM /THURSDAY THROUGH SATURDAY/...
A split flow over the country at the start of this period will
feature a low amplitude...progressive ridge in the east...while a
broad trough in the northern stream will cover all of Canada. This
will place a fairly tight baroclinic zone from the plains states to
the Great Lakes region and will be very favorable climatologically
for cutter storms. Earlier in the week...some guidance packages were
suggesting an ominous looking solution with a very deep storm
presenting the risk for a high wind event for our region...but that
scenario has since given way to various weaker solutions...all of
which lean away from wind problems while introducing the potential
for mixed precipitation. As for the day to day details...

Thursday should be a precipitation free day across our region...
despite a strengthening warm air advection pattern that will be
established over our region. This will all but guarantee a day that
will feature a wealth of alto-cu...but given the lack of upper
support and relatively dry air in the low levels...will not go any
higher than slight chc for pops for sites north of a line from
Dunkirk to Batavia and Rochester to the Tug Hill.

A relatively weak surface wave is forecast to eject out of the
central plains late Thursday and Thursday night...making its way
northeast within a broad inverted surface trough already in place
over the Mid West and Ohio Valley. This should tighten up the
aforementioned baroclinic zone over our region and encourage enough
forcing from the approaching sfc low to produce some light
precipitation over our region Thursday night. H85 temps are forecast
to climb to...or just above zero c across the bulk of Wrn NY...so
any light pcpn would favor some sort of mix...including freezing
rain. The highest chance for any freezing rain would be across the
Southern Tier and portions of the Finger Lakes region.

The surface low is then forecast to pass over...or just to the west
of...our region during the day Friday. Any mixed precipitation ahead
of this system would change to rain as temperatures for most areas
should climb into the 40s. The exception will be east of Lake
Ontario. Will maintain likely pops...although if the ECMWF is
correct...the day could be largely dry as its forecast track for the
storm system is several hundred miles further west. This outlier
solution would also encourage the Genesee Valley and some of the Srn
Tier valleys to approach 50 degrees. This forecast though...is based
more closely to the GFS...which is also favored by HPC progs.

Steady cold advection in the wake of this system will mean that any
mixed precipitation Friday evening will end as scattered snow
showers during the overnight....including some inconsequential lake
snow showers east of both lakes.

High pressure centered over the high plains late Saturday night will
nose to the east across our region for Sunday/Christmas Eve. This
would promote dry...uneventful weather for the bulk of the
region...although some weak lake snow showers would still be
possible east of both lakes.

Looking further down the road...medium to long range guidance is
looking very interesting for the period from Christmas to New Years.
For a few model runs now...this longer range guidance has been
hinting at a return to notably colder weather for the Great Lakes
region. A closed low over Siberia is forecast to break down in the
coming days with a chunk of its energy being ejected out across the
Kamchatka Peninsula and northern reaches of the Pacific ocean.
Eventually...this very robust bundle of mid level energy is forecast
to help carve out a full latitude trough over the heart of North
America. While highly anomalous ridging off the West coast would
extend from 20N all the way to the Pole...a large portion 0f the
polar vortex would settle south to northern Ontario. This newly
phased pattern would not only include a cross polar flow...but more
importantly would allow H85 temps of <-30c within the vortex to make
their way across the northern plains.

While this long range forecast would place the coldest air of this
outbreak over the plains states...the air would eventually make its
way to the Ohio Valley. Climatologically...this is exactly where it
should be to support significant southwest flow lake effect for our
region. This would also come at a time (between Christmas and New
Years) when impactful southwest flow lake storms seem to be most
common. In a nutshell...the week or so from Christmas to New Years
should feature colder than normal weather with the hint for
substantial lake snows. For what its worth...the Climate
Prediction Center is also projecting below normal temps for the
Great Lakes region for this same period. Stay tuned.

&&

.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
High pressure building into southern Ontario will keep a warm
front to the south of the region tonight. Satellite imagery
shows a sharp cut off in cloud cover, with BUF/IAG/ROC right
along the edge of an area of clouds with bases in the MVFR
category. Expect the flight category to vary between VFR/MVFR at
these sites. JHW is located closer to a frontal boundary with a
lower inversion and more low moisture. Expect periods of IFR
cigs mixed in with mainly MVFR conditions overnight.

On Sunday, expect mainly VFR conditions for most of the day
with the exception of some lingering MVFR cigs at JHW. The
surface high will shift to the east late in the day with the
warm front again approaching from the southwest. This will
result in lowering cigs toward the end of the 00Z TAF cycle.

Outlook...

Sunday night...MVFR with a chance of snow showers.
Monday...IFR/MVFR with a chance for rain and snow showers.
Tuesday...IFR/MVFR with rain likely.
Wednesday...IFR in lake effect snow likely SE of the Lakes,
MVFR/VFR in chance of snow elsewhere.
Thursday...Mainly VFR.

&&

.MARINE...
Winds have diminished with high pressure building toward the
region tonight. This will result in calmer conditions for the
remainder of the weekend.

Southwest winds will begin to freshen on Monday, as a warm front
lifts across the lower Great Lakes and a trough of low pressure
associated with a deep low pressure system over James Bay
approaches the region. This will likely necessitate a round of small
craft advisories for Lake Erie by Monday night, and eastern Lake
Ontario by Tuesday morning.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...None.

&&

$$

SYNOPSIS...APFFEL/TMA
NEAR TERM...APFFEL/TMA
SHORT TERM...JJR
LONG TERM...RSH
AVIATION...APFFEL
MARINE...APFFEL/TMA



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