Area Forecast Discussion
Issued by NWS Buffalo, NY

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467
FXUS61 KBUF 170049
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
749 PM EST Mon Jan 16 2017

.SYNOPSIS...
Low pressure over the lower Missouri Valley will track northeastward
across the Great Lakes later tonight and Tuesday. This low will
spread rain across the region tonight and Tuesday morning...which
may begin as a brief period of freezing rain or sleet before
eventually changing over to all rain as temperatures warm. A weak
cold front trailing the low will cross our region Tuesday night...
with leftover rain showers then winding down from west to east
during Wednesday.

&&

.NEAR TERM /THROUGH TUESDAY/...
Tonight low pressure over the Lower Missouri Valley will slowly
deepen while lifting to around Chicago...in association with its
parent mid level shortwave trough. Out ahead of this system...a
40-50 knot low level jet will extend northeastward across the Ohio
Valley...with both this and the strengthening warm air advection
regime out ahead of the low helping to spread increasing amounts
of forcing and GOMEX-based moisture into our region...particularly
overnight when isentropic lift will increase with the approach of
the main surface warm front...and low level convergence ramps up
along the nose of the advancing low level jet. As a result...we
can expect spotty light precipitation across far western New York
this evening to gradually give way to an increasingly better
potential for steadier light precip from about the Genesee Valley
westward overnight...with lower-end precip chances reaching the
eastern Finger Lakes before daybreak.

With respect to precipitation type...the strengthening warm air
advection regime/advancing low level jet will advect a nose of
warmer air aloft over a layer of colder air at the surface...which
will feature temperatures dipping to around or below the freezing
mark. Such a setup will be favorable for a wintry mix of rain...
freezing rain and sleet for a few hours in most locations...before
surface temperatures across far western NY warm above freezing and
lead to a changeover to plain rain later on tonight. The wintry mix
will likely result in some light ice accumulations of a few
hundredths to a tenth of an inch of ice.

On Tuesday the surface low will lift across the state of Michigan
with the associated surface warm front pushing northeast across
western and much of central New York. This will result in steadier
precipitation overspreading the remainder of the region from southwest
to northeast...with most locations again likely seeing a 2-3 hour
window of a light wintry mix and icing of a few hundredths to a
tenth of an inch...before steady warming of the atmospheric column
forces a changeover to plain rain. The exception to this will be
in the Saint Lawrence River Valley where low-level cold air and
a wintry mix will linger longer...and where a quarter inch or so
of icing will be possible.

Given all of the above...Freezing Rain Advisories remain in effect
for most areas except for Jefferson and Lewis counties...where a
Winter Weather Advisory is in effect due to the potential for some
light sleet accumulation as well.

Freezing rain aside, mesomodel QPF blend yields plain rain totals
close to a half an inch. Temperatures will also run above normal
across WNY with most locations seeing at least 40 by the afternoon
with Lake Erie Lakeshores possibly pushing into the upper 40s under
downslope flow.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH FRIDAY NIGHT/...
A low amplitude split flow found across the country at the start of
this period will amplify as we work our way through the week...as an
anomalously strong 190kt East Asian jet will slam the West Coast
with several robust shortwaves. This will carve out a broad trough
over the wrn states...which in turn will lead to an amplification of
a downstream ridge over the eastern states. The result will be above
normal temperatures normal temps across our forecast area with
nothing more than some leftover pcpn Tuesday night into Wednesday.

The pcpn early in the period will be supported by a shortwave within
the northern branch of the split flow. This feature...seen in WV
imagery over the high plains of Montana at 18z today...will track
east and eventually reinforce a mid level trough left behind in the
wake of an initial southern stream shortwave. While there could be a
short break in the pcpn between these features Tuesday evening...the
character of the night will be wet. Despite the pcpn being more
`showery` over the western counties...have raised pops to
categorical in that area to accompany the already 100 pops further
east. Despite the expectation of some fairly widespread rain
though...QPF will be under a quarter inch in most areas. The only
potential problem with the pcpn will be across the North Country
where overnight temps could settle into the lower 30s...thereby
posing the risk for a short period of freezing rain.

On Wednesday...while ridging building across the Lower Great Lakes
will bring an end to any leftover rain showers by midday...a wealth
of moisture will be trapped below 5k ft beneath a subsidence
inversion. This should keep the day shrouded by clouds with weak
terrain induced lift possibly generating a little drizzle from time
to time. Temperatures will reach the mid to upper 30s...although
some spots over the western counties could tickle 40.

A ridge axis to our south and west will support fair dry weather
Wednesday night...as temperatures will lower to within a couple
degrees of freezing.

Fair dry weather will persist Thursday and Thursday night...as
ridging will amplify over the Lower Great Lakes. This will be
accompanied by some weak warm advection...so temperatures Thursday
afternoon should be able to reach into the 40s across the majority
of western New York. A little more cloudiness over the eastern Lake
Ontario region will likely keep that area in the mid 30s.

Conditions will then deteriorate Friday afternoon and night...as a
weakening shortwave will track northeast across the forecast area.
Will maintain chc pops to cover this light pcpn event...which again
could include some spotty freezing rain (esp across the North
Country).

&&

.LONG TERM /SATURDAY THROUGH MONDAY/...
A highly amplified split flow will be found across the continent
during the period with the Great Lakes region being dominated by
Pacific modified air within the southern branch. While this will
keep above normal temperatures in place over our region...the period
will be highlighted by what could be a soaking to problematic rain
on Monday. More on this in a moment.

As we open this period on Saturday...a weak mid level shortwave and
its attendant sfc trough will stall over our region. Given the
consistency between the various operational packages that depict a
swath of relatively deep moisture that will accompany the weak
lift...have add low chc pops to our area for some light rain. The
silver lining to the more pessimistic pcpn forecast is that it will
be quite mild. Temperatures Saturday afternoon are expected to climb
well into the 40s...with some of the valleys west of the Finger
Lakes approaching 50.

Ridging should become dominate over our forecast area on Sunday...
but do not let the improving trend fool you. A deep closed low over
the Lower Mississippi Valley on Sunday will open the door for rich
GOMEX moisture to stream northwards across the Ohio Valley towards
our region. As we proceed through Sunday night into Monday...the
large storm system will drift northeast to the Upper Ohio valley.
While this will shift the origins of the sub tropical plume to the
Caribbean and Gulf stream of the western Atlantic...it will still be
directed at our forecast area. This will set the stage for what
could be a significant rain event for our region on Monday.

The stacked storm system will be quite dynamic as it nears our
region on Monday...with strong upper level jet dynamics and a
distinct divergent upper level flow helping to produce deep lift
over our region. This should lead to widespread rain over our
region...with the influx of sub tropical moisture enhancing the
potential for moderate to heavy rain.

There could also be strong downsloping winds between Lake Erie and
the Chautauqua Ridge later Sunday night into Monday...as southeast
low level jet of 50 kts near the top of the inversion is being
forecast to be in place.

&&

.AVIATION /01Z TUESDAY THROUGH SATURDAY/...
A storm system over Missouri will track to near Chicago tonight...
then across the Great Lakes Tuesday. An advancing warm front and low
level jet ahead of this low will spread precipitation northeastward
across our region through the TAF period. Near or sub-freezing surface
temperatures at the onset will allow for 2-3 hours of a light wintry
mix of rain...freezing rain...and sleet in many locations...before
surface temperatures warm above freezing and lead to a changeover to
plain rain later tonight and Tuesday.

In terms of flight conditions...general VFR conditions this evening
will deteriorate to MVFR and then IFR from southwest to northeast
overnight and Tuesday with the arrival of the steadier precipitation
and attendant copious low level moisture.

Outlook...
Tuesday night and Wednesday...IFR with showers transitioning to some
drizzle and fog.
Wednesday night through Friday...Mainly VFR.
Friday night and Saturday...chance of rain and some MVFR/IFR.

&&

.MARINE...
After a night of relatively light to modest winds across the Lower
Lakes Region...a warm front will cross the lakes Tuesday, with south
to southeasterly winds increasing to 10-15 knots on Lake Erie...and
east to southeasterly winds increasing to 15-25 knots on Lake Ontario.
This will bring a period of low-end advisory-level winds and waves
to the western half of Lake Ontario...for which a small craft advisory
has been hoisted for areas west of Hamlin Beach. After that...
conditions are expected to remain below advisory levels from Tuesday
night on through the rest of the week.

&&

.CLIMATE...
The main story for next week and beyond will be the extended
period of above normal temperatures not only in our region, but
for much of the eastern 2/3 of the nation. Over the next two
weeks, a strong closed low will remain parked over the Bering
Straits, forcing a strong Pacific East Asian jet to extend farther
east than normal. This will continue to bring a parade of Pacific
systems into the western United States, while also supporting
zonal flow and a flat ridge downstream across the central and
eastern part of the country. The westerly flow across the
continent will support strong Chinook warming off the Rockies,
with warmth spreading to the east coast and even well north into
southern and central Canada.

The warmth will last for another 12 days or so, but there is a
significant pattern change brewing beyond that. A Sudden
Stratospheric Warming event has just occurred in the northern
hemisphere. These events occur when planetary waves propagate
vertically into the stratosphere, with wave breaking and dampening
processes acting to rapidly warm the stratosphere over the high
latitudes and greatly distort the Stratospheric Polar Vortex.

This warming and disruption in the stratosphere has been shown in
numerous studies to slowly feed back into the troposphere, with a
strong tendency for high latitude blocking to increase about 2
weeks after the warming takes place. High latitude blocking
increases the ability of polar air to spread southward into the
mid latitudes, and increases the chances of cold and wintry
weather locking in for a longer period of time.

It appears the long range guidance is beginning to capture this
idea, with the GEFS and NAEFS ensembles suggesting a more highly
amplified flow starting late this month, with a ridge developing
over Alaska and the West Coast while a deep longwave trough
begins to establish across central and eastern North America. The
developing ridge in Alaska may also promote a period of cross
polar flow, draining frigid Siberian air into northern Canada.
GEFS ensembles also support a more negative NAO and AO pattern
towards the end of the month. Putting all this together, it
appears the pattern should become much colder and more wintry
around January 27-29. Past stratospheric warming events suggest
this cold pattern may last for quite some time, and may support
the potential for periods of well below normal temperatures by the
end of the month and first half of February. Stay tuned.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Winter Weather Advisory from 7 AM Tuesday to 4 AM EST
     Wednesday for NYZ007-008.
     Freezing Rain Advisory from 4 AM to 4 PM EST Tuesday for
     NYZ005-006.
     Freezing Rain Advisory from 1 AM to 1 PM EST Tuesday for
     NYZ003-004-013-014.
     Freezing Rain Advisory until 10 AM EST Tuesday for NYZ001-002-
     010>012-019>021-085.
MARINE...Small Craft Advisory from 7 AM to 4 PM EST Tuesday for LOZ042.

&&

$$

SYNOPSIS...JJR
NEAR TERM...JJR/SMITH
SHORT TERM...RSH
LONG TERM...RSH
AVIATION...JJR/SMITH
MARINE...JJR/SMITH
CLIMATE...HITCHCOCK



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