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Area forecast discussion 
National Weather Service Buffalo New York
1255 PM EST Wednesday Nov 26 2014

Synopsis...
a Nor'easter will lift along the Atlantic coastline through tonight
and bring light snow across our region through the evening hours. Snow
accumulations will range from a fresh coating across western areas
to several inches across the southern Genesee and Finger Lakes
region. This snow will taper off this evening from west to
east...though some limited lake enhanced activity will lingering
into Thanksgiving morning...especially southeast of Lake Ontario.

&&

Near term /through tonight/...
this early afternoon a deepening coastal low is found just to the
east of southeast Virginia. This low is spreading precipitation inland
across the northeast with a light general snowfall now reaching our
southern tier and Finger Lakes region. Have bumped snowfall
accumulations up an inch across the southern Genesee Valley...and
east of Lake Ontario where southern Lewis County may near 4 inches
from this storm before the snow ends.

For the details...during the course of today and tonight...this
coastal low will strengthen into a full-fledged Nor'easter while
lifting northeastward just offshore of the Atlantic coastline...with
the center of the low passing just to the south of Long Island this
evening...then lifting out into the Canadian Maritimes during the
remainder of tonight.

While this system will be responsible for the pre-Thanksgiving
snowstorm expected across New England and eastern New York...on this
track it will only manage to brush western and north central New
York with much lighter snowfall. The bulk of this will primarily
affect interior sections of The Finger lakes and the north country
this afternoon and evening...where a general 1-3" of snow will be
possible through tonight...with up to 4" or so possible across Lewis
County. Otherwise...expect fairly cloudy conditions with lower
probabilities of snow across the remainder of the region...where
any resultant accumulations should remain insignificant.

As for temperatures...cloudy skies and a developing northeasterly low level
flow will help keep today's highs mostly confined to the middle 30s...
with lows in the middle to upper 20s then following for tonight.

&&

Short term /Thursday through Friday/...
cold and cloudy conditions will prevail across western and
north-central New York for Thanksgiving day as the axis of a deep
upper level trough will be located directly overhead the region.
Cyclonic west-northwest flow and cold temperatures aloft will
support abundant lake-enhanced cloud cover across the forecast area
along with scattered flurries...but not much in the way of
accumulating snowfall as there will be some vertical directional
shear within the weak flow aloft coupled with a dearth of middle-level
moisture. Temperatures should top out right around the freezing mark
for most areas.

The chance for accumulating snowfall will improve somewhat as we
move into Thanksgiving night as a shortwave moving through the back
side of the longwave trough crosses western New York...raising
equilibrium levels to around 10kft on Lake Erie for a time on
Thursday evening and generating enough of a lake response to bring 1
to 3 inches to the vicinity of the Chautauqua ridge. The focus will
then shift to the area southeast of Lake Ontario as the shortwave
moves east overnight with an inch or two possible there as well. As
expected...with the upper level trough still overhead...readings
will run on the chilly side with lows in the middle to upper 20s.

Looking at the end of the week...we should see a few flurries or
light snow showers to start the day Friday before flow backs to the
southwest as a surface ridge of high pressure moves
overhead...effectively ending any lingering lake effect
precipitation. This will also allow for a few breaks in the cloud
cover inland from the lakes before middle/high clouds thicken once
again from the west later in the day as broad isentropic ascent
begins to take hold across the region. Enough cold air will remain
in place across the lower Great Lakes however to keep highs limited
to right around the freezing mark.

&&

Long term /Friday night through Wednesday/...
as alluded to above...the large scale pattern will change as we move
into Friday night with the formerly high amplitude upper level
pattern giving way to broad zonal flow across the nation. This will
serve to moderate temperatures considerably as we move through the
weekend with readings climbing into the upper 30s to lower 40s
Saturday and into the 50s Sunday as the jet stream lifts north of
the Great Lakes. However this warmup will not be accompanied by much
in the way of sunshine however as the region will be ensconced in a
zone of broad...but diffuse...isentropic uplift throughout the
weekend.

We may see a few snow showers Friday night as the leading edge of
the warm air moves across the region and there will remain a low
chance of rain and snow showers Saturday courtesy of the above
mentioned broad isentropic uplift. Probability of precipitation ramp up somewhat by later in
the day Sunday as a clipper swinging out of northwestern Canada
increases low-level frontogenesis and focuses ascent across the
Great Lakes. The resulting cold front is currently expected to swing
across the forecast area Sunday night into Monday...bringing a mix
of rain and snow showers. High pressure and colder temperatures
return for Monday in the wake of the front with highs only expected
to reach the middle to upper 30s...with 20s Monday night. Temperatures
will moderate some by Tuesday as the high shifts east of the area
and warmer air begins to once again push north into the region.

&&

Aviation /18z Wednesday through Monday/...
at 18z light snow has reached the southern tier and Finger Lakes
region from the coastal low. This snow is bringing visibilities down
to IFR range...with MVFR visibilities found on the outer periphery of the
snow. For the airfields expect a reduction to MVFR...and possibly
some IFR where the snow intensity will be briefly higher.

This system will pull away from our region tonight with light winds
backing around to northwesterly. Expect VFR/MVFR flight conditions
for the remaining 12 hours or so of the taf period with general dry
conditions for the airfields.

Outlook...
Thursday...snow showers and IFR/MVFR becoming likely across far
southwestern New York...otherwise mainly VFR with a chance of MVFR
in snow showers.
Friday...mainly VFR with a chance of snow showers/MVFR.
Saturday through Monday...mainly VFR with a chance of rain and snow
showers.

&&

Marine...
a developing storm system will lift northeastward along the Atlantic
coastline today and tonight. On its western side...a strengthening
northeasterly low level flow will bring a period of advisory-level
winds and waves to portions of the Southern Lake Ontario shoreline
late this afternoon and this evening...for which a Small Craft
Advisory is in effect as outlined below.

In the wake of this system...a secondary surface trough will then
cross the lower lakes region between later Thursday and Thursday
night...and will likely be accompanied by a another period of
advisory-level westerlies and attendant higher waves.

&&

Hydrology...
the flooding threat for western New York has largely ended as
temperatures have dropped below freezing...which ended the
snow melt run off. It is Worth noting that some of the slower
responding creeks across the area...namely Tonawanda creek in
northern Erie country will continue to rise over the next 18
hours...but should remain below flood stage.

&&

Climate...
after an extended period of cold during the middle of November it
appears temperatures will average above normal most of the time over
the next few weeks. There will be brief pushes of colder air at
times as progressive troughs amplify into the Great Lakes...but
these cold periods will be short lived...only lasting for a few days
at a time...and will be outnumbered by mild days.

Looking at the hemispheric pattern...a positive North Atlantic
oscillation /nao/ will persist into the first few days of December
based on the gefs ensemble mean. The mean longwave trough over the
North Atlantic in such a pattern will prevent any cold from locking
in over the northeast quarter of the United States. The Pacific
North American pattern /pna/ will remain negative through the first
few days of December...before trending positive based on gefs
ensemble members. This too will prevent cold from locking into the
northeast for more than a few days at a time.

The Madden Julian oscillation /mjo/ may play an important role in
driving pattern change through middle December. Analysis over the past
week has shown a moderately strong mjo event developing over the
Indian Ocean. A gefs ensemble forecast of the Wheeler phase/space
plot shows this mjo orbiting through phase 4 and 5 during the first
week in December as convection moves east across the maritime
continent. A look at composite charts of past events favors above
normal temperatures across much of the central and eastern United
States during phase 4 through 6 of the mjo.

Eventually as we get into the second week in December mjo convection
will continue its eastward orbit through the Pacific and into the
western hemisphere. If the mjo convection persists on its eastward
journey and reaches phase 7 of the Wheeler phase/space plot...it
would favor a significant pattern change towards colder than normal
temperatures over the central and eastern United States. The mjo
accomplishes this as sub-tropical convection influences the pattern
over the Pacific...forcing amplification of the eastward extension
of the east Asian jet which in turn forces downstream amplification
of the pattern across North America. Based on the forecast timing of
the mjo episode this would most likely occur by week 2 or 3 of
December and feed back into more high latitude blocking and more
long lasting cold.

&&

Buf watches/warnings/advisories...
New York...none.
Marine...Small Craft Advisory from 4 PM this afternoon to 1 am EST
Thursday for loz043-044.

&&

$$

Synopsis...Thomas
near term...jjr/Thomas
short term...wood
long term...wood
aviation...Thomas
marine...jjr
hydrology...wood/Thomas
climate...Hitchcock

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