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Area forecast discussion 
National Weather Service Buffalo New York
945 PM EST Thursday Dec 25 2014

Synopsis...
high pressure centered over the Tennessee Valley will ridge
northward across our area as it slides to the Carolina coast tonight
and Friday...before slowly drifting out into the western Atlantic on
Saturday. The high will provide our region with fair and dry weather
through Saturday...before a weak low pressure system swings another
cold front across the area Saturday night. Following this second
front...a return to colder and much more typical wintertime
temperatures is expected for next week.

&&

Near term /through Friday/...
during the near term period...high pressure over the Tennessee
Valley will ridge northward across our area as its center slides
to the Carolina coastline. This will result in any spotty light
leftover orographically-driven rain and snow showers across the
north country ending...with fair and dry weather otherwise
anticipated. At the same time...winds will also continue to diminish
back to much more typical levels...where they will then remain
through Friday.

All the above stated...skies should still average out fairly cloudy
right through the overnight. A pronounced subsidence inversion just
above 5k feet with ample upstream low level moisture streaming our way
will ensure that clouds will prevail through the night and into
Friday.

Do not expect the low clouds to even begin to break up until at
least sometime during the midday or early afternoon on Friday...when
the low level flow will back more southwesterly and potentially
allow somewhat drier air to work into the area from the Ohio Valley.
Should this actually come to fruition...this would eventually allow
for the return of some partial sunshine south of Lake Ontario during
Friday...while the north country would be more likely to remain
locked under low clouds for much if not all of the day.

With respect to temperatures...a decent gradient will still be in place
overnight...and this in conjunction with the aforementioned cloud
cover should help hold temperatures up above forecast low temperatures from the
met/mav guidance...with the lower elevations not dropping below the
30 to 35 f range...and the higher terrain only getting a few degrees
colder than that. On Friday...a modest southwesterly gradient and
925 mb temperatures within a degree or two either side of zero celsius
should then allow readings to recover to the lower 40s across the
higher terrain and the middle 40s elsewhere...assuming that the
expected partial sunshine south of Lake Ontario develops as
currently forecast.

&&

Short term /Friday night through Sunday night/...
Friday night and Saturday high pressure will remain centered over
the middle Atlantic and southeast states. General warm advection on
southwest flow will produce some cloud cover within the isentropic
upglide regime...but this should not become strong enough to support
any precipitation. Model guidance remains consistent with the timing of the
next system for Saturday night...and still appears slow enough to
keep Saturday completely dry. Southwest flow will boost 850mb temperatures
above 0c again Saturday afternoon which will support highs well into
the 40s in most areas. Some of the normally warmer spots in the
Genesee Valley may flirt with 50.

Saturday night through early Sunday morning a fast moving middle level
trough will swing across the Great Lakes and into Quebec...with a
trailing cold front pushing across the lower lakes. The advancing
upper level trough and a strengthening 160+ knot upper level jet
will provide some upper level divergence and large scale ascent...
with the advancing cold front providing some low level convergence.
Overall the front appears somewhat moisture starved...but may still
be strong enough to support a few rain showers moving from west to
east across the area. The best chances of rain showers will be east
of both lakes with some limited help from lake moisture and upslope
flow. The boundary layer remains warm enough for all liquid until
Sunday morning...but by then most of the moisture will be gone.
There is an outside chance of the rain showers ending as a few wet
flurries across the higher terrain if upslope enhancement lasts long
enough.

On Sunday ongoing cold advection will force temperatures to remain
steady or slowly fall through the middle and upper 30s. The airmass
quickly dries out so there may even be some sunshine developing
later in the day. Sunday night a dry northwest flow will take hold
with nothing more than some lake effect clouds overnight.

&&

Long term /Monday through Thursday/...
the trend through the long term period will be toward below average
temperatures for next week. With the colder temperatures will come
dry air and high pressure however...so it appears to be a mainly dry
period with a few minor exceptions.

Looking at the details...on Monday cold advection will continue
across the lower lakes as high pressure builds into the western
lakes. The close proximity of strong high pressure will yield a dry
airmass...shallow inversion heights and plenty of shear which should
prevent any lake response other than some clouds. On Tuesday a weak
frontal wave is forecast to cross the lower lakes by both the GFS
and European model (ecmwf)...with the European model (ecmwf) being a little more aggressive with
deeper moisture. This may produce a few flurries or light snow
showers with a Minor Lake response east of the lakes.

Wednesday and Thursday high pressure will build across the Ohio
Valley and middle Atlantic with a general cold westerly flow across the
Great Lakes. This may allow some lake response east of the lakes
depending on exactly how much synoptic scale moisture is available.
Outside of lake effect areas expect it to remain dry.

&&

Aviation /03z Friday through Tuesday/...
while high pressure extending north from the upper Ohio Valley will
produce fair weather across our region overnight...a wealth of low
level moisture will be trapped beneath a fairly strong subsidence
inversion. A quick peak at the 00z kbuf sounding depicts a 3 degree
inversion at 5600 feet...which is keeping the moisture from mixing
out. Infrared imagery is also showing more low level moisture pushing east
from lower Michigan...so ceilings will average 2500-3500 feet across the
lake plains with MVFR ceilings of 1500-2500 feet across the elevated taf
sites of the southern tier.

Any noteworthy improvement will hold off until the second half of
Friday...when the low level flow will back more southwesterly and
potentially allow somewhat drier air to work into the area from the
Ohio Valley. Should this actually come to fruition...this would
eventually allow conditions to improve back to VFR south of Lake
Ontario...while the north country would be more likely to remain
locked under MVFR ceilings for much if not all of the day.

Outlook...
Friday night and Saturday...VFR/MVFR.
Saturday night...VFR/MVFR with scattered to numerous rain showers.
Sunday...VFR/MVFR with a chance of rain and snow showers.
Monday...mainly VFR.
Tuesday...mainly VFR with a chance of snow showers.

&&

Marine...
all gale warnings have been discontinued.
An intense storm system tracking away from our region via northern
Quebec and high pressure centered over the upper Mississippi Valley
will keep a relatively strong surface pressure gradient in place over
our region through the night. As a result...fresh to strong
westerlies will remain in place with small craft advisories for all
of the nearshore waters along with the iag and St Lawrence rivers.

As we push through the day on Friday...a weakening pressure gradient
will allow winds and waves to drop below Small Craft Advisory levels on both lakes.

A weaker low pressure system is then expected to develop across the
western Great Lakes and lift across Georgian Bay and the Ottawa
Valley this weekend. This system will swing another cold front
across the lower lakes Saturday night...which will probably be
accompanied by another round of advisory-worthy conditions.

&&

Hydrology...
significant warming over the past couple of days significantly
increased rain and snow melt across the Tug Hill region and this
coupled with widespread rainfall from a cold frontal passage
pushed the Black River above action stage at Boonville. The river
is forecast to crest below flood stage tonight...with the crest
eventually working its way down to Watertown by Saturday...where
the river should crest just slightly above action stage on Sunday.

&&

Buf watches/warnings/advisories...
New York...none.
Marine...Small Craft Advisory until 5 am EST Friday for lez020.
Small Craft Advisory until 1 PM EST Friday for lez040-041.
Small Craft Advisory until 5 am EST Friday for loz030.
Small Craft Advisory until 1 PM EST Friday for loz042>044.
Small Craft Advisory until 3 PM EST Friday for loz045.
Small Craft Advisory until 5 am EST Friday for slz022-
024.

&&

$$

Synopsis...jjr
near term...jjr/rsh
short term...Hitchcock
long term...Hitchcock
aviation...rsh
marine...rsh
hydrology...jjr

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