Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 211731

Area Forecast Discussion
National Weather Service Buffalo NY
1231 PM EST Sat Jan 21 2017

Mild conditions will persist through tonight with low clouds and
patchy drizzle and fog. A complex area of low pressure will then
move northward along the east coast early next week. This system
will spread rain into the area Monday, which may change to wet snow
late Monday into Tuesday as colder air filters into the region. A
return to more typical mid winter cold and snow is expected to
arrive late next week.


The drizzle and fog have ended with low clouds persisting north of
the warm front, close to Lake Ontario. Sunny breaks have
developed south of this area allowing temperatures to surge well
into the 50s.

Tonight a weak ridge will build over the region, and force the low
level inversion to strengthen overnight. The strengthening inversion
and remaining low level moisture will continue to support low
stratus, which will likely expand again overnight. Expect fog and
drizzle to return as well, with the most widespread fog and drizzle
likely to be found across higher terrain and near the lakes.

Temperatures will remain way above average for late January. Expect
highs today in the low to mid 50s in many areas, with low to mid 40s
across the North Country. Record highs for today are 69 at BUF, 71
at ROC, and 57 at ART and are all well out of reach. Lows tonight
will only pull back into the lower to mid 40s in most locations,
with upper 30s across the North Country.


Ridging aloft will persist into Sunday, which, on the plus side,
will maintain the very mild temperatures across the region, but will
unfortunately also maintain the subsidence inversion keeping the
dreary low stratus and areas of drizzle in place. This will make
Sunday nearly a carbon copy of Saturday, with high temperatures
again topping out in the low 50s in western NY to the mid 40s in the
North Country.

The focus then becomes the developing storm system that is currently
coming onshore in southern California. This low pressure system will
track across the southern CONUS this weekend where it will
eventually turn north along the Appalachian Mountains Sunday night
into Monday. This anomalously deep low pressure system will be in
place near the Mid-Atlantic states on Monday with increasingly
anomalous easterly winds and Atlantic moisture advection across New
York state. This strong and efficient moisture advection into the
region combined with the impressive diffluent flow aloft ahead of the
closed 500mb low will generate widespread rainfall across the
forecast area on Monday.

The really tricky part of this forecast comes into play later Monday
afternoon and overnight Monday night, as the chance of precipitation
changing over to snow increases. There are several details that will
be critical to whether or not precipitation changes over to snow,
and where the heaviest precipitation will fall. First, global models
have struggled with the exact track of this low pressure system for
the last few days, but have settled back on a more westerly track
(conducive to more widespread precipitation across the region). As
this wave comes onshore today and moves into the SW CONUS, the RAOB
network will finally get a much better sampling, and thus today`s
model runs with this additional data should start to help clarify
whether this more westerly trend will hold. Second, models also are
having a very difficult time with the thermodynamic profiles, which
will be critical since the airmass with this storm is overall
lacking much in the way of true cold air. The difference between
rain and snow or significant accumulating snow will come down to
dynamical cooling processes, precipiation intensity and even
elevation. The GFS continues to be most modest with temperatures,
but still generates some snowfall across the North County where it
tracks the heaviest precipiation. The EC and Canadian are overall
colder and support more widespread snowfall, but any significant
accumulations could still be limited to where rates are highest to
force surface temperatures to near freezing. Unfortunately at this
point there are still a lot more questions than answers, but the
potential for significant accumulating snow is still on the table.
Given the latest model guidance, the best potential for significant
accumulating likely remains from near the Finger Lakes into the
North Country. Will continue to mention this in the HWO. By Tuesday
precipitation will taper off from west to east and high temperatures
will be held to the low to mid 30s.


Tuesday night into Wednesday the low pressure system will exit to
our east, but a shortwave trough on the leading edge of a broad
trough carving out across the CONUS will move through the Great
Lakes. This clipper will move from near Iowa Tuesday night to over
Lake Ontario by Wednesday evening while weakening. With marginal
temperatures already in place and warm advection ahead of the wave,
expect rain and snow showers to overspread the region Wednesday,
turning to mainly rain showers during the day Wednesday. Showers
will change over to mainly snow in the cold advection behind the
wave by Thursday with some increasing lake/orographic enhancement on
the cold advective westerly flow. Temperatures will slowly fall
through this period as large scale trough becomes established over
the Great Lakes, and will likely return to more normal or below
normal readings by the weekend. Along with this colder air will come
increasing chances for Lake Effect snows by next weekend.


Abundant low level moisture continue to support widespread IFR in
low stratus close to Lake Ontario from KIAG-KROC-KART north of a
warm front. VFR conditions area expected south of these sites
through the rest of the afternoon. KIAG and KROC may briefly
go VFR late this afternoon and early this evening.

Abundant low level moisture will remain in place tonight, and a
steepening low level inversion and nocturnal cooling will likely
allow stratus to expand again tonight. Expect a return to more
widespread IFR after 03Z Sun, with areas of fog and drizzle also
forming again and bringing IFR VSBY overnight. Conditions again
appear favorable for CIGS and possibly VSBY to drop to near airfield
minimums at times overnight, especially across higher terrain and
near the lakes.


Sunday...Areas of IFR/MVFR in low stratus, fog, and drizzle.
Monday and Monday night...Areas of MVFR/IFR with rain changing to
wet snow.
Tuesday...Areas of MVFR/IFR with wet snow mixed with rain.
Wednesday and Thursday...VFR/MVFR with a chance of rain and snow.


A weak pressure gradient will maintain light winds at less than 15
knots through Sunday morning. Low pressure will then develop and
move slowly north along the east coast early next week, while high
pressure remains parked over Quebec. The increasing gradient between
the two will bring stronger northeast winds to the Lower Great Lakes
late Sunday through Tuesday, with winds peaking Monday and Monday
night. This will likely bring higher end Small Craft Advisory
conditions to the lakes early next week.





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