Area Forecast Discussion
Issued by NWS Burlington, VT

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FXUS61 KBTV 272056

Area Forecast Discussion
National Weather Service Burlington VT
356 PM EST Thu Feb 27 2020

As low pressure tracks northward into central Quebec this afternoon,
snow showers will gradually diminish across the majority of the
area, while lake effect snow develops downwind of Lake Ontario
across portions of northern New York and northern Vermont. Lake
effect snow continues to affect the North Country through Friday
before ending Friday night. Quieter and colder conditions are
generally on tap for the weekend with just a few mountain snow
showers possible. Warmer temperatures return next week, along with
several chances for rain and snow showers, especially on Tuesday.


As of 354 PM EST Thursday...Vertically stacked low pressure continues
to track northward into Quebec this afternoon with widespread snow
gradually ending from south to north. Attention now turns to a
developing lake effect snow band that will bring additional
accumulating snow to portions of northern New York and even as far
east as the northern Green Mountains through Friday. Focus area for
the highest totals will be downwind of Lake Ontario specifically
along and south of State Route 3 across St. Lawrence and Franklin
counties where 6 to 12" is expected, with some additional
accumulations of 3-7" across western Essex county from Lake Placid
to Newcomb. Elsewhere across the North Country, while scattered snow
showers persist, especially across the northern Greens, areal
coverage will be much more limited with additional amounts of a
dusting to 2" possible to locally 4" across the higher terrain
through Friday. In addition, winds will continue to be blustery
through Friday as well with gusts in the 20-35 mph range likely.
Lows tonight will be teens to low 20s, and highs Friday mainly in
the low/mid 20s.

Friday night we`ll see upper level low pressure build southward over
the region with a surface boundary dropping north to south. We`ll
likely see some enhancement of snow shower activity along the
boundary, but it will also help to shift the lake effect band out of
the region with chances for snow showers gradually diminishing
through the night. Temps behind the boundary become more winter-like
again with overnight lows in the single digits to teens expected.


As of 354 PM EST Thursday...Most cloudy skies are forecast with
northwesterly flow continuing to influence our weather. See little
reason for these conditions to break given the meandering upper
level low will be in no hurry to move eastwards. With this, did
slightly increase chances for snow showers across portions of
northern Vermont. Cold air advection will bring in 850mb
temperatures around -17 C. So the lapse rates available for upslope
snow is fairly good. Highs on Saturday will likely struggle to get
above 20 over northern New York with much of Vermont around 20 to
the mid 20s.

Saturday night, the backside of the trough is finally going to slide
eastward. With the increased vorticity and a bit of deformation. The
period Saturday night is just starting to get in range of higher
resolution models, which are producing some light precipitation
signals. Froude numbers do fall with light west-northwesterly winds
in place, and there is still some low-level moisture hanging around.
Thus, any lingering snow showers atop the mountain summits could
retreat westward down to the foothills of the Greens and into the
eastern Champlain Valley. Would not be surprised to see some
mischief during the early hours before a shift to southwesterly flow
cuts off this potential by Sunday morning. Thus, a chance of snow
showers has been added over Franklin and Chittenden County. Any
accumulations would be minor. Not anticipating much in the way of
radiational cooling due to the clouds in place. As we all wake up
Sunday, the cold air mass in place should still yield temperatures
in the single digits above zero.


As of 354 PM EST Thursday...The main forecast challenges of the long
term will be the potential for mixed precipitation on Monday and
whether or not we see a strong warming trend or a subdued warming

As has been the pattern for the last several systems, we have a
split flow regime with a weaker northerly jet and the core of strong
upper level winds over the southern half of the US. A ridge will set
up over the US East Coast and a positively tilted trough with
embedded northern and southern stream shortwave features making for
a lower predictability forecast. Similar to previous instances of
this same pattern, there is disagreement on whether the southern
stream upper trough digs towards the Baja peninsula and cuts off or
remains an open wave. From here, model have typically underdone the
resulting downstream amplification of the ridge in the eastern US
and have taken the southern stream system too far south as the upper
low begins to open into a trough.

The differences mentioned above greatly affect precipitation
forecasts and how warm we get heading into the extended. On Monday,
a shortwave ridge will crest over the region with a subtle shortwave
just behind the crest. With warm advection, there will be some
precipitation. A 40kt LLJ should cause some shadowing in the
valleys. Before the strongest of the warm air advection comes, we
should start as snow and then transition to rain. Both the GFS and
the EC, but not the CMC, depict a clipper type system moving across
on Tuesday, which should bring some more widespread precipitation.
With an upper ridge developing to the south and the upper jet
shifting north, we will be in the favorable left exit region of a
jet. So have leaned towards a GFS/EC inclusion with the NBM. Also
nudged max temperatures downwards with the widespread precipitation
likely and with the potential for a low track just to our south.

Things become even murkier heading into Wednesday. Spread in
deterministic 850mb temperatures and low track is sizable. The 12Z
GFS is off the Atlantic Coast, the 12Z EC is nearly overhead, and
the 12Z CMC is over Lake Michigan at forecast hour 168. There are
some timing differences for the system as well, which will be
dependent on potential cut-off low near the Baja peninsula and
downstream ridging. Have stuck with a blended forecast, but think
something along the lines of the CMC/EC are more likely in relation
to what takes place next Wednesday or Thursday based on how things
have played out for much of this winter. Fortunately, we have plenty
of time to refine this forecast. The current forecast reflects highs
in the 40s and periods of rain and snow with 30%-50% precipitation


Through 18Z Friday...Gradually improving conditions from
LIFR/IFR to MVFR/VFR is expected this afternoon as precipitation
generally comes to an end. Exceptions will be ongoing LIFR snow
at KMSS through 22Z, and continued IFR lake effect snow through
the period at KSLK. Other aviation concern will be increasing
WSW winds through the period. Already seeing gusts of 20-35kts
at KMSS and KSLK, and those winds will be propagating westward
this afternoon with gusts 20-30kts expected at all sites through
the remainder of the period.


Friday Night: Mainly VFR, with local MVFR possible. Chance SHSN.
Saturday: VFR. Slight chance SHSN.
Saturday Night: VFR. NO SIG WX.
Sunday: VFR. NO SIG WX.
Sunday Night: VFR. NO SIG WX.
Monday: Mainly MVFR, with areas VFR possible. Slight chance SHRA,
Slight chance SHSN.
Monday Night: Mainly MVFR, with areas IFR possible. Chance SHSN,
Chance SHRA.
Tuesday: Mainly IFR, with areas MVFR possible. Chance SHRA,
Chance SHSN.


NY...Winter Weather Advisory until 4 PM EST Friday for NYZ030-034.


NEAR TERM...Lahiff
LONG TERM...Haynes
AVIATION...Lahiff is the U.S. government's official web portal to all federal, state and local government web resources and services.