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Area Forecast Discussion (AFD)

Issued by Burlington, VT (BTV)

FXUS61 KBTV 151440

Area Forecast Discussion
National Weather Service Burlington VT
940 AM EST Fri Dec 15 2017

High pressure over the North Country will continue to provide 
the region with clear skies and very cold temperatures today. 
An upper trough and surface low passing northwest of the region 
will bring a chance for snow showers for Friday night through 
Saturday, with the weekend ending cool and dry on Sunday.


As of 940 AM EST Friday...Quick update to the morning forecast 
to adjust PoPs across the lower St. Lawrence Valley. Lake effect
snow band has begun to shift into the forecast area as the low 
level flow back to the south and expect a light accumulation in 
the Edwards/Gouverneur area over the next hour or two. 
Otherwise, forecast for the band shifting just northwest of the 
river valley by the noon hour still looks good.

Previous Discussion...
Another dry and cold day is in store for today, with increasing
clouds through the day. A weak low pressure system and upper 
level trough will approach from the Great Lakes region this 
afternoon. Surface high pressure will shift eastward as these 
feature approach. Temperatures will be a bit warmer today than 
yesterday, about 5 degrees, as south southwesterly flow 
develops. This flow will also bring chance for lake effect snow 
showers to the Southern Saint Lawrence valley and parts of the 
Northern Adirondacks. Heaviest lake effect snow will remain 
south of our region across the tug hill plateau. 

Upper level trough swings across our forecast area tonight and
brings a better chance for light snow showers, especially in the
higher elevations. Temperatures will be closer to seasonal
normals overnight with clouds and snow, as well as winds. Best
chance at some accumulations will be along the Saint Lawrence
river with lake effect bands, then in the northwest upslope
regions of the Adirondacks and Green Mountains tonight into
Saturday, generally 1-3". The rest of the area should only have
an inch or less of snow with the widespread scattered light snow
showers. Slow warming trend will begin Saturday and temperatures
will be in the 20s across the area.


As of 343 AM EST Friday...Quiet weather is expected through
Saturday night and Sunday as a 1030mb high drifts to the east
over southern Quebec. The flow aloft will remain northwest as
weak ridging occurs aloft. There's a slight chance of some
western slope snow potential as the hires models are keying on
some 10-15dbz's in along the western slopes of the Greens. The
safe bet is we'll see some flurries but very little in the way
of accumulation. Temps should be on the chilly side over the
weekend with lows Saturday evening in the single digits, and
highs on Sunday only warming to the teens, to lower 20s.


As of 410 AM EST Friday....Coming out of the weekend we still 
anticipate a fairly active pattern. The medium ranged guidance 
still offers different ideas for how Monday shapes up. The GFS 
is still the outlier with a dry forecast so I continued the 
trend towards the CMC/EC with a weak warm advection shortwave 
that brings some light snow to the region Monday afternoon. 

By Tuesday the general consensus from the global models is that
we'll have trough of low pressure swing through the North
Country. We'll be under strong warm air advection in the morning and
we'll see temps warm enough to see rain at elevations below 
2000ft with some rain/snow mix in the 2000-3000ft range. The 
higher peaks will most likely stay as snow. Of course timing 
differences in when the precip arrives will have fairly large 
consequences on p-type so well just need to monitor and update 
as a single solution emerges. 

Regardless of the timing, a cold front will swing through which
leads to colder temps on Wednesday. We'll be looking at
northwest flow aloft with westerly flow at the surface, so we
should see mainly orographic snow showers along with some lake
effect snow developing. The temps should be in the upper 20s to
around 30 on Wednesday falling to the single digits to low teens

Based on the current guidance and trends, Thursday should be
fairly quiet as high pressure sits to our south. While we wont
see much in the way of precip, we'll still be fairly cloudy as
moisture rides along the northern edge of that high pressure
system. Highs will be in the 20s with lows Thursday night
slightly warmer than Wednesday in the upper teens to low 20s.


Through 12Z Saturday...VFR conditions will largely continue 
through the period. MVFR possible for KSLK and KMSS after 18z. 
Clear skies will give way to increasing mid/high clouds from 
the west/southwest with a gradual lowering after 15z to 040-080
by 18z. Snow showers in the vicinity of Lake Ontario and 
St.Lawrence valley during Friday, gradually shifting into 
Adirondacks after 00z Sat. WNW winds 5-8 kts this evening, 
becoming light and variable by midnight then eventually SSW 
around 5 kts by 12z. Have VCSH mentioned at all sites headed
into Saturday morning. 


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




NEAR TERM...Lahiff/Neiles