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  Wednesday December 13, 2017

 

NWS Area Forecast Discussion


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000
FXUS61 KBTV 101956
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
256 PM EST Sun Dec 10 2017

.SYNOPSIS...
Lake effect snow from Lake Ontario will move across parts of
the region tonight with minor snow accumulations
possible...mainly over portions of northern New York. Relatively
dry weather is expected on Monday before a low pressure system
moves across the area Tuesday into Wednesday and brings
widespread light to moderate snowfall to the North Country.

&&

.NEAR TERM /THROUGH MONDAY NIGHT/...
As of 255 PM EST Sunday...Isolated to scattered snow
showers will continue for much of the North Country through the
afternoon as an upper trough slides eastward across the area. These
will wind down later this afternoon once the trough shifts to our
east. However, snow chances will quickly ramp up again this evening
as the flow backs more to the southwest behind the departing trough.
This will allow the lake effect snow band to lift back north into
the northern Adirondacks into northern Vermont. In the meantime,
weak low pressure crossing southern Quebec will drag its attendant
cold front through NY and New England in its wake. This boundary
will help serve to focus additional snow shower activity over
northern NY and VT later tonight. Winds will turn west and
eventually northwest behind the front, once again shifting the lake
effect snow back south of our area. Colder and drier air will work
in behind the front as well, bringing the snow showers to an end by
mid morning Monday. All told, expect southern St Lawrence and
Franklin Counties in NY to see the most accumulation, generally 1 to
3 inches with locally higher amounts approaching 4 inches.
Elsewhere, snowfall will be 2 inches or less. Overnight lows will
range from the teens in the north to the lower to mid 20s in the
Champlain Valley and southern VT.

For Monday and Monday night...once the aforementioned front moves
through...again by mid morning or so... expect drier weather to
briefly move in as high pressure quickly skirts across the area.
Highs will be in the 20s, with the coldest readings coming in the
northern mountains. As we head into Monday night, the focus turns to
a clipper system approaching from the west. Precipitation associated
with warm air advection out ahead of this system will spread from
west to east overnight, but with dry air in place at lower levels,
it will take a bit before the snow is able to accumulate. Lows will
be in the teens pretty much areawide.

&&

.SHORT TERM /TUESDAY/...
As of 315 AM EST Sunday...By Monday night into Tuesday a well-
advertised northern stream clipper low will take a favorable
track toward and atop the area with a widespread light snow
event expected. Some surface low re- development of Miller
Type-B character does occur to our east in the Gulf of Maine
through the day on Tuesday. However the majority of the synoptic
forcing for snow in our area will come in two phases, the first
occurring during this period from broad warm advective
processes and upward lift in the mid-levels as the parent low
nears. At this point it appears the primary window for steadier
snowfall will occur from the pre-dawn hours through late-
afternoon on Tuesday before best synoptic lift pushes to our
north and east. Blended 24- 30 hour QPF output, with some
downward adjustment owing to typical warm-advective model bias
suggests totals in the 0.15 to 0.35 range with slight
enhancement possible along eastern slopes of the Greens/Dacks.
Time-averaged snow ratios in the 15-20:1 range support totals
generally ranging from 3-6 inches with local variation which
suggests a potential advisory- level event for favored areas.
Time will tell. Temperatures should be on the seasonably cool
side with lows mainly in the teens and highs on Tuesday from the
mid 20s to lower 30s. Winds light.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 315 AM EST Sunday...Phase two of our prolonged light snow
event then evolves over time by Tuesday night and especially
into Wednesday as secondary low pressure deepens significantly
while tracking into the Maritimes. The parent 700-500mb closed
low tracks atop our area during this period with deeper moisture
returning on evolving gusty northwest flow as pressure gradient
tightens significantly. Areal coverage of light snows/flurries
will have initially tapered off during the first half of Tuesday
night, but as aforementioned features pivot into the area a
general re-blossoming of light snows/snow showers should occur
as we progress into the daylight hours on Wednesday. The best
coverage should occur across favored northern higher terrain and
accompanying western slopes where orographic enhancement will
become increasingly favored. Additional light accumulations in
these areas look likely at this point which will be welcome for
resort areas gearing up for the Christmas Holiday. Temperatures
will trend colder during this period with lows Tuesday night in
the upper single digits to mid teens and corresponding highs on
Wednesday holding nearly steady in the teens with the brisk flow
creating somewhat uncomfortable wind chills in the single
digits.

Thereafter global models suggest the overall large-scale pattern
remains generally unchanged with a western CONUS synoptic ridge and
a corresponding downstream eastern U.S. trough. Weak ripples of
energy moving through the background cyclonic flow aloft will create
near daily chances of snow showers or flurries, with higher
chances during Friday and possibly again by later next weekend.
At least that`s the broad consensus at this point. Temperatures
will remain on the chilly side during Thursday (teens for
highs), though begin a slow moderation process from Friday
onward as core of continental polar airmass lifts gradually
northward.

&&

.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
Through 18Z Monday...VFR/MVFR conditions will prevail at most
sites through 00z Mon, with brief IFR possible in scattered snow
showers. More widespread snow showers will move into the region
after 00z Mon, both from lake effect as well as a weak frontal
boundary sinks south out of Canada. Still expect mainly MVFR
conditions, but IFR will be possible in any snow showers. Snow
showers will come to an end around 12z Mon, and ceilings will
gradually lift to VFR by Mon afternoon.

Outlook...

Monday Night: Mainly VFR, with local MVFR possible. Chance SN.
Tuesday: Mainly MVFR, with local IFR possible. Definite SN.
Tuesday Night: Mainly MVFR, with areas IFR possible. Chance SHSN,
Likely SN.
Wednesday: Mainly MVFR, with areas VFR possible. Chance SHSN.
Wednesday Night: Mainly VFR, with areas MVFR possible. Chance
SHSN.
Thursday: Mainly VFR, with local MVFR possible. NO SIG WX.
Thursday Night: Mainly VFR, with local MVFR possible. Slight
chance SHSN.
Friday: Mainly VFR, with local MVFR possible. Chance SHSN.

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...Winter Storm Watch from late Monday night through late Tuesday
     night for VTZ001>012-016>019.
NY...Winter Storm Watch from late Monday night through late Tuesday
     night for NYZ026>031-034-035-087.

&&

$$
SYNOPSIS...Hastings
NEAR TERM...Hastings
SHORT TERM...JMG
LONG TERM...JMG
AVIATION...Hastings



 
 
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