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  Wednesday December 13, 2017

 

NWS Area Forecast Discussion


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000
FXUS61 KBTV 101151
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
651 AM EST Sun Dec 10 2017

.SYNOPSIS...
A weak trough of low pressure will move across the area today
and bring snow showers to much of the region. Tonight lake
effect snow from Lake Ontario will move across parts of the
region 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/...
As of 617 AM EST Sunday...Area of light snow has flared up in
the vicinity of Lake Champlain this morning with activity
expected to hold together through mid-morning as it moves only
slowly eastward. Have updated forecast to account for this
enhanced area of light snow that may put down a dusting to two
inches of snow over parts of northwest Vermont this morning.
Rest of forecast in good shape with upper trough to our west
moving into the region...which will enhance the chances for snow
showers across northern New York as the morning wears on.

Previous Discussion...
Light snow has all but ended across southern and eastern
Vermont early this morning. Much of this area received
accumulating snow...anywhere from 1 to 5 inches. The winter
weather advisory that was in effect for southeast Vermont has
expired. Meanwhile...upstream upper trough is moving eastward
this morning and has been producing some light snow across
southeast Ontario and southwest Quebec Provinces. As this system
moves east we should see the potential for snow showers
increase across northern New York as the morning wears on and
eventually across the northern half of Vermont during the
afternoon. Any snow accumulations should generally be less than
an inch. With the trough moving across the region today...the
flow aloft will be more westerly and this will keep lake effect
snow from Lake Ontario to our south. However...tonight the flow
backs to the southwest and the lake band will move back up into
our area. Once again the southern portions of Saint Lawrence and
Franklin counties of New York will have the best potential for
some light snow accumulations. Some of the lake effect should
make it further downstream across the Champlain Valley and
northern portions of Vermont later tonight. Feature weakens late
tonight and flow becomes more westerly which will help bring an
end to any snow showers by mid-morning on Monday with dry
weather expected over the entire area Monday afternoon. High
temperatures today will be in the upper 20s to mid 30s and then
in the 20s to lower 30s on Monday.

&&

.SHORT TERM /MONDAY NIGHT THROUGH 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 /12Z SUNDAY THROUGH THURSDAY/...
Through 12Z Monday...Generally looking at VFR and MVFR
conditions through the period. Some brief MVFR/IFR conditions
will exist at KBTV and KRUT through 13z as a band of light snow
moves across these areas. Otherwise looking at scattered snow
showers throughout the period which could briefly produce
MVFR/IFR conditions. Light winds this morning but a front is
moving across the area and winds will become more southwest and
west with gusts in the 15 to 20 knot range before gradually
tapering off after 00z.

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

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...None.
NY...None.

&&

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



 
 
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