St. Johnsbury, Vermont 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

828
FXUS61 KBTV 210925
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
425 AM EST Thu Nov 21 2024

.SYNOPSIS...
A larger upper level low to our southwest will spawn multiple
low pressure systems that will bring rounds of rain, and
some snow primarily at high elevations, through the weekend.
Precipitation totals will be rather variable, although
eventually all locations will see substantial amounts. Somewhat
unsettled, seasonable weather will follow for the first part of
next week.

&&

.NEAR TERM /THROUGH FRIDAY/...
As of 425 AM EST Thursday...Beneficial rain remains on track,
especially in southern and western portions of the region. No
hazardous weather is expected, aside from some higher elevation
snow accumulations late tonight into tomorrow morning, primarily
in the Adirondacks and southern Greens.

An elongated upper level trough that will continue to spin
towards the southeast today will help intensify a coastal storm
that has been forming near the southern New Jersey coast. This
low pressure system will deepen as it moves northward and also
becomes elongated to the east. This large scale pattern will
draw abundant marine air on its northern flank, which will
continue to flood Vermont and northeastern New York with mild
air such that even the higher elevations look to stay all rain
as bands of rain lift northward. Meanwhile, slightly cooler air
aloft closer to the upper level low will help keep snow levels
lower in the Adirondacks, especially southwestern portions such
as from Newcomb to Star Lake. Rain will mix with wet snow in
this area later today with sloppy accumulations possible
tonight. Mainly just the summits will see substantial snow
through this period.

The aforementioned configuration of the storm system will also
help the low pressure area tend to retrograde tonight as it gets
captured by the upper level low. Steady precipitation will be
slow to expand northward, so much of northern Vermont, and
especially northeastern areas, will see little rain until
tonight. With a strongly east-northeast wind direction aloft and
near the surface, expect significant shadowing/enhancement of
precipitation amounts through this part of the event.
Precipitation areawide will taper off tomorrow morning as a
pronounced dry slot continues to be shown in all modeling.
Before it ends, there are indications of a boundary lifting
northward with colder air aloft pushing into the southern Greens
and a few hours in which wet snow may accumulate.

While temperatures will be above freezing at the surface, some
accumulation may occur which may affect some morning travel,
particularly above 1500 feet elevation. Forecast soundings show
sharp cooling in the low levels, and sufficiently so for a
changeover to snow near and just east of the southern Greens.
Farther north, cooling will tend to lag behind the precipitation
to reduce chances of any snow. Relatively mild air and daytime
mixing will quickly melt any accumulations as Friday generally
looks like a pleasant, seasonable day. Have left in some chances
of showers, but overall the daytime hours look dry.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY/...
As of 425 AM EST Thursday...We continue to see somewhat greater
chances of snow Friday night as another coastal storm develops
east of the previous one and again retrogrades to the west.
Still, there is little cold air to work with and snow levels
generally remain at or above 1500 feet. This time, precipitation
chances are focused farther east where PoPs peak in the 60 to
80% range, although some valley rain and higher elevation snow
could reach back into northern New York. With surface
temperatures still hovering near freezing, again any light
accumulations look to be of the wet kind. The most likely
precipitation amounts look to be only in the 0.1 to 0.3" range
during this period as heavier precipitation is favored farther
north and east. So even as snow becomes prominent, the snow
water equivalent does not suggest much of a snow load on
vegetation to produce utility concerns.

During the day on Saturday, surface low pressure is expected to
have moved into southeastern Canada, setting up a more typical
northwesterly upslope scenario. However, with fairly mild air
aloft and questions as to whether moisture will remain high
enough in the elevated snow growth zone, it is not an efficient
snow producing setup. Have some light mountain snow
accumulations during the day, but this won`t be a snowstorm for
those interested in recreational opportunities. While summit temperatures
will remain near or below freezing, non-summit temperatures
will range through the 30s while valley locations warm into the
lower 40s.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
As of 315 AM EST Thursday...Saturday night into Sunday, the upper low
that will have provided needed rain and some snow will start to lift
northeast with a sub 990mb low in the Canadian maritimes. We should
be in a favorable position for orographic enhanced showers and
perhaps additional precipitation here and there as a decaying upper
low opens up and gets sucked into the broader upper low exiting the
region, which will provide a little extra forcing. By Sunday
evening, vorticity will begin to shift away from the region, and the
process of gradually decreasing moisture will slowly taper mountain
showers to the Northeast Kingdom overnight. Finally, precipitation
should wrap up in the far northern Vermont mountains during the day
on Monday. The air mass behind the departing low is not terribly
cold. So upper 30s to mid 40s during the day and low to mid 30s at
night are expected both Sunday and Monday. Snow could make it as far
down as 700-1000 ft elevation Saturday night and 500-700 ft
elevation Sunday night, though accumulations should mainly be above
1000 feet. Snow levels during the daylight hours on Sunday should
climb to 1500-1800 ft elevation. Last thing of note here is the
breezy winds as surface low pressure deepens in the Canadian
Maritimes. Northwest gusts should climb up to 20 to 30 mph Sunday
afternoon, with some downslope gusts on eastern slopes of the
Adirondacks and southern Greens possibly up to 35 or 40 mph. GFS
forecast soundings suggests this is quite reasonable at this time,
and will monitor as we get closer.

The default ridging behind the upper low is fairly short-lived. An
elongated upper low or open upper trough will slide east Monday
night into Tuesday. With marginal moisture and relatively weak
forcing, it should produce some precipitation, but nothing
substantial. Thickness values are sufficiently cold, but the time of
arrival during the day into the afternoon will result in a lack of
cold air meaning mostly plain rain appears likely. However once the
trough shifts east of the region, cold advection could allow for
some snow to mix in before the system departs.

Beyond that, there`s not much of note after this, but there`s a
lot of small, weak disturbances. It`s possible a few of them
could allow for some scattered shower activity, but we`ll see
what they can muster as they draw closer. There`s mainly slight
chance to chance PoPs far out in the extended favoring the
northern mountains.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
Through 06Z Friday...Maritime air is resulting in pockets of
900-2800 ft agl ceilings, but is at least starting to clear fog
as an occluding front approaches. Ceilings are expected to trend
down across all terminals, but with some variability with
terrain as east to southeast flow increases in the mid-levels
and results in pockets of terrain shadowing for areas like
KRUT/KEFK/KSLK. Precipitation will be very slow to lift
northeast, but some rain could approach KRUT and KMSS about
12z-14z. The front will decay, though, with precipitation
slowing and breaking up before redeveloping after 18z. With
increasing rates, this could reduce visibilities to 3-5SM. Noted
a PROB30 of RASN at KSLK from 22z to 01z Friday. It appears
after 03z, that precipitation could begin to break up again as
winds at 2000 ft agl increase up to 40 to 45 knots, mainly over
southern Vermont. Have noted the LLWS for now at KRUT, but there
could be a trend towards more showery conditions and
intermittent increases in ceilings. Additional showers and winds
expected beyond 06z Friday.

Outlook...

Friday: Mainly VFR, with local MVFR possible. Likely SHRA.
Friday Night: MVFR/IFR conditions possible. Likely SHRA, Chance
SHSN.
Saturday: Mainly MVFR, with areas IFR possible. Likely SHRA.
Saturday Night: Mainly MVFR, with local IFR possible. Chance
SHRA.
Sunday: Mainly MVFR, with areas VFR possible. Chance SHRA, Chance
SHSN.
Sunday Night: Mainly VFR, with areas MVFR possible. Slight chance
SHSN.
Monday: Mainly VFR, with local MVFR possible. Slight chance SHRA.

&&

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

&&

$$
SYNOPSIS...Kutikoff
NEAR TERM...Kutikoff
SHORT TERM...Kutikoff
LONG TERM...Haynes
AVIATION...Haynes