Area Forecast Discussion
Issued by NWS Burlington, VT

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FXUS61 KBTV 202310
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
710 PM EDT Tue Oct 20 2020

.SYNOPSIS...
A frontal boundary wavering north to south across the area will
bring rain showers and patchy drizzle to the region through
tomorrow before high pressure and drier weather returns for
Thursday and Friday. Unseasonably warm temperatures persist
through the week as well, with a strong cold front passage
expected for the weekend. After a quiet weather day on Sunday,
active weather returns for next Monday.

&&

.NEAR TERM /THROUGH WEDNESDAY NIGHT/...
As of 710 PM EDT Tuesday...The semi-stationary boundary which
has been waffling across the area for the last several days is
currently located along an axis extending from Albany, NY into
southern VT and NH. Main forecast update was to match forecast
winds with current obs based on the placement on this front with
more northerly winds across VT trending light and variable
overnight as the front recedes back towards the north and west
again. Otherwise, forecast remains in really good shape at this
hour with no other changes needed.

Previous Discussion...Slow moving frontal boundary is
continuing to slides southwards. Better moisture and dynamics
have lifted north and east as upper level vorticity has ejected
northeastwards. Anticipate shower activity to generally wane as
the front slides towards, and then stalls, near Rutland/Windsor
Counties. This will impact overnight lows, with cooler
temperatures in the Northern St. Lawrence where partial clearing
should allow temperatures to fall in the upper 30s. Towards
southern Vermont, generally 50s are expected.

Overnight, the frontal boundary shifts back north. Light showers
are likely, and may be more drizzly in nature. As we head
towards morning, we should see much of Vermont dry out as broad
area of low pressure translates eastwards just north of Ottawa.
Ahead of the attendant cold front, tight pressure gradients
produced between this feature and strong Atlantic ridging will
drive a 50-60 knot LLJ across our forecast area. The good news
is that a 5 C inversion above the surface will need to be eroded
for these winds to reach the surface. Still channeled flow
should result in 20-30 mph, perhaps a few spot 40 mph, gusts
across the Champlain Valley, northern slopes of the Adirondacks.
After the front, a few spots in the St. Lawrence Valley could
also gust. This strong warm advection should make for an
anomalously warm day. Highs in the 60s to near 70 across the
forecast area.

Frontal boundary shifts towards the St. Lawrence Valley just
before noon. Fairly strong elevated instability (likely a result
of the strong inversion driven by southwesterly winds), could
produce a rumble of thunder as a band crosses east into northern
New York. This will shift east towards Vermont late afternoon
and evening, but will begin to weaken as shortwave energy again
lifts well north and east of our forecast area. Between now and
midnight Thursday, we should see an additional 0.10"-0.25"
Vermont, with highest amounts likely in the higher terrain, and
additional 0.33"-0.50" in the St. Lawrence and portions of the
Adirondacks. We quickly dry out after midnight Thursday. Low
temperatures will still be elevated as only weak cold advection
expected behind the front.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY/...
As of 237 PM EDT Tuesday...A mild and dry period is expected
Thursday into Friday as deep layer high pressure builds across
the region. Thursday should be the nicest day despite Friday`s
temperatures being warmer, mainly due to a lighter wind regime.
Highs to top out mainly from the upper 50s to mid 60s. On Friday
low to mid level southerly flow amplifies with breezy to windy
conditions expected, especially in the Champlain Valley where
gusts from 30-40 mph seem reasonable per latest forecast
sounding analysis. Highs to top out in the upper 60s to mid 70s
from the Champlain Valley west, and mainly in the lower to mid
60s east where a marine-modified airmass will hang tough.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
As of 237 PM EDT Tuesday...By Friday night a cold front will
march steadily east toward the area with higher threat of
showers arriving after midnight across the western Dacks/SLV.
Lows generally remain mild and in the 50s. Front pushes through
the area on Saturday but with primary dynamics lifting north
into eastern Canada rainfall chances gradually fade over time
with central/southern VT counties remaining largely dry despite
the wind shift. Highs a bit tricky given frontal placement but
looking at mainly low to mid 50s northwest and lower to mid 60s
southeast for now.

High pressure then settles atop the region for Sunday with a return
of fair and dry weather. It should be a pleasant, albeit cool day
with at least partial sunshine and light winds as highs top out in
the 40s to around 50.

Looking further out confidence continues to grow that next Monday
and Tuesday will trend quite wet as several waves of low pressure
ride along Saturday`s old frontal boundary while it lifts slowly
north back into the region.

&&

.AVIATION /23Z TUESDAY THROUGH SUNDAY/...
Through 18Z Wednesday...Frontal boundary continues to impact
aviation conditions. The front is near KBTV and KSLK where IFR
to LIFR conditions currently reside from 400-800ft ceilings and
visibilities between 3SM-5SM. This will slide towards KRUT and
KMPV in the next couple hours. Partial clearing expected behind
the front, with several sites expected to become VFR as it
departs. KRUT and KMPV will likely be the exception and hold
onto 1500-2500 ft ceilings after the front passes south around
22Z-00Z. Winds shifting out of the north behind the front, with
speeds decreasing to 5 knots or less this evening. After 06Z,
the frontal boundary lifts back north, bringing ceilings back
down to 700-2500ft agl and periods of drizzle. Winds becoming
southerly again. Towards 10Z-16Z, strong winds at 2000ft agl
develop over northern New York and much of Vermont, bringing
LLWS at all TAF sites, except KRUT. Towards 16Z, south winds
accelerate to 10 to 15 knots with gusts 20 to 30 knots. Partial
clearing possible, with band of moderate showers, with possible
storms reaching KMSS around 16Z Wednesday, then shifting east.

Outlook...

Wednesday Night: VFR. Chance SHRA.
Thursday: VFR. NO SIG WX.
Thursday Night: VFR. NO SIG WX.
Friday: VFR. Windy with gusts to 30 kt. NO SIG WX.
Friday Night: Mainly VFR, with areas MVFR possible. Chance SHRA.
Saturday: Mainly MVFR, with local IFR possible. Chance SHRA.
Saturday Night: Mainly MVFR, with areas VFR possible. NO SIG WX.
Sunday: Mainly VFR, with local MVFR possible. NO SIG WX.

&&

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

&&

$$
SYNOPSIS...Haynes
NEAR TERM...Haynes/LaRocca
SHORT TERM...JMG
LONG TERM...JMG
AVIATION...Haynes



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