Area Forecast Discussion
Issued by NWS Burlington, VT

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FXUS61 KBTV 210722
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
222 AM EST Tue Nov 21 2017

.SYNOPSIS...
Light snow will gradually diminish as the night wears on tonight.
Milder but breezy weather is expected for Tuesday with highs in
the 40s to around 50. A cold front will move through the region
late Tuesday night and Wednesday, bringing a few rain and snow
showers. Thanksgiving Day is expected to be dry with temperatures
in the 30s.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
As of 934 PM EST Monday...Quick update to match temperatures to
current conditions...falling a bit in northeast Vermont but
holding steady elsewhere. Should start to see a slow warming
after midnight. Otherwise...the lake effect snow that had been
affecting the area today continues to quickly decrease in areal
coverage with just some lingering light snow showers or flurries
left. No additional accumulations are expected for the remainder
of the night despite still seeing some light snow through about
midnight. Skies will also remain cloudy through midnight based
on satellite...but trends indicate a clearing line across
southern New York that is lifting northeast. This is associated
with the warm front that is lifting northeast as well and the
front should be north of the area by daybreak putting our area
in the warm sector. As a result...we should see temperatures
slowly warming after midnight across much of the area. Going
forecast has this idea handled well. Only tweaks were to sky
cover and precipitation chances to fit the scenario just
described.

Previous Discussion...
Well, still trying to play some catchup with the combo Lakes
Superior/Huron snow band that has moved across northern NY and
now into northern VT. The snowfall intensity and coverage has
ended up being more than even the hi-res models indicated, at
least here locally in the Champlain Valley and along the western
slopes. Given that it`s snow, radar doesn`t detect it very
well, so it wasn`t until it started snowing here in the
Champlain Valley that we could "see" it on radar. Appears that
there was some blocked flow that developed as well. That said,
it appears that using the GOES-16 IR channel has been working
well by using the -25C cloud top temperatures to show where the
best snows are occurring. Over the last hour, the overall trend
has been for cloud tops to start to warm. Although the hi-res
models were doing fairly well earlier this morning, they have
totally missed the snow here in the Champlain Valley and across
the Green Mountains. Have tried to enhance coverage of the snow
above what the models give, but even then, I`m still too low.

Will probably continue to forecast chase the snow band over the
next few hours. However, by this evening, wind flow will turn
more southwest and be disruptive to the bands that are out
there. So as we go on toward midnight, we will only be left with
clouds and a few flurries, especially across northern NY.

Southerly flow strengthens on Tuesday as the pressure gradient
tightens due to high pressure moving off the coast, and our next
weather system moving into the Great Lakes. Model soundings
indicate 35-40 knots of wind between 925-850mb, especially in
the Champlain Valley as topographically forced winds develop.
Won`t mix down all of that to the surface, but it will result in
a breezy day -- likely gusts to 30-35 mph. Southerly winds will
bring in a warmer airmass, with highs well into the 40s across
the region, even around 50F in the Champlain and St Lawrence
Valleys.

Precipitation ahead of a cold front will start moving into
northern NY Tuesday evening, reaching the Champlain Valley by
midnight. Boundary layer temperatures will be warm enough that
it will be all rain, with snow only above 2500-3000 feet. The
actual cold front will be a few hours behind the precipitation.
So in the pre-dawn hours on Wednesday, expecting the rain to
turn into snow showers across most of northern NY, with snow
levels decreasing across Vermont.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY/...
As of 222 AM EST Tuesday...Overall the short term period
continues to look quiet with high pressure cresting over the
region on Thanksgiving day. Variable cloudiness is expected
though with an upper trough exiting the region Wednesday night,
and mid/high clouds increasing Thanksgiving day in advance of
the next system, but we should see some peaks of sun. Temps will
be seasonably cool with lows in the teens/20s and highs ranging
through the 30s.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
As of 222 AM EST Tuesday...While the long term period continues
to look active, there are no really no big systems on the
horizon to speak of. The tail end of a decaying cold front will
bring some scattered snow showers to the region Thursday night
into Friday morning, followed by brief high pressure for the
remainder of Friday into early Friday night. The weekend
continues to look unsettled, but the latest trends are for one
area of low pressure to track well north of the region, and
another well offshore on Saturday, both delivering limited
impacts to the northeast. The best chance for precipitation
actually now appears to be post-frontal passage Saturday
afternoon/night and through the weekend where upslope flow will
enhance snow shower activity across the higher elevations. It
will be noticeably warmer for Friday and Saturday though with
deep southwesterly flow developing aloft. Highs should bump into
the 30s/40s before falling back into the 20s/30s for
Sunday/Monday as the upper trough settles overhead.

&&

.AVIATION /08Z TUESDAY THROUGH SATURDAY/...
Through 00z Wednesday...Areal coverage of light snow continues
to decrease across the area this evening and this trend will
continue as the night wears on. Thus visibilities should
generally be VFR for most of the period...with some brief MVFR
visibilities through about 04z in any light snow showers.
Extensive area of clouds persists over the area and ceilings are
generally MVFR and VFR. Ceilings should persist through about
08z before clouds lift north of the area as a warm front moves
north into Canada. Little in the way of cloud cover is expected
from 12z onward. Winds will generally be light and variable
until the warm front lifts north of the area and between 10z and
12z winds will start to increase from the south and southwest.
After 15z winds will strengthen with gusts in the 15 to 25 knot
range for the remainder of the period. Gusts to 30 knots will be
possible at KBTV.

Outlook...

Tuesday Night: Mainly VFR, with local MVFR possible. Chance SHRA,
Chance SHSN.
Wednesday: Mainly VFR, with local MVFR possible. Chance SHRA,
Slight chance SHSN.
Wednesday Night: Mainly VFR, with local MVFR possible. NO SIG WX.
Thanksgiving Day: Mainly VFR, with local MVFR possible. NO SIG
WX.
Thursday Night: Mainly VFR, with areas MVFR possible. Chance
SHSN.
Friday: Mainly VFR, with areas MVFR possible. Slight chance SHSN.
Friday Night: Mainly VFR, with local MVFR possible. Chance SHSN.
Saturday: Mainly VFR, with areas MVFR possible. Likely SHRA,
Likely SHSN.

&&

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

&&

$$
SYNOPSIS...Nash
NEAR TERM...Evenson/Nash
SHORT TERM...Lahiff
LONG TERM...Lahiff
AVIATION...Evenson



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