Area Forecast Discussion
Issued by NWS Burlington, VT

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975
FXUS61 KBTV 160358
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
1158 PM EDT Thu Aug 15 2019

.SYNOPSIS...
High pressure centered across southern Quebec will translate
eastward this evening, allowing a warm front and increasing
moisture to stream northeastward from western New York and
Pennsylvania. Periods of showers and a few embedded
thunderstorms are expected after midnight tonight. With more
humid air in place, additional chances for showers and a few
thunderstorms exist for Friday and over the weekend. Valley high
temperatures are generally expected in the 75 to 80 degree range
for both Friday and Saturday, and then moderating well into the
80s for early next week.

&&

.NEAR TERM /UNTIL 6 PM FRIDAY EVENING/...
As of 1154 PM EDT Thursday...Have adjusted pops to match crnt
radar trends, which is to expand cat pops faster north into
northern NY and central VT by 04z and into most of our cwa by
06z. Band of waa lift/moisture and associated elevated
instability continues to produce a ribbon of moderate to
occasional rain with embedded thunder across central/northern
NY into southern VT. Given short wave energy and available
moisture, this 2 to 4 hour window of precip should hold together
as it lift across our cwa late tonight into early Friday
morning. Also, ended back edge of precip quicker based on radar
trends and bumped temps up by 2 to 4 degrees.

Previous Discussion... Tranquil weather conditions through this
evening as surface anticyclone across southern Quebec remains
our controlling weather feature, along with low PBL dewpoints in
the upper 40s to lower 50s. Conditions will begin to change
overnight as developing warm front near the PA/NY line begins to
shift newd as surface high departs to the north and east. Have
noted scattered convective storms across the wrn half of PA this
afternoon, and air mass is much more moist south of the frontal
zone (sfc dewpoints in the mid-upper 60s and PW values 1.2 to
1.4" per RAP-based SPC mesoanalysis). Appears the North Country
will get into better 900-800mb warm advection by midnight as
850mb sswly flow increases to around 20kts. After a mostly clear
evening period, isentropic ascent leads to increasing clouds
and developing showers across the northern Adirondacks by 05Z or
so, and eventually overspreading central and northern VT during
the pre- dawn hours Friday. The 12Z NAM forecast soundings
indicate elevated CAPE values of 400-800 J/kg, and anticipate a
few rumbles of thunder associated with embedded convective
elements. Increased PoPs (80-90%) as well as rainfall
amts...with generally 0.25-0.40" rainfall expected across the
northern half of the forecast area. With best moisture and
temperature advection focused north and west, lower PoPs
(40-50%) and rainfall amounts for s-central VT tonight. Lastly,
with developing light sely flow east of the Greens, appears
we`ll see some modified maritime air move into eastern VT toward
daybreak. This should result in abundant low clouds continuing
into Friday morning. Overnight lows generally in the upper 50s
to lower 60s areawide.

Best low-level WAA moves out early Friday morning, and should
generally see showers ending/moving newd out of VT during the
early morning hours. Will see two different air masses in place
on Friday, with low-level sely flow maintaining low cloudiness
longer across the eastern half of VT. From the Champlain Valley
wwd, dewpoints should rise into the low-mid 60s in S-SSWLY
airstream across the region. This will also lead to potential
additional convective development Friday afternoon into Friday
evening. Kept highest chances for thunderstorms across northern
NY, with a slight chance of thunderstorms into the Champlain
Valley. Deep-layer shear reaches 35-40kts Friday afternoon, but
modest CAPE (500-1000 J/kg) will likely preclude any severe
storms. A few stronger cells with gusty winds will be possible -
mainly across nrn NY - mid to late afternoon on Friday. Appears
air mass won`t destabilize east of the Green Mtns with modified
maritime air mass in place. Temperatures should reach the
75-80F range for afternoon highs, with moderate humidity levels.

On Friday night, cyclonic mid-level wswly flow regime remains in
place, and may see some additional scattered shower activity.
Kept PoPs 30-40 percent across the region. Variable cloudiness
and winds south 5-10 mph should keep temperatures a bit warmer
as well, with overnight lows 60-65F.

&&

.SHORT TERM /6 PM FRIDAY EVENING THROUGH SATURDAY NIGHT/...
As of 238 PM EDT Thursday...A dry pocket of air between systems
will start Saturday morning before moisture will steadily
increase ahead of another shortwave in the train of weak upper
systems to lift across the North Country. Diurnally driven
instability will likely develop as temperatures warm into the
upper 70s to lower 80s with good synoptic driven support
indicated by a veering wind profile with height, a semi-coupled
jet streak, and a weakly negative-tilt trough. Destabilization
should not be too strong though, given time of day for Northern
New York, and then the slight easterly component to the low-
level flow keeping a more maritime air mass in place for
Vermont. Additionally, height falls will be minimal and model
soundings indicate a warm layer should exist around 800-700 hPa.
Thus, the threat for stronger storms will be minimal, but a few
that break the unfavorable thermodynamic conditions will
experience 0-6km shear of 35-40 knots, which could allow them to
produce gusty winds. Convection will likely develop off terrain
in the Adirondacks and propagate east into Vermont.

Weak upper ridging builds in Saturday night, so precip chances
should quickly end as instability decreases past sunset. Southerly
flow and a pocket of very moist air advecting into the region will
prevent most areas from falling below 60 for overnight lows.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
As of 238 PM EDT Thursday...The North Country will still be
aboard the shortwave express heading into next week, which means
several weak systems will periodically bring increased chances
for rain. We will also be looking at a substantial warm up as
925 hPa temps push upwards to 20-22 C. A few 90s will be
possible on Monday.

Forecast models are starting to come into something resembling
agreement for next week, but consistency of finer details are a bit
lacking. A shortwave passes through just about every day, but
disagreements in variables like location, time of day, moisture
content, and instability means the outcomes differ from model to
model, but the overall picture looks similar. By Wednesday, a
surface low should deepen in the vicinity of the North Country
as a sharp upper trough/closed low digs southward into Quebec.
Forecast models have not displayed great consistency with this
feature yet. For now, a blended approach seems reasonable. A
cooling trend can be expected after Wednesday at least.

&&

.AVIATION /04Z FRIDAY THROUGH TUESDAY/...
Through 00z Saturday...Areal coverage of showers and isolated
thunderstorms will continue to increase as it expands northeast
into the region later tonight and especially during the
overnight hours. This will take conditions from VFR to MVFR
between 05z and 12z and the precipitation moves across the area.
The wave of precipitation will lift northeast of the area after
12z and while visibilities return to VFR...ceilings will be in
the VFR and MVFR categories. After 18z expect scattered showers
and storms to redevelop over the area with a mix of VFR and MVFR
conditions. Winds will generally be under 10 knots through the
period.

Outlook...

Friday Night: VFR. Chance SHRA, Slight chance TSRA.
Saturday: Mainly VFR, with areas MVFR possible. Chance SHRA,
Chance TSRA.
Saturday Night: Mainly VFR, with local IFR possible. Chance SHRA,
Chance TSRA.
Sunday: Mainly VFR, with local IFR possible. Chance SHRA, Chance
TSRA.
Sunday Night: VFR. Chance SHRA.
Monday: Mainly VFR, with local MVFR possible. Chance SHRA, Slight
chance TSRA.
Monday Night: VFR. Chance SHRA.
Tuesday: VFR. Chance SHRA.

&&

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

&&

$$
SYNOPSIS...Banacos
NEAR TERM...Banacos/Taber
SHORT TERM...Haynes
LONG TERM...Haynes
AVIATION...Banacos/Evenson



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