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  Tuesday August 20, 2019

 

NWS Area Forecast Discussion


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000
FXUS61 KBTV 200501
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
101 AM EDT Tue Aug 20 2019

.SYNOPSIS...
A weak cold front crossing the North Country this afternoon and
evening will lead to clearing skies overnight and a reduction
in humidity levels for Tuesday. High pressure and the drier air
mass will lead to sunny conditions Tuesday with highs in the low
to mid 80s across the region. The next frontal system brings
scattered daytime showers and thunderstorms to the region on
Wednesday, followed by drier and noticeably cooler conditions
for late in the week.

&&

.NEAR TERM /UNTIL 2 PM THIS AFTERNOON/...
As of 1256 AM EDT Tuesday...Sfc cold front is moving across our
the CPV attm with drier and cooler air advecting into the FA.
Have slowed the rate of hourly temps drop based on obs and
delayed fog development due to winds and associated mixing.
Thinking fog develops in climo favored areas btwn 07-08z and
lingers until 12z. Lows generally mid/upper 40s slk to lower 60s
cpv.

Previous Discussion...Modest low to mid-level forcing
associated with mobile mid-level trough crossing nrn NY and VT
this afternoon is resulting in just isold shower/tstm
development over eastern portions of VT. This activity will
quickly move east of the forecast area through 20Z. Surface cold
front across the St. Lawrence Valley will follow this evening,
and generally move through with just a westerly wind shift. The
thermal gradient is rather weak in the sfc-850mb layer.
However, upstream 2-m dewpoints are in the 40s to lower 50s
across southeastern Ontario, and this will be our air mass for
tomorrow.

For the overnight hours, westerly winds 5-10 mph gradually
become light and variable toward midnight as weak surface high
pressure builds ewd from the Great Lakes. Strong drying and
clearing should lead to patchy dense fog development for the
climatologically favored river valleys of central/ern VT and the
valleys of the northern Adirondack region between midnight and
7am. Overnight lows will be somewhat cooler than recent nights.
Looking for lows generally in the 50s, except locally in the
upper 40s across the normally cooler spots within the northern
Adirondacks.

Tuesday will be a virtually cloudless day with sfc dewpoints
falling into the low-mid 50s. Daytime highs generally 80-85F
with PoPs NIL. Tuesday night will begin quiet. However,
combination of weak 850mb WAA and increasingly cyclonic flow
aloft should result in increasing mid-level clouds, and just a
slight chance of a shower or sprinkles toward daybreak Wednesday
across nrn NY into s-central VT. The higher precipitation
chances should hold off until later in the day Wednesday. With
increasing clouds, lows Tuesday night will remain a bit warmer,
generally 58-64F.

&&

.SHORT TERM /2 PM THIS AFTERNOON THROUGH WEDNESDAY NIGHT/...
As of 351 AM EDT Monday...The atmosphere will become more moist
and unstable Wednesday as deep southwesterly flow increases
ahead of an upstream upper-level trough and developing surface
low. The BTV forecast area will remain within the warm sector of
the cyclone during the day Wednesday, so another warm and muggy
day on tap for midweek. Precipitable water values increase to
1.5-1.75 inches Wednesday night and surface temperatures will be
in the low 80s. Amid the rising instability as the day goes on
(pockets of 1500+ J/kg MLCAPE per model forecast soundings),
models indicating a compact upper-level wave moving through
during peak heating hours. This wave, along with a pre-frontal
surface trough, will support the development of afternoon
showers and thunderstorms. Thunderstorm threat will be somewhat
conditional, based on the evolution of clouds after a warm
frontal passage earlier in the morning...but if we get enough
clearing the potential is certainly there for some embedded
thunderstorms. Best 0-6 km shear will be removed to the
northwest, but progged values 20 to 30 kts would support some
organized convection. Locally heavy rainers and gusty winds
would be the primary threat associated with any storms.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
As of 351 AM EDT Monday...A cold front will sweep through the
region Thursday, leading to a cooling trend for much of the long
term. The frontal passage itself looks to be fairly uneventful
given the lack of moisture as the boundary moves through, but do
expect some scattered light showers during the day Thursday.
High temperatures Thursday will depend on frontal timing, with
cooler highs expected in the northern forecast area and warmer
high expected further south. After the front clears the area, a
period of mainly dry weather is forecast through the weekend
with high pressure building in. Temperatures will be noticeably
cooler than the first part of the week, with highs generally in
the 70s and low humidity expected.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
Through 06Z Wednesday...Aviation challenge will be timing of
fog/br development as low level cold air advection continues
across our taf sites. Thinking bl will decouple in the next 1 to
2 hours, with cross over values being reached, helping in the
development of fog at slk/mpv btwn 07-08z. Still some concerns
on areal coverage as Whiteface is gusting to 36 knots and
soundings show 15 to 25 knots of wind around 500 feet agl, which
is expected to decrease quickly after 06z. Otherwise, expecting
lifr/vlifr at slk/mpv from 08-12z, with maybe a brief period of
mvfr/ifr at mss/pbg and btv around sunrise. Fog lifts with vfr
and light winds on Tues.

Outlook...

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

&&

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

&&

$$
SYNOPSIS...Banacos
NEAR TERM...Banacos/Taber
SHORT TERM...Duell
LONG TERM...Duell
AVIATION...Taber


 
 
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