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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KBTV 182004
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
404 PM EDT Fri Aug 18 2017

.SYNOPSIS...
The weekend will feature slightly unsettled weather Saturday and
Saturday night with a few light showers. Sunday will be mostly
sunny, dry and warm. That sunny and warm weather will continue
Monday, allowing for perfect conditions to view the solar
eclipse. Increasing chances for showers and thunderstorms return for
late Tuesday and into Wednesday.

&&

.NEAR TERM /THROUGH SATURDAY NIGHT/...
As of 350 PM EDT Friday...
Now-This Evening: As expected, most of the area has had a lull
in shower activity since mid/late morning (excepting southern
VT). Skies have cleared enough from the Champlain Valley
westward to push temperatures into the lower 80s. Low clouds
have remained stubborn east of the Green Mountains, and
temperatures are only in the mid 60s. With the warmer
temperatures west -- along with some relatively high dewpoints
(upper 60s-lower 70s), we are seeing some pretty significant
surface based instability develop. CAPE values are in excess of
2000J/kg across much of northern NY. However, that moisture is
pretty shallow -- both mid-level and low-level GOES 16 water
vapor imagery shows extremely dry airmass across northern NY.
Precipitable water value observations show this difference as
well -- 1.46" precipitable water currently in Burlington, with
1.10" in Watertown NY. Meanwhile, east of the Green Mtns,
instability is nil, even though moisture is deeper. So the
ingredients for deep/widespread convection are not coming
together all that well. Again, this was expected. End result, we
should still see a few showers/isolated thunderstorm develop
into the evening hours, but they shouldn`t be too much to worry
about. I like how the HRRR models depict this. As such, I`ve
removed the "heavy downpour" enhanced wording that we were
carrying in the forecast. PoPs for the evening are generally in
the 25-35% range.

Tonight: Otherwise it`s going to be a yucky sleeping night if
you don`t have AC. Dewpoints will remain in the mid-upper 60s,
so thats about as cold as it will get and it will feel muggy.
With the high humidity, we may see a light fog/haze develop in
most areas overnight. Perhaps a few patches of denser fog in
eastern Vermont.

Saturday: Another day that will be on the slightly warm and
humid side, but not an uncommon mid-summer day. At upper levels,
there will be a trough off to our west, putting us in deep
southwest flow. However the mid/upper levels will still be
relatively dry, so this will limit the potential for convective
activity. Hi-res models do indicate a few hit or miss (but
mostly miss) showers developing during the day. As such, have
some 20-35% PoPs, highest across the higher terrain of northern
Vermont. High temperatures will be a few degrees above normal,
with upper 70s to lower 80s.

Saturday Night: models all indicate the upper trough will be
passing overhead, and this passage will be accompanied by clouds
and a few light showers. Kept PoPs in the 25-35% range.

&&

.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
As of 350 PM EDT Friday...If you love outdoor summer activities,
Sunday will definately be a day to take advantage of it. Plenty
of sunshine, temperatures in the mid 70s to lower 80s, and most
importantly lower dewpoints -- all thanks to high pressure
ridging and a west/northwest flow bringing in the drier air.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
As of 350 PM EDT Friday...First...ECLIPSE. Partial for
CWA...basically 58-65 percent. Sky conditions looking very
favorable. Patial begins at BTV around 1725 UTC and ends around
1953 UTC according to NASA Eclipse sight.

Zonal flow across area on Monday with surface high south of area,
this will eventually allow for some increased humidity and clouds
but really not til Tuesday. A pretty nice eclipse day with Highs in
the 80s and sunshine.

The next system has been delayed as its awaiting a sharp, deep
shortwave from central Canada to drop across the Northern Plains
Tuesday and then rotate across the Great Lakes Tuesday night and
lift NE into Ontario/Quebec on Wednesday. The timing looking like
more of a Tue ngt-Wed feature. However...surface temps in the M-U80s
with rich dewpoints in the 60s and PWATs approaching 1.75 inches
should produce SFC based CAPES in the 1000-1500 range at least.
Also...despite the main dynamics and surface front still across the
Great Lakes, there are falling heights...diffluent flow aloft and
indications of some pre-fntl trof, thus chance for t-storms will
increase toward evening...esp NY and Intl border. Wind dynamics
don`t look too favorable and timing may just be too late but still
worth watching as they will increase Tue ngt.

Leading, strong shortwave and surface front move through Tue ngt-
midday Wed. By Wed aftn...front should be just east of CWA. Trof
axis still west of CWA Wed ngt-Thu with surface high still west as
well. Therefore, some unstable flow but PWATs fall to around 0.50
inches on Thu. Current thinking is largely mountain upslope
shower/sprinkle. Highs on Thu L-M70s.

Thu ngt-Fri deep trof axis passes area with surface high pressure
building into region thus primarly dry and cooler temperatures.
Highs in U60s-L-M70s. A cool start with lows in the 40s/50s and some
possible upper 30s. Friday ngt-Sat morning should be as cool or
cooler.


&&

.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
Through 18Z Saturday...a mix of conditions across the region,
with VFR across most of northern NY, and MVFR across
eastern/southern Vermont. A few showers are also near RUT as I
type. Trends should be toward VFR, except eastern Vermont where
MVFR ceilings will likely hang on. During the evening we expect
scattered showers to redevelop and move across the region.
However the confidence in exact timing and location are such
that "VCSH" is the best that can be placed into the TAFs right
now. Expect MVFR ceilings to also redevelop across much of the
area, along with at least a "light" (4-6sm) fog. Guidance
suggests that IFR due to visibilities of 1-2sm and ceilings
under 1000ft will develop in locations east of the Green
Mountains (eg: MPV), with some as well across the `Dacks.
Conditions will start to improve after 13z Saturday.

Outlook...

Saturday Night: VFR. Chance SHRA.
Sunday: VFR. NO SIG WX.
Sunday Night: VFR. NO SIG WX.
Monday: VFR. NO SIG WX.
Monday Night: VFR. NO SIG WX.
Tuesday: VFR. Chance SHRA...Slight Chance TSRA.
Tuesday Night: VFR. Chance SHRA...Slight Chance TSRA.
Wednesday: VFR/MVFR. Likely SHRA.

&&

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

&&

$$
SYNOPSIS...Nash
NEAR TERM...Nash
SHORT TERM...Nash
LONG TERM...SLW
AVIATION...Nash