904
FXUS61 KBTV 141738
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
138 PM EDT Wed Aug 14 2024

.SYNOPSIS...
An isolated shower with areas of fog will dissipate by mid morning
before additional widely scattered showers with embedded rumbles of
thunder redevelop this afternoon and continue into the overnight
hours. The areal coverage of precipitation will be limited today and
again on Thursday with the highest potential in the mountains, but
localized heavy downpours are possible. Temperatures warm into the
upper 70s to mid 80s both days with lows in the mid 50s to mid
60s. Friday is looking dry and mild with temperatures in the
80s, before more showers and thunderstorms are possible for the
upcoming weekend.

&&

.NEAR TERM /THROUGH THURSDAY NIGHT/...
As of 123 PM EDT Wednesday...Instability continues to increase
into early afternoon over our forecast area. Cumulus clouds have
grown increasingly agitated over the northern Adirondacks, and
have seen some popcorn showers pop up with a brief embedded
thunderstorm or two. Latest SPC Mesoanalysis has 2000+ J/kg CAPE
analyzed over much of northern NY, with slightly lower amounts
further east into Vermont. Deep moisture is still rather limited
as per latest RAP soundings, showing deep dry layer above 700 mb
which will limited overall coverage and depth of showers.
Nonetheless, a lot of instability to work with and slight
increase of moisture going into this evening...so will watch
showers and thunderstorms closely. Any thunderstorms that
develop have the potential for some briefly gusty winds/small
hail. Previous discussion follows...

Water vapor shows weak s/w moving acrs the SLV attm with pocket
of mid level moisture/instability that has helped to fire off a
few showers with even an embedded lightning strike or two.
Edwards mesonet site measured a quick 0.31" in a brief shower.
So have bumped pops into the 10-20% range to cover the isolated
activity over northern NY thru early this morning. In addition,
areas of patchy fog should lift by 9 AM.

The forecast challenge this aftn into the overnight hours is the
areal coverage of showers/storms associated with northerly flow
aloft. CAM guidance continues to highlight the eastern Dacks for
scattered activity this aftn after 18z with some potential acrs
northern VT, including the NEK toward 00z. Soundings show a rather
deep dry layer in place from 850 to 300mb, which wl limit areal
coverage of precip to 15-30%, but slow storm motions of <15 knots
could result in some isolated pockets of heavier rainfall
footprints. The eastern Dacks wl need to be watched closely for this
potential. The probability of svr is minimal today given 0-6km shear
<20 knots, but CAPE profiles of 1200 to 1800 J/kg does suggest some
robust convective updrafts are possible. Progged 925mb temps are a
degree or two warmer today, so thinking upper 70s to mid 80s.

For tonight have continued a 15-25% pop for most of the overnight
hours, as soundings continue to support instability with CAPE values
of 800-1200 J/kg. In addition, RAP and NAM both indicate better s/w
energy arriving aft 06z, especially northern/eastern VT, so this
forcing and instability results in some potential for
showers/storms. Generally movement from north to south. Once again
fog potential is challenging with clouds, but bl flow is weak and
moisture should increase aft sunset, so thinking climo favored areas
look likely for some fog development after midnight.

Little change in the upper lvl pattern as mid/upper lvl trof remains
anchored to our east, resulting in northerly flow with embedded
s/w`s. Slightly better moisture/instability and dynamics are present
on Thursday btwn 14-18z, especially northern/eastern VT, so have
kept pops in the high chc range with less coverage in the SLV. Deep
layer shear is once again <20 knots, so not looking at organized
convection, but with CAPE values approaching 2000 J/kg a few
stronger updrafts are likely, that could be capable of localized
wind gusts to 40 mph, small hail, and frequent cloud to ground
lightning. The cold pool aloft is still lingering acrs our
central/eastern VT zones on Thurs, where progged 500mb temps are in
the -16C to -17C, and hail CAPE of 700 J/kg, so thinking small hail
is definitely possible in the stronger convective elements. Temps
very similar to Weds with highs upper 70s to mid 80s.

&&

.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
As of 355 AM EDT Wednesday...A narrow upper level ridge will crest
over our region Friday morning and slide to our east through the
rest of the day. At the same time, surface high pressure centered to
our east will drift further northeast as a low pressure advances
into the western Great Lakes through Friday night where it will slow
to a crawl.

Following another night with perhaps a few showers and river valley
fog, expect seasonably warm and humid conditions to develop Friday.
Expect this heat to mainly impact outdoor workers and exercise. Wet
bulb globe temperatures (WBGT) may peak as high as the extreme level
in portions of the northern Champlain Valley during the afternoon,
tied to light winds and sunshine combining with temperatures in the
mid 80s and dew points in the low to mid 60s.

As the aforementioned low pressure area moves towards us Thursday
night, so too will the associated trough. The combination of
increasing upper level diffluence and moderately strong isentropic
lift will bring increasing chances of showers. With dry air aloft,
the low level moisture advection sweeping northeastward through the
North Country and northern Vermont may only result in rainfall
primarily in our western areas through daybreak Saturday. And even
in those areas at this time there are mixed signals on the degree of
moisture and instability, which is probably a timing difference more
than anything else. Forecast soundings show elevated instability
amidst deep warm cloud depths that could support some downpours. As
such, a faster scenario would yield more rainfall than forecast, and
a slower one could result in little or no rainfall through this
period.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
As of 355 AM EDT Wednesday...The long term period continues to look
rather wet, with rain likely at times each day. The latest multi-
model blend did trend towards slightly less rainfall based on
probabilistic data including 72 hour precipitation median, 90th
percentile, and probability of exceeding 2 inches of rainfall. That
being said, as we have seen numerous times this summer, convective
weather and anomalous precipitable water can combine for locally
excessive rainfall regardless of large scale rainfall forecasts. So
we will closely monitor the potential for heavy rain.

Overall, ingredients for convection look higher in northern New York
than Vermont over the weekend, then on Monday instability will
probably increase farther east. As such, the current forecast shows
chances of thunderstorms each day with the exception of portions of
eastern and/or northeastern Vermont on Saturday and Sunday. One
question will be how the depth of moisture will look, which could be
a limiting factor on rainfall rates. All forecast scenarios show
high relative humidity and southerly/south-southwesterly flow at 850
millibars, and somewhat drier southwesterly flow at 700 millibars,
through the weekend. The associated 500 millibar moisture shows a
lot more variability. Generally, without deep convection, we would
not expect excessive rainfall over the weekend. Again, convective
chances may increase Monday and/or Tuesday associated with a frontal
passage or potential pre-frontal trough. That will be something to
monitor as we move forward, along with the return of cooler and
drier air next week.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
Through 18Z Thursday...Some scattered showers will develop
between 18Z and 21Z, persisting into the evening and overnight
hours through 06Z. A few embedded thunderstorms are possible as
upper-level shortwave energy drops southward through our
forecast area. At this time, coverage is expected to be
scattered enough that have elected to keep mention of showers
out of most TAF sites, though will update if coverage begins to
increase. Any showers that go over a terminal will bring a brief
visibility reduction, and any thunderstorms have the possibility
for gusty winds/small hail. Otherwise, conditions will remain
VFR this evening into early overnight, with main aviation hazard
again being the formation of nocturnal dense valley fog in the
climatologically favored valleys. This is mainly expected to
impact KMPV, KSLK and KEFK between 07Z and 13Z with IFR/LIFR
visibilities and ceilings. After 13Z, widespread VFR conditions
are forecast through 18Z.

Outlook...

Thursday Night: VFR. Patchy BR.
Friday: VFR. NO SIG WX.
Friday Night: VFR. Slight chance SHRA.
Saturday: Mainly VFR, with local MVFR possible. Chance SHRA,
Slight chance TSRA.
Saturday Night: Mainly VFR, with areas MVFR possible. Likely
SHRA, Slight chance TSRA.
Sunday: Mainly MVFR, with local IFR possible. Likely SHRA, Slight
chance TSRA.
Sunday Night: Mainly MVFR, with areas IFR possible. Chance SHRA.
Monday: Mainly MVFR, with areas IFR possible. Likely SHRA, Slight
chance TSRA.

&&

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

&&

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