-- Discussion containing changed information from previous version are highlighted. --
831
FXUS61 KBTV 201424
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
1024 AM EDT Thu Jun 20 2024

.SYNOPSIS...
One more day of dangerous heat and humidity expected for today with
highs in the 90s combining with humid conditions to create heat
index values up to 100F. Please continue to take appropriate
precautions to avoid heat stress as heat can have a compounding
effect. Scattered to numerous showers and thunderstorms will develop
again this afternoon into the evening, some of which could become
strong to severe, capable of producing gusty winds, frequent
lightning, heavy downpours, and hail.

&&

.NEAR TERM /THROUGH FRIDAY/...
-- Changed Discussion --
As of 1019 AM EDT Thursday...No significant changes needed with
this update. Forecast area is largely dry ahead of our
anticipated afternoon thunderstorms. Some spots in the Champlain
Valley are a little slow to heat up with Lake Champlain so close
and clouds overhead, but clear sky appears to approach, so no
changes to our highs in the upper 80s to mid 90s with this
update as there is plenty of time for additional warming.
Previous discussion below:

Previous discussion...One last day of oppressive heat and
humidity today as we await the arrival of a cold front. We`re
already starting out quite mild and muggy with temperatures in the
upper 60s to upper 70s while dewpoints generally range from 65 to
75F. We will once again warm well into the 80s and 90s by this
afternoon. However, like the past couple of days, the development of
showers and thunderstorms and associated cloud cover will keep
heating less than optimal periodically through the afternoon. A cold
front will start to cross the region from north to south during the
afternoon as well, also helping to limit heating. Still, expect
highs to range from the upper 80s across the north to the low/mid
90s in central and southern locations. Dewpoints will remain on the
uncomfortable side, so heat index values of 90 to 100F are
anticipated. Therefore, the Heat Advisory still remains in effect
until 8 pm this evening. Please continue to follow the necessary
precautions to avoid heat- related illnesses.

The other main concern for today is the aforementioned showers and
thunderstorms. Like the past couple of days, instability will be
ample due to the hot and muggy conditions; CAPE values of 1800+ J/kg
are expected by this afternoon. As we saw yesterday, it doesn`t take
much to get thunderstorms going once they start to develop, and
today, we actually have a trigger in the form of a cold front which
will move out of Canada and into our northern areas this
afternoon/evening. Also note ongoing convection east of Lake
Ontario, and some CAM guidance indicates this activity could
gradually shift E/NE through the morning hours, spreading into
northern NY and perhaps central VT, though waning as it does so.
Should this occur, it could lessen instability for a bit in those
areas, at least until the atmosphere has some time to recover.
However, it could also serve to lay some outflow or other
boundaries, also helping to trigger additional convection this
afternoon. Indeed, note that while some guidance is showing fairly
cohesive convection firing up ahead of the cold front, there also
looks to be another round potentially developing over portions of
northern NY/VT, possibly from the morning`s convection or perhaps
even just from daytime heating. Either way, expect storms will
become rather robust once they start to develop. Although shear
isn`t all that impressive, generally 25 kt or less at 0-6km, given
the trends from yesterday, wouldn`t be surprised for storms to
become strong to locally severe, capable of producing gusty to
damaging winds and small to marginally severe hail. Moisture is also
very ample; PWATs will approach or even exceed 2 inches. With warm
cloud depths exceeding 12 kft, expect very efficient rainfall
processes. Hence heavy rainfall will be possible with any
thunderstorms today, and can`t totally rule out some localized flash
flooding, especially in areas that see multiple thunderstorms. The
above thinking on storm threats matches well with SPC`s latest Day 1
Convective Outlook, which has areas along/south of a Wanakena NY to
Montpelier VT to Littleton, NH into a Slight Risk; areas north to
the international border are included in a Marginal Risk. Meanwhile,
the Day 2 Excessive Rainfall Outlook from WPC has nearly our entire
area included in the Marginal Risk area, excluding only the St
Lawrence Valley and far northern Adirondacks. Anyone with outdoor
plans today should keep on top of the latest forecasts and remain
weather aware with an eye to the sky. Make sure you have at least 2
reliable methods to receive weather warnings.

Showers and thunderstorms will wane after sunset as we lose daytime
heating and instability lessens. The cold front will push south to
just about the MA/VT/NH border by Friday morning. Unfortunately, the
incoming airmass isn`t much drier than our current one, so overnight
lows will still be a touch uncomfortable, ranging from the upper 50s
to the upper 60s. Patchy fog will be possible by daybreak,
especially in eastern VT valley locations that receive a decent
amount of rain. Friday will see temperatures once again warm to
above seasonal normals, but highs will be some 5 to 10 degrees
cooler than today. Showers and thunderstorms will develop again in
the afternoon, though they will be focused mostly in central and
southern portions of our forecast area, closer to the front. Severe
weather is not anticipated.
-- End Changed Discussion --

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY/...
As of 318 AM EDT Thursday...The cold front will stall just to the
south of the region Friday night. There could be a few showers
across southern Vermont but overall most places will stay dry.
Despite being north of the front, the Canadian high pressure
struggles to gain much influence over the region so while being a
little cooler and drier, it will not be overly refreshing. Lows only
fall back into the 60s. The front will gradually work its way back
north through the region on Saturday, bringing some showers and
possible embedded thunderstorms with it. The instability should
mostly be elevated so there is not much of a severe threat. PWATs
will rise back between 1.5 to 2 inches and some areas of heavy
rainfall are possible. With the slow moving nature of the front,
entraining storms could lead to isolated flash flooding. However,
there will not be much instability and the forcing from the front
looks on the weaker side, so this should keep the threat of flash
flooding more localized. Therefore, the marginal risk ERO from the
WPC seems reasonable.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
As of 318 AM EDT Thursday...The front looks to stall during the day
on Sunday and its exact placement will be key for any flooding or
severe threat. Ensemble guidance has shifted to favoring the front
to stall a little farther north over Quebec. This would allow the
region to get into the warm sector and modest CAPE would be able to
develop. Right now, the GFS/Euro ensembles bring between a 30-60
percent chance of higher than 500 J/Kg across the area, with the
highest values to the south and the lowest values to the north. With
adequate deep layer shear in place, this could lead to the
possibility of a couple severe storms. However, if the front were to
stall over the region, there would likely be a higher flooding
threat and less of a severe threat. Showers and storms look to train
along the front, and with a low approaching from the west, the
synoptic lift looks to increase as the day goes on. Also, PWATs will
continue to be between 1.5 to 2 inches so there will be favorable
conditions for heavy rainfall. The scenario could cause some flash
flooding to occur, particularly since there will have been a decent
amount of previous rainfall. Right now, the WPC has a moderate to
slight ERO for the region due to the threat of the heavy rainfall
and this makes sense. However, if the front continues to trend to
the north, this might need to be downgraded. The low moves through
the region Sunday night into Monday and brings widespread rainfall.
Behind it next week, drier and cooler air gradually filters down
from Canada, but it will take some time for the air to feel
refreshing.   .AVIATION /... Through 18Z Monday...There is a line
of showers and thunderstorms slowly moving eastward across northern
New York. It will likely hold together and pass over MSS and SLK
this morning. Whether it sticks together into PBG and Vermont is
questionable but there will at least be scattered showers and
thunderstorms around during the afternoon. Scattered storms will
develop across northern New York as well in the afternoon, but due
to their hit or miss nature it cannot be definitively determined if
they will hit any of the airports or not. Besides being able to
produce frequent lightning, the showers and storms will briefly
lower visibilities at any terminal they reach to MVFR and possibly
IFR. The storms should dissipate overnight before developing again
tomorrow morning. Patchy fog will likely develop across the region
tonight and there is a decent chance it develops at SLK and MSS.
Winds are generally light and southerly during this period. LLWS is
not a concern.

&&

.AVIATION /14Z THURSDAY THROUGH MONDAY/...
Through 12Z Friday...VFR conditions this morning to trend toward
MVFR in showers and thunderstorms this afternoon. Areal
coverage of showers/storms to increase toward noontime with some
localized strong to severe storms possible. Any storms will
have the potential to produce strong/gusty outflow winds up to
40 mph, frequent cloud to ground lightning and MVFR vis in
heavier rain. The greatest potential will be between 17z and 22z,
with conditions improving toward sunset. Have used VCSH/VCTS
for now, but as confidence in timing improves prevailing groups
and tempos for MVFR cigs/vis will be needed. Another round of
potential fog after 06z Friday, especially in areas that see
rain. Have gone with 3SM in BR with sct IFR deck at
KMPV/KSLK/KEFK.

Outlook...

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

&&

.CLIMATE...
Hot temperatures will result in values near records. Below are
some of the records under threat of being broken.

Record High Temperatures:

June 20:
KBTV: 95/2012 Forecast 92
KMPV: 90/2020 Forecast 90
KPBG: 94/1964 Forecast 88
KMSS: 92/2012 Forecast 88
KSLK: 92/1995 Forecast 86


Record High Minimum Temperatures:

June 20:
KPBG: 70/1953 Forecast 73
KSLK: 68/2012 Forecast 65

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...Heat Advisory until 8 PM EDT this evening for VTZ001>011-
     016>021.
NY...Heat Advisory until 8 PM EDT this evening for NYZ026>031-034-
     035-087.

&&

$$
SYNOPSIS...Hastings
NEAR TERM...Hastings/Storm
SHORT TERM...Myskowski
LONG TERM...Myskowski
AVIATION...Hastings
CLIMATE...Team BTV