-- Discussion containing changed information from previous version are highlighted. --
219
FXUS61 KBTV 220811
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
411 AM EDT Wed May 22 2024

.SYNOPSIS...
-- Changed Discussion --
Hot and moderately humid conditions are expected across the
North Country today. High temperatures may reach 90 degrees in
a few valley locations. Isolated thunderstorms are possible this
afternoon, some of which could be strong to locally severe.
Another round of scattered thunderstorms is possible tonight
into Thursday in association with a cold front approaching from
west. Cooler and drier conditions return on Friday into the
holiday weekend, although temperatures remain above seasonal
averages for late May.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH THURSDAY/...
-- Changed Discussion --
As of 408 AM EDT Wednesday...Areas of fog have developed as winds go
calm at the surface and there remains plenty of moisture in the
boundary layer from the showers and thunderstorms yesterday
afternoon into evening. As a result, areas of patchy fog has
developed in the typically climatologically favored valley and
sheltered locales. Otherwise, the rest of the overnight into pre
dawn hours will feature mainly quiet albeit muggy conditions.
Temperatures generally remain in the 60s.

Brief ridging builds in during the day today, so most locations
should stay dry during the morning into early afternoon hours. This
would also allow temperatures to warm into the mid 80s to low 90s,
with similar heat index values. While the forecast apparent
temperatures fall shy of Heat Advisory criteria (95F or higher for 2
or more hours), we will continue to message the heat risk impacts,
particularly for sensitive groups and those without access to
cooling means due to the lack of acclimatization this early in the
season.

Showers and thunderstorm chances do increase by later this
afternoon, mainly after 3 PM with some latest hi-res guidance even
showing convection delayed till early evening. The one kink in the
forecast is the potential for thunderstorms to develop here in the
Champlain Valley, as early as early afternoon off the lake breeze
boundary. The water temperatures are still near 60 degrees, and with
925mb temperatures reaching +23 to +26C on a southwesterly flow,
some of the hi-res guidance does suggest thunderstorm initiation off
the lake. Storms that do form could be strong or even locally
severe, with forecast soundings showing decent mid-level lapse rates
of 6.5 to 7C/km and up to 1000 J/kg of downdraft CAPE. The main
limiting factor appears to be the unimpressive shear of 15-20 kt,
but that could be compensated by the steep low-level lapse rates and
1500 to 2000 J/kg of surface based CAPE. Boaters and folks planning
on recreating on or near the waters of Lake Champlain should pay
close attention to the latest forecast and have multiple ways to
receive real-time alerts.

The more potent pre-frontal trough crosses the region very late
Wednesday afternoon into the early overnight hours. For this main
round of thunderstorms, the best chance for a few stronger to
locally severe storms would be across the St Lawrence valley and
perhaps as far east as the Adirondacks. This is where the best
overlap of 500-1000 J/kg of CAPE and 20-25 kt of shear occurs.
Further east, it will be a race against time with sunset so thinking
that the second round of thunderstorms that come through later in
the evening into the early overnight hours should be sub severe for
the Champlain valley and points east.

Overall, the latest Day 1 SPC convective outlook now has marginal
risk (level 1 of 5) all the way to the Champlain Valley, which seem
reasonable given the aforementioned lake breeze trigger, strong
daytime heating balancing the overall weak shear and unimpressive
forcing. PWATs are in the 1.2 to 1.4 inches range, which is in the
90th percentile according to the SPC sounding climatology for the
Albany, NY upper air site. While locally heavy downpours are
possible with any storm that develop, flooding threat is low given
the overall fast moving nature. Temperatures wise, southerly flow
means overnight lows will generally be in the mid to upper 60s, with
similar dew points making for a rather muggy night. Winds gusting 15
to 25 mph at times would help it feel more tolerable.

Surface cold front comes through on Thursday with height falls and
temperatures aloft falling during the day from west to east. Dew
points should fall rather quickly into the 40s and 50s by the
morning hours across northern NY, but could stay near 60 across
Vermont. As such, the best chance for decent shear to overlap with
surface-based instability is east of our CWA on Thursday afternoon.
This is reflected in SPC`s Day 2 convective outlook, which has the
marginal severe risk south and east of our CWA. At this time, while
a few stronger storms are possible, they should stay mainly below
severe criteria. Temperatures wise, best probability of low to mid
80s would be across Vermont, with cooler temperatures in the low to
mid 70s across northern NY.
-- End Changed Discussion --

&&

.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY/...
-- Changed Discussion --
As of 408 AM EDT Wednesday...The longwave trough will be tracking
across eastern Canada with the North Country in between waves
Thursday night and Friday. This will keep conditions dry with
clearer skies under relative high pressure. As such, Friday could be
marginally warmer, a degree or so, than Thursday with highs in the
mid/upper 70s to around 80 before a mostly dry cold front can drop
out of southern Canada late Friday afternoon and begin cooling in
earnest.
-- End Changed Discussion --

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
-- Changed Discussion --
As of 408 AM EDT Wednesday...Models favor keeping the position of the
longwave over eastern Canada and at times the Great Lakes/North
Country regions as well. This position will favor cooling
temperatures after a relative neutral advection day on Saturday
where highs will continue to be unseasonably warm in the mid/upper
70s to 80 degrees. With troughing over portions of the Northeast,
the storm track will shift back to the vicinity of the northern New
York and Vermont. Shower chances will increase Saturday through mid
week mainly due to brush by systems associated with lifting energy.
However, some models are beginning to shift the axis of the longwave
eastward Tuesday into Wednesday next week which would promote a
deepening longwave and stronger fetch out of the Mid Atlantic. The
could open the door for a full meridional trough towards the latter
half of next week if the pattern evolves as model guidance suggests.
Either way, a marked cooling trend back to seasonal averages is
expected Sunday into next week with probable highs/lows generally
68-75 degrees and lows in the mid 40s to mid 50s.
-- End Changed Discussion --

&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
Through 06Z Thursday...Thunderstorms have ended across the
region, with VFR conditions to prevail through the remainder of
the TAF period. The exception will be some localized MVFR
visibilities in patchy fog 09-12z, mainly at KMPV. Winds
generally light south- southwest today at 5 to 10 kt. Convection
wise, there could be a stray shower or thunderstorm this
afternoon but it is hard to pin point the precise impacts on any
terminal. After Thursday 00z, there is the increased chance for
more widespread showers and thunderstorms but TAF categories are
generally expected to stay VFR except for locally MVFR
conditions.

Outlook...

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

&&

.CLIMATE...
Record High Temperatures:

May 22:
KBTV: 93/1977
KMPV: 90/1994
KMSS: 89/1977
KSLK: 91/1911

Record High Minimum Temperatures:

May 22:
KBTV: 70/1911
KPBG: 65/1975
KSLK: 63/1921

May 23:
KPBG: 65/1964

&&

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

&&

$$
SYNOPSIS...Chai
NEAR TERM...Chai
SHORT TERM...Boyd
LONG TERM...Boyd
AVIATION...Chai
CLIMATE...Team BTV