-- Discussion containing changed information from previous version are highlighted. --
419
FXUS61 KBTV 230239
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
1039 PM EDT Sat Jun 22 2024

.SYNOPSIS...
Numerous strong to severe thunderstorms are expected on Sunday,
particularly during the afternoon into early evening hours. A
few tornadoes are possible along with damaging straight line
winds. Heavy rainfall could also lead to isolated flash
flooding. Next week looks to feature quieter weather and
seasonable temperatures.

&&

.NEAR TERM /THROUGH MONDAY/...
-- Changed Discussion --
As of 1026 PM EDT Saturday...Some rain showers continue across
portions of the forecast area, although they have been pretty
light. Some convection has been ongoing across New York this
evening, although it has been weakening as it moves east.
Overall, minimal changes needed with this update.

Previous Discussion...For the rest of today, the thunderstorm
threat is mainly to our south as we remain in the cool sector with a
stable atmosphere. Not the nicest of weekend days with plenty of
clouds and scattered showers around but it is an improvement from
the recent heat and storms. So other than dodging a few showers or
downpour, with a low chance of a thunderstorm across our southern
zones, the rest of this afternoon into the evening hours look benign
weather wise.

Sunday could look to be the highest end severe weather day that we
have had in North Country so far this year. A warm front lifting
northwards, along with a triple point in the vicinity will lead to
an elevated threat of tornadoes along with damaging winds and heavy
rain. Even taking an ensemble approach to ingredient based
forecasting leads to rather concerning severe weather parameters.
Here is a sampling of the 12z HREF CAM (5 hi-res guidance over 2
time steps) parameters across Addison county, VT for Sunday
afternoon: 2500 J/kg of surface CAPE, 700 J/kg of downdraft CAPE,
600 ft LCL, 800 ft LFC, 100-200 J/kg of 0-3 km SRH, 30-40 units of
bulk shear, and PWATs of 1.9 which is near maximum of SPC sounding
climatology. Between the tornadic, damaging wind and wet microburst
threat, Sunday could be one of the higher end severe weather days in
recent years. With a 10 percent tornado and 30 percent damaging
straight line wind probability, we coordinated with SPC to introduce
a Day 2 Enhanced risk (level 3 of 5) for parts of the area, mainly
across the southern and eastern half of Vermont. This area could be
expanded with future updates so do not pay too much attention to
where the Slight and Enhanced risk areas are delineated. The main
severe storm threat timing is between 11 AM and 8 PM. Having said
that, there could be a round of strong to locally severe storms
during the early morning hours, but the coverage looks to be much
more isolated. There also looks to be a window of 3 to 4 hours of
relatively calm or quiet weather between the early morning hours
disturbance and the more widespread coverage of strong to severe
storms in the afternoon to early evening. Flash flooding threat
looks to be relatively localized given the fast moving nature of the
storms, i.e. less residence time for the heavy rain to cause more
significant flooding issues. Nonetheless, given that PWATs are near
maximum of SPC sounding climatology, poor drainage or street
flooding is certainly possible with any deluge that occurs with the
thunderstorms. Finally, wet microbursts are also a possibility in
addition to the tornadic and damaging straight line wind threat.

As with every forecast, there could always be a wrinkle or a wrench
thrown in. As with warm front or triple point forced severe weather
in the Northeast, the key word is conditional. The early morning
convection could certainly impact the afternoon coverage and
intensity of the storms, but all the parameters currently point to a
higher-end severe outbreak with a few tornadoes possible. Now is the
time to prepare and make sure you have multiple ways of receiving
warnings and severe alerts. The severe threat should wane shortly
after sunset, though there could certainly be a few lingering
stronger or even locally severe storms headed into the evening hours
depending on how quickly the atmosphere recovers with the earlier
convection.
-- End Changed Discussion --

&&

.SHORT TERM /MONDAY NIGHT/...
As of 323 PM EDT Saturday...An upper level low will move overhead or
just north of our forecast area through the day on Monday, which
will result in another showery day. Given the compact nature of
this low, there is still some model spread on the exact timing and
track of the low. The NAM puts the low almost directly overhead
Monday afternoon, which is a favorable setup for scattered to
numerous showers with potentially a few embedded thunderstorms.
However, the GFS/ECMWF move the low through earlier , which would
result in lower coverage of showers/t- storms during the afternoon as
heights build for the second half of the day. Have stayed close to
the National Blend for the forecast for Monday, with seasonably cool
highs in the mid 60s to low 70s under the upper low. Shower chances
will be highest around midday to early afternoon, again depending on
the timing of the low. Have kept PoPs in the 40 to 60 percent range
during the daytime hours. Given surface temperatures only expected
to reach into the upper 60s/mid 70s, instability will be marginal
and thunderstorm coverage is expected to be in the isolated to
widely scattered range.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 323 PM EDT Saturday...Building ridging over the southwestern US
with broad troughing over northeastern Canada will keep our forecast
area within a progressive and relatively active northwesterly flow
regime for next week.

For Tuesday, upper-level low will have departed to the east and
brief ridging will build in. If you`re looking for the driest day
coming up, Tuesday is your day. Highs will be in the low to mid 80s
with plenty of sunshine. Dewpoints in the 50s won`t feel overly
oppressive, but it will be a warm summer day. Within the progressive
flow, the next system quickly moves in from the northwest bringing
renewed rain and thunderstorm chances for Wednesday. For
Wednesday`s system, instability looks to be quite high (1500+ J/kg),
with 40+ knots of 0-6 km Bulk Shear. Thus, the ingredients are
lining up for some severe weather Wednesday, and we`ll certainly be
this system closely over the next few days. Once Wednesday`s
systems clears the area, the remainder of the week will generally be
dry before the next system arrives over the weekend. Temperatures in
the longterm will hover fairly near seasonable levels, with highs in
the 70s/80s and lows in the 50s/60s.

&&

.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
Through 18Z Sunday...A warm front will slowly pass through the
region today and into tonight, bringing showers and low
ceilings. A few of the showers will likely be heavy enough to
briefly lower visibilities to MVFR. Plenty of low-level
moisture remains trapped in place, so the clouds will be much
more stubborn than typical during the day. All terminals are
forecast to be out of IFR by around noon but it looks unlikely
that any of the terminals will improve to VFR conditions that
are not already there. Ceilings should fall back tonight and low
MVFR and IFR conditions look to develop at many of the
terminals again. Patchy fog will probably develop again as well.
It will take until tomorrow morning for the front to push to
the north and have southerly flow clear out the low clouds and
fog. However, a low-level jet will pass overhead and cause LLWS
to develop at all the terminals. Winds at the surface will
generally be light during the period though they will begin to
increase tomorrow morning. Then towards the end of the TAF
period, especially after 15z Sunday, there is increasing potential
for widespread thunderstorms, some of which could be severe
producing damaging wind gusts.

Outlook...

Sunday: Mainly VFR, with local IFR possible. Definite SHRA,
Chance TSRA.
Sunday Night: Mainly MVFR, with local IFR possible. Chance SHRA,
Chance TSRA.
Monday: MVFR/IFR conditions possible. Chance SHRA.
Monday Night: VFR. Chance SHRA.
Tuesday: VFR. NO SIG WX.
Tuesday Night: VFR. Chance SHRA.
Wednesday: Mainly VFR, with local MVFR possible. Chance SHRA,
Chance TSRA.

&&

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

&&

$$
SYNOPSIS...Chai
NEAR TERM...Chai/Kremer
SHORT TERM...Duell
LONG TERM...Duell
AVIATION...Chai