362
FXUS61 KBTV 300603
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
203 AM EDT Sun Jun 30 2024

.SYNOPSIS...
Steady rain is expected to continue through the afternoon hours with
a break in rainfall early this evening. Several rounds of convection
are expected tonight and again on Sunday which could produce a few
strong to locally severe storms. Very localized flash flooding also
remains possible with any convection tonight that moves over the
same area. A cold front on Sunday will put an end to rain and
thunderstorm chances with a dry start to July on tap for the North
Country.

&&

.NEAR TERM /THROUGH MONDAY/...
As of 203 AM EDT Sunday...Challenging forecast early this
morning with dynamic weather and mesoscale features driving
showers and thunderstorms. Overall, forecast is playing out well
with minor changes needed. A lull in precipitation was expected
during these late night hours with coverage becoming widely
scattered. Precipitation has settled mainly along a line from
the Adirondack High Peaks east north-eastward through northern
Caledonia and adjacent Essex counties in Vermont. Instability
here is low, so rainfall rates have been only moderate. In
contrast, potential downpours will exist with activity farther
northwest, with showers near the International Border in
northern New York. This environment is much more unstable, and
we are watching upstream thunderstorm complexes in Ontario for
triggering organized thunderstorms in our region towards 4 or 5
AM. This could result in strong thunderstorms across a swath of
northern New York into northern Vermont.

PREVIOUS DISCUSSION...Infrared satellite shows cloud top
cooling occurring across northern NY with GLM detecting a couple
of cloud flashes moments ago across southern Clinton county.
After an unseasonably cool late June day for North Country
standards, temperatures are not expected to drop all that much
and actually even rise a few degrees as warmer air aloft is
advected into our region in the next few hours. Surface analysis
shows the actual surface warm front still well south of our
area. While there are some subtle signs of environmental
destabilization, the expectation is that thunderstorms that do
develop this evening into the first half of the overnight hours
should be of garden variety, with potential for torrential
downpours given that the PWATs of 1.9 inches is near max of SPC
sounding climatology for the Albany, NY upper air site.

As a warm front pushed through the North Country, there was a
quick burst in isentropic forcing west of the Adirondacks
earlier that allowed for a period of heavy rain which has since
subsided. So far, rainfall totals are on track with anywhere
from a quarter of an inch in Vermont upwards to an inch in
northern New York. Rainfall associated with the warm front will
continue into the late afternoon or early evening hours before
we see a brief break in rainfall. Some gradual destabilization
is expected within the warm sector, especially across northern
New York, this evening which is expected to act as a catalyst
for additional showers and thunderstorms. At this time, flooding
looks unlikely given the additional showers and storms will be
rather scattered and rainfall totals thus far haven`t been
anything excessive. However, we continue to monitor the
potential for a wet microburst or two this evening across
northern new York. There are some pros and cons for this
potential which we will highlight. Pros:
DCAPE near or in excess of 1000 J/kg, strong low level shear
profiles, and mid-level dry air entrainment. Cons: Potential capping
due to rain cooled air and lack of SBCAPE and MUCAPE. With that all
said, there could be enough negative buoyancy associated with the
DCAPE to punch through any cap briefly. It`ll be something to watch
for sure but remains a very conditional set-up.

As the sun begins to rise on Sunday, so will our severe
probabilities. We have an unusual set-up on Sunday where our severe
potential is expected to peak by late morning and end by mid-
afternoon. Our airmass tomorrow will be highlighted by a very moist
low level environment with a decent bit of dry in the mid and upper
levels. This dry air remains a concern as it is expected to limit
areal coverage of thunderstorms. A pre-frontal trough is expected to
act as a trigger Sunday morning but just how many thunderstorms
develop remains very questionable. We will have a very favorable
environment tomorrow morning which will be highlighted by 1500+ J/kg
of CAPE, 50-60 knots of 0-6 km shear, and upwards of 800-1000 J/kg
of DCAPE. There is a potential nothing happens tomorrow while there
is also the potential for several strong to severe thunderstorms.
All of the high-res CAMs show 1-3 storms in the aforementioned
environment which could be long-tracked and could be strong to
severe but disagree on the placement of the thunderstorms. It`s more
important, in this case in particular, to understand the forcing
mechanisms and the background environmental fields rather than
trying to see where any single CAM is trying to depict a storm.
Timing also remains a bit of uncertainty as the last several runs
have an early pre-frontal trough although some ensemble guidance
suggests a later passage. A later passage would increase severe
potential while earlier passage would decrease it. We will be
monitoring this and should have a much better idea come Sunday
morning.

Following the pre-frontal trough, we will see a cold front lag
around 3 hours behind which should help scour out the low level
moisture and humid conditions. Decreasing rain chances will be seen
late Sunday afternoon through the overnight hours with a few gusts
of winds from the northwest following the FROPA. Temperatures will
return to more seasonal values Sunday night following the FROPA
which will be appreciated as no one really likes 70 degree
dewpoints.

&&

.SHORT TERM /MONDAY NIGHT/...
As of 318 PM EDT Saturday...A cooler, drier airmass moves into the
region for Monday. Dew points will fall into the 50s and 40s by the
end of the day. There is the chance of an isolated shower over the
higher terrain of Vermont during the day, but with dry low levels
and marginal conditions, anything would be very light. There is no
threat for thunder. Temperatures drop back into the 40s and 50s
overnight, in what will be the coldest night of the week. The
boundary layer should decouple in many areas and the coldest hollows
could drop into the low 40s or maybe even upper 30s.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
As of 318 PM EDT Saturday...Ridging builds in from the south for
Tuesday and Wednesday, sending temperatures above normal and
bringing the humidity back. Dew points eventually rise into the 60s
and temperatures will rise into the 80s. A weakening cold front
passes into the region Wednesday night and will bring some showers
and possible embedded thunderstorms. The most likely solution is
that it passes through northern New York in the evening and through
Vermont around and after midnight. However, there is still decent
ensemble spread so put a lot of chance PoPs on either side for now
until confidence grows. While there is the chance of thunderstorms,
there is no severe risk. While the front will not bring in a dry
airmass behind it, it will shunt the ridge back to the south before
it can become entrenched over the area send the temperatures and
humidity to high levels. The formal front generally dissipates but
there will still be a bit of a boundary in place on Thursday. There
is the possibility that a few showers fire along this but anything
would be light and scattered. Overall, the shower threat for the
Fourth of July is decreasing and thunderstorms are also not expected
regardless. A region of low pressure looks to move into the region
for the weekend and bring more chances of showers.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
Through 06Z Monday...A mix of VFR and MVFR ceilings are in place
with widely scattered showers. More organized showers and
thunderstorms become more likely over the next several hours, a
given location is relatively unlikely to be directly hit. Have
indicated vicinity thunderstorms across the SLK-PBG-BTV area in
the 10-14Z time frame where/when predictability is a bit
higher. Thunderstorm chances peak between 14 and 18Z ahead of a
cold front, generally shifting south and east with time,
although coverage of storms may remain sparse. Heavier rain will
produce IFR conditions. Winds will trend westerly during this
time. Then a secondary boundary will gradually shift through the
airspace between 21Z and 01Z with scattered showers which will
lead to more widespread MVFR conditions and northwesterly winds
mainly 6 to 10 knots with a brief period of 20 knot gusts
possible.


Outlook...

Monday: VFR. NO SIG WX.
Monday Night: VFR. NO SIG WX.
Tuesday: VFR. NO SIG WX.
Tuesday Night: VFR. NO SIG WX.
Wednesday: VFR. Chance SHRA.
Wednesday Night: Mainly VFR, with local IFR possible. Chance
SHRA, Slight chance TSRA.
Independence Day: Mainly VFR, with local IFR possible. Slight
chance SHRA.

&&

.HYDROLOGY...
The threat for localized heavy downpours and isolated flash flooding
continues across our region although looks less likely than
before.  The Weather Prediction Center Day 1 Excessive Rainfall
Outlook has been reduced to just a 5% chance of rainfall
exceeding flash flood guidance within 25 miles of a given point.
We`ve generally seen between 0.25" and 1" of rain thus far with
the highest amounts of rain across St. Lawrence County. An
additional 0.25" to 1" of rain is expected through Sunday
afternoon but rainfall rates overall will likely not support
flash flooding. However, several round of showers and
thunderstorms are expected tonight and again on Sunday. Should
one location see several rounds of convection, the additional
rainfall coupled with what has already fallen may lead to
localized flash flooding.

&&

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

&&

$$
SYNOPSIS...Clay
NEAR TERM...Clay/Kutikoff
SHORT TERM...Myskowski
LONG TERM...Myskowski
AVIATION...Chai/Kutikoff
HYDROLOGY...Clay