795
FXUS61 KBTV 150235
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
1035 PM EDT Sun Jul 14 2024

.SYNOPSIS...
After a quiet end to the weekend, heat, humidity, and scattered
showers and thunderstorms are forecast for Monday and Tuesday,
followed by an additional chance for thunderstorms on Wednesday.
Following a cold front passage Wednesday night, cooler and drier
weather is expected for the end of the week and into next weekend.

&&

.NEAR TERM /THROUGH TUESDAY/...
As of 1035 PM EDT Sunday...Forecast remains in good shape with
chances of showers still on track to largely ramp up after
midnight with greatest chances generally from Franklin County,
New York eastward across northernmost portions of Vermont.
Mesoanalysis shows a sharp moisture gradient with 850 millibar
transport pointed east-northeastward, such that eventually
clouds will lower and showers should develop in spite of weak
dynamic forcing and lack of instability. Southerly low level
flow will help help increase surface convergence in the northern
Champlain Valley, as well, so PoPs up into the 30-40% range
towards daybreak look good in that area. Most locations that see
rain will only see a few hundredths of an inch of rain, with
perhaps a spot or two that sees over a 0.1".

Previous Discussion...
Surface high pressure and a weak ridge aloft provided a
beautiful end to the weekend with warm temperatures in the 80s
and slightly more comfortable dewpoints in the lower 60s.
Tonight, a decaying mid-level shortwave trough will track
eastward from the Great Lakes and bring a chance for showers and
embedded thunder to portions of northern New York, but most of
Vermont should remain dry. Clouds increase across the entire
region through the overnight, helping to keep min temps mild in
the mid-60s to low-70s. On Monday the remnant shortwave energy
passes through the region and combined with increasing humidity
and instability, we should see scattered showers and
thunderstorms develop through the afternoon. A lack of any deep
layer shear supports storms being more of the garden variety,
but based on low flash flood guidance and PWATs surging back
towards 2", any stronger cores will be capable of producing some
isolated flash flooding if rainfall exceeds 1" in an hour,
especially across central and northern Vermont. In addition,
with high temps rising into the upper 80s to low 90s and
dewpoints back into the upper 60s, heat indices are expected to
rise into the mid/upper 90s for portions of central/southern
Champlain Valley where a heat advisory has been issued.

Afternoon convection should wane with the loss of surface
heating after sunset, with some lingering isolated showers and
thunderstorms through midnight. It should be another steamy
overnight with lows only in the upper 60s to low 70s again, and
dewpoints only a few degrees below for humidity close to 100%.

&&

.SHORT TERM /TUESDAY NIGHT/...
As of 256 PM EDT Sunday...Tuesday is likely to be another warm and
humid day. Heat indices are likely to climb into the 90s across the
region as warm, moist air lifts northeast ahead of a cold front
stretching out to our west. Interestingly, the source of moisture on
Tuesday will be from a round about connection from the Pacific Ocean
up through the Baja into the Intermountain West before making a
beeline across the Plains. This leaves me slightly skeptical we can
achieve truly oppressive dewpoints we can get out of the Gulf of
Mexico, but almost all guidance has upper 60s to lower 70s. It`s
hard to beat persistence. Heat Advisories are presently covering
part of the Champlain Valley, and will likely be needed for the
Connecticut River Valley as well. It will likely be added to the
existing Heat Advisory tomorrow.

The picture for thunderstorms is somewhat complicated. There are
some timing discrepancies with the shortwave expected to cross the
area Tuesday afternoon. It seems Monday night`s convection and
trough will place some stable air across the region initially. This
should allow the efficient warming expected on Tuesday, but the
question is how much instability recovery can take place. If the
shortwave is too early, we may be able to escape much impact, but if
the shortwave is delayed until later in the afternoon, there will be
upwards of 1500 J/kg of CAPE, 0-6km shear of 30 to 40 knots, and
1.50-2.00" PWATs. As noted before, the meso-beta vectors are slow,
and so thunderstorms may not be in any real hurry or could backbuild
despite some present flow. So the western half of Vermont and
northern New York are in a marginal risk outlook for excessive rain,
and we are in a marginal risk outlook for localized severe storms.
Given the potential seems conditional, this all seems reasonable.
Some lingering showers are expected overnight, followed by a
prefrontal trough that shifts everything out, and that means a humid
night in the mid 60s to lower 70s is anticipated.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 256 PM EDT Sunday...The extended begins with a frontal boundary
at our doorstep. The stretched out cold front to our west will only
slowly shift east. However, a large upper trough begin to force it
to make some eastward progress. The question is, exactly how fast
will that be. A slower front means a warmer Wednesday with more
chances to destabilize, while a faster front would result in
activity limited to the Green Mountains eastwards. The upper trough
is going to lag behind, but it will send cooler, less humid air
eastwards. So if things don`t line up well, we could be on the drier
side. Probabilistic guidance suggests one should not be too
optimistic with the chance of exceeding 0.10" at greater than 50
percent. The clustering of drier ensembles are less than 20 percent
too. To complicate matters, the 12z deterministic runs came in with
a relatively dry Wednesday with a fast frontal progression, though.
For now, the forecast changes little from the previous forecast. The
focus is most likely to be the southern half of Vermont though, and
so have stuck closely to blended data for rainfall forecasts for now
which highlights that well enough.

A few showers could develop on Thursday as the upper trough ambles
east, but there will be a lot of happy people as temperatures trend
slightly below normal! Dry high pressure sets up, and we`ll be
looking at pleasant weather conditions through Saturday. Although
temperatures will begin to climb back up above normal, there will
not be the oppressive humidity. Then, there`s a reinforcing cold
front sometime early next week. It will come with some showers, but
nothing significant as it comes from the north without a tropical
moisture feed.

&&

.AVIATION /03Z MONDAY THROUGH FRIDAY/...
Through 00Z Tuesday...VFR conditions will prevail through the
period. Temporary visibility reductions due to an unlikely
direct hit of a heavier shower, especially late in the period,
is possible at most sites. However, coverage of these variety
of showers and thunderstorms looks isolated.

In the 00Z to 02Z period, an area of light showers currently
over eastern Lake Ontario may move through KMSS and KSLK
overnight but shouldn`t flight conditions. Additional very light
rain is possible there and possibly up through the northern
Champlain Valley through 12Z. Towards 16Z, scattered showers
and thunderstorms will develop with skies SCT-BKN.

Winds overnight will be mainly <5kts, then south/southwest at
6-11kts after 14Z Monday.

Outlook...

Monday Night: VFR. Scattered SHRA, Scattered TSRA.
Tuesday: Mainly VFR, with local MVFR possible. Chance SHRA,
Slight chance TSRA.
Tuesday Night: Mainly VFR, with local MVFR possible. Chance SHRA.
Wednesday: Mainly VFR, with local MVFR possible. Chance SHRA,
Slight chance TSRA.
Wednesday Night: VFR. Chance SHRA.
Thursday: Mainly VFR, with local MVFR possible. Chance SHRA,
Slight chance TSRA.
Thursday Night: VFR. Slight chance SHRA.
Friday: VFR. NO SIG WX.

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...Heat Advisory from noon Monday to 8 PM EDT Tuesday for VTZ005-
     009-011.
NY...Heat Advisory from noon Monday to 8 PM EDT Tuesday for NYZ035.

&&

$$
SYNOPSIS...Lahiff
NEAR TERM...Kutikoff/Lahiff
SHORT TERM...Haynes
LONG TERM...Haynes
AVIATION...Kutikoff/Lahiff