887
FXUS61 KBTV 160346
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
1146 PM EDT Mon Jul 15 2024

.SYNOPSIS...
Heat will remain the rule for a few more days until a cold front
reaches the area on Wednesday afternoon. Intervals of showers
and storms, a few strong, will move through the region late this
evening into tonight, and then redeveloping Tuesday afternoon.
The higher chances for stronger storms will be Tuesday
afternoon.. Following one last round of showers with a cold
front Wednesday evening, cooler and drier weather is expected
for the end of the week and into next weekend.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
As of 1139 PM EDT Monday...Issued a quick update to match
PoPs/Wx up to current conditions. Large swath of moderate to
heavy rain with embedded thunder is lifting across VT at this
hour. The heaviest activity is moving into the northern
Champlain Valley, with another stronger cell down across south-
central VT. This activity is all pushing to the north and east,
and will produce heavy rainfall as it does so. Winds will become
a little gusty with the more robust cells, but nothing severe
anticipated as storms should remain elevated. Other than the
above, the forecast is in good shape and no other changes were
needed.

Previous discussion...It was a chain reaction once the first
thunderstorm developed in west-central St. Lawrence County, with
several storms quickly pulsing up across northern New York and
far western Vermont between 8 and 10 PM. Activity has finally
waned a bit outside of the northern Lake Champlain area.
However, the cluster of thunderstorms entering Rutland County is
expected to help trigger more storms across Vermont, with
activity finally exiting northeastern Vermont after 2 AM. We
have had isolated areas of 1-1.5" of rain in northern New York
in 1 to 2 hours time, so we cannot rule out an instance of flash
flooding through this evening. That being said, instability
will gradually be diminishing out ahead of the upstream
convection such that intensity of rain/thunderstorms should be
weakening. Other than revising the current six hour QPF to
better reflect observations and latest model guidance, no
significant changes made.

It`s a hot day across the forecast area. Mid 80s to lower 90s
with dewpoints in the mid 60s to lower 70s is causing heat
indices in the upper 80s to mid 90s across the region. Satellite
suggests fair weather cumulus remains quiescent. A few showers
have popped up along the Addison- Rutland county line, but
there`s dry subsidence still hanging over the region from this
morning`s activity.

Upstream, we`re monitoring a weakening upper shortwave across
western New York State presently producing strong to severe
storms near Buffalo. Convective processes are expected to
briefly reverse the shortwave`s weakening trend, with strong
850hPa southwesterly flow pivoting just up to upstate New York.
Strong low-level convergence and elevated instability should
allow showers and storms to continue propagating northeast
overnight. The lack of surface instability should keep this
sub-severe, but parts of southern St. Lawrence County, the
Adirondacks, and the far southern half of Vermont may have to
remain watchful for gusty winds if outflows can maintain
themselves into our region. We will track its progress to see
how well it holds together as the threat for strong to locally
severe storms is non-zero. A marginal risk outlook (Level 1 of
5) is present for that region), and a small portion of St.
Lawrence County in a Slight Risk (Level 2 of 5). Overnight lows
will remain warm given the south flow. Rain may cool things off
somewhat, but still expecting temperatures in the mid 60s to
lower 70s.

For Tuesday, we could see some lingering clouds as this
shortwave is somewhat slow to move out. There could be a few
pockets of showers still in the Northeast Kingdom early in the
morning. Dry, subsident air behind the shortwave should produce
sufficient heating, but this may be tempered by initial cloud
covers. Eastern Windsor has been added into the Heat Advisory
tomorrow as increasing dewpoints will counter the somewhat
cooler daytime highs. Heat indices should again reach the mid to
upper 90s across the Champlain Valley and in the Connecticut
River Valley. Thunderstorms will again fire as the result of a
mesoscale vortex from convection in the Plains. This one appears
more likely to hold itself together and arrives a bit earlier
than today`s. So a Slight Risk for severe thunderstorms (Level 2
of 5) covers much of the region due to the higher shear and
better time of day for convection. This also appears more
capable of producing heavy rainfall. Grounds will be primed by
tonight`s activity. So it will not take much to result in flash
flooding in common trouble spots.

&&

.SHORT TERM /WEDNESDAY NIGHT/...
As of 308 PM EDT Monday...There remains considerable spread amongst
the guidance what we can expect weather wise here in the North
Country on Wednesday. Global ensemble guidance shows a general
consensus of members with low pressure centers tracking along the St
Lawrence River valley from eastern Ontario into western Quebec. That
does favor the development of scattered thunderstorms on Wednesday
out ahead of a surface cold front. SPC currently has the eastern
two-thirds of our CWA in a Day 3 marginal severe risk. On the other
hand, WPC has Day 3 marginal excessive rainfall outlook (ERO) to our
south. The thinking is that what kinds of hazardous weather we get
on Wednesday will depend on where the boundary sets up, which at
this point could range from the Adirondacks to the Connecticut River
valley.

With Mesoscale Convective Systems (MCSs) setup, it is not uncommon
for higher-resolution guidance to not get a good handle on until 6-
12 hours prior to their development. In plain language, if the
Midwest gets a long-lasting MCS to form and come through our region
in the overnight hours, there could be little convective activity
during the daylight hours. PWATs still do look elevated, although
not extreme on Wednesday, generally in the 75-90th percentile range
of SPC sounding climatology for the Albany, NY upper air site. If we
do get convection to come through on Tuesday night, then it is
certainly plausible that Wednesday might well turn out to be a
relatively benign day with drier air starting to make its way into
the region. Looking at deterministic guidance, it does look like the
CAPE/shear combination is not nearly as robust as on Tuesday. So it
is reasonable to wager that storms, if they do become strong or
severe, would be much more isolated or scattered in coverage. But
then again, a lot hinges on the convective development and evolution
on Tuesday into Tuesday night.

Long story short, it is prudent to utilize a bit of a wait and see
approach at this time. Given the considerable uncertainty, largely
stuck to a blend of guidance for this forecast period. The best
chance for locally heavy rainfall, or a few stronger storms, would
be across the southeast portion of our CWA. But for those tired of
the seemingly relentless heat and humidity, relief is coming. Cold
air advection should begin in earnest by overnight Wednesday, with
gusty northwest winds sending PWATs from the 75-90th percentile
range of SPC sounding climatology to the 10-25th percentile range by
Thursday morning. Refer to the long term discussion for details.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 308 PM EDT Monday...Overall, the long term portion of the
forecast would feature delightful weather for mid July standards in
the North Country. The main question for Thursday would be whether
we get isolated to scattered shower activity as the upper low builds
in or we get mainly dry weather. For now, have only had slight
chance PoPs for parts of the region on Thursday with only at worst
isolated to widely scattered showers. Either way, no adverse weather
impacts are anticipated as it is just a question of we start a
stretch of much- deserved break from the recent heat and humidity
heading into the weekend. Expect dew points in the 50s (with 40s in
spots) Friday into the weekend. Daytime temperatures would trend
near to even slightly below climatological normal with mid 70s to
low 80s on tap. 50s would return to the forecast for overnight lows,
with 40s in the colder hollows and low 60s in the urban centers.
Indeed, the CPC 6- 10 day outlook does indicate a trend towards near
to just above normal temperatures for our region. It would be music
to the ears to see the 6-10 day outlook indicate below normal
rainfall for the period. After a wet first third of July, the dry
stretch will be much welcome. Overall, largely stuck to blended
guidance for this portion of the forecast but the main take home
message is to look forward to a pleasant if not absolutely
delightful stretch of weather heading into the weekend.

&&

.AVIATION /04Z TUESDAY THROUGH SATURDAY/...
Through 00Z Wednesday...Showers, and perhaps a few storms,
will lift northeast across the region between 00z and 07z. The
areal extent should cover most terminals, but location of where
rain is heaviest will still need some time to see how well
convection holds overnight, and have kept a general 6SM in
showers. Afterwards, we may see fog after rain lifts northeast,
and have 3-4SM visibilities after rain clears at
KSLK/KMPV/KEFK/KMSS. There will be some lowering ceilings about
1500-2500 ft agl, locally to 900 ft at KSLK. After 12-13z, any
lingering showers and fog should dissipate with a trend to VFR
conditions with southwest winds continuing about 4 to 8 knots.
Additional showers will be possible Tuesday afternoon, but
difficult to time at this point.

Outlook...

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

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...Heat Advisory until 8 PM EDT Tuesday for VTZ005-009-011.
     Heat Advisory from noon to 8 PM EDT Tuesday for VTZ021.
NY...Heat Advisory until 8 PM EDT Tuesday for NYZ035.

&&

$$
SYNOPSIS...Haynes
NEAR TERM...Hastings/Haynes
SHORT TERM...Chai
LONG TERM...Chai
AVIATION...Neiles