Severe Thunderstorm Warning 43, NWS Burlington, VT

Area Forecast Discussion
National Weather Service Burlington VT
410 PM EDT Wed Jul 8 2020

.SYNOPSIS...
A mid-level trough will bring scattered showers and
thunderstorms to the North Country today, especially from the
Adirondacks eastward across Vermont. A few strong to severe
storms are possible, with damaging winds, brief heavy
rainfall, and dangerous cloud to ground lightning the primary
threats. Hazy, hot and humid conditions move in for Thursday and
Friday. Heat index values are expected in the mid to upper 90s
across the Champlain and St. Lawrence Valleys for Thursday and
Friday. Any thunderstorm development Thursday and Friday is
expected to be isolated.

&&

.NEAR TERM /THROUGH THURSDAY NIGHT/...
As of 409 PM EDT Wednesday...

     SEVERE THUNDERSTORM WATCH 343 IN EFFECT UNTIL 10 PM EDT THIS
EVENING...
     HEAT ADVISORY IN EFFECT FROM NOON THURSDAY TO 7 PM EDT FRIDAY...

Watching scattered convection in two areas, in northern VT and
across south-central VT. Instability up to 2000 J/kg and 0-6km
bulk shear up to 35 kt will lead to showers and thunderstorms
with a risk of severe weather including damaging winds, hail,
and heavy downpours mainly in VT through this evening.

Clearing skies tonight will lead to some locally dense fog
especially in the river valleys and where rain has fallen with
dewpoints remain mid 60s to lower 70s which are also the low
temperatures that can be expected.

Ridging aloft on Thursday with large scale subsidence and SW
flow will bring hazy conditions with dewpoints in the 60s. 850mb
temperatures +18 to 20C, will lead to near-record temperatures
in the low-mid 90s (see climate section for record values). With
the increased humidity, should see heat index values in the
mid-upper 90s in the Champlain/St. Lawrence Valleys. Subsidence
aloft and associated CIN should put a cap on convective
development, but will keep one eye on the terrain.

Thursday night strong ridging aloft will continue and light SW
flow at the surface. It will be a warm one as well with lows in
the mid 60s to lower 70s, especially warm near BTV.

&&

.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
As of 359 PM EDT Wednesday...It will be a warm and humid start to the
day. In the St. Lawrence Valley and northern Champlain Valley, it
will quickly become another scorcher as temperatures in the low-
levels look similar to Thursday and there will be plentiful sunshine
during the morning. Thankfully there will be a little more wind with
an increasing surface pressure gradient. Slightly cooler and more
moist air will advect into our southern areas as the upper level
ridge overhead begins to retreat eastward with the approach of low
pressure near the DelMarVa Friday morning. Initially, high-based
clouds will overspread the region during the afternoon from south to
north. This will provide some relief to the excessive heat for
southern portions of our forecast area. Therefore, have trended a
little cooler for high temperatures in the southern Champlain Valley
and points east. Clouds will lower with time and expect bands of
scattered showers capable of producing brief downpours to spread
into the Adirondacks and the southern half of Vermont by evening.

Overall, while models have come into better agreement with the warm
core low lifting northward, there is enough spread to make the exact
track uncertain, and therefore precipitation forecast. With the
forecast consensus further west today, confidence has increased that
areas from the Green Mountains eastward should see heavy rainfall
Friday night, especially with development of a southeast to easterly
low-level jet providing good upslope enhancement of rainfall.
Potential exists for a wide swath of 1 to 2 inches of storm total
rainfall with locally higher amounts.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
As of 359 PM EDT Wednesday...A complex weather situation will develop
over the weekend with two low pressure systems moving through the
region. On Saturday morning rainfall will lift northward with at
least some precipitation areawide associated with the tropical
system. Still looks like the greater rainfall amounts will be across
Vermont, with perhaps a break in shower activity across southern
areas by afternoon. Expect a heavy rain threat without severe
weather based on extreme precipitable water in excess of 2 inches.
Thankfully relatively fast motion of the system will reduce a
widespread flood threat, but this will be monitored closely.

A vigorous shortwave trough from the west will follow the tropical
system closely and encourage additional shower development Saturday
afternoon. This activity will spread northeastward across the North
Country. A dry slot appears to be limited to only a brief period
Saturday night, with more rain and thicker overcast associated with
the surface low pressure area moving into northern New York by
Sunday morning. Bottom line is a lot of beneficial rainfall appears
likely for this weekend with somewhat cooler daytime temperatures
due to increased cloud cover.

Yet another shortwave trough digs southward near Lake Erie on Monday
putting us in a favorable location for more scattered showers and
possible thunderstorms. The upper-level trough finally passes to our
east by Tuesday night, so precipitation chances will fade away at
that time. Both Monday and Tuesday will see temperatures near
normal. Temperatures trend upward midweek due to an expansive upper-
level ridge expanding east-northeastward from the desert southwest.
Global models differ on how quickly this builds into the North
Country, but expect another hot stretch beyond the seven day
forecast.

&&

.AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
Through 18Z Thursday...Main concern is scattered thunderstorm
development through the early evening with an upper level trof
and a weakening surface front. Tough to pinpoint timing or
location, so have mention in TAF and will amend as they storms
evolve. A few severe storms are possible, and may impact the
TAF locations. Damaging winds are the primary threat. It will be
mainly VFR with scattered cumulus and cumulonimbus. Brief IFR
and gusty winds possible near any thunderstorms. Winds at BTV
generally south 10-12kt with gusts to 20kts becoming light
overnight. Anticipate IFR nocturnal fog after 06Z tonight at
SLK/MPV. On Thursday, hot and humid conditions with some haze
but little if any showers or storms expected.

Outlook...

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

&&

.CLIMATE...
Max Temp Records the next several days. Near record highs are possible
Thursday (7/9) and Friday (7/10).

Date     KBTV     KMPV     K1V4     KMSS     KPBG     KSLK
07-08  98|1921   95|1988  90|2010  95|1988  96|1981  95|1921
07-09  97|1988   94|1988  86|2010  96|1988  94|1981  94|1928
07-10  96|1911   92|1955  88|2005  96|1988  94|1955  96|1936

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...Heat Advisory from noon Thursday to 7 PM EDT Friday for VTZ001-
     002-005-009.
NY...Heat Advisory from noon Thursday to 7 PM EDT Friday for
     NYZ026>028-035-087.

&&

SYNOPSIS...Sisson
NEAR TERM...Sisson
SHORT TERM...Kutikoff
LONG TERM...Kutikoff
AVIATION...Sisson
CLIMATE...Banacos

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