St. Johnsbury, Vermont 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

491
FXUS61 KBTV 290627
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
227 AM EDT Mon Jun 29 2026

.WHAT HAS CHANGED...
As of 226 AM EDT Monday...

Dangerous heat and humidity is still on track for Wednesday through
at least Thursday, and perhaps into Friday. The threat for severe
thunderstorms has increased for Tuesday night and Wednesday.

&&

.KEY MESSAGES...
As of 226 AM EDT Monday...

1. Dangerous heat and humidity are expected for mid to late
week. Heat headlines will likely need to be issued by subsequent
shifts.

2. Strong to severe thunderstorms are possible Tuesday and
Wednesday.

3. Dangerously hot and humid conditions will linger into the
holiday weekend along with daily chances of showers and
thunderstorms.

&&

.DISCUSSION...
As of 226 AM EDT Monday...

KEY MESSAGE 1: Today starts a gradual warming trend that will continue
into the latter half of the week. High pressure will build eastward
from the Ohio River Valley, while a warm front lifts toward and
eventually across our region Tuesday into Wednesday. While today
will remain fairly comfortable, humidity will increase markedly as
the front moves through, making for very muggy conditions by late
Tuesday into Tuesday night. Guidance continues to keep Tuesday a
touch colder than previous runs owing to cloud cover and
precipitation chances (more on that below), so while it will be hot
and humid, expect heat index values to generally remain at or below
90F. Heat builds on Wednesday, with 925mb temperatures approaching
26-28C, and perhaps even warmer if the GFS holds true. As such, we
expect this will be the first day to warrant heat headlines,
particularly since dewpoints will be 70F or better across much of the
region. However, there`s still considerable spread in
shower/thunderstorm timing/placement/coverage on Wednesday, which
could potentially impact high temperatures. Regardless, the heat
will continue into Thursday and perhaps beyond, with dewpoints
remaining in the upper 60s to low 70s. If precipitation holds off
and everything comes together just right, heat index values of 95 to
105 are very much possible both Wednesday and Thursday. And there
will be little relief overnight as muggy conditions will keep lows
close to or above 70F. Given that the core of the heat is still 48+
hours away and there`s some uncertainty how Wednesday`s temperatures
will play out, have opted to not issue any heat headlines at this
time. However, please use this time to prepare for potentially
dangerous heat later this week, and follow forecast updates closely.

KEY MESSAGE 2: We`ll remain on the northeastern periphery of an upper
level which which will be centered near/over the Ohio River Valley.
Model guidance continues to indicate the potential for several
shortwaves/ridge rollers to ride over the top of the ridge and down
through the northwest flow that will be in place over New England.
As these disturbances move along the upper flow, we also look to be
influenced by waves of an EML, either right overhead or moving just
off to our west. This will increase instability, even into the
overnight hours, thus aiding any night time convection. Timing these
sorts of ridge rolling systems is notoriously difficult, but at this
time, guidance seems to be keying in one moving through
northern/western New England and NY sometime later Tuesday into
Tuesday night, with another one potentially following sometime
Wednesday. If convection moves in during daylight hours, SB CAPE
will be ample, generally 500-1500+ J/kg from the Champlain Valley
westward on Tuesday. This would become more widespread and increase
on Wednesday, with SB CAPE an impressive 1000-2000+ J/kg across much
of the area (note both the NAM and GFS have values as high as 3000
J/kg, though placement differs between the models). Shear both days
will be a respectable 35-50 kt. Hence, if convection does develop
during the daylight hours, strong to severe thunderstorms capable of
large hail, damaging winds, especially in any supercells. Any
overnight storms would be elevated but still capable of some small
hail. And any storms would be capable of producing very heavy
rainfall, with PWATs 1.5 to 2+ inches and warm cloud depths 10-12+
kft. This thinking is reinforced by both SPC, which has us included
in a Marginal Risk (level 1 of 5) for Tuesday and Tuesday night,
while WPC likewise has a Marginal Risk (level 1 of 4) of excessive
rainfall over our region. This is a complex scenario and there`s
still plenty of uncertainty, so please stay tuned for future
forecast updates, especially if you have outdoor plans.

KEY MESSAGE 3: Prolonged heat will likely be ongoing into the end of
the week with ample humidity, even as temperatures trend less
extreme. While we show another day of high heat index values on
Friday with peak values well into the 90s at elevations below 1000
feet, the potential for a mesoscale convective system and its effect
on temperatures makes this forecast somewhat uncertain. Furthermore,
some guidance is more amplified with the ridge centered to our
southwest, which allow for more anomalous low level temperatures to
remain in our area. The mean 925 millibar temperatures range from
merely very warm (close to 20 Celsius) in the cooler scenario to hot
(close to 26 celsius) in the hotter scenario, translating to high
temperatures either mainly mid to upper 80s or mid to upper 90s in a
mainly dry scenario. This spread continues on Saturday (July 4th)
and Sunday, but the high end temperatures trend less hot as the
ridge begins to break down. As such, the story for the weekend may
be potential for flooding, as a surface boundary may eventually
become stationary to our south with rounds of showers and
thunderstorms moving across the Northeast. The details of this are
rather unclear and due to the convective nature of precipitation the
signals for widespread heavy rain are low, but this hazard alongside
strong to severe thunderstorms over the weekend will need to be
watched, especially where earlier week convection had occurred.

&&

.AVIATION /06Z MONDAY THROUGH FRIDAY/...
Through 06Z Tuesday...VFR conditions amidst high pressure will
prevail across the next 24 hours. Cannot rule out a brief or
intermittent period of fog at SLK, MPV, or even MSS in the pre-dawn
hours but cross over temperatures based on yesterday`s dry air are
quite low, making it unfavorable for fog despite the clear skies and
calm winds. Winds will remain light as in recent days, generally up
to 5-8 knots out of the north.

Outlook...

Tuesday: VFR. Chance SHRA, Slight chance TSRA.
Tuesday Night: Mainly VFR, with local MVFR possible. Chance SHRA,
Chance TSRA.
Wednesday: Mainly VFR, with local MVFR possible. Chance SHRA,
Chance TSRA.
Wednesday Night: VFR. Chance SHRA, Chance TSRA.
Thursday: VFR. Chance SHRA, Chance TSRA.
Thursday Night: VFR. Chance SHRA, Slight chance TSRA.
Friday: Mainly VFR, with areas MVFR possible. Chance SHRA, Chance
TSRA.

&&

.CLIMATE...
Extreme heat and humidity is possible later this week,
especially on Wednesday and Thursday, which could lead to some
daily records. Below are the current daily high and low
temperature records in jeopardy at our area climate sites.

Record High Temperatures:

June 30:
KBTV: 93/2018

July 1:
KBTV: 96/2018
KMPV: 92/2018
KPBG: 94/1968
KMSS: 94/2018

July 2:
KBTV: 97/2018
KMPV: 90/2018
KMSS: 94/2018

July 3:
KMPV: 91/2002


Record High Minimum Temperatures:

July 1:
KBTV: 76/2018
KPBG: 73/1971
KSLK: 69/2018

July 2:
KPBG: 77/2002
KSLK: 68/2002

July 3:
KBTV: 76/1911
KPBG: 73/2002

July 4:
KPBG: 71/1973
KSLK: 67/1952

&&

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

&&

$$

WHAT HAS CHANGED...Hastings
DISCUSSION...Kutikoff/Hastings
AVIATION...Kutikoff
CLIMATE...NWS BTV