443
FXUS61 KBOX 210526
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
126 AM EDT Fri Jun 21 2024

.SYNOPSIS...
Scattered strong to severe thunderstorms remain possible this
evening...mainly across northern MA where a Severe Thunderstorm
Watch is in effect. A backdoor cold front moves in from northeast to
southwest Friday...bringing another round of showers and
thunderstorms. The bulk of this activity should be across interior
Massachusetts and Connecticut...where some of the storms may become
severe and also result in a localized flash flood threat. Warm
and muggy this weekend with rain and thunderstorm chances both
Saturday and Sunday. A cold front sweeps across the region Monday
with additional showers and storms, briefly less humid on Tuesday,
but summer warmth and humidity returns for midweek.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
10 PM Update

The severe thunderstorm threat has ended with storms loosing
strength very quickly after sunset as capping inversion
developed. A few lightning strikes are still being observed,
mainly over the waters, but more stratiform showers have become
the more dominant precipitation mode over the last hour or so.
We expect that showers will continue to dissipate over the next
two to three hours, with dry conditions expected well before
sunrise.

Given the lack of instability/forcing after sunset, the Severe
Thunderstorm Watch has been cancelled.

Previous update...

745 PM Update

* Strong to Severe T-Storms through late evening in areas north
  of the CT/RI/MA State lines

* Localized damaging wind gusts & torrential rainfall which may
  result in a very localized flash flood threat

Shortwave energy across northern New England coupled with
outflow and MLCapes still over 2000 J/KG has resulted in a
solid line of strong to severe t-storms to enter northwest and
northern MA early this evening. We think enough outflow will
result in a risk for severe storms over the next 1-3 hours in
areas at last north of the CT/RI/MA state lines. This is also
supported by the latest machine learning probs from the CSU to
the Nadocast and HRRR Neural network...which are all showing a
quite robust signal for localized damaging wind gusts. Main
question is how far south this convection will survive as it
out-runs the greater forcing. Given that DCapes are still over
1000 J/KG...we expanded the Severe T-Storm Watch to the CT/MA
border and extended it through 11 pm. Also...these storms will
be capable of producing torrential rainfall and a localized
flash flood threat.

Once this activity winds down later this evening...much of the
overnight hours should feature dry/muggy weather. Overnight low
temps will mainly be in the upper 60s to the lower 70s. We also may
see some patchy ground fog develop overnight given light winds/high
dewpoints especially where rain falls earlier in the evening.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/...
Key Points...

* Showers & t-storms anticipated Fri PM with the severe weather
  threat/very localized flash flood threat across interior MA/CT

* Much cooler across eastern MA but still hot & humid towards the CT
  River Valley where Heat Advisories remain posted

Details...

Friday...

A backdoor cold front will be moving westward across the region
Friday morning and into the afternoon. This will hold high temps in
the 80s across much of eastern MA and temps along the immediate
coast will probably fall into the 70s by afternoon. Further
inland...high temps will top off in the upper 80s to the lower 90s
with the warmest of those readings in the CT River Valley. The Heat
Advisory for Friday will only cover portions of southwest
MA/CT...where Heat Indices are expected to top off between 95 and
100 degrees.

The other concern will be for another round of showers & t-
storms...which looks to be Friday afternoon/early evening. The focus
for this will be along the backdoor cold front and will be enhanced
by shortwave energy in west to northwest flow aloft. While a few
showers & t-storms may impact the entire region...thinking the main
focus for the potential of severe weather/localized flash flooding
will be across western/central MA & northern CT. This is where the
greater instability will reside on the order of 1500 to 2000 J/KG.
These backdoor cold fronts can be a recipe for training and a
localized flash flood threat. The CSU Machine learning probs
highlight this risk nicely with again the focus across the interior.
There also is a severe weather risk with the main concerns being
locally damaging wind gusts with hail a secondary risk. This is
depicted nicely by the machine learning probs as well as the HREF
Updraft Helicity Swaths/Radar Simulations.

Friday night...

The convection should dissipate Friday evening. Otherwise...we will
have to watch for areas of low clouds and fog developing. Overnight
low temps will be mainly in the 60s.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Highlights:

* Warm and muggy this weekend with rain chances both Saturday and
  Sunday.

* Cold front sweeps across the region on Monday, drier and returning
  heat into mid next week.

The mid-level ridge continues to deamplify, as 500mb heights lower
from north to south, which is a consistent theme for the upcoming
weekend. At the surface an area of higher pressure near Bermuda
wanes and surface pressure lowers across the northeast. This area of
low pressure developing over the northern Great Lakes, drives our
weather conditions late this weekend into Monday, as the trailing
cold front, south of the low, sweeps across the northeast sometime
Monday. Beyond Monday, high pressure builds back Tuesday through
Thursday, with a cold front possibly pushing across the region later
on Friday/Saturday.

In addition, most of next week trends warmer than normal, and at
this point, next week doesn`t look to be as extreme as this current
week. Though the ensemble situational awareness tables indicates
Monday through Thursday, surface temperatures could be running
between the 90th and 99th percentile (of climatology), with a return
of average temperatures post cold front, sometime late Friday into
Saturday.

Saturday & Sunday:

Getting closer to home, there is a quasi-stationary frontal boundary
across the region, running from east to west through southern New
England and through Upstate New York on Saturday. Weak area of low
pressure tries to develop along the boundary, with the greatest area
for showers and storms along and north of the Mass Pike during the
mid to late afternoon. At this point, not expecting anything severe,
and SPC has most of the region under general thunder. A slightly
more elevated issue would be the potential for excessive rainfall.
The ERO from WPC highlights much of central/western Massachusetts
and northern Connecticut for a `Marginal` risk. Given PWATs are
above two inches, isolated and locally heavy downpours could lead to
urban street and poor drainage flooding.

Aforementioned frontal boundary becomes a warm front Saturday night
into early Sunday, lifting northeast, and placing us in the warm
sector. Scattered showers into the overnight hours, though the best
forcing appears to be concentrated further north. A prefrontal
trough and shortwave pivot through, with showers and thunderstorms
later Sunday afternoon/evening.

As for temperatures, Saturday will be the `cooler` day, the warmest
location will be the Connecticut River Valley, highs here are in the
mid 80s. Much cooler in northwest Massachusetts where highs are low
to middle 70s with the northeast flow. Nightly lows are still mild
which isn`t ideal for sleeping with windows open, lows are in the
middle to upper 60s to 70 degrees in the Connecticut River Valley on
Saturday night, then 2-4 degrees warmer Sunday night.

Next Week:

Warm and muggy day ahead of a surface cold front with temperatures
climbing into the 80s and dew points in the 60s. Storms develop mid
to late afternoon with the surface cold front, a bit a relief behind
the front with lowering dew points into the 50s and leads to a nice
Tuesday with comfortable, albeit warm day, with dew points in the
upper 50s to 60F. High pressure reestablishes across the northeast
leading to a drier week with return of summer warmth. Highs are in
the middle and upper 80s and lows in the 60s with a sign of cooler
temperatures by late in the week.

&&

.AVIATION /05Z FRIDAY THROUGH TUESDAY/...
Forecast Confidence Levels:

Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

12z TAF Update...


Friday...Moderate Confidence.

More showers and thunderstorms this afternoon with more north to
south coverage compared to Thursday when storms stayed north of
the MA Turnpike. Anticipating VFR conditions, with the exception
of patchy IFR due to fog, through 15Z after which time storms
will bubble up. VFR/high end MVFR with cigs around 3500ft
outside of storms. MVFR to IFR in storms with potentially
torrential downpours and vsby reductions. Will be difficult to
pinpoint exact storm location but terminals at greatest risk are
BAF, BDL, ORH, PVD. Winds variable today, from the ENE from ORH,
east, and from the NW/W across the CT River Valley as cold
front pushes west towards interior southern New England.

Friday night...Moderate Confidence.

Bulk of storms wind down by 00Z tonight, but residual moisture
and onshore ENE flow will allow pockets of fog to develop.
Generally MVFR to IFR due to cigs.

Saturday... moderate confidence.

Another afternoon of scattered thunderstorms, though confidence
on intensity and aerial coverage is low at this time. Could
impact all terminals, or none at all with the best chance for
tstorms coming after 17Z. Conditions improve from IFR/MVFR to
VFR with perhaps the exception of east coastal MA where MVFR
will persist. Locally lower flight categories likely again in
storms.

KBOS TAF... Moderate confidence.

Expect thunderstorm activity to stay inland of Boston this
afternoon, but can`t rule out a stray storm. Generally VFR this
morning becoming MVFR/IFR overnight due to low stratus/fog.
Winds quickly shift to the ENE this morning and will persist.

KBDL TAF...Moderate Confidence in TAF.

Another round of thunderstorms this afternoon with the best
chance to impact BDL between 17-22Z. Storms wane quickly after
sunset. VFR outside of storms, MVFR in storms, MVFR to IFR
developing tonight due to fog. Winds from the West for much of
the period but depending on the position of the back door cold
front, could go N or ENE late in the period.

Outlook /Saturday Night through Tuesday/...

Saturday Night: Mainly IFR, with local MVFR possible. Chance
SHRA, isolated TSRA, patchy BR.

Sunday: Mainly VFR, with local IFR possible. Breezy. Chance
SHRA, isolated TSRA, patchy BR.

Sunday Night: Mainly VFR, with areas IFR possible. Breezy. SHRA
likely, isolated TSRA, patchy BR.

Monday: Mainly VFR, with local IFR possible. Breezy. Chance
SHRA, isolated TSRA, patchy BR.

Monday Night: VFR. Breezy. Chance SHRA.

Tuesday: VFR.

&&

.MARINE...
Forecaster Confidence Levels:

Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.


Through Saturday...High Confidence.

Back door cold front will move across the northeastern waters on
Friday morning but likely stalls somewhere across the southern
waters, which will lead to converging winds; northeast vs
westerly.

Afternoon showers and thunderstorms across the mainland may
impact the waters very late both today and Saturday, but
confidence is low as storms are expected to lose their strength
after sunset. Winds and seas should stay below SCA criteria.

Fog and stratus development likely tonight and will linger into
the day on Saturday. Reduced vsbys should be expected.

Outlook /Saturday Night through Tuesday/...

Saturday Night: Winds less than 25 kt. Chance of rain showers,
isolated thunderstorms, patchy fog. Visibility 1 to 3 nm.

Sunday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Local rough seas. Slight chance of rain showers,
isolated thunderstorms, patchy fog. Visibility 1 to 3 nm.

Sunday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Areas of rough seas. Rain showers likely,
isolated thunderstorms, patchy fog. Visibility 1 to 3 nm.

Monday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of rough seas. Rain showers likely, isolated
thunderstorms, patchy fog. Visibility 1 to 3 nm.

Monday Night: Winds less than 25 kt. Local rough seas. Chance
of rain showers, isolated thunderstorms, patchy fog. Visibility
1 to 3 nm.

Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft.

&&

.CLIMATE...
All Time June High Temperature Record (Daily)

BOS - 100 F (06/06/1925, 06/26/1952 and 06/30/2021)
BDL - 100 F (06/26/1952, 06/30/1964)
PVD - 98 F  (06/25/1943, 06/15/1945 and 06/30/1945)
ORH - 98 F  (06/26/1952)

Most recent day of 100 F (or greater)

BOS - 100 F (07/24/2022)
BDL - 100 F (07/21/2019)
PVD - 100 F (07/28/2020)
ORH - 102 F (07/04/1911)*

* For ORH this is the only 100+ degree day in its period of record.

Daily High Temperature Records...


June 21st

BOS - 96 F (2012)
BDL - 96 F (1953 and 2012)
PVD - 96 F (1941)
ORH - 91 F (Multi-Years)

Daily Warmest Low Temperatures Records...

June 21st

BOS - 80 F (2012)
BDL - 73 F (1923 and 2012)
PVD - 75 F (2012)
ORH - 74 F (1923 and 2012)

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory until 7 PM EDT this evening for CTZ002>004.
MA...Heat Advisory until 7 PM EDT this evening for MAZ008>011.
RI...None.
MARINE...None.

&&

$$

SYNOPSIS...Frank/Dooley
NEAR TERM...Frank/KS
SHORT TERM...Frank
LONG TERM...Dooley
AVIATION...KS
MARINE...Frank/Dooley
CLIMATE...BL