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950
FXUS61 KBOX 140840
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
419 AM EDT Fri Jun 14 2024

.SYNOPSIS...
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Warm and muggy Friday with dewpoints in the middle 60s.
Scattered severe thunderstorms possible north and west of
interstate 95 with the passage of a cold front this afternoon and
evening. A few lingering spot showers are possible early
Saturday...otherwise high pressure brings dry and beautiful weather
for the weekend with low humidity. A warm-up begins on Monday with
an extended period of excessive heat and humidity possible beginning
Tuesday and continuing through Friday.
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&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

Key Points

* Warm and muggy start to the day
* Scattered severe thunderstorms NW of I-95

Friday will be a warm and humid day with temperatures quickly rising
into the mid to upper 80s and dew points reaching the mid to upper
60s. This will help set the stage for scattered severe thunderstorms
as a potent shortwave trough and cold front drops SE across the
region in the afternoon.  As the cold front moves through, a very
narrow corridor of instability will be set up across western MA and
CT. There continues to be some disagreement among the hi-res HREF
guidance on how much instability will be available mainly due to
timing differences on convective development. HREF mean shows near
1000 J/kg of SBCAPE with the 90th percentile showing around 2000
J/kg. With deep layer shear approaching 30-40 knots, the environment
will be supportive of organized clusters of severe thunderstorms.
Initiation remains a bit uncertain with some members of the
HREF initiating storms shortly after 12pm, while others holding
off as late as 4pm. latest 06z guidance is trending towards a
faster solution with height falls from the shortwave arriving
earlier in afternoon. Storms likely initiate off the high
terrain in Western MA/CT and southern VT/NH then move ESE
through the afternoon. Storms should quickly weaken as the
approach eastern MA and RI as they run into a more stable
environment with less instability and shear. The severe threat
at this time looks highest north and west of the I-95 corridor
as highlighted by the SPC slight risk.


Severe threats:

The primary severe threat will be strong to damaging winds with
steep low level lapse rates, DCAPE values near 700 J/kg, and
linear storm mode promoting straight line winds. The hail threat
has increased since yesterday due to models steepening mid
level lapse rates to 6-7 C/km. The freezing level still remains
above 10kft which should help to melt most hail before reaching
the surface. The tornado threat remains very low at this time
with 0-3km SRH around 100 m/s and the Sig Tor parameter well
less then 1.0. Storm mode also appears to favor linear clusters
with upscale growth. Not completely out of the question that a
discreet supercell could form at initiation before merging with
other cells into line segments or clusters.

Heavy Rain Threat:

Although the storms will be progressive with little to no training
expected, PWATS will be increasing into the 1.5-1.6 inches. CAPE
profiles have become more fat and supportive of hail over the last
24 hours due to steepening mid level lapse rates. Warm cloud depths
have also decreased to 8000ft. Despite these less favorable changes
in the environmental parameters, the HREF 3hr PMM does still
highlights a small area in western MA and CT with 10% probs for
greater then 3 inches of rain in 3 hours. This could lead to areas
of street and poor drainage flooding along with isolated instances
of flash flooding.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
Tonight

Thunderstorms quickly weaken into showers as they move east into
less favorable environment and lose support from daytime heating.
The shortwave axis crosses through the region overnight which
will prolong the rain for eastern MA before tapering off by
morning. Overnight lows stay on the warm side in the low 60s
with overcast skies and rain.

Tomorrow

Shortwave moves offshore with rising heights and high pressure
beginning to build in for the weekend. There may be some
lingering light showers in the morning in eastern MA, otherwise
mainly dry conditions with clearing skies in the afternoon.
Winds turn northerly advecting in cooler air for Saturday with
highs only in the mid to upper 70s. Humidity will also be
noticeably lower with dewpoints dropping into the 50s and even
the 40s across the western interior.

&&

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

Key Points...

* Dry/cool Sat night followed by a beautiful Sunday with low humidity
* Warmup begins on Mon with excessive heat & humidity Tue through Fri
* Heat & Humidity Peak in the Wed through Fri time frame
* Near Record Highs possible...Heat Indices between 95 & 104 at times

Details...

Saturday night and Sunday..

Large high pressure will build over southern New England Sat night
into Sun. A relatively dry airmass in place for mid June
standards...coupled with mainly clear skies/light winds will yield a
good night of radiational cooling. Overnight lows should bottom out
in the 40s across the outlying locations with 50s in the urban
centers. Plenty of sunshine on Sunday will allow for a beautiful day
along with low humidity. Highs will be well up into the 70s to
perhaps near 80 in a few spots.

Next Week...

Confidence continues to grow in excessive heat and humidity next
week. An anomalous upper level ridge will build northward into
southern New England next week. A warming trend begins on Monday,
but the significant heat/humidity potential looks to begin Tuesday
and peak in the Wed through Fri time frame.

There has been a strong signal amongst all the model guidance for
the last several days. The EPS/NAEFS situational awareness table
indicates parameters outside the models climatology which is signal
for the potential of a highly anomalous event...in this case heat &
humidity. Near record high temperatures will be possible. There are
fairly high probs of temps reaching well into the 90s for a couple
days and perhaps flirting with 100 degrees in some spots. Afternoon
heat indices in the 95 to 104 degree range are possible at times. It
will remain quite muggy at night so that will be another concern.

Strong upper level ridging in place will promote mainly dry weather
for much of next week. That being said...near record heat may
trigger the risk of a few t-storms at times but given lack of
synoptic scale forcing dry weather will dominate.



&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
Forecast Confidence Levels:

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

Today: Moderate Confidence

VFR with gusty SW winds to start today. Still some uncertainty
with how thunderstorms evolve today with some guidance showing
thunderstorms developing by 16 to 17z over southern VT and NH
and moving ESE. The highest confidence in thunderstorms is at
the BDL, BAF, and ORH between 18-22z. Further east, still some
uncertainty on how well thunderstorms will hold together for
BED, BOS, and PVD between 19-23z. FMH, HYA, and ACK should only
see rain showers but not out of the question for embedded
thunder after 00z.

Tonight: Moderate Confidence

Showers begin to taper off after 00z in the west and 06z in the
east. MVFR/IFR possible across eastern terminals.

Tomorrow:

VFR with northerly winds at 10-15 knots.


KBOS TAF...Moderate confidence in TAF.

VFR with gusty SW winds to start today. Guidance has sped up
timing of the thunderstorms now to 19z though 22z. Low chance
for a second round of thunderstorms after 22z. Light rain and
MVFR CIGS after 02z


KBDL TAF...High confidence in TAF.

VFR with gusty SW winds to start today. Strong thunderstorms are
likely starting 20/21z through about 23z/00z.


Outlook /Saturday Night through Tuesday/...

Saturday Night through Sunday Night: VFR.

Monday through Tuesday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels:

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

Today:

Increasing SW winds gusting up to 25 knots. A cold front will
sweep across the waters this evening. Thunderstorms will form
along this cold front inland this afternoon and weaken as they
approach the waters. A couple storms could still reach the
waters and bring strong wind gusts and lightning near the
coastal waters this evening. Seas 2-4 feet.

Tonight:

Steady light to moderate rain with embedded thunder possible.
Winds shift WNW and decrease to 5-10 knots overnight. Seas 2-3
feet.

Tomorrow:

Rain tapers off in the morning with clearing conditions in the
afternoon. Winds turn north and gust 15 to 20mph. Seas 2-4 feet.

Outlook /Saturday Night through Tuesday/...

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

Sunday: Winds less than 25 kt. Seas locally approaching 5 ft.

Sunday Night through Tuesday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 8 AM this morning to 8 PM EDT this
     evening for ANZ230>237-251.
     Small Craft Advisory from 11 AM this morning to 11 PM EDT this
     evening for ANZ250-254.

&&

$$

SYNOPSIS...KP/Frank
NEAR TERM...KP
SHORT TERM...KP
LONG TERM...Frank
AVIATION...KP/Frank
MARINE...KP/Frank