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003
FXUS61 KBOX 131314
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
914 AM EDT Thu Jun 13 2024

.SYNOPSIS...
Sunny and warm today with gusty southwest winds. Warm and muggy
Friday with dewpoints in the 60s. Scattered severe thunderstorms
possible with the passage of a cold front Friday afternoon and
evening. A few spot showers will remain possible across
eastern MA/RI into Saturday, but otherwise a dry weekend with
cool nights and mild days with much less humidity is expected.
Near record high temperatures along with excessive heat/humidity
are possible next week...beginning Tuesday and perhaps
continuing through Thursday or Friday.

&&

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

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9 AM Update...

Very few changes were made to the forecast with this update,
with just minor modifications to dewpoints which are running a
few degrees higher than forecast across the Cape and the
Islands. Given slightly elevated dewpoints, we continue to have
heightened awareness regarding some stratus/fog that is
currently east-southeast of Nantucket that may back in across
the island this afternoon.

Key Point

* Sunny and warm with increasing dewpoints

Southwest flow and WAA begins to kick in today allowing for
850mb temps to climb to +15C. With much warmer temps aloft, the
convective temp jumps into the mid 80s across the region,
meaning the diurnal cumulus will not be as widespread as the
previous two days. With mostly sunny skies and WAA, temperatures
should be able to reach the mid to upper 80s. Dewpoints will
also be on the rise tomorrow into the upper 50s to low 60s.
Winds will become gusty up to 20mph in the afternoon with steep
low level lapse rates and mixing potential up to 6-7kft.
-- End Changed Discussion --

&&

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

Still under SW flow, dewpoints continue to rise into the low 60s
overnight. Even with mainly clear skies, temperatures will stay on
the warm side overnight only dropping into the mid 60s. SW winds
continue to increase overnight gusting 20mph.

Tomorrow

Key Points

* Warm and muggy start to the day
* Scattered severe thunderstorms across western MA and CT

Friday will be a warm and humid day with temperatures quickly rising
into the mid to upper 80s and dew points reaching the low to mid
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 is some disagreement among the hi-res guidance on how much
instability will be set up with the HRRR only showing 500 J/kg of
SBCAPE while the NAM3K shows up to 1200 J/kg. Deep layer shear
increases with the passage of the shortwave up to 30-40 knots,
supportive of organized linear clusters of severe
thunderstorms. Storms likely initiate off the high terrain in
Western MA/CT and southern VT shortly after 12pm. Storms then
move east through the afternoon, but quickly weaken approaching
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 across western MA and CT 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 and linear storm mode promoting straight
line winds. The hail threat looks very low at this time with very
meager mid level lapse rates only between 4-5C/km and the freezing
level above 10kft. The tornado threat also appears very low
with very little low level shear and linear storm mode will
promote upscale growth rather then discrete supercells.

Heavy Rain threat:

Although the storms will be progressive with little to no training
expected, PWATS will be increasing into the 1.6-1.8 inches. Long
skinny CAPE profiles and warm cloud depths approaching 10kft are
supportive of heavy downpours. HREF 3hr PMM does highlight 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.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Key Points...

* Weakening showers/t-storms work towards the south coast Fri evening
* A few lingering spot showers possible across eastern MA/RI Sat
* Dry & very pleasant Sat night & Sun with low humidity
* Excessive Heat/Humidity begins Tue possibly continuing through Fri
* Near record highs next week...Heat indices may reach between 95-104

Details...

Friday night...

Scattered strong to severe storms that are expected to the northwest
of I-95 into early Friday evening will be weakening on approach and
especially southeast of Boston to Providence corridor. Given the
loss of diurnal heating coupled with southwest flow and poor mid
level lapse rates...instability will be tough to maintain after
sunset. So while the activity will probably survive to the Cape &
Islands it will be in a weakening form. So expect the severe weather
threat to have come to an end.

Some showers may linger into the overnight hours especially across
eastern MA/RI. This a result of upper level energy approaching from
the west and hints of an inverted trough.

Saturday...

A few low topped showers will remain possible on Sat across eastern
MA/RI with lingering upper level shortwave energy/cold pool aloft.
Not expecting a washout and it will be cooler with lowering humidity
through the day. High temps will generally be in the middle to upper
70s...but a few spots may approach 80 in the lower CT River Valley.

Saturday night and Sunday...

High pressure building over the region will result in good
radiational cooling conditions Sat night...especially with the dry
airmass moving into the region for mid June standards. Overnight
lows will bottom out in the middle to upper 40s in some of the
coolest outlying locations in western MA with mainly 50s elsewhere.
Plenty of sunshine on Sunday will result in highs mainly in the
upper 70s to near 80 with low humidity...so quite a comfortable day
to close out the weekend.

Next Week...

The main concern continues to be the potential for excessive heat
and humidity next week. An anomalous upper level ridge will build
northward into southern New England. A warming trend begins on
Monday, but the significant heat/humidity potential looks to begin
Tuesday and perhaps continue through Thursday or Friday. Timing and
magnitude of the heat/humidity are uncertain at this time...but
current indications are that it may peak in the Wed/Thu time frame.

There has been a strong signal amongst all the model guidance 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 at least 1-
2 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. We should have a better idea on the magnitude and timing of
the heat in the next few days.

&&

.AVIATION /13Z THURSDAY THROUGH MONDAY/...
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Forecast Confidence Levels:

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

12z TAF Update...

Today: High Confidence.

VFR with SW winds increasing to between 10 and 15 knots.

Tonight: High Confidence

VFR. SW winds at 10-15 knots. Low risk some stratus and fog
scrape the Cape/Islands...but confidence not high enough to
insert into the TAFS at this time.

Tomorrow: Moderate Confidence

VFR and dry in the morning. Thunderstorms will develop across
eastern NY and Western MA and CT in the mid to late afternoon.
Thunderstorms then move east and begin to weaken in the evening.
Some storms may have strong winds and torrential rainfall.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Friday Night through Monday/...

Friday: VFR. Breezy. Scattered SHRA, isolated TSRA.

Friday Night: Mainly VFR, with areas MVFR possible. Chance
SHRA, slight chance TSRA.

Saturday: VFR. Breezy. Chance SHRA.

Saturday Night through Sunday Night: VFR.

Monday: VFR. Breezy.
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&&

.MARINE...
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Forecaster Confidence Levels:

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

Today and tonight:

Increasing SW winds gusting to 20 knots. Seas increase to 2-4
feet.

Tomorrow:

Cold front approaches the waters Friday evening. Low risk for
small craft conditions across the northeast waters with gusts to
25kt possible. Seas approaching but generally less than 5 ft.

Outlook /Friday Night through Monday/...

Friday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Isolated rain showers.

Friday Night: Winds less than 25 kt. Chance of rain showers.

Saturday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain showers.

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 Monday: Winds less than 25 kt.
-- End Changed Discussion --

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

$$

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