267
FXUS61 KBOX 060724
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
324 AM EDT Fri Jun 6 2025

.SYNOPSIS...

Numerous showers and thunderstorms are expected to develop this
afternoon and evening with the greatest areal coverage north of the
Connecticut and Rhode Island borders. A few of these storms may
become severe and also result in localized flash flooding. Some
showers and perhaps a few isolated thunderstorms linger into
Saturday with seasonable temperatures making a return and
continuing into early next week. Dry conditions expected Sunday
heading into Monday before the next chance for some showers
arrives on Tuesday.

&&

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

Key Messages...

* Numerous showers & thunderstorms develop this afternoon/early
  evening...greatest areal coverage north of the CT/RI/MA border

* Scattered severe thunderstorms possible with the greatest risk in
  western/central and northeast MA

* Flood Watch issued for western/central and northeast MA as the
  ingredients support a localized flash flood risk

* Time of concern for severe weather is between noon and 10 PM with
  the highest risk in the 2 PM to 8 PM time frame

Details...

An active day of weather is on tap for the region later today into
this evening. A warm and humid airmass in place will generate modest
instability this afternoon. While it will not be as hot as
yesterday...highs will reach into the 80s with dewpoints in the 60s.
SPC SREF is indicating decent probs that Capes may reach or exceed
2000 J/KG today. This instability will be combining with a shortwave
and frontal/sea breeze boundaries to generate numerous showers and
thunderstorms. While we can not rule out an isolated shower/t-storm
this morning...expect the main show to be in the noon to 10 pm time
frame and particularly between 2 and 8 pm.

The instability is favorable for severe weather this afternoon and
evening...but there are some limiting factors too. The low level
wind fields are quite weak and the effective shear is marginal.
However...it does appear we may see a swath of 0-6 km shear reach 25-
35 knots with the focus north of the CT/RI/MA borders. That
certainly is enough for some storm organization along with the
threat of scattered severe thunderstorms. In fact...the
HRRR/RRFS/NAM/HREF all showing solid UH swaths in the 2-5 KM layer
which is often a good signal for severe weather. There also is good
support from various machine learning guidance which highlights those
areas in the best severe weather probs. This guidance also indicates
that the main threat will be localized damaging wind gusts. There is
a secondary concern for hail with decent mid level lapse rates.
Given the weak low level wind fields...feel the tornadic risk is
quite low which is also reflected in the machine learning guidance.

We also should mention that the forcing/deeper moisture is better to
the north of the CT/RI borders...but mid level lapse rates are
steeper to the south on the order of 7 C/KM. K index values though
indicate limited moisture...so any convection that is able to
develop will be isolated to scattered at best. However...given the
steeper mid level lapse rates and better instability any storm that
is able to develop may become severe. And perhaps the greatest risk
of hail from near I-90 to just south of the CT/RI border...where
forcing overlaps a bit better with the better ML Lapse rates.

Lastly...given Pwats exceeding 1.5 inches and relatively light low
level wind fields pockets of torrential rainfall will result in a
localized flash flood threat. The EMC HREF is indicating some probs
of the 6 hour QPF exceeding the 10 and even low probs of exceeding
the 100 year ARI. The HREF indicates 30 percent probs of rainfall
exceeding 3" inside 3 hours...which is often a good signal for the
potential of a localized flash flood threat. Given the above...we
have opted to issue a Flash Flood Watch for western/central and
interior northeast MA this afternoon into this evening. The risk for
2-3" of rain falling inside 2 hours will bring the potential for
localized flash flooding...particularly if it were to occur over a
vulnerable urban center.

&&

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

Key Messages...

* Bulk of the showers & t-storms diminish late this evening

* Additional showers/iso t-storms are expected Sat but severe
  weather is not expected...highs mainly between 75 and 80

Details...

Tonight...

The bulk of the showers and thunderstorms will wind down later this
evening as the shortwave departs coupled with the loss of diurnal
heating/instability. While a few spot showers will remain possible
overnight...another round of showers/isolated t-storms may begin to
work into our area toward daybreak Sat with the cold front. Low
temps tonight will mainly be between 60 and 65 degrees.

Saturday....

The approaching cold front will cross the region on Saturday. The
forcing along the front will bring another round of showers and
isolated thunderstorms to the region. The instability will be
considerably less than today...with MLCapes generally under 1000
J/KG. Therefore...the severe weather threat on Sat is rather low.
High temps will mainly be in the 75 to 80 degree range.

&&

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

Key Messages:

* Dry Sunday into Monday before more rain is possible Tuesday

* Clearing Wednesday into Thursday with highs reaching the low to
  mid 80s

Details...

Drier air moves in post-FROPA Sunday, bringing a break from the rain
through early Monday. Onshore flow Sunday afternoon will also bring
some relief from the heat to east coast areas. Sunday`s high temps
likely in the upper 70s to low 80s across the interior, especially
in the Connecticut River Valley, with the eastern coast and Islands
in the low 70s. Onshore flow continues through Monday, allowing for
a lengthier period of cooling and allowing for high temps to remain
in the low 70s across southern New England. Some guidance is
indicating a low moving to the northeast off the coast to our south
on Monday, bringing some scattered showers to the Cape and Islands;
however, there is also a good chance this low misses completely and
those areas remain dry. Southeast flow makes a return for Tuesday,
along with more rain chances.

A warm front is expected to move through Tuesday, placing the region
in the warm sector and elevating surface moisture, once again
bringing rain chances. With rain looking possible for most of the
day, highs are likely to remain in the 70s. A cold front passes
through Tuesday night/Wednesday morning, shifting winds back to the
west and ushering in some drier air. Drier and clearer conditions
look likely Wednesday heading into Thursday post-FROPA. With the
clearing skies, high temps look to rebound into the 80s for the
midweek period. Lows through the extended period not expected to
change much from night to night, remaining mostly in the 50s and 60s
across southern New England.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...

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

06z TAF Update...

Today...Moderate confidence.

Varying conditions across the region with mainly VFR conditions this
morning. Numerous showers and t-storms are expected to develop this
afternoon into this evening with the focus for them across
western/central and northeast MA. These storms will be capable of
producing pockets of torrential rainfall and locally strong wind
gusts. This activity will result in MVFR-IFR conditions with brief
LIFR conditions too possible in the stronger t-storms. Winds
generally less than 10 knots from varying directions across the
region.

Tonight...Moderate confidence.

The bulk of the showers and thunderstorms will wind down later this
evening as the shortwave departs. However...enough low moisture is
present to allow cigs/vsbys to drop into the MVFR-IFR levels tonight
across much of the region. Light S winds.

Saturday...Moderate confidence.

The cold front will approach the region from the west on Sat. This
will bring another round of showers and isolated t-storm to the
region. MVFR conditions will dominate but some improvement to VFR
levels may occur later in the day across the interior. Light SW
winds will begin to shift to the NW behind the cold front by late in
the day.

BOS TAF...Moderate confidence in TAF. Sea breeze kicks in by
12z/13z. Greatest risk for showers and thunderstorms in the vicinity
of the terminal will be in the 18z to 00z time frame.

BDL TAF...Moderate confidence in TAF. The main risk for showers and
thunderstorms in the vicinity of the terminal will be in the 18z to
00z time frame.

Outlook /Saturday Night through Tuesday/...

Saturday Night through Sunday: VFR.

Sunday Night through Monday: VFR. Slight chance SHRA.

Monday Night: Mainly VFR, with local IFR possible. Slight
chance SHRA.

Tuesday: MVFR/IFR conditions possible. Chance SHRA, isolated
TSRA.

&&

.MARINE...

Forecaster Confidence Levels:

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

Today through Saturday...High confidence.

The gradient will remain weak enough to keep winds/seas below small
craft advisory thresholds today and tonight. We think the bulk of
the convection will remain to the north and west of our waters later
today and tonight...but will have to watch the waters adjacent to
northeast MA. The other issue for mariners will be areas of fog
developing tonight...so vsbys may be reduced especially across the
southern waters.

A wave of low pressure will track near the Benchmark on Sat as a
cold front approaches the waters from the west. Some showers and
perhaps an isolated t-storm may accompany this front. Although winds
will remain below criteria...southerly swell may result in 5+ seas
developing on Sat and later shifts may need to consider headlines.

Outlook /Saturday Night through Tuesday/...

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

Sunday Night through Monday: Winds less than 25 kt. Seas
locally approaching 5 ft. Slight chance of rain showers.

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

Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Chance of rain showers, isolated thunderstorms.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Flood Watch from noon EDT today through this evening for
     MAZ002>006-008>012-026.
RI...None.
MARINE...None.

&&

$$

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