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618
FXUS61 KBOX 151836
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
236 PM EDT Tue Jul 15 2025

.SYNOPSIS...
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Building heat and humidity continues week, peaking tomorrow,
but possibly lasting into Thursday or Friday as high pressure
remains offshore. A cold front should bring showers and
thunderstorms Thursday and Friday before relief from the heat
arrives this weekend.
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&&

.NEAR TERM /THROUGH TONIGHT/...
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230 PM Update:

Key Messages:

* Isolated (a couple?) showers or garden variety thundershowers
  along seabreezes thru sundown, but mainly dry weather for the vast
  majority of Southern New England.

* Low clouds and fog return, similar to last few nights. Muggy lows
  upper 60s to low 70s.

Details:

Remains a very warm to hot day across Southern New England, with
dewpoints in the upper 60s to low 70s leading to elevated heat
indices. First-order stations (ASOS METAR reports) have reported
heat indices in the mid 90s as of this writing, although the
usual variation exists comparing these to mesonet sites.
Although we are condtionally-unstable with sfc-based CAPEs in
the 1500-2000 J/kg range, lack of forced synoptic ascent and
weak capping have largerly stunted any showers or thunderstorms
from popping up. There has been some showers along the CT-RI
south coastal seabreeze, and we could see a pop-up shower or
thunderstorm develop into the Merrimack Valley too due to the
seabreeze there and perhaps in/around the terrain. Other than
these mesoscale- driven areas, the vast majority of Southern New
England ends up being dry, so kept PoP at no worse than 20%
along the interior and along the south coast. Any shower or
thundershower activity which pops up will diminish after
sundown.

Aside from that though, the forecast for the evening should end up
being pretty similar to the last few overnights. Once the sun goes
down, stratus/mist re-develops and returns northward from the
southern coastal waters. Warm and humid evening with lows upper 60s
to lower 70s.
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&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
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230 PM Update:

Key Messages:

* Hot, humid and dry Wednesday, the peak of the spell of heat
  and humidity. High heat indices in the upper 90s to lower
  100s.

* Increasing clouds, scattered passing showers with brief downpours
  moving in during the second half of the overnight. Hazardous
  weather isn`t expected. Very warm and muggy night with lows in the
  low to mid 70s!

Details:

Hot and humid weather continues into Wednesday as well, as a
shortwave ridge briefly builds into Southern New England. In
addition to even warmer temperatures aloft, subsidence aloft brought
on by this shortwave ridge will serve to suppress any diurnal
showers or thundershowers despite otherwise ample instability. Heat
Advisory still remains valid, with air temps in the low to mid 90s
contributing to heat indices around the upper 90s to lower 100s.
Daytime seabreezes look to develop too, but these won`t do very much
at all to cut into the heat and humidity.

Shortwave ridge axis pulls offshore during the midafternoon
hours on Wed, and this will allow for a weak shortwave trough
now over the OH Valley to slowly progress ENE through the
northern mid-Atlc and Southern New England Wed evening.
Increasing cloud cover from both the coastal waters and from
interior western New England should keep temps warmer during the
overnight with lows in the mid 70s! The shortwave trough will
also bring with it a threat for showers or rumbles of thunder;
with PWAT values on the rise to nearly 2" per SREF mean output,
brief downpours can`t be ruled out but the coverage of showers
may end up being more scattered and those that do develop should
be moving along. Given those factors, we are not expected to
see the really high rain rates/heavy rain footprints like we saw
during the early morning hours late last week.
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&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
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Key Messages:

* Heat and humidity persists into Thu or Fri with increasing chances
  of showers/storms.
* Relief arrives this weekend.

We remain in hot/humid airmass through end of this week, awaiting
approach of mid level short wave and fairly strong cold front which
will eventually bring relief from the heat and humidity this
weekend. Not seeing large timing differences with this cold front
passage, which should be sometime Thursday night into Friday
morning. Larger timing differences are present with this front when
it likely returns back as a warm front Sunday, then moves offshore
again as a cold front Monday.

Still thinking Thursday is the day with the greatest risk for
afternoon and evening showers and thunderstorms. Given the heat and
humidity expected to be in place, a few thunderstorms could produce
strong winds. The greater concern remains the possibility for
downpours and localized flooding. Friday and Saturday have trended
more rain-free behind the aforementioned cold front. Then had to
mention more showers Sunday into Monday, although confidence in
the timing is rather modest.
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&&

.AVIATION /18Z TUESDAY THROUGH SATURDAY/...
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Forecaster Confidence Levels...

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

18z TAFs: High confidence.

Other than a hit-or-miss SHRA thru 23z, vast majority of the
TAFs are currently VFR/dry except for continued LIFR stratus at
ACK. IFR- LIFR stratus and fog return northward tonight for
most areas near and south of I-95 as well as in the CT Valley,
but unlikely to advance much further north/east from there.
Expect stratus and fog to dissipate/retreat into the southern
waters by 13-14z Wed with VFR conditions. Better chance at
widespread MVFR-IFR Wed evening with possible SHRA 2nd half of
the Wed overnight/early Thurs AM.

Light south winds, seabreezes near the coasts dissipating
dissipating by 00z Wed. Similar theme regarding winds on
Wednesday, although speeds around 5-10 kt.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Thursday through Saturday/...

Wednesday Night: Mainly VFR, with local MVFR possible. Chance
SHRA, patchy BR.

Thursday: Mainly VFR, with local MVFR possible. Breezy. Chance
SHRA, chance TSRA.

Thursday Night: VFR. Breezy. Slight chance SHRA.

Friday through Saturday: VFR.
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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.

High confidence through end of the week.

Sub-SCA winds and seas through Wednesday night with modest SW
flow persisting. Patchy marine fog and stratus could hamper
visibility for mariners tonight. Dry weather on Wednesday but we
could see scattered showers develop on the waters overnight
Wednesday evening/early Thursday morning along with returning
marine fog.

Outlook /Thursday through Saturday/...

Wednesday Night: Winds less than 25 kt. Slight chance of rain
showers, patchy fog. Local visibility 1 to 3 nm.

Thursday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of seas approaching 5 ft. Chance of rain
showers, slight chance of thunderstorms.

Thursday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Slight chance of rain showers.

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

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

Saturday: Winds less than 25 kt.
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&&

.BOX WATCHES/WARNINGS/ADVISORIES...
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CT...Heat Advisory until 7 PM EDT Thursday for CTZ002>004.
MA...Heat Advisory until 7 PM EDT Thursday for MAZ003>007-010>021-
     026.
RI...Heat Advisory until 7 PM EDT Thursday for RIZ001>007.
MARINE...None.
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&&

$$

SYNOPSIS...Belk/Loconto/FT
NEAR TERM...Loconto/FT
SHORT TERM...Loconto/FT
LONG TERM...Belk
AVIATION...Belk/Loconto/FT
MARINE...Belk/Loconto/FT