848
FXUS61 KBOX 160508
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
108 AM EDT Wed Jul 16 2025

.SYNOPSIS...
Building heat and humidity continues this 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.

&&

.NEAR TERM /THROUGH TODAY/...
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 lower 70s.

Rather quiet weather continues into this evening. Mainly clear
to start, but already spotted fog and stratus forming off the
coast. Much like past night, this fog and stratus should reach
at least the coastal plains of RI and southeast MA. A light
southwest wind should limit the northward extend of this across
eastern MA. Thinking the I-90 is the northernmost limit. Low
clouds and fog could be farther north than that within the CT
River valley.

Minor tweaks to bring temperatures back in line with observed
trends.

Previous Discussion...

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 largely 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.

&&

.SHORT TERM /TONIGHT THROUGH 6 PM THURSDAY/...
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 mid afternoon
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.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
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.

&&

.AVIATION /05Z WEDNESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels...

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

High confidence.

Low clouds and fog will bring IFR/LIFR conditions to much of
South Coast, Cape Cod, and Islands through sunrise, possibly
advancing into NE CT and most of RI/SE MA. These lower ceilings
will retreat southward after sunrise leaving VFR conditions by
early afternoon, but will then return around sunset and persist
tonight once again with widespread IFR/LIFR into Thu morning.

Otherwise, VFR with S/SW winds through tonight. Gradient remains
weak enough to allow for sea breezes along E MA coast for a time
later this morning into early afternoon, before S winds return.

Later tonight, areas of MVFR ceilings develop with showers
possible in western New England overnight, perhaps spreading
into more of southern New England Thu morning. Conditions then
improve again to VFR but we may see a round of showers/storms
later in day, especially in western MA/western CT.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Thursday Night through Sunday/...

Thursday Night: VFR. Breezy. Slight chance SHRA.

Friday through Saturday: VFR.

Saturday Night: VFR. Slight chance SHRA.

Sunday: Mainly VFR, with local MVFR possible. Chance SHRA,
slight chance TSRA.

&&

.MARINE...
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 Night through Sunday/...

Thursday Night: Low risk for Small Craft Advisory winds with
gusts up to 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.

Saturday Night: Winds less than 25 kt. Slight chance of rain
showers.

Sunday: Winds less than 25 kt. Chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
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.
     Air Quality Alert from 11 AM this morning to 11 PM EDT this
     evening for MAZ008>011.
RI...Heat Advisory until 7 PM EDT Thursday for RIZ001>007.
MARINE...None.

&&

$$

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