886
FXUS61 KBOX 220617
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
217 AM EDT Tue Jul 22 2025

.SYNOPSIS...
Cooler pattern persists through Tuesday night under high
pressure.Warming trend starts midweek and humidity increases going into
Friday. Dangerous heat is possible for Friday as highs approach the
upper 90s and heat indices climb into the lower 100s. Heat and
humidity continue through the weekend, but at a lesser degree
following a cold front Friday. The chance for showers and storms
returns Friday through the weekend after dry conditions for much of
the week.

&&

.NEAR TERM /THROUGH TODAY/...
2:30 PM Update:

Key Message:

* Pleasant weather continues through the rest of the afternoon with
  just a few fair weather diurnal cumulus and haze aloft.

* Efficient radiational cooling overnight with widespread lows
  in the 40s and 50s

* Similar conditions on Tuesday with seabreezes

Details:

Rest of the Afternoon:

High pressure over Ontario continues to build over New England
through this afternoon. At the surface this as resulted in pleasant,
albeit breezy conditions. Northwest winds should continue to
decrease through the remainder of the afternoon as the pressure
gradient wanes. Otherwise, high temperatures are running a few
degrees higher than the NBM, especially in the interior. Still
thinking that most locations top off in the upper 70s to perhaps the
lower 80s with fall-like dewpoints.

Overnight:

Clear skies continue overnight as the center of high pressure crests
over the region. These clear skies and a decoupling boundary layer
will result in strong radiational cooling regionwide. Certainly a
comfortable, if not slightly chilly night ahead with most areas
dropping into the lower 50s and perhaps as low as the upper 40s in
places where cooling is maximized. There is also a chance for some
localized patchy fog along portions of the CT river valley and in
low-lying swampy areas.

&&

.SHORT TERM /TONIGHT THROUGH 6 PM WEDNESDAY/...
230 AM Update:

Key Messages:

* Cooler weather continues

* Weaker synoptic-scale winds allow for stronger seabreezes

Details:

Cool temperatures Tuesday morning quickly recover as the column
quickly becomes well-mixed. Expecting slightly warmer temps
tomorrow with lower winds. Highs should top out in the upper 70s
for most, but a few more interior locations will eclipse the
80-degree mark. Weaker synoptic pressure gradient allows for
stronger seabreezes tomorrow afternoon. Furthest inland extent
of the seabreezes will be across eastern Massachusetts where the
low level wind field shifts to the east as high pressure shifts
offshore. As a result, the NBM has high temperatures staying in
the low to mid 70s across coastal Massachusetts.

Another cool night on tap Tuesday night with radiational cooling
driving temperatures down into the middle 50s. Rising dewpoints
should keep temperatures from falling as much as Monday night.
Moisture will continue to increase early Wednesday as return flow
behind high pressure increases.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Key Messages:

* Warming trend kicks off midweek, along with increasing humidity
  through Friday

* Elevated heat indices Thursday, possibly reaching dangerous levels
  by Friday. Heat headlines possible.

* Dry through Thursday before front arrives Friday, bringing a
  chance for showers and storms that may extend into the weekend.
  However, uncertainty remains.

Details...

An upper level ridge settled over much of the eastern US and surface
high pressure over the waters just east of southern New England
begins to shift more south and east midweek heading into Friday.
This will help kick off a warming trend and allow humidity to
increase with it. Thursday heat indices are expected to reach the
mid 90s, but Friday is expected to be the hottest day of this
stretch with heat indices in the low 100s possible. Overall guidance
is in good agreement in Friday being the hottest; 925 mb
temperatures across the deterministic models are approaching +30C,
and the ensembles are just under that with mean 925 mb temperatures.
With good mixing, some breezier conditions can also be expected, but
it won`t be much relief from the heat. Heat headlines may be needed
further down the line, especially for Friday.

With a cold front approaching Friday, there`s a low chance for some
showers and storms this weekend. There is still some uncertainty,
though, on severity and timing. CSU ML guidance has the region under
a low (5%) probability for severe weather on Friday, and NSSL ML
probs are also still low at this time for Friday. Severe risk will
depend on if the front arrives in time to use peak heating to kick
off some storms, so its track and timing is something we will
continue to monitor.

Guidance is still indicating that this cold front may stall over the
waters just south of southern New England, leading to a more
unsettled pattern for the weekend. Any showers and storms that pop
up will likely remain around wherever the front ends up stalling
out. Highs this weekend will decrease slightly following the front`s
passage, but it will still be warm and humid across the region. Not
much recovery from the heat is expected overnight starting Thursday
night and lasting through Monday morning, as lows will only dip into
the low 70s and upper 60s.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
Forecaster Confidence Levels...

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

06z TAF Update:

Tuesday...High confidence.

VFR. Light N winds 5-10 kts. Seabreezes develop on both coasts
which could develop on the earlier end of seabreeze climo,
around 14z-15z for BOS. Few areas of diurnal FEW-SCT cloud
decks may develop toward the afternoon around 5-8 kft. Sea
breezes kick out between 00-03z with winds turning back S.

Tuesday Night: Moderate confidence.

VFR conditions. Light S/SSW winds. Potential for areas of
radiation FG/BR for BDL/BAF and SE MA. Lower confidence on the
coverage/extent of it.

Wednesday: High Confidence.

VFR. SW/SSW winds 6-12 kts.

KBOS terminal...High confidence in TAF.

KBDL terminal...High confidence in TAF.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: VFR.

Thursday through Thursday Night: VFR. Breezy.

Friday through Friday Night: VFR. Breezy. Slight chance SHRA.

Saturday: VFR. Chance SHRA, isolated TSRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Through Tuesday Night: High confidence.

NW winds then subside to light levels tonight, which remain
light northerly on Tue (nearshore seabreezes). Winds then become
S/SW around 5-10 kt Tue night. Seas mainly 3 ft or less through
the period, except nearing 4 ft early this morning. No
obstructions to visibility expected thru Tue night.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: Winds less than 25 kt.

Thursday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas locally approaching 5 ft.

Thursday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of seas approaching 5 ft.

Friday: 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 Night: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain showers, isolated thunderstorms.

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

&&

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

&&

$$

SYNOPSIS...Hrencecin/FT
NEAR TERM...FT
SHORT TERM...FT
LONG TERM...Hrencecin
AVIATION...Mensch
MARINE...Hrencecin/FT