918
FXUS61 KBOX 201741
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
141 PM EDT Mon Jul 20 2026

.WHAT HAS CHANGED...
Gale Watch issued for Tuesday afternoon through Wednesday early
evening.

&&

.KEY MESSAGES...

- Seasonable summer weather today with temperatures in the 70s
  to mid 80s, with seabreezes near the coasts.

- Active weather Tuesday and Wednesday. Potential for hazardous
  marine conditions, high surf, soaking downpours and a limited
  risk for severe weather.

- Drying out late-week with a return to more seasonable
  temperatures and lower humidity levels into next weekend.

&&

.DISCUSSION...
KEY MESSAGE 1...Seasonable summer weather today with temperatures in
the 70s to mid 80s, with seabreezes near the coasts.

Another great day of pleasant summer weather to open the
workweek. High pressure near vicinity of Cleveland OH builds
south, and brings a modest WSW to SW wind later in the day.
Local seabreezes still look to develop, but full sun with highs
in the upper 70s to mid 80s. A touch cooler along the coasts
with the seabreezes. Clear skies continue tonight but we`ll be
starting to increase moist advection. There could be some patchy
mist or low clouds in interior portions of Southern New England
but probably not much impact.

KEY MESSAGE 2...Active weather Tuesday and Wednesday. Potential for
hazardous marine conditions, high surf, soaking downpours and a
limited risk for severe weather.

As the aforementioned high pressure cell moves offshore, in its
wake is an approaching frontal system over the Great Lakes
region with rather strong mid-upper level winds accompanying it.
Besides also leading to a tightening southerly pressure
gradient, a southerly 925-850 mb jet upwards of 60 kt will
permit strong moist advection and high IVT as PWATs rise to
2.25" along the system`s cold front/frontal occlusion Tue
night/Wed. Several potential issues to Southern New England
Tuesday into Wednesday. Ranked in order of highest to lowest
confidence, these range from hazardous marine conditions/high
surf, another round of soaking downpours, and a more limited
risk for strong/severe thunderstorms potentially into the
overnight hours.

See the Marine portion for more details. Gale Watches have now
been hoisted on most waters starting Tuesday afternoon through
Wednesday early evening; multi-model-ensemble 34+ kt wind probs
remain in the 50-75% range in the Gale Watch area, highest the
further east/offshore one goes. The issue is on mixing in the
southwesterly warm advection pattern, which those coarser-res
ensembles can struggle to resolve, but potential exists for
parts of or all of the Watch to see gusts into gale force range.
Although they`re mostly wind waves in a southerly fetch, waves
build to upwards of 12 ft and while not a beach day by any
stretch of the imagination, the potential exists for high surf
and later shifts will need to consider high surf or rip current
headlines. Less common to see gale watches in the summer
months, so hopefully getting the Watch out now conveys to
mariners that conditions could turn hazardous especially Tuesday
night and into Wednesday when factoring in the winds and
building rough seas.

Showers and thunderstorms begin to increase Tuesday afternoon,
and especially late in the day and into the Wednesday morning as
a combo of rising dewpoints and increasing upper support from
being placed in the poleward exit region of a 70-kt 500 mb
jetstreak provides additional upper support. Although severe
weather potential looks quite a bit greater well to our west,
increasing MUCAPEs and K- indices into the Tue overnight support
a risk for embedded stronger storms. Given the lower-level
winds improve overnight, some risk for straight line wind damage
and/or a brief spin-up are possible, but would hinge on
mustering enough 0-3 km CAPE. Wednesday might harbor a better
chance at stronger daytime storms as the front will have moved
offshore allowing for greater destabilization, and we`d be
placed under the upper trough with still favorable mid/upper
windfields.

In terms of rainfall, it looks like areas along the southern CT,
south coast and the Cape and Islands stand to see the most rain, at
the expense of interior Southern New England. Ensemble 24-hr QPF
probs paint moderately high (40-70%) probs of rain totals AOA 1 inch
along the southern/southeast coast, and lower (< 40%) to the north
and west. These areas have been getting quite a bit of rain lately,
especially out over Cape Cod. But high FFG owing to the sandy
soil could limit flooding. If we do get persistent downpours in
some of our RI/southeast MA larger cities along a stalling
frontal zone, then the risk would increase but this is
uncertain.

KEY MESSAGE 3...Drying out late-week with a return to more
seasonable temperatures and lower humidity levels into next weekend.

Cold front stalls well offshore by Thurs, with an expansive high
pressure across the Great Lakes ridging into the area late this week
into the weekend. Temperature profiles are pretty cool for late
July, at around +6 to +10C, but hard to get too cool with the sun
angle being as high as it is. Thus expect seasonable temperatures,
low humidity and dry weather late this week right through most of
the weekend. Really not until Sunday when we get into a southerly
return flow and with that comes increasing humidity levels.

&&

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

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

18Z TAF Update:

Through Tonight: Moderate confidence.

Mainly VFR; Sea breezes along the south shore and north coast,
but in-and-out around Boston Harbor. Chances for fog increase
more during the early morning in interior Southern New England
and mentioned MVFR mist as a starting point. Winds become light
SW.

Tuesday: Moderate confidence.

General deterioration to MVFR-IFR ceilings by afternoon, with
risk for showers and possible storms after 18z. Better potential
for storms Tue night. Winds become SE to S and increase to
10-15 kt with gusts 20-25 kt.

KBOS Terminal...Moderate confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday Night through Saturday/...

Wednesday: Mainly VFR, with local MVFR possible. Windy with
gusts up to 35 kt. Chance SHRA, chance TSRA.

Wednesday Night: VFR. Windy with local gusts up to 30 kt.
Chance SHRA.

Thursday through Saturday: VFR.

&&

.MARINE...
Forecaster Confidence Levels...

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

Tranquil boating conditions are expected today and into tonight.
Winds turn southeast near the coasts around 10 kt this
afternoon; otherwise winds to turn SW around 10 kt, to around
10-20 kt overnight. Seas around 3 ft or less, but build to
around 3-4 ft tonight.

Gale Watches have been posted for most of the eastern and
southern waters for Tue afternoon through Wed evening.
Strengthening southerly winds Tuesday but more into the SCA
range during the daytime hours. Mariners will need to be
prepared for onset of gale-force gusts for Tue night into the
first part of Wed. Seas will build and become increasingly
rough, especially by Tue night, and could reach upwards of 12
ft on the southern outer offshore waters. Risk for
thunderstorms, too. The combo of all of these means dangerous
marine conditions are possible.

Outlook /Tuesday Night through Saturday/...

Wednesday: Moderate risk for gale force winds with gusts up to
40 kt. Rough seas up to 11 ft. Chance of rain showers, chance
of thunderstorms.

Wednesday Night: Low risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 11 ft. Chance of rain
showers.

Thursday: Winds less than 25 kt. Areas of rough seas. Chance of
rain showers.

Thursday Night: Winds less than 25 kt. Seas up to 5 ft. Chance
of rain showers.

Friday: Winds less than 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.

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Gale Watch from Tuesday afternoon through Wednesday evening
     for ANZ231>235-250-254>256-280>283.

&&

$$

DISCUSSION...Loconto
AVIATION...McMinn
MARINE...Loconto