Severe Thunderstorm Warning 18, NWS Boston/Norton, MA

Area Forecast Discussion
National Weather Service Boston/Norton MA
306 PM EDT Thu Jun 18 2026

.WHAT HAS CHANGED...
Gale Warnings posted for the eastern coastal waters as well as
the MA bays and sounds.

&&

.KEY MESSAGES...

- Gusty southerly winds with scattered showers and thunderstorms possible
  late this afternoon and evening. Risk for a few severe storms
  with damaging wind as the primary threat.

- Dry weather Friday and Saturday with gusty west winds.

- Chances for a widespread rain Monday into Tuesday. Drier with
  seasonable temperatures follow for midweek.

&&

.DISCUSSION...
KEY MESSAGE 1...Gusty southerly winds with scattered showers and
thunderstorms possible late this afternoon and evening. Risk for a
few severe storms with damaging wind as the primary threat.

Plentiful cloud cover around this morning and early afternoon has
lead to limited building of instability so far this afternoon ahead
of the cold front. However, we are starting to see breaks in the
clouds in western MA and CT. SPC mesoanalysis shows fairly strong
shear/helicity values with 0-6 km shear 60 kts or greater and SRH
values 200-500 m2/s2 which is not surprising given the strong LLJ
presence in the region. This is generally on track with what
was anticipated previously with a low instability, high shear
environment for this afternoon and evening. We are still seeing
the threat for scattered showers and thunderstorms this
afternoon/evening, but there is some question on the coverage
due to the limited instability. Based on high-res CAMs the main
line of storms pushes into western MA closer to 3 PM pushing
eastward through the early evening timeframe. Based on the
environment, it is still supportive of some strong to severe
storms with damaging winds as the main threat followed by a low
risk for a tornado or two given the strong helicity values. Any
linger showers or storms push out of the east coast/Cape area by
10 PM.

KEY MESSAGE 2...Dry weather Friday with gusty west winds.

Dry conditions expected Friday post-cold front. A strong
pressure gradient remains in place as low pressure tracks to the
north resulting in gusty west winds 25-35 mph in the
afternoons. Temperatures will be fairly seasonable ranging in
the mid 70s to low 80s with comfortable humidity levels.

KEY MESSAGE 3...Chances for a widespread rain Monday into
Tuesday. Drier with seasonable temperatures follow for midweek.

Gusty westerly winds continue into Saturday, but will be dry with
high temperatures in the mid 70s to low 80s near the coast and low
humidity. For Sunday, temperatures in the 80s creep a bit farther
inland, with a little higher humidity. There does look to be some
chances for afternoon showers Sunday afternoon into the evening, but
better potential for a widespread rain comes Monday and into Tuesday
as low pressure tracks northward through the Mid Atlantic and into
New England. NBM probability for at least 0.75" of rain Monday
morning through Tuesday morning are between 60% and 75% for the
area. Some uncertainty remains in the track of the low, as there is
some variation among the global models. This will influence the
forecast rainfall amounts, but overall, does look to be a good
wetting rain.

Behind this system, high pressure starts to push in from the west,
bringing a return to drier weather and seasonable temperatures
through the middle of the work week.

&&

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

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

Today...Moderate confidence.

A period of MVFR with even localized IFR conditions possible in
areas near the Cape. The main threat for scattered SHRA and
TSRA will be this afternoon and early evening ahead of the cold
front. A few strong to severe TSRA are possible. Main threat
will be between 19-00Z for showers/storms.

A strong LLJ will result in southerly wind gusts of 25 to 35 kt
by afternoon with a few gusts perhaps near 40 kt.
Localized/brief stronger winds possible if any severe TSRA
develop. LLWS expected towards the Cape and islands.

Tonight...High confidence.

Any lingering SHRA/TSRA should depart the coast by 01Z with
conditions quickly improving to VFR thereafter. Lower cigs/vsbys
may linger until midnight or so for parts of the Cape and
Islands. WSW winds 10-15 kts shifting to the W overnight.

Friday...High Confidence.

VFR. Gusty W winds up to 20-30 kt.

KBOS Terminal...Moderate confidence in TAF.

KBDL Terminal...Moderate confidence in TAF.

Outlook /Friday Night through Tuesday/...

Saturday through Saturday Night: VFR. Breezy.

Sunday: VFR. Chance SHRA, slight chance TSRA.

Sunday Night: VFR. Slight chance SHRA.

Monday: Mainly VFR, with local IFR possible. Breezy. Chance
SHRA, slight chance TSRA.

Monday Night: Mainly VFR, with local MVFR possible. Windy with
local gusts up to 30 kt. SHRA likely, slight chance TSRA.

Tuesday: VFR. Breezy. Chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Through Friday: High confidence.

Gusty S to SW winds expected today. Gale Warnings still in place
to account for the gusts 30-40 kts. Small Craft Advisories
continue for the southern waters, but will continue to monitor
for gusts that may exceed criteria for Gales as it may be close.
Rough seas and gusty winds likely linger across the outer
southern coastal waters into Saturday, but not confident enough
yet to extend the existing advisories.

Outlook /Friday Night through Tuesday/...

Saturday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of rough seas.

Saturday Night: Winds less than 25 kt. Local rough seas.

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

Sunday Night: Winds less than 25 kt.

Monday: Low risk for Small Craft Advisory winds with local
gusts up to 30 kt. Areas of rough seas. Slight chance of rain
showers. Local visibility 1 to 3 nm.

Monday Night: Strong winds with gusts up to 30 kt. Rough seas
up to 10 ft. Rain showers likely, slight chance of
thunderstorms.

Tuesday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas up to 5 ft. Chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Gale Warning until 7 PM EDT this evening for ANZ230-251.
     Gale Warning until 10 PM EDT this evening for ANZ231>234-250-
     280.
     Small Craft Advisory until 8 PM EDT Friday for ANZ235-237-
     254>256.
     Small Craft Advisory until 7 PM EDT this evening for ANZ236.

&&

DISCUSSION...Mensch/Sava
AVIATION...Mensch
MARINE...Mensch