Lexington Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 272328
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
728 PM EDT Thu Aug 27 2026

.WHAT HAS CHANGED...
The overall threat for severe weather across southern New England 
has decreased. However, a risk for strong to severe storms remains 
for areas west of the Connecticut River through this evening.

&&

.KEY MESSAGES...

- A few stronger storms are possible, mainly west of the CT
  River Valley today.

- Spot shower or thunderstorm possible Friday, otherwise a 
  mainly dry and pleasant late-summer day.

- Seasonable temperatures and dry weather this weekend.

- Cloudy and unsettled early to mid next week with several
  opportunities for showers and storms, but the timing of them
  is uncertain.

&&

.DISCUSSION...
KEY MESSAGE 1...A few stronger storms are possible, mainly west of 
the CT River Valley today.

A seasonably warm and humid day is ongoing, helping fuel 
thunderstorms from the Mid-Atlantic into the New York City metro. 
However, the threat for severe storms across southern New England is 
decreasing, albeit not zero. This is highlighted by the current 
outlook, which indicates the greatest risk is mainly west of the 
Connecticut River Valley, where a Marginal Risk (level 1 out of 5) 
exists. The greatest concern is across the Berkshires and points 
west, where a Slight Risk (level 2 out of 5) exists. Driving today's 
weather is a mid-level closed low over southern Hudson Bay and a 
neutral to slightly positively tilted trough. Dynamics are modest, 
with 0-6 km bulk shear around 35 kt, CAPE values of 1,000-1,500 J/kg 
west of the Connecticut River, and effective helicity of 50-100 
m2/s2.

It is a tricky forecast, as there is sufficient instability across 
southern New England, with the greatest CAPE values remaining west 
of a Willimantic-Worcester-Fitchburg line. However, some high-res 
guidance suggests ongoing convection from the Mid-Atlantic into the 
NYC metro may work over the environment to our south, limiting the 
northward transport of higher instability into southern New England 
this afternoon. This could ultimately reduce the amount of 
instability available for storms later today. Nevertheless, any 
storms that do develop will have the potential for gusty winds, 
which remain the primary concern given DCAPE values around 800 J/kg. 
Small hail is also possible, and an isolated tornado cannot be ruled 
out. We continue to feel the greatest risk for any stronger storms 
is west of the Connecticut River Valley.

Today's 12z suite of guidance continues to support storm development 
across New York State by mid-afternoon, reaching western New England 
between 5-8 PM. The greatest risk for stronger storms will be during 
the late afternoon and early evening, primarily west of the 
Connecticut River Valley. Farther east, decreasing instability with 
the loss of daytime heating, marginal mid-level lapse rates around 
5.5-6.5 C/km, and limited moisture should result in a less favorable 
environment. A few storms may survive eastward into central and 
eastern southern New England, but coverage and intensity should 
diminish.

Mild overnight with stratus advecting in from the south, which may 
lead to low clouds and areas of fog mainly across RI into 
southeastern MA. 


KEY MESSAGE 2...Spot shower or thunderstorm possible Friday, 
otherwise a mainly dry and pleasant late-summer day.

Clouds early to start Friday, followed by seasonably warm and humid 
conditions. A cold front moves across the region during the morning 
into early afternoon, providing a focus for isolated to scattered 
showers and perhaps a garden-variety thunderstorm. Much of the day 
should remain dry, with any shower or thunderstorm activity brief 
and localized.

The cold front clears the coast Friday evening, with winds shifting 
to the northwest behind it. A more comfortable and less humid air 
mass arrives overnight into early Saturday. 


KEY MESSAGE 3...Seasonable temperatures and dry weather this 
weekend.

Nice weekend shaping up for Southern New England as large high 
pressure cell centered over southeast Ontario early Sat shifts 
southeastward through Long Island and offshore by Sunday. Expect 
full sun and good mixing helping to temper dewpoints/humidity levels 
to tolerable levels. Seasonable highs in the upper 70s to low 80s 
with good radiational cooling both Sat and Sun nights supporting 
lows in the upper 50s to low 60s. Enjoy the weather this weekend as 
we turn more active and unsettled starting Monday - more on that to 
follow below. 


KEY MESSAGE 4...Cloudy and unsettled early to mid next week 
with several opportunities for showers and storms, but the 
timing of them is uncertain.

Our weather pattern then turns more unsettled starting Monday into 
midweek, as the northern mid-Atlantic and Southern New England 
remains entrenched between cooler northerly flow over northeast New 
England and a strong surge of warm, humid air on southwest flow over 
the Ohio Valley and Upper Midwest. Quasi-stationary/backdoor sfc 
frontal boundary looks to be draped in vicinity of Southern New 
England Monday thru Wednesday, with embedded hard-to-time shortwaves 
in a fast NW flow in mid-levels, atop the stalled frontal boundary, 
favoring several opportunities for showers and thunderstorms along 
its extent. 

Other than it being a pattern which favors cloud cover and periods 
of showers and storms, given the coarser-resolution ensemble 
guidance available at this point, confidence in the timing of 
showers/storms is lower than average. The position of the quasi-
stationary front will also affect the timing and placement of where 
showers and storms are more favored day-by day; as we move though 
time, the initial lean is for the frontal boundary to adjust 
southwestward, but will wait to see incoming guidance before 
adjusting PoPs beyond NBM. Expect a narrower range in high/low temps 
Monday through Wednesday, with highs running a little cooler than 
normal and lows slightly milder than normal.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
Forecaster Confidence Levels...

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

00z TAF Update:

Through Tonight...Moderate confidence.

Low risk for TSRA at BDL thru 03z. VFR should otherwise govern
through 03z, although stratus with MVFR-IFR ceilings works its
way from south to north thereafter. South winds around 5-10 kt,
decresing to 5 kt or less overnight. 

Friday...High confidence in trends, lower confidence in storm 
coverage.

Conditions improve to VFR with ceilings 050-080 after 14-16z. Pop-up 
TSRA possible between 18-00z, which may result in brief MVFR/IFR 
conditions. Light W/SW winds become WNW by late afternoon.

Friday Night...High confidence.

VFR ceilings for most, though MVFR possible along the immediate 
south coasts of RI/MA, Cape Cod, and the Islands. Light NW winds.

KBOS Terminal...Moderate confidence. VFR/dry early tonight.
Stratus looks to return northward late tonight and overnight at
MVFR levels with TEMPO IFR pre-dawn. VFR return early Friday
morning. Possible SHRA/TS Fri aftn between 19z Fri-00z Sat but
confidence too low for TAF mention.

KBDL Terminal...Moderate confidence. Still a low chance for TSRA
before 03z. VFR otherwise then deteriorates to MVFR-IFR ceilings
overnight until early Fri AM. 

Outlook /Saturday through Tuesday/...

Saturday through Saturday Night: VFR. 

Sunday: VFR. Breezy. 

Sunday Night: VFR. Slight chance SHRA.

Monday: VFR. Slight chance SHRA, slight chance TSRA.

Monday Night: VFR. Chance SHRA, slight chance TSRA.

Tuesday: Mainly VFR, with local IFR possible. Slight chance
SHRA, slight chance TSRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Through Friday Night...High confidence.

Chances for showers and thunderstorms increase tonight, mainly south 
of the Islands. Southerly winds remain less than 20 kt, with seas 3 
to 4 ft across the southern waters and 2 to 3 ft across the eastern 
waters. Another round of scattered showers and thunderstorms is 
possible nearshore Friday afternoon with the passage of a cold 
front. Winds shift to the west behind the front Friday afternoon, 
then become northerly Friday night into Saturday morning.

Outlook /Saturday through Tuesday/...

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

Saturday Night through Sunday: Winds less than 25 kt. 

Sunday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain showers. 

Monday: Winds less than 25 kt. Seas locally approaching 5 ft.
Slight chance of rain showers, slight chance of thunderstorms. 

Monday Night: Winds less than 25 kt. Chance of rain showers,
slight chance of thunderstorms. 

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

&&

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

&&

$$

DISCUSSION...Loconto/Dooley
AVIATION...Loconto/Dooley
MARINE...Loconto/Dooley