Lexington Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 252316
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
716 PM EDT Mon May 25 2026

.WHAT HAS CHANGED...
Areas of locally dense fog overnight, otherwise no significant 
changes to the forecast.

&&

.KEY MESSAGES...

- Rain ending this afternoon, areas of fog develop overnight,  
  warm and pleasant conditions Tuesday afternoon.

- Warm conditions continue Wednesday and slightly cooler  
  Thursday, with only a low risk for isolated afternoon showers 
  and thunderstorms.

- Temperatures trend near or below normal heading into the  
  weekend as rain chances return Saturday.

&&

.DISCUSSION...
KEY MESSAGE 1...Rain ending this afternoon, areas of fog develop 
overnight, warm and pleasant conditions Tuesday afternoon.

A frontal boundary shifts offshore today, bringing an end to the 
rain along with gradual clearing this afternoon. Behind the front, 
somewhat drier air moves in and clouds begin to disperse. A surface 
1020 mb high pressure system builds across the Northeast tonight, 
with continued clearing, especially north and west of I-95. A 
combination of clear skies and light to calm winds should support 
radiational cooling; however, given the high surface moisture and 
elevated dew points, lows will only fall into the 50s. That said, 
lingering moisture from the weekend rainfall will support the 
potential for areas of locally dense fog overnight into early 
Tuesday morning. Expect fog to linger through at least the first 
half of the Tuesday morning commute. As temperatures warm after 
sunrise, boundary layer mixing will increase and allow the fog to 
dissipate. Tuesday afternoon looks fairly pleasant as the 
atmospheric column continues to dry out, with perhaps some passing 
high clouds filtering the sunshine. However, Cape Cod and the 
Islands may hold onto scattered to broken low-level cloud cover, as 
less dry air remains over this portion of the region. As for 
temperatures Tuesday afternoon, mixing appears to reach roughly 
850mb, where temperatures are forecast to be +12C to +14C, 
supporting highs in the lower to middle 80s inland. It will not be 
as warm along the south coast due to the development of a sea 
breeze, where coastal areas can expect highs in the lower to middle 
70s. Some locations, such as Block Island and Nantucket, may 
struggle to get out of the 60s. 

KEY MESSAGE 2...Warm conditions continue Wednesday and slightly 
cooler Thursday, with only a low risk for isolated afternoon showers 
and thunderstorms.

Wednesday and Thursday will feature the chance for pop-up showers 
and thunderstorms, though a washout is not expected. In fact, most 
locations will remain dry for a significant portion of both days. 
There will be a relatively small window each afternoon for the 
development of isolated convection. On Wednesday, the better mid-
level forcing remains south of southern New England, although the 
12z NAM depicts a subtle 850mb trough and weak shortwave that could 
provide enough ascent for a few storms to develop. However, moisture 
will be somewhat limited, especially aloft, which could hinder 
updraft strength. Instability also appears limited, which should 
further inhibit storm development. Wind fields are not particularly 
impressive, though 30-35 kt of deep-layer shear could help organize 
any storms that do develop. At this point, the worst-case scenario 
appears to be a couple of rogue showers or rumbles of thunder, along 
with localized sub-severe wind gusts. On Thursday, a modest mid-
level trough and shortwave pivot through New England, although PWATs 
decrease through the afternoon. As the previous forecaster 
mentioned, cooling aloft may support some diurnally driven pop-up 
showers or thunderstorms. However, mid-level dry air remains a 
limiting factor and should inhibit stronger updraft development. 
Machine learning guidance has not highlighted a severe weather 
threat at this time, which supports the current thinking of isolated 
storms with general thunder at most. Temperature-wise, Wednesday 
looks to be the warmest day of the week, with west to west-northwest 
flow promoting warmer conditions and some downsloping/compressional 
warming off the higher terrain. Highs should climb well into the 80s 
and 70s at the coast. Thursday becomes more complicated, 
particularly across eastern Massachusetts, where temperatures will 
depend heavily on wind direction. A northeast wind would advect 
cooler marine air inland from the relatively cold ocean waters, 
supporting highs only in the upper 60s to lower 70s, with the 
warmest readings likely south and west of Boston. A land breeze 
influence toward the south coast of Massachusetts and Rhode Island 
could allow temperatures there to approach the mid-70s. Farther 
inland, winds should trend more northerly to north-northwesterly, 
promoting some compressional warming off the higher terrain of 
southern Vermont into the Connecticut River Valley. Combined with 
greater sunshine compared to eastern Massachusetts and Rhode Island, 
this would support highs in the middle to upper 70s.

KEY MESSAGE 3...Temperatures trend near or below normal heading into 
the weekend as rain chances return Saturday.

Overall model guidance has continued to trend on the cooler side for 
temperatures in the wake of a cold front heading into the weekend, 
but there remains uncertainty in just how cool we could get. 

Ensemble guidance continues to be in good agreement that a surface 
low pressure will spin up over the James Bay sometime Friday and 
move south along the fringes of an upper-level trough into New 
England, bringing another round of potentially beneficial rains for 
Saturday. The latest runs of deterministic guidance have also honed 
in on this development; however, there remains significant 
uncertainty in when and where the low could travel...therefore, 
confidence in how much rain SNE could see remains low at this time. 
Canadian guidance indicates more of an eastward progression, keeping 
the low (and the rainfall) further north into the Eastern Townships 
and northern New England, but ECMWF guidance brings that low further 
south along through VT, NH, and further into MA. GFS remains more of 
a centrally located solution and indicates more of a graze along the 
northeastern MA/NH coast. Regardless, portions of SNE are likely to 
see at least some rain this coming weekend. 

Given the high amount of uncertainty in the guidance, anticipating 
that both PoPs and temperatures for this weekend remain in flux for 
the next few forecast updates.

&&

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

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

00z TAF Update:

Tonight...Moderate confidence in trends and timing.

Generally VFR except IFR to MVFR ceilings likely across the 
Cape and Islands. Areas north and west of I-95 will be most 
favorable for the development of radiational fog, with localized
dense fog possible; however, confidence in exact placement 
remains low. Otherwise, winds become light and variable to calm 
overnight.

Tuesday...High confidence.

Becoming VFR and dry across southern New England by 12-15z. 
Winds become SW 8 to 12 kt.

Tuesday Night...Moderate confidence.

VFR. Marine stratus may develop south of the Islands overnight 
and drift toward the south coast. Winds remain SW less than 10 
kt.

Wednesday and Thursday...Moderate confidence.

Generally VFR, though there will be a daily chance for 
afternoon SHRA/TSRA. Winds on Wednesday will be WNW at 5 to 10 
kt inland and 10 to 15 kt along the coast. Winds shift northerly
on Thursday, although eastern Massachusetts may see an ENE to 
NE wind. Winds across the interior will be 10 to 15 kt, while 
coastal areas see 8 to 12 kt.

KBOS...Moderate confidence in TAF.

Low confidence regarding fog development tonight, though 
current thinking favors less restrictive conditions than 
suggested by LAMP/GLAMP guidance.

KBDL...Moderate confidence in TAF.

Localized fog remains possible overnight, though confidence in 
occurrence and exact timing remains moderate.

Outlook /Thursday Night through Saturday/...

Wednesday: VFR. Breezy. Isolated SHRA, isolated TSRA.

Wednesday Night: VFR. Isolated SHRA.

Thursday: VFR. Breezy. Isolated SHRA, isolated TSRA.

Thursday Night through Friday: VFR. Slight chance SHRA.

Friday Night: Mainly VFR, with local MVFR possible. Chance
SHRA.

Saturday: Mainly VFR, with areas MVFR possible. Chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Monday Night through Thursday...High confidence.

Marginal Small Craft Advisory conditions continue tonight across the 
outer ocean waters, with seas of 4 to 6 ft. These seas gradually 
subside by daybreak Tuesday, followed by generally tranquil boating 
conditions through Thursday, with seas mainly 2 to 4 ft. Winds 
remain light and somewhat variable on Tuesday as high pressure moves 
overhead. By Wednesday, winds become more southwesterly around 15 
kt, with occasional gusts up to 20 kt possible over the nearshore 
waters south of the coast. While conditions appear marginal, there 
is a low chance of localized stronger gusts that could warrant a 
brief Small Craft Advisory. Given the start of the boating season, 
this potential bears monitoring despite the marginal setup. Heading 
into Thursday, winds shift more ENE to NE. Both Wednesday and 
Thursday afternoons feature the chance for isolated pop-up showers 
or thunderstorms, though a washout is not expected.

Outlook /Thursday Night through Saturday/...

Wednesday: Winds less than 25 kt. Seas locally approaching
5 ft. Isolated rain showers, isolated thunderstorms. 

Wednesday Night through Thursday: Winds less than 25 kt.
Isolated rain showers, isolated thunderstorms. 

Thursday Night through Friday: Winds less than 25 kt. Slight
chance of rain showers. 

Friday Night: Winds less than 25 kt. Chance of rain showers. 

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 AM EDT Tuesday for ANZ250-254>256.

&&

$$

DISCUSSION...Dooley/McMinn
AVIATION...Dooley/McMinn
MARINE...Dooley/McMinn