Lexington Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 011855
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
255 PM EDT Thu Oct 1 2026

.WHAT HAS CHANGED...
A Small Craft Advisory has been issued for gusty prefrontal winds 
and elevated seas across the southern waters Friday into Friday 
evening. Also introduced a low chance for an isolated thunderstorm 
Friday afternoon/evening as a cold front pushes through southern New 
England. Otherwise, there were no significant changes to the 
forecast.

&&

.KEY MESSAGES...

- Late taste of summer Friday with highs around 80, followed by 
  showers and a few thunderstorms Friday night.

- Cooler and drier Saturday, followed by a chilly Saturday
  night.

- Watching if a wave of low pressure tracks far enough north to
  bring a period of showers sometime Sun into Sun night. 

- Coolest air of the season works into the region Mon night-Wed.
  Areas of frost expected Tue night/early Wed AM. Dry weather 
  for most if not all of the next work week. 

&&

.DISCUSSION...
KEY MESSAGE 1...Late taste of summer Friday with highs around 80, 
followed by showers and a few thunderstorms Friday night.

Mid-level flow remains generally zonal through Friday, while high 
pressure remains anchored off the coast of the Carolinas, returning 
the low-level flow out of the southwest.

Still a bit cloudy tonight with mild temperatures, as lows only fall 
into the 60s. Brief clearing develops Friday, allowing temperatures 
to quickly warm. 925mb temperatures rise to +20C to +23C Friday 
afternoon, supporting highs in the lower 80s for much of the region. 
Dewpoints also climb into the 60s, providing a late taste of summer 
for the second day of October. For perspective, this falls near the 
climatological last 80 degree day of the year for Boston, which is 
September 30th. Winds will also be elevated Friday with southwest 
flow and mixing up to around 925mb, where winds aloft are 20-30 
knots. Thus, gusts of 20 to 25 mph are not unreasonable during the 
afternoon.

High pressure drifts east as a cold front approaches from the west 
late Friday into Friday evening. Timing-wise, the 12z high-res 
guidance shows the cold front and associated showers/storms pushing 
through from northwest to southeast between roughly 3/4 PM and 10/11 
PM. Plenty of moisture accompanies the front, with PWATs nearing or 
exceeding 2 inches, which is well outside of climatology for early 
October. Given modest forcing along the front and lower values of 
instability, with only a few hundred J/kg of CAPE, cannot rule out a 
thunderstorm or two. Low-level lapse rates are fairly steep at 7-
8C/km, though mid-level lapse rates are less impressive around 
5C/km. There could be a few stronger gusts with DCAPE values of 600-
800 J/kg, though currently feel sub-severe gusts are more probable 
than severe gusts. In addition, locally heavy but brief downpours 
are possible given the anomalously high PWATs.

KEY MESSAGE 2...Cooler and drier Saturday, followed by a chilly 
Saturday night.

Behind the front, high pressure builds across the eastern Great 
Lakes Saturday with the aforementioned cold front just offshore. 
This may lead to a period of clouds and a few showers offshore early 
Saturday. Otherwise, drier and cooler Saturday with 925mb 
temperatures falling to around +10C, supporting highs generally in 
the upper 60s to around 70 degrees. High pressure moves into 
southern New England Saturday night into early Sunday, setting the 
stage for good radiational cooling. Lows fall into the 40s for much 
of the region, with the warmest readings in urban centers such as 
Boston around 50F. The coldest locations, especially across the 
higher terrain of western Massachusetts, could fall into the upper 
30s.

KEY MESSAGE 3...Watching if a wave of low pressure tracks far 
enough north to bring a period of showers sometime Sun into Sun 
night. 

There remains considerable disagreement on the northern extent of a 
precipitation shield associated with a wave of low pressure on Sun-
Sun night. Seems like the majority of the 12z deterministic guidance 
keeps the northern extent of the rain shield south of our 
region...perhaps briefly flirting with the south coast. 
However...the ECWMF as well as some individual GEFS/CMC ensemble 
members are further north and indicate the potential for a period of 
showers. Greatest risk for a period of showers seems to be south of 
the MA turnpike...but it is too early to rule out some showers 
reaching the NH border or on the flip side of the coin remaining 
completely south of southern New England. Either way...not expecting 
any significant impacts even if rain does impact part of our region 
for a time Sun into Sun night. Given the uncertainty...mainly kept 
pops in the chance levels for now with the highest of those near the 
south coast. High temps should be in the 60s...but it could end up a 
bit cooler depending on the northern extent of the rain shield.

KEY MESSAGE 4...Coolest air of the season works into the region
Mon night-Wed. Areas of frost expected Tue night/early Wed AM. 
Dry weather for most if not all of the next work week. 

A pleasant/seasonable day of weather is on tap for Mon with highs 
well into the 60s...perhaps even flirting with 70 in a few spots. 
However...it will be a bit breezy on Mon as a cold front crosses the 
region. Low level moisture is lacking...so expecting mainly a dry 
frontal passage or worst case being just a few brief showers. Either 
way...the main impacts will be the coolest air of the fall season 
working into southern New England Mon night through Wed. Highs may 
struggle to break 60 on Tue along with a breezy northwest wind. High 
pressure building overhead will allow for the coolest night of the 
young fall season Tue night. Low temps by daybreak Wed should be 
down into the 30s for many locations...perhaps flirting with the 
freezing mark in some of the normally coolest outlying locations. 
Frost is likely in many spots as well. 

The large high pressure system shifts east of the region by Thu. 
This should allow for a southwest flow of milder/seasonable 
temperatures to return by Thu afternoon. 

Dry weather should pretty much dominate most if not all of the 
upcoming work week. There is little moisture/forcing to support 
precipitation.

&&

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

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

18z TAF Update: 

Through 00z Friday: High confidence. 

SCT-OVC multi-layered VFR cloud decks. SW winds around 8-12 kt,
with occasional gusts to 20 kt for the Cape and Islands. 

Tonight: High confidence. 

Continued multi-layered VFR cloud decks at SCT-OVC coverage.
SWly winds around 5-10 kt, with low-level wind shear starting
around 01-03z as jet of 35 kt at 2000 ft traverses Southern New
England. 

Friday: High confidence in trends but moderate on timing. 

VFR continues, but a cold front will be approaching between
18-00z and bring with it a risk for showers, possibly a rumble
or two of thunder, but the exact timing is still uncertain. A
best estimate would be between 20-23z for BDL and 21-03z for 
remaining terminals. SW winds around 10 kt, shifting to W/WNW
with frontal passage.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Saturday through Tuesday/...

Saturday: VFR. 

Saturday Night: Mainly VFR, with areas IFR possible. Patchy BR.

Sunday: VFR. Breezy. Slight chance SHRA.

Sunday Night: Mainly VFR, with local IFR possible. Chance SHRA.

Monday: VFR. Breezy. Slight chance SHRA.

Monday Night: VFR. Windy with local gusts up to 30 kt. 

Tuesday: VFR. Breezy. 

&&

.MARINE...
Forecaster Confidence Levels...

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

Thursday afternoon through Sunday morning...High confidence.

Area of high pressure south of New England and off the coast of the 
Carolinas will shift east as a cold front approaches the southern 
New England coastal waters Friday evening. Ahead of the front, 
southwest flow will bring gusts of 20-25 knots across the southern 
nearshore waters, including Cape Cod Bay, with marginal seas of 5-6 
feet across the southern outer waters. A few showers and an isolated 
thunderstorm are possible with the frontal passage Friday evening. 
High pressure briefly returns Saturday with tranquil boating 
conditions.

Outlook /Saturday through Tuesday/...

Saturday: Winds less than 25 kt. Seas up to 5 ft. 

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

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

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

Monday: Winds less than 25 kt. Seas up to 5 ft. Slight chance
of rain showers. 

Monday Night: Low risk for gale force winds with gusts up to
35 kt. Seas up to 5 ft. 

Tuesday: Low risk for Small Craft Advisory winds with gusts up
to 30 kt. Local rough seas. 

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 11 AM to 8 PM EDT Friday for 
     ANZ231>235-237.
     Small Craft Advisory from 11 AM Friday to 2 AM EDT Saturday 
     for ANZ254>256.

&&

$$

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