Lexington Weather

Lexington, Massachusetts, USA

60°F

9/20/2026 8:51pm

Lexington Conditions: Overcast
Temperature: 59.9°F / 15.5°C
Dew Point: 56.7°F
Relative Humidity: 89%
Wind: Calm, 10-min avg: Calm, gust: None
Barometer: 29.95 in Steady
Visibility: 9 miles
Rain Today: 0.00 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 161118
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
718 AM EDT Wed Sep 16 2026

.WHAT HAS CHANGED...
No significant changes to the forecast.

&&

.KEY MESSAGES...

- Warmer temperatures expected today with increased humidity levels. 

- Scattered showers possible Thursday evening into Friday morning, 
  followed by dry conditions Friday. 

- Rain chances return for the second half of the weekend. There
  remains uncertainty in the details such as coverage, timing,
  amounts.

&&

.DISCUSSION...
KEY MESSAGE 1... Warmer temperatures expected today with
increased humidity levels. 

Patchy fog possible early this morning, but should burn off with 
sunrise. High pressure in place will keep things mainly dry today. 
The exception is a line of light showers moving through upstate NY 
early this AM. At most this line may bring a sprinkle and period of 
clouds as it moves through this morning.

Expect a warmer day with a touch more humidity. A strong upper level 
ridge/high remains positioned across the southeast CONUS, subtly 
building into the northeast. Warmer mid-level temperatures advect in 
within the SW flow with 925mb temperatures 16-18C. This should yield 
highs in the mid and upper 70s with low 80s in the valleys 
(seasonably warm for mid-Sept). There will also be some moisture 
advection as well within the SW flow which will bring dewpoints back 
up into the low 60s. This will make it feel more humid than the 
previous day or two. 

KEY MESSAGE 2...Scattered showers possible Thursday evening into Friday
morning, followed by dry conditions Friday. 

The first part of Thursday should remain dry with shower chances 
increasing later in the day as a weak shortwave trough approaches. 
Ahead of this shortwave, a plume of anomalous moisture advects in 
from the west. PWATs run around 180-200 percent of normal or more 
directly put, PWAT values 1.7-1.9". This has also been signaled as 
anomalous across the NAEFS guidance. Despite the anomalous moisture, 
the lift/forcing with this wave is weaker. Most guidance tracks the 
better forcing further north (New England). Being further from the 
stronger forcing will likely limit the potential for widespread 
heavy rain across the region. For timing, showers become more 
likely late afternoon into early evening, continuing through 
early Friday morning. For rain totals, ensembles show low 
probabilities (< 15%) for rain totals greater than 0.50". 
Amounts generally range from a trace to a few tenths across the 
GFS/ECMWF/Canadian are their ensembles. If this wave tracks 
further south as a small portion of guidance has been 
indicating, amounts will likely trend higher so this will
continue to be monitored. There is potential for some elevated 
instability Thursday night which could result in an isolated 
heavier downpour, but otherwise the model consensus leans toward
a period of showers with overall lighter amounts. 

A drier airmass pushes in behind the exiting shortwave Friday which 
will gradually clear clouds through the day. Temperatures are likely 
to be in seasonable ranges in the 70s. A cooler airmass sinks across 
the region by Saturday bringing the return of Fall-like 
temperatures. Surface high pressure dominates bringing dry 
conditions. 

KEY MESSAGE 3... Rain chances return for the second half of the weekend.
There remains uncertainty in the details such as coverage, timing,
amounts. 

Confidence in the pattern decreases for the second half of the 
weekend into early next week. Ensembles continue to indicate 
potential for a shortwave trough to drop southward across the 
northeast Sunday into Monday. The strength/track of the trough and 
how it interacts with a surface high over the Great Lakes has varied 
across guidance leading to uncertainly in rain chances, timing,
and amounts. If the shortwave tracks closer to southern New 
England the lift associated with the wave combined with a plume 
of anomalous moisture will better support rain across the region
Sunday. However, there are also solutions that favor a stronger
high pressure that would suppress the system further south/west
resulting in more limited shower chances. Still plenty of 
details to iron out, but should become more clear as we get 
closer. 

Surface high pressure shifts across eastern Canada into early 
next week. There are indications across ensemble guidance for 
another disturbance to push through potentially bringing a 
period of showers in the Tue-Wed timeframe. Confidence remains 
on the lower end with question on how the high pressure 
suppresses the incoming system and moisture advection.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels...

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

12z TAF Update...

Today and Tonight...High confidence.

VFR. SW winds near 8-12 kts, "strongest" for Cape/Islands
terminals. At BOS, low chance for a late day sea breeze (after 
18Z) out of the SSE/SE. Not included in BOS TAF due to low 
confidence. Mid-level cloud deck begins to move in overnight 
into early Thursday morning. 

KBOS Terminal...Moderate confidence in TAF.

There is still a low probability for a sea breeze to come in
late day (after 18Z). Most model guidance keeps SW winds 8-10
kts in the boundary layer today which would more likely favor
the "no sea breeze" scenario. However, if winds end up a few kts
lighter a SSE/SE sea breeze may be able to sneak in late day.
Due to the low prob, kept out of TAF. 

KBDL Terminal...High confidence in TAF.

Outlook /Thursday through Sunday/...

Wednesday Night: Mainly VFR, with local MVFR possible. 

Thursday: Mainly VFR, with local IFR possible. Slight chance
SHRA.

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

Friday through Friday Night: VFR. Breezy. 

Saturday: VFR. 

Saturday Night: VFR. Chance SHRA.

Sunday: Mainly VFR, with local MVFR possible. Chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Surface high pressure continues with SW winds 10-15 kts today
and Thursday. Occasional gusts 18-22 kts are possible both days
in the afternoon/evenings.

Outlook /Thursday through Sunday/...

Wednesday Night through Thursday: Winds less than 25 kt. 

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

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

Friday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of seas approaching 5 ft. 

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

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

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

&&

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

&&

$$

DISCUSSION...Mensch
AVIATION...McMinn
MARINE...Mensch