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 181551
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1151 AM EDT Fri Sep 18 2026

.WHAT HAS CHANGED...

Small craft headlines issued for many of our waters tonight into 
Saturday morning. 

&&

.KEY MESSAGES...

- Dry with fall-like weather tonight through Sat night. Lows 
  both nights mainly in the 40s-lower 50s. Highs Sat mainly in 
  the 60s perhaps flirting with 70 in the lower CT River Valley.

- Next chance for rain Sunday into Monday. There remains
  uncertainty in the details such as coverage, timing, and
  amounts. Showers may linger through early next week.

&&

.DISCUSSION...

KEY MESSAGE 1...Dry with fall-like weather tonight through Sat 
night. Lows both nights mainly in the 40s-lower 50s. Highs Sat 
mainly in the 60s perhaps flirting with 70 in the lower CT River 
Valley.

A very pleasant fall-like airmass is on tap for the region tonight 
through Sat night. This as high pressure builds eastward across 
Quebec tonight and into northern New England/Canadian Maritimes Sat 
into Sat night.

Drier and cooler air works into the region tonight. Winds should 
decouple enough overnight for lows to drop into the 40s across many 
locations...but lower-middle 50s in some urban centers as well as 
the Cape/Islands where a stiff N breeze will keep temps from 
bottoming out. Plenty of sunshine on Sat...but cool NE flow will 
result in highs mainly in the 60s perhaps flirting with 70 in parts 
of the Lower CT River Valley. Coolest high temps Sat will be found 
along the immediate eastern MA coast, Cape and Islands where highs 
will be held in the lower to middle 60s. 

High pressure slowly shifts east of the region Sat night. 
However...think there will be enough of a window for a good night of 
radiational cooling before thicker mid-level clouds move in toward 
daybreak. Low temps should be well down into the 40s in most 
locations with lower 50s in the urban heat island of Boston. 

KEY MESSAGE 2...Next chance for rain Sunday into Monday. There 
remains uncertainty in the details such as coverage, timing, and
amounts. Showers may linger through early next week. 

The main surface high exits offshore Saturday night into early 
Sunday as the next system approaches from the west with our next 
chance of precipitation Sunday into Monday. The ingredients are 
generally in place for at at least a soaking rainfall across 
southern New England. A shortwave approaches from the northwest 
coupled with an 850mb jet positioning over southern New England. 
This provide ample moisture advecting and synoptic scale lift for 
precipitation. PWATS increase to 1.0-1.8" (150-180 percent of 
normal), which is anomalous compared to climo. A low pressure system 
tracks east from the Great Lakes region Sunday putting southern New 
England in the warm sector as its warm front shifts northward. With 
the ample moisture and additional forcing this raises some flags for 
heavy rain potential or at least embedded heavy showers.

There is still variance across guidance in the exact track of 
the system/low pressure which has resulted in lower confidence 
in the details such as timing, amounts, and the potential for 
heavy rain. There has also been lacking consistency run to run 
within individual guidance as well. There is at least a general 
consensus across guidance that the higher moisture and better 
forcing(warm front) will more likely be south. This would favor 
our more south, southwest areas for higher rain totals. GFS and 
Canadian solutions (deterministic & ensemble) seem to reflect 
that pattern with higher amounts south while the ECMWF has a 
wider footprint with generally higher totals. When it comes to 
amounts solutions vary from 0.30" to 1.0" across ensembles based
on the 25-50th percentiles. Deterministic guidance had 
displayed more "aggressive" solutions with swaths of higher 
amounts >1.0". However, these solutions have had the most 
variance from run to run which further adds to the uncertainty. 
The most likely case at this point will be anywhere from a few 
tenths to an inch. This seems reasonable given the mean track. 
There isn't much indication of instability which should limit 
the heavier rain rates. If the warm frontal forcing shifts north
enough, we could get embedded heavy rain supporting by the 
added lift and efficient rain processes. So overall, there is 
confidence that we will get at least a soaking rain with rain 
arriving through the day Sunday continuing into Monday. We'll 
need to continue monitoring for the isolated heavy rain 
potential as models come into better agreement with the track 
over the next day or so. 

It is also possible showers may linger across the south coast and 
Cape and Islands Monday into Tuesday. This will depend on if the low 
or a boundary stalls across the waters. Wednesday leans mainly dry 
with potential for another system to arrive late-week with rain 
possible.

&&

.AVIATION /15Z FRIDAY THROUGH TUESDAY/...

Forecaster Confidence Levels...

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

18z TAF Update...

Tonight...High confidence.

VFR. N winds generally 10 knots or less...except 7-15 knots across 
the Cape/Islands with some 20+ knot gusts possible in those locales 
after midnight.

Saturday...High confidence.

VFR. Light NE winds become E...except for a few 20-25 knots gusts in 
the morning across the Cape and especially Nantucket. 

Saturday night...High confidence. 

VFR. Calm/light S winds. 

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Sunday through Tuesday/...

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

Sunday Night: MVFR/IFR conditions possible. Breezy. SHRA
likely, isolated TSRA, patchy BR.

Monday: Mainly VFR, with local MVFR possible. Breezy. Slight
chance SHRA.

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

Tuesday: VFR. Windy with areas of gusts up to 30 kt. Chance
SHRA.

&&

.MARINE...

Forecaster Confidence Levels...

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

Tonight through Saturday night...High confidence.

As high pressure builds into Quebec tonight...expect a period of N 
wind gusts near 25 knots across many of our waters given good mixing 
in the cool air advection pattern over the relatively mild ocean. We 
did include Cape Cod Bay/Nantucket sound as they should see a period 
of good mixing with 925T dropping to between +5C and +7C and SST 
still on the order of +21C/+22C. 

Outlook /Sunday through Tuesday/...

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

Sunday: Winds less than 25 kt. Chance of rain showers. 

Sunday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Rain showers likely, isolated thunderstorms, patchy fog. 

Monday: Low risk for Small Craft Advisory winds with gusts up
to 30 kt. Seas up to 5 ft. Chance of rain showers, slight
chance of thunderstorms. 

Monday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Seas up to 5 ft. Chance of rain showers. 

Tuesday: Strong winds with gusts up to 40 kt. Seas up to 5 ft.
Chance of rain showers. 

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...High Risk for Rip Currents from Saturday morning through Saturday 
     evening for MAZ007-015-016-019-022.
RI...None.
MARINE...Small Craft Advisory from 11 PM this evening to noon EDT 
     Saturday for ANZ231-232.
     Small Craft Advisory from 8 PM this evening to noon EDT 
     Saturday for ANZ250-251-254>256.

&&

$$

DISCUSSION...Frank/Mensch
AVIATION...Frank
MARINE...Frank/Mensch