Lexington Weather

Lexington, Massachusetts, USA

60°F

9/20/2026 8:49pm

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 191739
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
139 PM EDT Sat Sep 19 2026

.WHAT HAS CHANGED...
No significant changes.

&&

.KEY MESSAGES...

- Dry with fall-like temperatures today and tonight. 

- Rain likely Sunday into Monday, although there still remains 
  uncertainty in the exact amounts. Showers may linger through 
  early next week. A coastal system is possible late week.

&&

.DISCUSSION...
KEY MESSAGE 1...Dry with fall-like temperatures today and
tonight. 

A cooler airmass settles over the region early this morning 
resulting a cool start to the day today with temperatures in the 40s 
and 50s this morning. Expect dry conditions today with surface high 
pressure in place. The cooler airmass stays put with 850mb 
temperatures 6-9C. This will support fall-like temperatures in the 
mid 60s for most, flirting with 70 in the CT Valley. Northeast flow 
with likely keep the immediate eastern coastal areas cooler in the 
low 60s. Tonight, high pressure begins to shift offshore as our next 
system approaches from the west. With cloud cover not increasing 
until sunrise, there should be enough of a window with clear skies 
and light winds to support efficient cooling tonight. Temperatures 
likely fall into the 40s for a good part of southern New England. CT 
and RI may end up a little warmer as WAA begins to push in after 
2AM which would limit their window of cooling. 

The extended period of NE winds will help develop a swell with 
longer wave periods across the eastern waters for today. This will 
increase the risk for rip currents for the east-facing beaches 
including Nantucket today. If you plan on heading to the beach 
despite the cooler temperatures, please use caution. 


KEY MESSAGE 2...Rain likely Sunday into Monday, although there 
still remains uncertainty in the exact amounts. Showers may 
linger through early next week. A coastal system is possible 
late week. 

Model guidance continues to stay in general agreement to support 
rainfall Sunday into Monday. A shortwave approaches from the 
northwest coupled with an 850mb jet positioning over southern New 
England allow advection of moisture from the south and increased 
lift. PWATS increase to 1.2-1.8", around 160-180 percent of normal. 
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 its cold front trailing from the west, this 
should provide sufficient convergence for widespread rainfall. Model 
guidance has consistently been indicating lacking instability with 
this system which would likely limit the rain rates and thus limit 
the threat for heavy rain and flash flooding. There is still some 
spread in expected totals liking owing to track differences, 
but ensembles show a more likely range of a few tenths to around
1 inch. Some solutions such as the ECMWF/ensemble indicate 
potential for greater than 1.0" with ensemble probabilities of 
20-50% along the east slope of the Berkshires. Other solutions 
lean lighter with amounts 0.25-0.50". 3 and 6 hour QPF doesn't 
approach FFG, but some pockets of moderate or very brief heavy 
rain are possible. In terms of timing, rain likely spreads from 
west to east Sunday morning with widespread rain arriving by the
afternoon. Rain continues overnight into Monday. 

How long the rain lingers Monday will depend on how progressive the 
system/front is. There are difference across guidance in the speed 
which has led to some uncertainty in how long showers linger around 
on Monday. If showers were to linger, it would more likely effect 
areas more south and east (Cape/Islands or south coast). Fall-like 
temperatures are likely behind the front on Monday with breezy 
northerly winds. There is potential for another system to brush 
southern New England Tuesday bringing showers; however, this is 
lower probability as there lacking agreement with how north this 
system tracks at this time. 

There is good agreement across model guidance with a fairly strong 
surface high shifting over Quebec Tuesday into mid-week. This will 
keep a cooler than normal airmass over the northeast supporting cool 
more fall-like temperatures continuing through the week. 
Deterministic and ensemble guidance continues to hint at the 
potential for a coastal low pressure system sometime Thursday into 
Friday. However, there is still a fair amount of uncertainty in the 
details of the pattern that will influence the track of this low. 
Some solutions feature a low track closer to southern New England 
while others well off shore. Pretty low confidence at point, but 
warrants monitoring as it would bring potential for stronger winds, 
rough seas for the coastal waters and potentially another round of 
rainfall.

&&

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

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

18Z TAF Update:

Through Tonight...High confidence.

VFR through tonight. Light NE winds becoming E/ESE this afternoon. 
Winds shift to the S this evening at less than 10 kt, with some 
areas becoming calm overnight.

Sunday...High confidence in trends, moderate confidence in timing.

VFR to start, deteriorating to MVFR and then IFR from west to east 
during the afternoon as rain overspreads the region. LLWS could 
become a concern after 18z as the system moves through. Surface 
winds generally SE at 5-10 kt. Chances for TS are low to near zero.

Sunday Night...High confidence in trends, moderate confidence in 
timing.

IFR to LIFR with areas of 2-4SM visibility in continued RA. Winds 
shift to the N at 8-12 kt.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.


Outlook /Monday through Thursday/...

Sunday Night: MVFR/IFR conditions possible. Breezy. SHRA.

Monday: Mainly VFR, with local MVFR possible. Breezy. 

Monday Night through Tuesday: VFR. Breezy. 

Tuesday Night: VFR. Windy with local gusts up to 35 kt. 

Wednesday: VFR. Strong winds with local gusts up to 40 kt.

&&

.MARINE...
Forecaster Confidence Levels...

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

Through Sunday Night...High Confidence.

An area of high pressure moves east of the coastal waters overnight 
and toward the Canadian Maritimes by Sunday night. With the 
departure of the high, a low pressure system riding along a frontal 
boundary ushers in unsettled weather by late Sunday morning, with 
rain becoming widespread Sunday afternoon. There is a low chance for 
a few rumbles of thunder, primarily across the southern waters. Rain 
ends early Monday morning, though a few showers could linger across 
the southern outer waters as the front sags to the south. Seas 
throughout this period remain between 2-4 ft, with the greatest wave 
heights across the outer waters. Winds are northeast through this 
evening, then become southeast on Sunday. As the front pushes south, 
winds shift to the north/northeast. Gusts begin to increase with 
cold air advection Monday morning, which may require Small Craft 
headlines.

Outlook /Monday through Thursday/...

Sunday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Rain showers. 

Monday: Moderate risk for Small Craft Advisory winds with gusts
up to 30 kt. Areas of seas approaching 5 ft. Slight chance of
rain showers. 

Monday Night: Low risk for Small Craft Advisory winds with
gusts up to 30 kt. Local rough seas. Slight chance of rain
showers. 

Tuesday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 10 ft. Slight chance of
rain showers. 

Tuesday Night: Strong winds with gusts up to 40 kt. Rough seas
up to 11 ft. Slight chance of rain showers. 

Wednesday: Strong winds with local gusts up to 45 kt. Rough
seas up to 13 ft. Slight chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...High Risk for Rip Currents until 8 PM EDT this evening for MAZ007-
     015-016-019-022-024.
RI...None.
MARINE...None.

&&

$$

DISCUSSION...Mensch
AVIATION...Dooley
MARINE...Dooley