Lexington Weather

Lexington, Massachusetts, USA

50°F

5/23/2025 11:53pm

Lexington Conditions: Overcast
Temperature: 50.4°F / 10.2°C
Dew Point: 48.4°F
Relative Humidity: 93%
Wind: SSE 1 mph, 10-min avg: 2 mph, gust: 5 mph
Barometer: 29.75 in Steady
Visibility: 10 miles
Rain Today: 0.35 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 171907
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
307 PM EDT Sat May 17 2025

.SYNOPSIS...

An approaching cold front may bring a few strong to severe 
thunderstorms across western Massachusetts and northern Connecticut 
this evening...but the greater threat may stay across northern New 
England. Any of this activity will weaken as it tries to work into 
eastern Massachusetts and Rhode Island later this evening. 
Otherwise...drier and cooler air works into the region overnight. 
Considerable cloudiness is on tap for Sunday and Sunday night with 
dry weather dominating...but a few passing showers will be possible 
at times especially north of the Massachusetts turnpike.
Unseasonably cool air is on tap for much of the upcoming work 
week...especially later Wednesday into Thursday when a late season 
Nor'easter may bring a cold/windswept rain.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...

Key Messages...

* A few severe storms possible across western MA/CT this evening
  but greater areal coverage/risk across northern New England

* Drier overnight with most of the activity coming to an end by 
  midnight and lows bottoming out in the 50s

Details...

The main concern revolves around the convective threat into 
this evening. Low clouds were scouring out across western MA/CT as 
of mid to late this afternoon. This trend will overspread the rest 
of the region allowing for partial sunshine to develop from west to 
east in the next few hours.

The partial sunshine developing will allow a modest amount of 
instability to develop across the interior with MLCapes rising into 
the 1000-2000 J/KG range by late afternoon/early evening. There also 
is a fair amount of effective shear on the order of 35 to 45 knots. 
At the same time...a relatively strong shortwave is lifting into 
northern New England. Although we expect a fair amount of 
instability/shear our region will be on the edge of the stronger 
forcing. So there is uncertainty on how much convection will be able 
to develop across our region. However...given the amount of 
instability expected to develop with the strong shear...any storms 
that develops in western MA/northern CT will be capable of becoming 
severe with the main threats being localized damaging wind gusts and 
hail. This also looks to be a rather late show...mainly after 5 pm 
across western MA/CT until about 10-11 pm this evening.

So in a nutshell...a few severe thunderstorms are possible across 
western MA/CT into this evening. However...confidence in areal 
coverage/intensity is less than in northern New England given more 
limited forcing. 

What ever activity develops should weaken this evening...as it out 
runs better instability/forcing. So while a rumble or two of thunder 
may survive onto the I-95 corridor...the severe weather threat 
appears low in this region. 

By midnight...most of this activity will have dissipated as drier 
air begins to work into the region behind the cold front. Overnight 
low temps bottom out mainly in the 50s. Low clouds and fog patches 
should mainly be confined to areas towards the south coast this 
evening...but improving conditions after midnight as the winds shift 
to the west behind the cold front.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...

Key Messages...

* Partly-mostly cloudy Sun/Sun night with a few passing showers 
  possible especially north of I-90...but dry weather still dominates

* Highs Sun mainly in the upper 60s to the lower 70s with a W breeze

* Lows Sun night upper 40s to the lower 50s and it will be breezy

Sunday and Sunday night...

Anomalous closed upper level low moves across northern New England 
Sun and gradually slides off the Maine coast Sun night. The result 
will be a cyclonic westerly flow of air across the region Sun 
shifting to the northwest Sun night. The cyclonic flow will result 
in partly to mostly cloudy skies Sun/Sun night...but a few peeks of 
sunshine will be possible during the daylight hours. While dry 
weather will dominate...shortwave energy and the associated cold 
pool aloft may allow a few showers to drop south into our region at 
times Sun into Sun night. This is especially true to the north of 
I-90...closer to the shortwave energy in northern New England.

High temps on Sun should mainly be in the upper 60s to the lower 70s 
with a westerly breeze. A secondary cold front will cross the region 
Sun night shifting winds to the NW and it will be breezy. In 
fact...gusts of 25 to 30 mph will be possible especially toward 
daybreak. Overnight low temps Sun night will bottom out in the upper 
40s to the lower 50s. 

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...

Key Messages:

* Dry and seasonable Monday

* Cooling trend returns Tuesday through the rest of the week

* Another system likely brings significant rain and gusty winds to 
  southern New England for the second half of the week

Details...

Northwesterly flow dominates Monday as a low makes its exit offshore 
towards the Maritimes by Monday night, helping to mitigate daytime 
temperatures. Monday's highs hover in the high 60s to low 70s. Flow 
shifts northeasterly for Tuesday on the back end of the low, further 
cooling temps for the mid-week: Tuesday through Thursday remaining 
mostly in the 50s and low 60s.

Later this week continues to look highly unsettled, with a late 
season Nor'Easter tracking up the east coast towards southern New 
England. This would likely bring significant rainfall and gusty 
winds sometime Wednesday evening through Friday; however, timing and 
track still vary greatly in the guidance. The ECMWF and GFS both 
have the system arriving around the same time on Thursday, but the 
ECMWF takes a more coastal track while the GFS keeps the system more 
offshore. The GEM has consistently indicates a later arrival on 
Friday, with a slightly offshore track. A more coastal track would 
bring heavier and longer duration rains with gustier winds than a 
more offshore track. Regardless, can expect the later half of the 
week to be unsettled and cool with continued broad cyclonic flow and 
cooler temperatures aloft.

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...

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

18z TAF Update....

This afternoon into tonight...Moderate Confidence. 

MVFR with localized IFR conditions will probably improve to
mainly VFR by late afternoon/early evening in most locations... 
although some IFR to even LIFR conditions may persist well into 
the overnight hours towards the south coast/Cape and Islands. 

The main issue will be the potential for scattered showers and 
thunderstorms mainly after 20z/21z across interior MA and CT. 
Forcing is better across northern New England...but any storm 
that develops in western MA/northern CT into this evening may 
become strong. The activity should weaken as it approaches the 
BOS-PVD corridor...probably not until after 00z. Not sure if a 
few rumbles of thunder survive towards the I-95 corridor...but 
regardless expect a weakening trend. Most of the activity should
dissipate after midnight as winds become West at 5 to 15 knots.

Sunday and Sunday night...High Confidence.

A scattered to broken deck of clouds are expected Sun into Sun
night...but some marginal MVFR cigs will be possible too. Much 
of this time will be dry...but a few showers will be possible at
times Sun into Sun night. West winds on Sun will shift to the NW
Sun Night. Winds will gust to between 20 and 25 knots at times
and perhaps up to 30 knots in a few spots very late Sun night.

KBOS TAF...Moderate Confidence. Main concern is for cluster of 
weakening scattered showers approaching the terminal 00z. 

KBDL TAF...Moderate Confidence. Main concern is for a few strong
thunderstorms roughly after 20z/21z through 01z/02z. 

Outlook /Monday through Thursday/...

Monday: Mainly VFR, with local MVFR possible. Windy with gusts
up to 30 kt. 

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

Tuesday: Mainly VFR, with areas MVFR possible. Breezy. 

Tuesday Night: Mainly VFR, with local MVFR possible. 

Wednesday: Mainly VFR, with local IFR possible. Breezy. Chance
SHRA.

Wednesday Night: Mainly MVFR, with local IFR possible. Breezy.
SHRA likely.

Thursday: Mainly MVFR, with areas IFR possible. Breezy. SHRA
likely.

&&

.MARINE...

Forecaster Confidence Levels:

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


Tonight through Sunday night...High Confidence.

A cold front will cross the waters later tonight with the main 
impact being S winds shifting to the W and drier air working into 
the region. A closed upper level low will track across northern New 
England Sunday will exit the Maine coast Sun night. Enough of a 
gradient will result in W wind gusts of 20 to 25 knots shifting to 
the NW Sun night with gusts increasing to between 25 and 30 knots. 
Therefore...we have hoisted small crafts for some of our waters Sun 
and all of our waters by later Sun night.

Outlook /Monday through Thursday/...

Monday: Low risk for Small Craft Advisory winds with gusts up
to 30 kt. Areas of seas approaching 5 ft. 

Monday Night through Tuesday Night: Winds less than 25 kt.
Areas of seas approaching 5 ft. 

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

Wednesday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of rough seas. Chance of rain showers,
isolated thunderstorms. 

Thursday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 11 ft. Rain showers likely.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 2 AM to 8 PM EDT Monday for ANZ230-
     231-236-250-251.
     Small Craft Advisory from 8 AM Sunday to 8 PM EDT Monday for 
     ANZ232>235-237-254>256.

&&

$$

SYNOPSIS...Frank/McMinn
NEAR TERM...Frank
SHORT TERM...Frank
LONG TERM...McMinn
AVIATION...Frank/McMinn
MARINE...Frank/McMinn