Lexington Weather

Lexington, Massachusetts, USA

51°F

5/23/2025 10:58pm

Lexington Conditions: Light rain, Overcast
Temperature: 50.5°F / 10.3°C
Dew Point: 48.6°F
Relative Humidity: 93%
Wind: WSW 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 171738
AFDBOX

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

.SYNOPSIS...

An upper level low pressure over Michigan will be responsible
for scattered showers and thunderstorms. Some storms this
afternoon in interior Southern New England could become severe.
Turning cooler and drier tonight, with blustery conditions also
developing on Sunday. Dry to start the week, and a cooling 
trend sets in Tuesday that will continue through the week. 
Unsettled weather returns once again in the second half of the 
week into the weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

Key Messages...

* A few severe storms possible across western MA/CT after 4-5 pm
  today but greater areal coverage across northern New England

* Much of today may end up dry with partial clearing and highs
  well up into the 70s to near 80 with some humidity too

Details...

A complex forecast into this evening...which we will explain 
below. Low clouds covered much of region at mid-morning...but 
enough diurnal heating with the strong May sun angle should 
allow for partial sunshine to develop through the afternoon. 
Highs should be well into the 70s to near 80 with modest 
humidity too.

The main concern revolves around the convective threat today.
The latest guidance is fairly limited with the threat of
elevated activity through mid afternoon with better forcing and
moisture to our northwest. While a few isolated showers and 
perhaps an isolated t-storm can not be ruled out...thinking
dry weather may prevail across much of the region through mid
afternoon. 

We do expect a modest amount of instability to develop
across the interior with MLCapes rising into the 1500-2000 J/KG
range. There also will be a fair amount of effective shear on 
the order of 35 to 45 knots. At the same time...a relatively
strong shortwave will be lifting into northern New England.
Although we expect a fair amount of instability/shear we will be
on the edge of the stronger forcing. So that may keep any
activity that develops across our region isolated to scattered
with better coverage in northern New England. However...given 
the amount of instability and shear and storm 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 4-5 pm 
across western MA/CT. This is supported by the CAMs and machine 
learning guidance tend do have some severe probs into this 
region...but hint at a better chance to our north.

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.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...

Key Messages:

* Drier and much less humid tonight, although still some cloud
  cover around.

* Partly to mostly cloudy Sunday, breezy with generally 
  seasonable temps. Hit or miss shower possible north of the 
  Mass Pike. 

Details:

Our weather pattern for tonight into Sunday then becomes more 
strongly governed by the upper level low over Michigan. This
looks to be accompanied by below-average 850 mb temps and still
quite a bit of low to midlevel RH. So while we do clear out
tonight and trend dry, there could still be at least partly
cloudy skies tonight but not the low clouds we've had the last
couple nights. The biggest change though is that dewpoints will
plummet back into the 40s to low 50s, so a considerably less
humid airmass. 

Sunday is looking partly to mostly cloudy and rather breezy 
with WNW winds around 10-15 mph with gusts to 20 mph. Couldn't 
rule out a hit or miss shower north of the Mass Pike Sunday but 
probably not widespread or capable of washouts. It's possible
that adiabatic downsloping could boost areas such as metrowest
Boston to around 70 degrees, but highs could struggle to reach
the low to mid 60s in interior Southern New England.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...

Key Messages:

* Dry and seasonable Monday

* Cooling trend returns Tuesday through the rest of the week

* Another system may bring significant rain and gusty winds to 
  southern New England midweek

Details...

An upper level low makes its exit offshore towards the Maritimes 
Monday night. Northwest flow kicks in in its place while the cooler 
temperatures aloft remain, which will help keep the region cooler 
and drier; highs Tuesday through Thursday will remain mostly in the 
50s and low 60s.

Towards the second half of the week, another upper level low is 
expected to dig into the Great Lakes. An associated surface low is 
then expected to move up along the east coast towards southern New 
England. The late spring Nor'Easter would likely bring significant 
rainfall and gusty winds sometime Wednesday evening through Friday, 
however, timing still varies greatly in the guidance. Deterministic 
guidance also still varies significantly on the track of the low's 
center, and the GEM generally has the system approaching slightly 
later than the other models do and moves it further to the south of 
the region. This would keep most of the rain to the south and glance 
the south coast. Generally, though, the consensus is that the end of 
next week will be unsettled and cool with continued broad cyclonic 
flow and cooler temperatures aloft.

&&

.AVIATION /17Z SATURDAY THROUGH WEDNESDAY/...

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 Wednesday/...

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

Monday Night: VFR. Breezy. 

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

Tuesday Night: Mainly VFR, with local IFR possible. 

Wednesday: MVFR/IFR conditions possible. Chance SHRA.

&&

.MARINE...

Forecaster Confidence Levels:

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

High confidence overall.

Winds and seas remain below SCA levels through tonight. However
fog is a concern for boaters this morning, and there could be
thunderstorms over the southern waters late this morning to
early afternoon. 

West to northwest winds increase tonight and especially on
Sunday to around 20-25 kt, with seas increasing to 3 to 5 ft.
Small craft advisories have been hoisted for Sunday and into
Sunday night for the southern waters. Conditions look borderline
on the eastern waters for SCAs but could be considered in later
updates.

Outlook /Sunday Night through Wednesday/...

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

Monday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of rain showers. 

Tuesday 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. Slight
chance of rain showers.

&&

.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...Loconto
NEAR TERM...Frank
SHORT TERM...Loconto
LONG TERM...Hrencecin
AVIATION...Frank/Hrencecin
MARINE...Loconto/Hrencecin