Lexington Weather

Lexington, Massachusetts, USA

51°F

5/23/2025 10:33pm

Lexington Conditions: Light rain, Overcast
Temperature: 50.5°F / 10.3°C
Dew Point: 48.4°F
Relative Humidity: 92%
Wind: SW 1 mph, 10-min avg: 2 mph, gust: 6 mph
Barometer: 29.76 in Steady
Visibility: 10 miles
Rain Today: 0.35 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 200807
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
407 AM EDT Tue May 20 2025

.SYNOPSIS...
Cloudy with unseasonably cool high temperatures for the
remainder of the work week that will run 10 to 20 degrees below 
normal! A late season Nor'eater likely brings a cold windswept
heavy rain to the region late Wednesday into early Friday. The
brunt of this storm appears to be Thursday, when wind gusts of 
40-50+ mph will be possible along the coast with pockets of 
minor coastal flooding also possible. The soaking rain will 
likely come to an end Friday morning, but a few showers will 
remain possible at times through the holiday weekend.
Temperatures will slowly moderate, but still remain below 
normal into this weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Key Messages: 

* Some peeks of sun early in western New England, but it's a
  continued overcast day for most of Southern New England.
  
* Sprinkles or patchy drizzle as onshore flow increases this
  afternoon, though most areas are dry. 

* Highs low 60s western New England, and in the mid 50s for most
  of eastern MA and RI.

Details:

By late-May standards, it's a really chilly early morning!
Current temps are in the mid 40s to around 50, with air temps
being kept up by a blanket of overcast, along with northwest
winds running around 10-15 mph with gusts to 25 mph. Wind chills
in interior Southern New England have been into the low to mid
30s too. Just underscores how chilly it is out there, now only 
a few days away from Memorial Day Weekend. The main synoptic 
features really haven't changed much over the last 24 hours, 
with a well- developed upper level low located near Nova Scotia,
making little eastward progress amid a blocky pattern in the 
North Atlantic. Maritime-polar origin moisture from Atlantic 
Canada continues to be advected in from the northeast, which is 
contributing to the overcast cloud cover.

A ridge of high pressure over NY early this morning should move
into western New England this morning, which will help in easing
northerly winds to around 10 mph, and should allow for some sun
and comparatively milder temperatures in western MA and
Tolland/Hartford Counties in CT (highs in the low 60s).
Eventually here, overcast rebuilds in but that should hold off
until late this afternoon or even early evening.

For eastern/central MA and RI, it's more of a question mark how
much (if any?) diurnal warming we can generate today. The 
moisture associated with this ongoing overcast is somewhat 
shallow so it could be prone to some peeks of sun, but that 
moist layer becomes a little deeper per BUFKIT cross sections as
we move into late morning to afternoon. Winds will also be 
turning northeasterly around 5-10 mph in central and eastern MA 
and RI. Some of the model QPF guidance shows "speckles" coming
in as the moist onshore flow increases this afternoon, so there
could be some sprinkles or patchy drizzle then, although the 
vast majority of time will be dry. This is not a scenario which 
leads to much warming. Leaned toward maintaining overcast and 
I've built highs off the hourly raw guidance temps, which only 
brings highs in the mid 50s. It's not as cold as the NAM 
guidance, but it's also on the colder end of forecast guidance.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
Key Messages:

* Overcast, periods of drizzle or sprinkles and strengthening
  northeast winds tonight and continuing into Wednesday. 

* Anomalously cold high temperatures Wednesday in the low to mid
  50s, which will feel even colder with northeast breezes.
  Normal highs in the upper 60s to low 70s.

Details:

Conditions won't really change very much through this period, as
a strong sfc ridge of high pressure builds southward into Wed. 
Model thermal fields indicate a cold-air damming type look, with
925 mb temps dropping to an unseasonably cold +2 to +4C! The 
sfc ridge will also keep the leading edge of steadier rains 
associated with a rather strong late- season Nor'easter 
suppressed to the northern mid- Atlantic states thru Wed aftn. 

Expect onshore NE flow and overcast conditions to continue. 
There could be some patchy drizzle or very light rain showers 
that should make greater inroads into interior Southern New
England into early Wed, but the vast majority of the time is 
dry. NE winds start off at relatively modest levels through 
tonight (around 5-10 mph), but then becomes more of a moderate 
NE breeze into Wed with speeds around 10-15 mph and some gusts 
to 20 mph especially near the coast. 
 
The story is the unseasonably cold temperatures, especially 
with regard to the Wednesday highs. There won't be much change 
to temperatures tonight, with lows in the mid to upper 40s. The 
cold advection, overcast and increasing NE breezes on Wednesday 
will mean highs also won't rise much if at all, especially near 
the coast. The CT Valley has the best chance at seeing highs Wed
into the middle/upper 50s. But the majority of Southern New 
England otherwise should stay in the lower 50s. I did take a 
peek at daily record lowest maxes and we're not close to those 
but it will nonetheless feel quite chilly. FWIW...with a high 
temp in Boston of 52 degrees, Boston has experienced a high temp
of 52 degrees or colder on May 21st 9 times in its period of 
record, most recently in 1990.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Key Messages...

* Unseasonably cool for the remainder of this week, with some 
  improvement this weekend into Memorial Day

* Nor'easter will bring a cold, windswept rain late Wed into
  early Fri, with Thu afternoon temps in the mid 40s to lower 
  50s

* ENE wind gusts of 40-50+ mph possible along the coast Thu, 
  with perhaps some pockets of minor coastal flooding during 
  high tide

* The widespread rain comes to an end Fri morning, but a few
  showers will remain possible at times for this holiday weekend

Details...

Not much change to the idea of a widespread rainfall arriving
Wednesday night and continuing into at least part of Friday.
While the guidance has started to come into better agreement
with the track and overall timing, it's still a bit early to set
this forecast in stone. Latest guidance consensus still favors 
a track just inside the 40N/70W benchmark, although there
remained some guidance, like the global GEM, that are hinting at
a more offshore track.

Rainfall totals between 1-2 inches is still possible, but not a
guarantee. Latest NationalBlend probabilities for 48-hour 
rainfall ending 8 AM Friday in excess of 1 inch was only about
35-55% across southern New England. The highest probabilities
were in the Worcester Hills, where some upslope could enhance
rainfall.

Another concern from this storm will be strong winds as this 
low pressure passes bu our region. The latest NationalBlend 
probabilities for 24-hour max wind gusts in excess of 40 mph
ending 2 AM Friday were only 40-60%. Will keep an eye on this as
the track will be critical. Should we achieve better mixing,
peak wind gusts could approach 50 mph. With leaves on the trees,
there may be a little more impact than a similar storm during
the winter.

Lastly, while astronomical tides are not that high, the
potential exists for 1.5 to 2.5 foot storm surge. If this 
occurs, we may see some minor coastal flooding along the eastern
MA coast onto Nantucket during the Thu high tide cycle depending 
on specific timing and the magnitude of the winds/wave heights.

This low pressure system will lift off into the Canadian
Maritimes Fri into this holiday weekend. This will bring an end 
to the threat for the widespread rain Fri morning. However, a
deep upper level anomalous trough will be slow to depart. This 
will bring us the risk of a few showers at times through this 
weekend, but it will not be a washout. 

Below normal temperatures expected into late this week. High
temperatures only anticipated to be a few degrees higher than
our normal low temperatures for late May. We should start to
warm up more substantially later this weekend, but perhaps not
approach normal temperatures until Sunday into Monday.

&&

.AVIATION /07Z TUESDAY THROUGH SATURDAY/...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

06z TAF Update: 

Through 12z Tuesday: High confidence. 

SCT-OVC mainly VFR bases. NW winds around 10-15 kt with gusts
20-25 kt, slowly easing into daybreak. 

Today: High confidence in trends, though moderate on timing.

SCT-OVC VFR bases at least initially, with NW/N winds around 10
kt. Ceilings then deteriorate to MVFR soonest in northeast MA
and then gradually spreading southwest. This will also occur 
with a windshift to NE with speeds 5-10 kt. Timing of MVFR and 
NE onshore breezes is still a bit uncertain, could happen as 
soon as 15z but better chance after 17z into aftn. 

Tonight and Wednesday: High confidence. 

Widespread MVFR cloud bases with little change. NE winds around
5-10 kt tonight, which then increase to around 10-15 kt with
gusts to 25 kt.
 
BOS TAF...High Confidence in TAF. 

BDL TAF...High Confidence in TAF. 

Outlook /Wednesday Night through Saturday/...

Wednesday Night: Mainly MVFR, with local IFR possible. Breezy.
Chance RA.

Thursday: Mainly MVFR, with areas IFR possible. Windy with
areas of gusts up to 30 kt. RA.

Thursday Night: MVFR/IFR conditions possible. Breezy. RA.

Friday: MVFR/IFR conditions possible. Breezy. Chance RA, chance
SHRA.

Friday Night: Mainly VFR, with local IFR possible. Chance SHRA.

Saturday: Mainly VFR, with areas MVFR possible. Chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Today Through Wednesday: High confidence. 

NW winds around 20-25 kt early today decrease into early this
morning, then become NE late morning to afternoon. NE winds 5-10
kt this afternoon and tonight, increasing to 10-15 kt with gusts
20-25 kt Wed. Seas may still be near 5 ft in southeast waters
today through Wed.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas up to 5 ft. Chance of rain. 

Thursday: Strong winds with gusts up to 30 kt. Rough seas up to
12 ft. Rain, isolated thunderstorms. 

Thursday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Rough seas up to 13 ft. Rain likely. 

Friday: Winds less than 25 kt. Rough seas up to 13 ft. Chance
of rain, slight chance of rain showers. 

Friday Night: Winds less than 25 kt. Local rough seas. Slight
chance of rain showers. 

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 AM EDT this morning for 
     ANZ230>234-251.
     Small Craft Advisory until 8 AM EDT Wednesday for ANZ250-254-
     255.

&&

$$

SYNOPSIS...Belk/Loconto
NEAR TERM...Loconto
SHORT TERM...Loconto
LONG TERM...Belk
AVIATION...Belk/Loconto
MARINE...Belk/Loconto