Lexington Weather

Lexington, Massachusetts, USA

51°F

5/23/2025 11:14pm

Lexington Conditions: Overcast
Temperature: 50.5°F / 10.3°C
Dew Point: 48.6°F
Relative Humidity: 93%
Wind: SW 2 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 201853
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
253 PM 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 will bring 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 
Friday afternoon into Saturday. Temperatures will slowly 
moderate, but still remain below normal into this weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...

Key Messages...

* Cool and cloudy today with sprinkles and patchy drizzle possible, 
  especially east. 

* Lows in the upper 40s. 

Placement between an a slowly exiting mid level trough and ridging 
over the Great Lakes has southern New England beneath cool 
northerly/northeasterly flow today while a layer of moisture in the 
800-900mb layer contributes to deck of clouds keeping solar 
insolation to a minimum. Thus, temps have not made it out of the 
50s for most locations. As the ridge approaches this afternoon it 
has allowed the wind gusts this morning to calm down and that will 
continue into tonight. Persistence forecast into tonight with 
ridging overhead and cool, moist low level onshore flow directing 
patchy drizzle or light showers into SNE, especially eastern areas. 
Soundings indicated saturated low/mid levels leading to thick/low 
clouds overnight as patchy drizzle continues. 

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...

Key Messages...

* Temps a bit cooler than Tuesday, with clouds and patchy drizzle. 

* Rain moves in late Wednesday night. 

More of the same weather expected on Wednesday, except even a bit 
colder and with even less breaks of sun. This is due to continued 
low level moisture/clouds moving from northeast to southwest off the 
ocean as well as mid/upper level moisture/clouds moving in from 
southwest to northeast ahead of the approaching frontal system. Cold 
advection continues on northeast flow in the low levels, with 925 mb 
temps dropping from 5-6C Tuesday to 1-2C Wednesday. This will lead 
to high temperatures in the low to mid 50s for most; locations in 
the CT Valley will benefit from some downslope flow and may reach 
60. 

A cold, windswept rain arrives Wednesday night ahead of a late 
season nor'easter. The parent low over the Ohio Valley Wednesday 
will generate a secondary coastal low along the frontal boundary 
Wednesday night moving off the mid Atlantic coast into Thursday. The 
plume of moisture ahead of the system together with a 25-35kt LLJ 
will generate a precip shield slowly expanding into most of SNE by 
8am. As the pressure gradient tightens we'll also see winds at the 
surface become increasingly gusty toward sunrise, gusting 20-30 mph 
but the bulk of the rain and wind arrive later Thursday.  

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...

Key Messages...

* Late season Nor'easter Thu into early Fri brings 1-2" of rain with 
  localized 3" amounts along with poor drainage street flooding

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

* A few showers will remain possible Fri into Sat but these will be 
  hit or miss...followed may mainly dry weather Sun and Mon

* Unseasonably chilly temps Thu gradually moderate through the 
  Holiday Weekend, but we probably do not break 70 until Memorial Day

Details...

The main forecast concerns continues to be the late season 
Nor'easter which will bring windswept heavy rain to the region Thu 
into early Fri. The other concerns revolve around the potential for 
strong winds along the coast along with pockets of minor coastal 
flooding possible. We will break it down more below.

1) Heavy Rain 1-2" with localized 3" amounts late Wed into early Fri

The latest 12z guidance continues to be in good agreement in 
intensifying low pressure system that will pass inside the Benchmark 
Thu into early Fri. This will combined with a modest high pressure 
system in the Maritimes to result in an anomalously strong easterly 
LLJ. The 850 mb LLJ is 3+ standard deviations outside climatology 
for this time of year. In addition...a closed 700 mb low will lift 
across southern New England resulting in a mid level deformation 
zone. Putting all these ingredients together...the stage is set for 
a widespread heavy rain event. We are thinking 1-2" of rain are in 
store for much of the region...but some localized 3" amounts are 
possible especially near any coastal front or mid level deformation 
axis. This may result in some poor drainage street flooding 
especially in some of those typically prone urban locations. 
However...not expecting any serious type flash flooding.

In addition...high temperatures on Thursday will be running 20 to 25 
degrees below normal for this time of year. Near record low high 
temperatures in the 45 to 55 degree range are expected. It will feel 
even chillier with the wind.

2) Period of easterly wind gusts of 40-50+ mph along the coast

The other issue will be a period of easterly wind gusts of 40-50+ 
mph along the coast that will be associated with the anomalously 
strong easterly LLJ. The 850 mb jet is expected to increase to 
between 50 and 60 knots that will be pointed toward the coast. 
Thinking that we will need some wind headlines across the Cape and 
Islands and perhaps all the way up the eastern MA coast. Given this 
is a 4th period event will not issue with this package...but we 
probably will need to issue in the next 24 hours. 

3) Potential for minor coastal flooding with the Thu PM high tide

The anomalously strong easterly low level flow will help to build 
seas to 10-15+ feet offshore. Astronomical high tides are not that 
high with Boston at 10.0 MLLW Thu evening. However...appears that a 
1.5 to 2.5 foot storm surge off the coast with rather high seas off 
the coast will bring the potential for pockets of minor coastal 
flooding during the Thu evening high tide cycle along the eastern MA 
coast/Nantucket. A coastal flood advisory may eventually be needed 
for this region in later forecasts.

Friday afternoon through the Holiday Weekend...

After the steady rain departs Fri morning...a few showers will 
remain possible at times Fri afternoon into Sat but a washout is not 
expected. A lot of these scattered showers will be diurnally driven 
with anomalous shortwave energy/cold pool aloft overhead. This 
anomalous upper level trough begins to shift to the northeast Sun 
and Memorial Day...which should bring mainly dry weather. 

Temperatures will be slow to moderate through the Holiday Weekend, 
but they will gradually as the trough begins to push east of the 
region. Highs in the 50s to near 60 in spots Fri and probably into 
the 60s in most locations by Sat and especially Sun. Appears we 
finally may break 70 in spots by Memorial Day.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

18z TAF Update: 

This afternoon: High confidence in trends, moderate on timing.

SCT-OVC VFR bases for most terminals, 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. 

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.

Wednesday Night: Moderate confidence. 

IFR with increasing rain chances as heavier precipitation moves
in from the southwest. E/ENE winds 10-20 kts, increasing toward
12Z. 
 
BOS TAF...High Confidence in TAF. 

BDL TAF...High Confidence in TAF. 

Outlook /Thursday through Sunday/...

Thursday: Mainly IFR, with local MVFR possible. Strong winds
with gusts up to 40 kt. RA.

Thursday Night: Mainly IFR, with areas MVFR possible. Windy
with gusts up to 35 kt. RA likely.

Friday: Mainly MVFR, with local IFR possible. Windy with local
gusts up to 30 kt. Chance SHRA.

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

Saturday: MVFR. Breezy. Chance SHRA.

Saturday Night: Mainly VFR, with local MVFR possible. Slight
chance SHRA.

Sunday: VFR. Breezy. 

&&

.MARINE...
Forecaster Confidence Levels:

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

Today Through Wednesday night: High confidence. 

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 night.

Outlook /Thursday through Sunday/...

Thursday: Moderate risk for gale force winds with gusts up to
40 kt. Rough seas up to 11 ft. Rain. Visibility 1 to 3 nm.

Thursday Night: Low risk for gale force winds with gusts up to
40 kt. Rough seas up to 13 ft. Chance of rain. 

Friday: Moderate risk for Small Craft Advisory winds with gusts
up to 30 kt. Rough seas up to 11 ft. Chance of rain showers. 

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

Saturday: Winds less than 25 kt. Seas up to 5 ft. Slight chance
of rain showers. 

Saturday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. 

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Gale Watch from Thursday morning through late Thursday night 
     for ANZ230-236.
     Gale Watch from late Wednesday night through late Thursday 
     night for ANZ231>235-237-254>256.
     Small Craft Advisory until 8 AM EDT Wednesday for ANZ250-254-
     255.
     Gale Watch from late Wednesday night through late Thursday 
     night for ANZ250-251.

&&

$$

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