Lexington Weather

Lexington, Massachusetts, USA

64°F

7/26/2026 10:04pm

Lexington Conditions: Clear
Temperature: 63.9°F / 17.7°C
Dew Point: 52.3°F
Relative Humidity: 66%
Wind: Calm, 10-min avg: Calm, gust: None
Barometer: 29.82 in Steady
Visibility: 10 miles
Rain Today: 0.00 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 210806
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
406 AM EDT Tue Jul 21 2026

.WHAT HAS CHANGED...
Gale Watch converted to Small Craft Advisories due to low
confidence in widespread/consistent gale-force winds tonight and
Wednesday.

&&

.KEY MESSAGES...

- Scattered showers and thunderstorms return this evening
  through Wednesday morning. Risk for a few strong to severe
  storms and heavy downpours. Localized flash flooding possible
  in poor drainage areas. 

- Scattered thunderstorms possible later Wednesday, but will be
  dependent on degree of clearing during the day.

- Drying out Thursday into the latter part of the week
  with seasonable temperatures and lower humidity into the
  weekend.

&&

.DISCUSSION...
KEY MESSAGE 1...Scattered showers and thunderstorms return this evening
through Wednesday morning. Risk for a few strong to severe 
storms and heavy downpours. Localized flash flooding possible in
poor drainage areas. 

An upper level trough slowly pushes across eastern U.S./Canada today 
through Thursday with a several pieces of shortwave energy moving 
through the flow. At the surface, this will sweep a few frontal 
boundaries across the northeast as a surface low tracks across 
Quebec. This will support the return of unsettled weather with 
potential for strong storms and minor localized flash flooding 
tonight into Wednesday. A 40-50 kt LLJ with be the main player with 
the set-up, helping advect in richer moisture (dewpoints around 70F) 
with precipitable water values rising to 1.5-2.0"+ across southern 
New England this evening. Instability varies from marginal to 
moderate across high-resolution guidance with MU/SBCAPE values 800-
1500 J/kg. This is sufficient to support thunderstorm development if 
instability is available while aligning with an incoming shortwave. 
Model soundings do show hodographs supportive of stronger shear and 
helicity values in the 0-3 km layer. This environment will not only 
be support of heavy downpours, but also a strong to severe storm or 
two with damaging winds. Can't rule out the low risk of a brief 
"spin-up" given the supportive wind/shear profiles. 

Anomalous PWATs combined with warm cloud depths of 11,000-13,000+ ft 
allow for efficient rain processes and more importantly support 
heavy rainfall. As far as the QPF probs go, 18z guidance backed off 
a little with the probs of 1"+ and 2"+ overall, but it's just one 
run. We are still overall seeing a good signal for 24hr amounts 1"+ 
shown by the moderate to high probabilities (50-80%) especially 
along the south coast and Cape and Islands and low to moderate 
probabilities for 2"+ focused along the immediate south coast and 
Cape/Islands. 

The timeframe at which this falls will be the big factor for flash 
flooding potential. Given that embedded storms are possible, 
localized flash flooding is certainly a concern. The HREF PMM 
reflects this well with localized areas of 2"+ across western CT, RI 
and southeast MA, but also many streaks of 1-1.25" across the 
region. Slow storm motion will not be a concern with mid-level 
flow >30kts; however, there is a prominent LLJ suppling 
plentiful moisture upstream while steering storms consistently 
SW to NE. Training of heavier rain and thunderstorm may be 
possible as a result. The HREF probability of 1 hr precip 
exceeding 1 hr FFG reflects this well with higher probabilities 
in NJ and southern NY with low probs extending into western CT. 
There are a few spots of low probs across MA and RI 
tonight/early Wednesday. All this is pointing to is a lower 
probability of seeing widespread flash flood impacts. The HREF 
showing scattered low probabilities(< 20%) of >1.0"/hr rain 
rates mainly across portions of CT and moreso RI and southeast 
MA/Cape & Islands. So we'll have to keep an eye on localized 
minor flash flooding issues, especially in the more flashy areas
or urban/poor drainage areas (Providence, Hartford). This is 
fairly consistent with the previous forecast with us seeing the 
risk for localized flash flooding; however, it is not widespread
enough of a threat to warrant a Flood Watch for portions of 
southern New England. 

For timing, this will primarily be and evening and overnight event 
into the early morning hours of Wednesday. Depending on the timing 
of these shortwaves showers/storms could develop may develop as 
early as late afternoon; however, chances increase for the evening 
and overnight timeframe. 

KEY MESSAGE 2...Scattered thunderstorms possible later Wednesday,
but will be dependent on degree of clearing during the day.

Rain continues through the early morning hours of Wednesday. There 
is some question on when the bulk of the rain exits and the coverage 
of showers. Most model guidance has the bulk of rain out by late 
morning; however, there is more spread on the degree of "clearing" 
in the afternoon. If there are lingering showers, as some guidance 
suggests, the suppressed heating will likely end up lowering the 
risk of storms later in the day. If we get enough of a window with 
clearing or breaks in the clouds, instability will be sufficient to 
support thunderstorms developing ahead of a cold front with values 
1000-1800 J/kg of SBCAPE. Moisture won't be as anomalous as the 
previous evening through the whole column; however, the HREF has 
been keen on another surge of higher dewpoint air ahead of the 
front. Across the individual CAMs, there is plenty of spread with 
regards to the timing, coverage, and intensity of convection (if 
any). A couple hint at the potential for scattered showers and 
thunderstorms developing after mid-afternoon moving eastward into 
the evening. The western and central portions of southern New 
England likely have a higher risk given they would likely clear 
earlier and have longer to recover and heat through the day. 
Instability and shear values are sufficient to support a strong to 
severe storm or two as well. This will become higher confidence as 
models develop a better consensus on the extent of clearing 
Wednesday. 

KEY MESSAGE 3...Drying out Thursday into the latter part of the
week with seasonable temperatures and lower humidity into the 
weekend.

The cold front exits the region by Thursday morning, leaving 
drier and seasonable conditions in its wake. With the front, the
upper level trough centered over Quebec also moves off to the 
northeast. High pressure starts to build in over southern New 
England from the Great Lakes, continuing the drier conditions 
into the weekend. Temperatures aloft fall slightly, with 925 mb 
temperatures falling to around 16C for much of the second half 
of the week. Notably, Wednesday night will likely be cooler as 
925 mb temperatures may fall to as low as 10C over the interior.
Lows there could get into the low 50s. 850 mb temperatures are 
expected to mostly be around 10C as well through the back half 
of the week. Even with these reduced temperatures, the continued
high sun angle will keep temperatures from falling too low, 
keeping them seasonable. Conditions remain dry and seasonable 
until around Sunday when the flow shifts more S again, 
increasing humidity. A surface low may also pass just offshore, 
but any impacts from it -- if any at all -- are not certain at 
this time.

&&

.AVIATION /07Z TUESDAY THROUGH SATURDAY/...
Forecaster Confidence Levels...

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

06Z TAF Update: 

Through 12Z...High Confidence. 

VFR. A small percentage of high-resolution guidance continues 
to hint at the possibility for patchy early morning fog over 
the interior which could result in patch MVFR or lower cigs
nearby. This is too low probability and lower coverage to
include in interior terminal TAFs. Otherwise upper level clouds
move in this morning with light southerly winds. 

Today...Moderate confidence. 

General deterioration to MVFR-IFR ceilings by late afternoon.
Risk of showers increased after 18z from W to E. A few embedded
thunderstorms are possible, but too low probability to include
in TAF at this time. Better potential for thunderstorms will be
this evening/tonight. Winds become SE to S and increase to 
10-15 kt with gusts 20-25 kt.

Tonight...Moderate confidence.

MVFR/IFR possible in any SHRA or TSRA even to LIFR at times for
south coast and Cape terminals. Rain overspreads the region this
evening and tonight with chances for TSRA across the region. 
Included PROB30s for +SHRA at this time to message potential for
heavy downpours though they may be replaced in spots with TSRA 
in future TAF issuances with increasing confidence in embedded
thunderstorms tonight. Winds 10-20 kt sustained particularly 
over SE MA, Cape & Islands. Gusts 20-25 kt remain possible 
through the nighttime period in these areas as well. There is a
low risk for a few higher gusts at the Cape/Island terminals
tonight up to 30 kts. 

KBOS Terminal...Moderate confidence in TAF. Timing shower
arrival and deterioration of ceilings lower confidence. Should
see showers around after 20Z with ceilings falling to MVFR with
their arrival by 23/00Z. Localized heavy downpours possible in 
heavier showers and embedded thunderstorms after 00Z. Lower 
confidence on potential for thunderstorms due to uncertainty in 
how far east the instability extends tonight. Kept TSRA of the 
PROB30 for now and messaged as a PROB30 for +SHRA. 

KBDL Terminal...Moderate confidence in TAF.
Showers developing mainly after 18Z with localized downpours 
and embedded thunderstorms possible after 20Z.

Outlook /Wednesday through Saturday/...

Wednesday: Mainly VFR, with local IFR possible. Windy with
gusts up to 35 kt. Chance SHRA, isolated TSRA.

Wednesday Night: VFR. Windy with local gusts up to 30 kt.
Slight chance SHRA.

Thursday through Saturday: VFR. 

&&

.MARINE...
Forecaster Confidence Levels...

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


The probability for more widespread and consistent gusts at or
above gale force has decreased thus leading to the cancellation
of the Gale Watch and conversion to SCAs. However, some model 
guidance has still indicated potential for brief more patchy 
areas of gusts to gale force across the outer waters tonight 
into early Wednesday as a strong low level jet pushes in. Rough
seas 10-12 ft. Near-shore waves along the southern coast, 
Islands, and outer Cape are likely in the 6-10 ft, and 
warranted High Surf Advisories starting early Wednesday and 
lingering late into Thursday. Strong Rip Currents and waves near
6 ft are possible, especially across the outer Cape, Thursday 
as the cold front stalls out near the coast, prompting the later
ending to the High Surf Advisory. SCAs currently go out through
Wednesday night; however, will likely need to be extended for
most zones (southern waters and outer waters) as 5ft+ waves 
linger. 

Showers and embedded thunderstorms tonight into early
Wednesday bringing hazards of heavy downpours, reduced
visibilities to less than 2 miles for brief periods in heavier 
showers/storms, and lightning. 

Outlook /Wednesday through Saturday/...

Wednesday: Low risk for gale force winds with gusts up to
35 kt. Rough seas up to 13 ft. Chance of rain showers, slight
chance of thunderstorms. 

Wednesday Night: Low risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 12 ft. Chance of rain
showers, slight chance of thunderstorms. Local visibility 1 to
3 nm.

Thursday: Winds less than 25 kt. Rough seas up to 12 ft. Chance
of rain showers, slight chance of thunderstorms. 

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

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

Friday Night through Saturday: Winds less than 25 kt. Seas
locally approaching 5 ft. Slight chance of rain showers. 

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...High Surf Advisory from 6 AM Wednesday to 8 PM EDT Thursday 
     for MAZ020>024.
RI...High Surf Advisory from 6 AM Wednesday to 8 PM EDT Thursday 
     for RIZ006>008.
MARINE...Small Craft Advisory from 8 PM this evening to 8 PM EDT 
     Wednesday for ANZ231>235-237-250-254>256.

&&

$$

DISCUSSION...Hrencecin/Mensch
AVIATION...Mensch
MARINE...Mensch