Lexington Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 121852
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
252 PM EDT Mon Oct 12 2026

.WHAT HAS CHANGED...
Increased rain chances and winds for the late week/weekend 
storm as confidence increases. Will need to monitor coastal
water levels for the Tuesday morning high tide around Nantucket
Sound.

&&

.KEY MESSAGES...

- Low clouds and rain showers return overnight into Tuesday
  night with a rumble of thunder possible. 

- Isolated shower possible Wednesday, but drier overall. Dry
  conditions return for Thursday with seasonably cool  
  temperatures. 

- Low pressure system expected to bring rain Friday into early 
  Saturday. Gusty northwest winds and below normal temperatures.

&&

.DISCUSSION...
KEY MESSAGE 1...Low clouds and rain showers return overnight
into Tuesday night with a rumble of thunder possible. 

Still tracking another band of lower clouds moving south across
our region. Eventually, even these clouds will dry up with the
daytime heating. The same cannot be said for later tonight. A 
backdoor front should arrive from the NE and push well into 
southern New England before a low pressure to our north gets 
close enough to increase southwest winds and drive this front 
back to the north some time Tuesday afternoon into Tuesday 
night.

The main impact will be some lower clouds and perhaps some
patchy drizzle late tonight. A passing shortwave over northern
New England increases the risk for more significant showers the
closer one gets to northern MA. Could even see some rumbles of 
thunder given some weak elevated instability above am inversion,
again with a greater risk towards northern New England.

Persistent east to southeast winds could keep waters level up
towards Nantucket Sound. Will need to monitor the Tuesday
morning high tide. Impacts look marginal right now, so no
headlines at this time. 

KEY MESSAGE 2...Isolated shower possible Wednesday, but drier
overall. Dry conditions return for Thursday with seasonably 
cool temperatures.

A trailing cold front shifts across the region Wednesday with
surface high pressure building in from the west through the day. 
Model soundings show increased mixing in the boundary layer
supporting drier conditions and also westerly winds with gusts
20-30 mph. Westerly, downslope flow combined with 925mb
temperatures +17- 18C will support a warm fall day with high
temperatures in the 70s in many areas. There are indications of 
a stray shower or two as a weak wave moves through, but this 
will be fairly limited in coverage and at most a light 
shower/sprinkle due to the drier lower levels.

As high pressure settles in further into Thursday, the airmass
dries out even more. Thursday will likely be dry, although
cooler than Wednesday. A cooler airmass will also have moved in 
with 925mb temperatures around 10C cooler than Wednesday. This 
will yield seasonably cool temperatures mainly in the lower 
60s.

KEY MESSAGE 3...Low pressure system expected to bring rain
Friday into early Saturday. Gusty northwest winds and below 
normal temperatures.

Deterministic and ensemble guidance show a stronger/deeper
northern stream shortwave trough push across the Great Lakes 
and the northeast Friday into Saturday. There is synoptic 
support with this system as an upper level jet positions near 
southern New England yielding large scale ascent while also 
advecting in a plume of above normal moisture northward into the
region. This will set the stage for a widespread rain. Despite 
plentiful moisture, instability appears to be limited thus 
minimizing the potential for heavy rain impacts. Ensemble 
guidance ranges amounts generally from 0.25 to 0.60" with the 
ECMWF and Canadian leaning wetter than the GFS solutions. Across
those particular models, amounts closer to an inch are 
possible. These higher amounts are not out of the question if we
can tap into better forcing with the warm front. Finer details 
such as exact timing of arrival and exit of rain are less 
certain as there are difference across guidance still. Rain more
likely arrives in the Friday morning timeframe, continuing 
overnight. Most guidance shows this system to be fairly 
progressive meaning it won't be lingering the whole weekend. The
bulk of the rain likely exits early Saturday morning. In 
addition, the initial southerly LLJ with this system nudges in 
Friday which if mixed sufficiently, will bring breezy to gusty 
southerly winds (gusts 20-30 mph).

A strong cold front pushes across the region by early Saturday
morning putting the northeast within a classic cold air
advection pattern with gusty NW winds, cooler temperatures, and 
isolated showers. A NW 40-50 kt LLJ positions across the region 
Saturday. The tighter gradient and CAA to help steepen lapse 
rates will support deeper mixing and thus gusty NW winds. The 
degree or mixing and strength of the LLJ are still less certain 
this far out, but ensembles show a signal for gusts 35-45 mph 
possible, potentially higher across the coastal waters. 925mb 
temperatures range between - 2C to +2C Saturday yielding likely 
the coolest temperatures of the season so far. Highs will likely
struggle to get out of the 40s across the interior with low 50s
in the valleys and coastal plain. RH fields show residual
moisture within the cyclonic flow pattern. This may be enough to 
support some isolated showers. Some of the higher elevation 
points across the Berkshires may only hit the 40 degree mark on 
Saturday. It's a bit too early to say the "S word" just yet
(snow). However...if the timing aligns, a morning flurry or
shower can't be ruled out in those higher terrain spots out
west. Expect a cold night Saturday night with high probabilities 
for the interior to at least drop to freezing. Higher elevation 
locations may drop into the upper 20s.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
Forecaster Confidence Levels...

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

Through 00Z:

Mainly VFR with areas of MVFR cigs. Lingering IFR across the
Cape and islands lifts to at least MVFR after 20Z. 

Tonight: High confidence in trends, but moderate on timing
backdoor cold front. 

VFR early tonight for most. A backdoor cold front progresses 
southward from NH/ME. Timing approximately 02-04z for BED, and 
around 04-07z for the remaining TAFs. This will bring lowering 
ceilings again into the MVFR-IFR range, light -RA and winds 
turning NE around 5-10 kt, strongest near the coast.

Tuesday: Moderate confidence.

MVFR-IFR ceilings, with lighter rains or drizzle. Possible
MVFR-VFR optimism by mid to late afternoon. NE/E winds around
5-10 kt, turning SE/S by afternoon and increasing to around 10
kt.

Tuesday Night: Moderate confidence.

MVFR-IFR to start. Some areas improve to VFR late, mainly in the
valleys and towards RI and southeast MA.

KBOS Terminal...High confidence in trends. Moderate confidence
in timing.

KBDL Terminal...High confidence in trends. Moderate confidence
in timing.

Outlook /Wednesday through Saturday/...

Wednesday through Thursday: VFR. Breezy. 

Thursday Night: VFR. Chance SHRA.

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

Friday Night: Mainly VFR, with local MVFR possible. Strong
winds with local gusts up to 45 kt. Chance SHRA.

Saturday: VFR. Strong winds with local gusts up to 45 kt. 

&&

.MARINE...
Forecaster Confidence Levels...

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

Through Tuesday Night: High confidence.

The remnants of Hurricane Isaias are currently working their way 
across the southern waters. Seas 5 to 10 ft and wind gusts
20-30 knots. SCAs are in effect for the southern waters, 15-20
kts with gusts to 25kt possible, especially on the southern 
outer waters. Seas 6-9 ft on southern waters, 3-6 ft on the 
eastern waters.

Monday night: High confidence. 

NE winds 10-15 kts with gusts 20-25 kts on the eastern waters.
Seas 3-5 ft. 

Tuesday: High confidence. 

SE winds 10-15 kts with increasing gusts to 20 kts. Seas 3-5 ft.
RA over the eastern waters.

Outlook /Wednesday through Saturday/...

Wednesday: Low risk for Small Craft Advisory winds with gusts
up to 25 kt. Areas of rough seas. 

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

Thursday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas up to 5 ft. 

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

Friday: Moderate risk for Small Craft Advisory winds with gusts
up to 30 kt. Areas of rough seas. Rain showers. 

Friday Night: gale force winds with local gusts up to 45 kt.
Rough seas up to 12 ft. Chance of rain showers. 

Saturday: gale force winds with gusts up to 45 kt. Rough seas
up to 12 ft. Slight chance of rain showers. 

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 1 AM EDT Tuesday for ANZ235-237.
     Small Craft Advisory from 8 PM this evening to 2 AM EDT 
     Wednesday for ANZ250.
     Small Craft Advisory until 8 PM EDT Wednesday for ANZ254.
     Small Craft Advisory until 8 AM EDT Tuesday for ANZ255-256.

&&

$$

DISCUSSION...Belk/Mensch
AVIATION...Belk/Mensch
MARINE...Belk/Mensch