Lexington Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 161901
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
301 PM EDT Fri Oct 16 2026

.WHAT HAS CHANGED...
Gale Watches have been replaced with Small Craft Advisories for the 
applicable waters, excluding the outermost zones where Small Craft 
Advisories are not issued. Post-frontal NNW winds are expected to 
gust 25-35 kt Saturday, with occasional gusts approaching gale force 
possible, especially across the southern and southeastern outer 
waters Saturday night into early Sunday.

&&

.KEY MESSAGES...

- Morning showers exit, followed by a brief lull this afternoon
  before a cold front brings additional showers and
  thunderstorms this evening. A few strong to isolated severe
  thunderstorms are possible.

- A few showers may linger along the southern coast early
  Saturday. Otherwise, drier and noticeably colder conditions
  are expected Saturday.

- Dry with a modest warmup through mid next week, but monitoring
  coastal storminess near or south of the mid-Atlantic waters
  which could bring periods of light rain, enhanced northeast
  winds and building waves/possible erosion to southeast New
  England.

&&

.DISCUSSION...
KEY MESSAGE 1...Morning showers exit, followed by a brief lull this 
afternoon before a cold front brings additional showers and 
thunderstorms this evening. A few strong to isolated severe 
thunderstorms are possible.

As anticipated, gloomy conditions to wrap up the workweek. Earlier 
this morning, a warm front lifted through southern New England, 
bringing the first round of showers. The region is now positioned 
within the warm sector. Dew points are increasing into the lower 60s 
along the coast, while interior locations remain in the 50s. 
However, by midafternoon, anticipate temperatures and dew points 
continuing to climb into the 60s. Increasing dew points could lead 
to pockets of instability. High-resolution guidance suggests limited 
surface-based CAPE; however, as we've previously mentioned, the jet 
dynamics associated with the approaching cold front are impressive.

A line of showers and embedded thunderstorms is developing across 
western New York and extending southwest into Ohio. This activity is 
associated with our cold front, which is marching eastward, aided by 
a fairly robust mid-level trough. Ahead of the trough, SSW flow 
allows for WAA, supporting mild afternoon temperatures despite the 
clouds and rain. Highs should reach the middle 60s across northern 
areas, while upper 60s to near 70 degrees are possible farther south.

Today is not anticipated to be a high-end severe weather day by any 
stretch of the imagination; however, it is a day we cannot 
completely ignore. Instability remains limited, generally 100-300 
J/kg of MUCAPE, though strong bulk shear may compensate for the 
limited instability and support a few stronger storms. Over the last 
24 hours, the greatest shear has shifted a bit farther south, 
favoring areas around NYC and points southwest. Nevertheless, a 
couple of stronger storms remain possible. Feel as though these 
storms could produce sub-severe wind gusts of 40 to 50 mph, with a 
much lower chance of severe gusts exceeding 60 mph. CAMs continue to 
indicate that the greatest potential for thunderstorms across 
southern New England will be between 5 PM and 11 PM as the cold 
front progresses from west to east.

Additional rainfall amounts of 0.25 to 0.50 inches are expected.

KEY MESSAGE 2...A few showers may linger along the southern coast 
early Saturday. Otherwise, drier and noticeably colder conditions 
are expected Saturday.

Heading into the overnight hours, the area of low pressure 
associated with the cold front tracks northeast through the Saint 
Lawrence Valley as broad high pressure expands across the Great 
Plains. The surface low deepens to below 990 mb, with some guidance 
suggesting it could reach 985 mb by Saturday afternoon. A tightening 
pressure gradient supports gusty NNW winds at the surface, while 
northerly flow strengthens aloft. Meanwhile, 850 mb temperatures 
fall to between -6C and -4C, a rather significant drop considering 
values were between +15C and +17C Friday afternoon.

While the majority of precipitation should exit with the cold front, 
some guidance suggests the potential for an anafrontal wave to 
develop along the departing boundary early Saturday. This could 
allow showers to linger across the southern coast, Cape Cod, and the 
Islands into Saturday morning. Highs Saturday afternoon are not 
anticipated to be much warmer than the lower 50s across the coastal 
plain and middle to upper 40s farther inland. However, with gusty 
winds, apparent temperatures are expected to be 5 to 10 degrees 
colder than the actual air temperatures.

Very cold conditions are expected Saturday night into Sunday morning 
as strong high pressure builds into the region. With the combination 
of very cold temperatures aloft, diminishing winds, and favorable 
radiational cooling, temperatures are expected to fall below 
freezing across much of southern New England, leading to widespread 
frost/freeze conditions. However, since we are outside the 
climatological growing season, our frost/freeze program ended on 
October 11, and no Frost or Freeze headlines will be issued. 
Nevertheless, if you purchased any sensitive tropical plants or 
palms from the garden center this summer, now would be a good time 
to bring them indoors!

KEY MESSAGE 3...Dry with a modest warmup through mid next week, but 
monitoring coastal storminess near or south of the mid-Atlantic 
waters which could bring periods of light rain, enhanced northeast 
winds and building waves/possible erosion to southeast New England.

Expansive area of high pressure will maintain itself over most or 
much of Southern New England through midweek and potentially longer 
as it becomes reinforced by another strong high pressure coming out 
of the northern Canadian Prairie region by midweek. This will at 
least drive dry weather and a gradual warming trend away from the 
southeast coast with pretty strong diurnal temperature ranges (mild 
days, cool nights). These conditions could linger into much of the 
upcoming workweek, away from the southeast coast.

However we continue to monitor coastal storminess depicted across 
the NWP and ensemble suite near the mid-Atlantic waters Sunday. 
There seem to be an increasing number of model guidance which brings 
a portion of this feature's moisture northward or northeastward into 
a weakness in the above surface ridge at some point Monday into 
Wednesday, mainly impacting the coastal plain and southeast New 
England. Exactly when and/or for how long it rains is still quite a 
bit unclear as the rain will be moving into a very dry ridge and 
should create a sharp NW to SE gradient in rain, but it doesn't look 
to be a soaking rain in looking at ensemble QPF probabilities. The 
bigger potential issue is mainly for the southern waters/coastlines 
with respect to increasingly gusty ENE winds and building rough seas 
which could lead to beach erosion for east- or northeast-facing 
beaches. With a persistent easterly fetch over several days, it's a 
conduit for building waves and latest significant wave heights are 
in the 12-15 ft range south and east of Nantucket and Martha's 
Vineyard. ECMWF probabilities of gale force gusts have increased 
into the moderate to high (50-70%) range for Monday into Tuesday, 
while the GFS is more tempered at around 30-50%, with lower 
probabilities for the northeast waters. It may also turn breezy over 
the land as well with gusts up to 30 mph at times. We'll re-evaluate 
the risk for coastal flooding given several tidal cycles, but astro 
tides are decreasing through midweek, which should mitigate 
significant issues. So as it looks right now, there appears to be a 
growing risk for at least impacts to mariners, including potential 
gale force gusts that could warrant headlines in the coming days as 
well as rough seas. Some risk for rains would exist as well for 
southeast New England, but at the moment rainfall doesn't look 
particularly significant or substantial at this point.

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
Forecaster Confidence Levels...

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

18z TAF Update...

This afternoon into this evening...Moderate confidence.

IFR to localized LIFR conditions dominated the region at mid
afternoon. There were still a few showers across RI/southeast
MA...but otherwise most of the region was in a lull with just
areas of drizzle and fog. Main concern is between 22z and 02z 
as a cluster showers and potentially embedded t-storms sweeps 
across the region. Greatest risk for thunder will be across 
CT/RI/SE MA...but that is possible across the rest of the region
as well. Brief localized strong wind gusts/heavy rainfall may 
accompany this cluster of showers even if there is not any 
lightning. 

Otherwise...LLWS will continue to be an issue at times into this
evening. 

Overnight into Saturday...High confidence. 

Conditions should improve to VFR across most areas northwest of
I-95 later this evening. Scattered showers will linger well 
into the overnight hours and even into part of Sat across 
parts of RI/SE MA...especially across the Cape/Islands allowing 
lower ceilings lingering a bit in this region. Meanwhile...the 
rest of the region will see VFR conditions as drier air works 
into the region. NW winds gusts will increase to between 20 and 
30 knots during the day Sat. 

KBOS Terminal...Moderate confidence in TAF. Main concern is
between 23z and 02z when a cluster of showers with perhaps
embedded thunder work across the region. Even if there is not
any thunder...brief strong wind gusts are possible with the
frontal passage. 

KBDL Terminal...Moderate confidence in TAF. Main concern is
between 22z and 01z when a cluster of showers with perhaps 
embedded thunder work across the region. Even if there is not 
any thunder...brief strong wind gusts are possible with the 
frontal passage. 

Outlook /Sunday through Wednesday/...

Saturday Night through Sunday: VFR. Breezy. 

Sunday Night: VFR. 

Monday: VFR. Breezy. 

Monday Night: VFR. Breezy. Slight chance SHRA.

Tuesday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels...

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



Outlook /Sunday through Wednesday/...

Saturday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Rough seas up to 8 ft. 

Sunday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of seas approaching 5 ft. 

Sunday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. 

Monday: Moderate risk for Small Craft Advisory winds with gusts
up to 30 kt. Chance of rain showers. 

Monday Night: Low risk for Small Craft Advisory winds with
gusts up to 30 kt. Chance of rain showers. 

Tuesday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Slight chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 PM EDT Saturday for ANZ230-236.
     Small Craft Advisory until 2 AM EDT Sunday for ANZ231-251.
     Small Craft Advisory until 8 AM EDT Sunday for ANZ232>235-237-
     250.
     Small Craft Advisory until 11 AM EDT Sunday for ANZ254>256.
     Gale Watch from Saturday evening through Sunday morning for 
     ANZ281>283.

&&

$$

DISCUSSION...Loconto/Dooley
AVIATION...Frank
MARINE...Loconto/Dooley