Old Res Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 211842
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
242 PM EDT Wed Oct 21 2026

.WHAT HAS CHANGED...
Adjustments to marine headlines - either time extensions and/or
conversions from Gale Watches to Gale Warnings - were made.
Otherwise no significant changes.

&&

.KEY MESSAGES...

- Offshore storm brings continued enhanced northerly gusts 
  through Friday morning. Mainly light rain or even light 
  sprinkles are expected overnight tonight into early on 
  Thursday for the immediate southeast New England coastal areas
  before tapering off Thursday afternoon.

- Prolonged stretch of dry weather Friday into Wednesday. 
  Cooler Friday, followed by moderating temperatures into 
  Monday. Turning cooler toward the middle of next week.

&&

.DISCUSSION...
KEY MESSAGE 1...Offshore storm brings continued enhanced 
northerly gusts through Friday morning. Mainly light rain or 
even light sprinkles are expected overnight tonight into early 
on Thursday for the immediate southeast New England coastal 
areas before tapering off Thursday afternoon.

There has been no substantial change to the forecast, messaging
and impacts to Southern New England through Friday regarding 
the distant offshore low pressure slowly meandering northward, 
located well to the east of the mouth of the Chesapeake Bay as 
of Wednesday afternoon. This system is mainly bringing some 
lower-level cloud cover to southeast New England, along with 
enhanced NE winds with gusts in the 20-25 mph range over most of
the mainland, and around 35-45 mph gusts for Cape Cod and the 
Islands. A rather sharp gradient in cloud cover is noted north 
and west of I-95, being governed by expansive surface ridging 
associated with a cooler and drier airmass. 

Composite radar mosaic imagery as of Wednesday afternoon is 
picking up on the western extent of the offshore system's rain 
shield in our far southeastern ocean waters; latest guidance 
continues to indicate a continued northwestward creep of this 
rain shield into the waters near the Islands and eventually 
spreading toward the south coast and Cape Cod tonight. This rain
shield will be fighting dry advection (e.g. dewpoints in the 
30s) as it attemps to progress north/west; even across the south
coat and the Cape, rain intensities end up being quite light 
and could struggle to even measure/reach the ground. The best 
chance at steadiest light rains is across Nantucket and Martha's
Vineyard overnight tonight into early Thursday morning. As the 
distant offshore storm passes toward the northeast on Thursday, 
expect a decrease in both southeastern New England rain showers 
and a decrease in cloud cover. Dry weather is anticipated for 
the remainder of Thursday into Friday as reinforcing surface 
ridging builds back in from northern Canada.

The main impact for most of Southern New England ends up being 
enhanced northeast to northerly breezes, strongest for the Cape 
and Islands in the 35-45 mph range into Thursday noontime, 
before slowly decreasing into the 20-35 mph range Thursday night
into Friday. Seas will continue to build and remain rough, with
the greatest impact being for our marine interests. 

As has been the case the past couple days, differences in cloud
cover and northerly onshore winds has driven a wide range in 
temperatures. As the coastal low departs, it draws down an 
increasingly cool airmass in for Thursday night. Clear skies and
lighter northerly winds are supporting a larger diurnal range 
in temperatures across most areas along and northwest of I-95, 
with chilly nights and milder days with more sunshine. Lows 
tonight should range in the upper 30s to mid 40s from NW MA to 
I-95 and in between, with highs in the low to mid 60s on 
Thursday; with a cold airmass coming in Thursday night, lows are
in the 28-34F range for these same areas. Meanwhile toward the 
southeast coastal areas, a tighter diurnal range in temperatures
where cloud cover and northerly winds are the strongest. For 
these locations, high temperatures end up cooler in the mid to 
upper 50s are more common, while lows are "milder", in the mid 
40s to lower 50s due to the cloud cover and the breezes. 

KEY MESSAGE 2...Prolonged stretch of dry weather Friday into
Wednesday. Cooler Friday, followed by moderating temperatures into  
Monday. Turning cooler toward the middle of next week.

Not much change to this portion of the forecast. High pressure 
dominates our weather into early next week, providing dry weather. 
Turning cooler Friday with the initial arrival of this high pressure 
from eastern Canada, followed by moderating temperatures into Monday.

The forecast for Tuesday and Wednesday gets more complex. A front 
gets sandwiched between the initially discussed high pressure, over 
the central Appalachians by Monday, and another high pressure over 
Manitoba and Saskatchewan. This pattern makes it difficult to 
project the timing and movement of this front, as it will greatly 
depend on which high pressure is stronger. At this time, thinking 
the high pressure over Canada will ultimately become the stronger of 
the two, with the result being this front sweeping across southern 
New England some time Monday night into into Wednesday. Just how 
fast this happens, and how far south this front gets pushed, will 
need to be refined with later forecasts.

There does not appear to be much moisture associated with this 
front. At this time, the most likely outcome will just be a period 
clouds and lower temperatures mid week. That said, it would not take 
much additional moisture to warrant a mention of showers in later 
forecasts.

&&

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

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

18Z TAF Update:

Through Tonight: High confidence in TAF/trends but moderate on
rain shower chances. 

VFR with high confidence for TAFs north and west of I-95. For
BOS, PVD and the Cape airports, SCT-BKN VFR to MVFR ceilings
develop and or persist into tonight. Best chance for most
persistent MVFR ceilings and generally VFR-visibility light 
rain are both restricted to the Cape and Islands. 

For the eastern and southeast coast...NE winds around 12-20 kt 
with gusts 20-35 kt, on the higher end of that range at ACK and
lower near the coastal plain. For the interior, northerly winds
5-10 kt.  

Thursday: High confidence. 

Any VFR-visibility rains end by mid-Thursday morning, with any
sub-VFR ceilings over southeast New England TAFs becoming VFR
along the same timeframe. Thus VFR should prevail by 15-17z
Thursday, although northeast to northerly winds around 10-15 kt
with gusts to 25-30 kt should continue along the southeast coast
and around 5-10 kt for interior Southern New England. 

Thursday Night: High confidence. 

VFR. Light northerly winds for the interior, but northerly winds
around 10-13 kt for BOS, PVD and Cape and Islands. 

KBOS Terminal...High confidence in TAF. 

KBDL Terminal...High confidence in TAF.

Outlook /Thursday Night through Monday/...

Friday: VFR. Windy with local gusts up to 30 kt. 

Friday Night through Saturday: VFR. 

Saturday Night through Monday: 

&&

.MARINE...
Forecaster Confidence Levels...

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

Through Friday: High confidence.

Several adjustments to marine headlines were made into Friday,
which involved either extensions-in-time of existing SCAs and
Gale Warnings and/or conversion of Gale Watches over to
Gale Warnings. These changes are being driven by the closest 
approach of the offshore low pressure as it moves over our far 
southeast ocean waters Thursday night into Friday. 

Gale Warnings over the southern waters were extended until 00z 
Friday, as ongoing gale force gusts in the 35-40 kt range continue
until that point, before decreasing within the small craft 
advisory range Thursday night into Friday. 

For the eastern and southeastern waters (including Cape Cod and
the Islands), gale warnings were extended into 18z Friday with
gusts in the 35-45 mph range. 

For the northeast waters (along and offshore of the mouth of 
the Merrimack River), SCAs were maintained through early 
Thursday morning with gusts to around 30 kt, then ramping up 
into gale conditions with gusts 35-40 kt by Thursday afternoon, 
which necessitated shifting the Gale Watch into Gale Warnings 
starting Thursday morning through Friday 18z. 

Seas will continue to build and become rough, especially for the
eastern and southeastern waters where seas could peak upwards of
16 ft in the outer ocean waters.

Outlook /Friday Night through Monday/...

Friday Night: Winds less than 25 kt. Rough seas up to 11 ft. 

Saturday: Winds less than 25 kt. Areas of rough seas. 

Saturday Night: Winds less than 25 kt. Local rough seas. 

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

Sunday Night through Monday: Winds less than 25 kt. 

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 2 AM EDT Friday for ANZ230.
     Gale Warning until 2 PM EDT Friday for ANZ231>234-254-255-281-
     282.
     Gale Warning until 8 PM EDT Thursday for ANZ235-237-256-283.
     Small Craft Advisory until 8 PM EDT Thursday for ANZ236.
     Small Craft Advisory until 8 AM EDT Thursday for ANZ250-251.
     Gale Warning from 8 AM Thursday to 2 PM EDT Friday for ANZ250-
     251-280.

&&

$$

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