905
FXUS61 KBOX 152325
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
725 PM EDT Tue Sep 15 2026

.WHAT HAS CHANGED...
No significant changes to the forecast.

&&

.KEY MESSAGES...

- Dry and cool tonight. Heat and humidity begin to build for Wednesday.

- Shower chances Thursday evening into Friday morning, followed
  by drier conditions Friday.

- Next chance for rain returns Sunday, though confidence in
  exact timing remains low at this time.

&&

.DISCUSSION...
KEY MESSAGE 1...Dry and cool tonight. Heat and humidity begin
to build for Wednesday.

High pressure continues to dominate through Wednesday; however,
it will begin to weaken and move offshore tonight/early
Wednesday. This will lead to winds turning more
south/southwesterly... advecting higher temps and dewpoints into
southern New England into Wednesday. Given relatively clear
skies and calm winds tonight, expecting another round of
radiational cooling, although perhaps not as strong as last
night. Overnight temps should drop into the upper 40s/low 50s
tonight. Southwesterly flow Wednesday should begin to surge
dewpoints back into the low 60s, and with temperatures climbing
into the upper 70s or near 80, humidity will be on the rise
leading to a muggy, sticky feeling.

KEY MESSAGE 2...Shower chances Thursday evening into Friday
morning, followed by drier conditions Friday.

Mainly dry for Thursday; however, a northern-stream shortwave
trough arrives late in the day and exits early Friday, bringing
another round of showers to southern New England. Clouds are on
the increase Thursday morning as higher moisture is pumped into
the region. PWAT values are roughly 2 inches, which is near the
maximum of climatology based on sounding climatology at Chatham.

Where confidence is lacking is with the forcing. The 15/12z NAM
12km and, to some extent, the 3km (though model guidance
doesn`t extend beyond 00z Friday) show robust forcing near the
NYC metro. Meanwhile, farther northeast, there is less-than-
ideal forcing over southern New England. The ECMWF favors
central New England for the better forcing, while the GFS and
Canadian have very minimal forcing across central New England.
Another limiting factor is the presence of dry air aloft in the
mid-levels.

That being said, a subtle shift in the guidance to the
northeast needs to be monitored, given the impressive swath of
2-4", locally 5 inches, of rain this past Sunday. We`d like more
confidence in this part of the forecast given it is only a few
days out, though when you have weakly forced environments, it
can be difficult to pinpoint the exact details.

Current thinking favors the forcing across central New England,
as there has been continuity from run to run over the past 24
hours and across multiple models. Went with a blend for the QPF
forecast between our current forecast, NBM, and WPC. QPF is
generally a few hundredths of an inch along the southern coast
and perhaps a tenth of an inch along our northern borders with
VT/NH. That said, I wouldn`t fully discredit the NAM just yet.
Something to monitor. Stay tuned for updates!

KEY MESSAGE 3...Next chance for rain returns Sunday, though
confidence in exact timing remains low at this time.

A transient high pressure system moving out of the southern
Canadian Prairies brings a dry stretch of weather Friday and
Saturday. Seasonably mild temperatures are expected Friday, with
highs in the middle 70s and elevated dew points initially in
the lower 60s, though those fall into the 50s by Friday
afternoon. Then a shift to more fall-like conditions on
Saturday, with highs in the middle to upper 60s and crisp air as
dew points fall into the 40s to lower 50s.

The weekend looks split, with rain returning Sunday. It`s
possible the early hours of the day start off dry, with
conditions declining into the afternoon and evening. There
remains a bit of spread among the deterministic models, though
the AI GFS and ECMWF are in fairly good agreement that there
will be unsettled conditions as an 850 mb open wave tries to
close off across western NY. This would lead to increasing
southwest flow and higher PWATs advecting into the region, with
values around 1.5 inches.

It`s worth mentioning there is strong 1030+ mb high pressure
building to the north during this time, and depending on the
setup, this could suppress Sunday`s system farther south. Yet
another thing to monitor. Beyond Sunday into early next week,
there is variability in the forecast, mainly with the arrival of
high pressure expanding out of Quebec. This may impact how
quickly the moisture departs Sunday into Monday.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels...

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

00z TAF Update...

Tonight...High confidence.

VFR. Winds becoming light S to SW. Patchy fog possible in
valleys.

Wednesday through Wednesday Night...High confidence.

VFR. SW winds near 10 kts with a few gusts near 15 kts around
the Cape/Islands. Mid-level cloud deck begins to move in later
Wed PM/overnight into Thurs.

KBOS Terminal...High confidence in TAF.

A low chance for a late day sea breeze, after 18z. Did not
include in current TAF due to low confidence.

KBDL Terminal...High confidence in TAF.

Outlook /Wednesday Night through Sunday/...

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

Thursday Night: Mainly VFR, with local MVFR possible. Chance
SHRA.

Friday: VFR.

Friday Night: VFR. Breezy.

Saturday: VFR.

Saturday Night: VFR. Chance SHRA.

Sunday: Mainly VFR, with local IFR possible. Breezy. SHRA
likely.

&&

.MARINE...
Forecaster Confidence Levels...

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

High pressure overhead continues to bring light easterly winds
through tonight. Winds shift around to the S/SW overnight into
Wednesday as the high pressure center shifts offshore.

Outlook /Wednesday Night through Sunday/...

Thursday: Winds less than 25 kt.

Thursday Night through Friday: Winds less than 25 kt. Chance of
rain showers.

Friday Night through Saturday: Winds less than 25 kt.

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

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

$$

DISCUSSION...Dooley/McMinn
AVIATION...Dooley/McMinn
MARINE...McMinn