729
FXUS61 KBOX 010552
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
152 AM EDT Tue Sep 1 2026

.WHAT HAS CHANGED...

Slightly increased rainfall totals for today with the Connecticut
River Valley likely seeing the highest totals. Otherwise, cloudy and
dry weather Wednesday and an increasing chance for showers and
perhaps isolated severe weather Thursday.

&&

.KEY MESSAGES...

 - Widespread rain today, possibly heavy at times. Watching for
   the potential for localized urban and poor-drainage
   flooding.

- Cloudy but drier on Wednesday with decreasing shower chances.
  Precipitation chances return Thursday with an increasing
  chance for showers and thunderstorms throughout the day.

- Improving weather Friday and into the holiday weekend. Other
  than a spot diurnal shower each day, dry weather prevails with
  a mix of clouds and sun. Cooler than normal with highs in the
  70s and lows in the 50s, along with onshore breezes.

&&

.DISCUSSION...
KEY MESSAGE 1...Widespread rain today, possibly heavy at times.
Watching for the potential for localized urban and poor-drainage
flooding.

Rain continues to overspread the region this morning and likely
reaches the I-95 corridor by sunrise. Radar shows areas of heavier
rainfall along and ahead of a warm front that will bring in a more
moisture-rich higher theta-e airmass. Will see enough low level
convergence for banded precipitation and areas of locally heavy
rainfall through much of the day today. CAMs show that the greatest
risk for heavy rains will be found across portions of central
Massachusetts and Connecticut. Not entirely surprising given BUFKIT
soundings depicting warm cloud depths increasing to 10-12k feet to
the SW of the warm front. Notably, the HREF shows 10-30% probs of
>1" of QPF in 3 hours in these same areas. Thus, this corridor will
have the greatest risk for isolated urban/ poor drainage flooding.
Further NE, cooler stratiform rain processes will be more dominant
resulting in lighter rainfall rates.

In terms of general rainfall totals, expecting a half an inch to an
inch, with locally higher amounts of 1.5 to 3 inches SW of I-95.
Further northeast, totals are in the range of a quarter to half an
inch. Since these are showers versus stratiform rain, there could be
areas of higher and lower amounts within a relatively short
distance. Additionally, there`s a lower chance for thunder, mainly
Tuesday afternoon, with a few hundred J/kg of CAPE across mainly
western Massachusetts and Connecticut, although it`s not a
significant risk.

Rain tapers off from W to E this afternoon, with drier conditions
overspreading the region overnight. Guidance shows lingering areas
of drizzle and light showers but this will be the exception and not
the rule. Given extensive cloud cover, expect a much cooler day
today, with highs mainly in the upper 60s to lower 70s. A true nod
to the first day of meteorological fall.


KEY MESSAGE 2...Cloudy but drier on Wednesday with decreasing shower
chances. Precipitation chances return Thursday with an increasing
chance for showers and thunderstorms throughout the day.

1025 mb high pressure over the Maritimes should provide dry weather
much of Wed, especially across eastern MA, while a frontal boundary
lurks to the west and southwest of SNE. This front will eventually
move northeast as a warm front later Wed and especially Wed night,
resulting in an increased risk for showers and thunderstorms across
SNE late Wed/Wed night. Cooler temps Wed, with 1025 Maritime high
and ESE onshore flow, limiting max temps in the upper 60s and lower
70s.

Greater risk for more widespread shower and thunderstorm activity
Thursday as a short wave and surface cold front arrive from the
west. Guidance is coming into better agreement with respect to
increasing instability Thursday afternoon. The latest NBM shows
widespread 60 to 80% probs of CAPE exceeding 1000 J/kg mainly along
and S of the Mass Pike Thursday afternoon. These values are higher
than previous runs so it is likely that guidance has trended north
with the extent of the  warm sector over our CWA. Latest NSSL and
CSU machine learning probabilistic guidance support these trends and
highlight southern New England in a 15 percent chance for severe
weather Thursday. Heat and humidity return Thu with warm sector
airmass, highs in the lower 80s and dew pts in the upper 60s and
lower 70s.

KEY MESSAGE 3...Improving weather Friday and into the holiday
weekend. Other than a spot diurnal shower each day, dry weather
prevails with a mix of clouds and sun. Cooler than normal with highs
in the 70s and lows in the 50s, along with onshore breezes.

Definitely a sign of fall approaching, with robust northern stream
Friday yielding a baroclinic 998 mb maritime low late Fri/Sat. This
will yield a cool, brisk NE flow into the SNE over the weekend.
Highs likely remaining in the 70s and overnight lows in the 50s. It
will feel even cooler over southeast MA, including Cape Cod and the
Islands, with northeast winds 15-25 mph. Cool cyclonic flow aloft
will yield diurnal clouds each day and possibly a spot shower.
Otherwise, dry weather prevails. Possibly warmer and less wind for
Memorial Day Monday, as high amplitude trough moves offshore and
1025 mb high settles over SNE.


&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
Forecaster Confidence Levels...

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

06z Update...High confidence in trends, moderate confidence in
timing.

Widespread MVFR with pockets of IFR underneath bands of SHRA as
they continue to spread from west to east through 12z.
Conditions eventually deteriorate to LIFR across interior
terminals by 08-10Z, with visibilities lowering to 2-5 SM. There
is a very low chance of lightning, with the greatest
probability across western terminals in southern New England,
particularly KBDL. Southwest winds shift to the southeast
between 10 and 12z this morning, remaining light across interior
southern New England and increasing to 8-10 kt at coastal
terminals.

Today...Moderate confidence.

Pockets of LIFR to start; otherwise, a mixture of IFR and MVFR
ceilings persists, with periodic showers and isolated TSRA
possible mainly across interior terminals. East-southeast winds
of 10-15 kt are expected at coastal terminals and 6-10 kt at
interior terminals.

Tuesday Night...Moderate confidence.

MVFR ceilings generally prevail along and east of I-95, while areas
farther inland remain IFR to LIFR. Onshore easterly winds and
chances for SHRA continue.

KBOS Terminal...High confidence in trends, moderate confidence in timing.

KBDL Terminal...High confidence in trends, moderate confidence in timing.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: MVFR/IFR conditions possible. SHRA, slight
chance TSRA.

Thursday: Mainly VFR, with local IFR possible. Breezy. SHRA
likely, chance TSRA.

Thursday Night through Friday Night: VFR.

Saturday: VFR. Breezy. Slight chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Through Tonight...High confidence.

Rain and areas of poor visibility overspread the waters this
morning ahead of an approaching warm front. Expecting SW winds
to shift to the SE as the front passes through around sunrise
this morning with speeds of 10 to 15 kt and gusts around 20 kt.
Seas remain below 2 ft tonight, then slowly build to 2 to 3 ft
today with marginal Small Craft conditions developing for the
outer waters overnight into Wednesday. Later forecasts may
warrant a Small Craft Advisory if trends continue.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Chance of rain showers.

Thursday: Winds less than 25 kt. Seas up to 5 ft. Rain showers
likely, slight chance of thunderstorms.

Thursday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Chance of rain showers, slight chance of
thunderstorms.

Friday through Friday Night: Winds less than 25 kt. Seas
locally approaching 5 ft.

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

&&

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

&&

$$

DISCUSSION...FT
AVIATION...FT
MARINE...FT