Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 242001

Area Forecast Discussion
National Weather Service Boston/Norton MA
401 PM EDT Sun Sep 24 2023


Periods of rain will continue tonight into the first part of
Monday with the focus shifting south of the  Massachusetts
Turnpike...while partial sunshine should develop north of that
region Monday afternoon. A few showers linger on Tuesday across
portions of southern Rhode Island and southeast Massachusetts,
along with a raw and cool feel. Building high pressure system
over Quebec will provide benign conditions midweek, but there is
uncertainty with how long the quiet weather will stick around
as guidance diverges Friday into next weekend.



4 PM Update...

* Showers along with areas of drizzle persist into early evening

The remnants of T.S. Ophelia across the mid-Atlantic combined
with high pressure across eastern Canada were generating a
cool/moist east to northeast flow of air across southern New
England. Despite some mid level dry air...shortwave energy was
resulting in enough ascent for showers along with areas of
drizzle too. This will persist into early this evening with
temps mainly in the upper 50s to the lower 60s. Northeast winds
will gust up to 20 mph at times and up to 30 mph across the
Islands. So another rather cool afternoon in progress.



Key Points...

* Widespread Rain develops later this evening south of the MA
  Turnpike and continues into Monday...perhaps heavy in parts of CT

* Rain potential decreases north of I-90 and partial sunshine will
  be possible by Monday afternoon

* Breezy overnight into Monday with NE wing gusts of 20-30 mph


Tonight and Monday...

A more widespread/steady rain will develop later this evening and
persist into much of Monday south of the MA Turnpike as the remnants
of Ophelia lift northward. At the same time...dry mid level air will
result in decreasing rain potential to the north of the MA Turnpike.
The exact cutoff between the steady rain is always difficult to
forecast...but a sharp QPF gradient will likely exist in that
general vicinity. The GFS/NAM also indicate very impressive 700-850
mb frontogenesis north of the remnant mid level circulations and the
northern edge of the dry slot. Therefore...additional rainfall
amounts of 0.50 to 1.50" inches are possible tonight into Monday
south of the MA Turnpike with perhaps localized amounts of 2"+
across parts of CT if heavier band sets up far enough north.

While wet weather is anticipated south of I-90 through much of
Monday...but drier air will be confining most of that to areas near
the south coast by late afternoon. This process will happen much
faster north of I-90. While some showers may impact areas north of
the MA Turnpike early Monday...drier air will be resulting in
generally dry weather by Monday afternoon. In fact...we should see
partial sunshine develop too.

High temperatures regionwide should generally be in the 60s
regionwide. In fact the warmest readings should be in northern
MA...where some locations should hit the middle to upper 60s with
partial sunshine developing.

Lastly...1035 mb high pressure system building southward across
eastern Canada will increase the pressure gradient across our
region. This will be aided by the remnant circulation of Ophelia to
our south. Therefore...expect northeast wind gusts to increase
overnight and gust between 20 and 30 mph during the day Monday.

Monday night...

High pressure will continue to send drier air further south into
southern New England. Perhaps a few showers linger near the
southeast New England coast...most of the region should see dry
weather by Monday night. We still will need to watch for the
formation of more low clouds though given persistent NE flow.
Winds may still gust to between 20 and 30 mph across the Cape
and Islands. Overnight low temps mainly in the 50-55 degree
range...but may see some upper 40s across portions of western MA
depending on cloud cover.




* Raw and cool on Tuesday along with a few lingering showers.

* Dry and more seasonable Wednesday and Thursday.

* Plenty of uncertainty with the forecast Friday into next weekend.


Likely another cooler and raw day across southern New England with
some improvement by the end of the day. Generally, the forecast is
on track, with some slight modifications to the previous forecast.

The synoptic setup, a building area of high pressure over eastern
Quebec and weak surface pressure over the southern waters. The
moisture to the south is associated with Ophelia, or what is left of
the tropical system. Given the position of remnant Ophelia and a
strong surface high to the north, continued east/northeast winds are
on tap for Tuesday. Gusty early, but winds ease throughout the day.
A bit of good news, winds will not be as blustery as Monday with
sustained winds 10 to 15 mph and periodic gust to 20 or 25 mph. In
addition, clouds will be abundant along and south of the Mass
Turnpike and a few lingering showers. During this update did opt to
keep `slight chance` POPs across southeast MA and southern RI due to
the persistent northeast flow and lower ceilings. In fact, areas
with a POP between 8 and 14 did opt to include `slight chance` of
drizzle and that will be more or less confined to area south of
Willimantic, Providence, and Taunton.

Next, it will be cool, similar to the past several days. The 925mb
temperatures are below normal, consistent with our region placed
under a Canadian high pressure system. That said, at 925mb we are
seeing values of +5C and +8C for areas east of Worcester to
Willimantic, locations west have values of +7C and +10C. What it all
boils down to, another afternoon of below normal temperatures. Look
for temperatures between 60F-64F, with a few spots across the
central CT River Valley reaching towards 68F-70F.

Heading into the overnight the surface high to the north continues
to extend south, which should help to clear most of the clouds. The
exception may be areas of southern RI and southeast MA. Winds ease
overnight as well, which should promote radiational cooling. Highest
confidence are those towns along and north of Route 2 across
northern MA with the lower confidence the further south we get. If
clouds forecast do not work out, the current temperatures could be
too cold. That said, current thinking, many sheltered areas that are
prone to radiational cooling will fall to the upper-30s and lower-
40s, while the metro of Boston holds onto the upper-40s if not 50F.

Wednesday and Thursday:

Fairly benign weather midweek for southern New England with 1030mb
high centered over Quebec. PWATs fall to around 1/2 inch for both of
the days, comfortable dewpoints, upper-40s to low-50s and daytime
highs in the middle and upper-60s. Easterly winds do continue, but
are weaker, generally less than 10 mph. Given the easterly flow,
warmest spots are inland, and in particular the CT River Valley as
there is some downsloping off of the Worcester Hills, leading to
adiabatic heating. Here the highs are in the upper-60s. As for night
time, radiational cooling and fog develop each night with lows in
the low and middle-40s Wednesday night and the middle and upper-40s
Thursday night. Each night the metro of Boston will have a low in
the low-50s.

Friday into Next Weekend:

Canadian high to the north has not gone anywhere and still fairly
strong at 1025mb. And as mentioned by the previous forecaster, a mid-
level low over the Ohio River Valley ejects east, but does seem to
get absorbed in a mid-level ridge. Will say, this period of the
forecast does come with a lot of uncertainty. Global models do
maintain this period as dry, but the global ensembles have
increasing number of members with precipitation coming in later in
the week, likely due to the weak surface wave to the south and the
mid-level wanting to develop some sort of trough. Lots can go on
between now and then, worth keeping an eye out for the next chance
of precipitation. Did lower POPs as NBM had widespread POPs of 35 to
50 POP Thursday and Friday. Did keep any POPs closer to the southern
waters for Thursday, but did allow it to increase on Friday, but due
to the uncertainty, did cap the POPs at `Chance` less than 54 POP.
As for temperatures during this time we are fairly seasonable in the
middle and upper-60s during the day and upper-40s and lower-50s at
night. As they say, pounds of time to watch this period of the
forecast, as there will likely be further changes.


Forecast Confidence Levels:

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

18Z TAF Update...

This afternoon into tonight...Moderate Confidence.

Low end MVFR to IFR conditions will persist this afternoon into
this evening in showers and areas of drizzle. We may see some
improvement after midnight north of the MA Turnpike as drier air
attempts to work into the region. Meanwhile...a band of steady
rain will impact areas south of the MA Turnpike and perhaps
heavy for a time in parts of our CT zones. NE winds 5 to 15
knots with gusts on the order of 20-25 knots for the Cape and

Monday...Moderate Confidence.

Conditions should improve to MVFR-VFR levels near and north of
the MA Turnpike on Monday as drier air works in from the north.
South of the MA Turnpike....steady rain may impact areas
especially during the first part of the day. But enough mid
level dry air will probably allow these areas to improve to at
least MVFR conditions during the afternoon. NE winds 10 to 20
knots with gusts of 20-30 knots along the coasts.

Monday night...Moderate Confidence.

VFR conditions probably dominate during the evening with enough
dry air working down from the north. However...we will need to
watch for some MVFR ceilings re-developing after midnight with
northeast low level flow and cooling boundary layer temps
overnight. NE winds 10 to 15 knots with some 20-25 knot gusts
possible along the coast at times.

KBOS Terminal...Moderate Confidence in TAF. Biggest uncertainty
how quickly dry air works down from the north very late tonight
into Monday and allows cigs/vsbys to improve.

KBDL Terminal...Moderate Confidence in TAF.

Outlook /Tuesday through Friday/...

Tuesday: Mainly VFR, with local MVFR possible. Windy with local
gusts up to 30 kt.

Tuesday Night: Mainly VFR, with local IFR possible. Breezy.
Patchy BR.

Wednesday: VFR. Breezy.

Wednesday Night: Mainly VFR, with local IFR possible. Patchy

Thursday: VFR. Breezy.

Thursday Night: Mainly VFR, with local IFR possible. Patchy BR.

Friday: VFR. Breezy. Slight chance RA.



Forecaster Confidence Levels:

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

Tonight through Monday night...High Confidence.

1035 MB High pressure system building southward across eastern
Canada with the remnants of Ophelia to our south will increase the
pressure gradient overnight into Monday. NE winds gusts of 25 to 35
knots are expected into Monday night with the strongest winds across
the southern waters where we have hoisted Gale Warnings. SCA are
hoisted for the rest of our waters. Rough seas on the order of
4-7 feet are expected.

Outlook /Tuesday through Friday/...

Tuesday: Low risk for Small Craft Advisory winds with gusts up
to 30 kt. Rough seas up to 8 ft. Chance of drizzle, slight
chance of rain.

Tuesday Night: Winds less than 25 kt. Seas up to 5 ft. Chance
of drizzle.

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

Friday: Winds less than 25 kt. Seas up to 5 ft. Slight chance
of rain.


MARINE...Small Craft Advisory from 8 AM Monday to 2 AM EDT Tuesday for
     Small Craft Advisory from 10 PM this evening to 8 AM EDT
     Tuesday for ANZ231.
     Small Craft Advisory until 8 AM EDT Tuesday for ANZ232>235-237-
     Gale Warning from 8 AM Monday to 2 AM EDT Tuesday for ANZ255-


LONG TERM...Dooley
MARINE...Frank/Dooley is the U.S. government's official web portal to all federal, state and local government web resources and services.