890
FXUS61 KBOX 191817
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
217 PM EDT Sat Sep 19 2026

.WHAT HAS CHANGED...
No significant changes.

&&

.KEY MESSAGES...

- Quiet through the rest of today, cooler tonight, with clouds
  returning before sunrise.

- Briefly dry early to mid morning, then beneficial rain
  overspreads southern New England and continues through the
  evening and overnight hours. Flooding concerns remain low.

- Showers may linger through early next week. A coastal system
  is possible late week.

&&

.DISCUSSION...

KEY MESSAGE 1...Quiet through the rest of today, cooler tonight,
with clouds returning before sunrise.

A 1020-1025 mb high pressure system responsible for today`s gorgeous
weather drifts offshore tonight ahead of our next system for Sunday.
Before that arrives, continued fall-like weather is expected this
afternoon and overnight. Winds decouple overnight, becoming fairly
light to calm in some areas. In addition, feel the cloud cover will
be slower to move in. While clouds push in from the west overnight,
thinking these will initially be mainly high clouds. Thus, should
still see a period of good radiational cooling during the first part
of the night, while eastern areas of southern New England may see a
majority of the night before clouds fully arrive.

As is typical with this setup, the NBM appears too mild, so have
blended in the cooler MOS/MET/MAV guidance. This really highlights
the colder pockets along the I-495 corridor, the hollows of northern
Massachusetts, and the Vineyard. All of these areas fall well into
the lower 40s tonight, though it is not out of the realm of
possibility to see an upper 30 sprinkled in there. Otherwise, urban
centers such as Boston, Providence, and Hartford remain in the upper
40s to lower 50s. Worcester stays relatively mild as well, given the
city`s elevation and location near the top of the nocturnal
inversion.

KEY MESSAGE 2...Briefly dry early to mid morning, then beneficial
rain overspreads southern New England and continues through the
evening and overnight hours. Flooding concerns remain low.

As advertised, conditions Sunday aren`t ideal for outdoor
activities, with a raw, cool, and rainy day expected. Highs are
mainly in the lower to middle 60s across the coastal plain, with
middle to upper 50s across the higher elevations of southern New
England.

A subtle mid-level northern stream trough arrives from the west
early Sunday morning, accompanied by a modest 850 mb jet, though the
jet weakens in magnitude as it shifts east. This should provide
enough forcing to capitalize on PWATs ranging from 1.4 to 1.9
inches, or roughly 150-200 percent of normal. Despite the anomalous
moisture, we aren`t concerned about impacts similar to those
experienced with last Sunday`s heavy/torrential rainfall and
flooding. Last Sunday`s event was considerably more convective in
nature, while Sunday`s rainfall should be predominantly stratiform.
This should favor lower rainfall rates and greatly reduce the
potential for localized torrential downpours that contributed to
flooding last weekend.

Timing this out, widespread rain develops during the mid to late
morning and persists well into the evening. There is pretty good
agreement among the 19/12z suite of high-res guidance. By 18z/2 PM,
rain should be widespread across much of the region. The exception
will be the outer Cape and Nantucket, which may remain dry for an
additional hour or two. There is some, albeit limited, instability
near the south coast, where we cannot rule out a rumble of thunder
and briefly heavier rainfall. One other area to monitor is near the
Mass Pike and the transition from the coastal plain into the higher
terrain of central Massachusetts. High-res guidance shows a
convergence boundary developing in this vicinity, which may lead to
a corridor of enhanced rainfall.

Overall, rainfall amounts of 0.5-1.0 inch are expected, though some
variability from town to town is likely, especially near any areas
of enhanced rainfall. The HREF maximum does show localized amounts
approaching 2 inches, representing the upper end of the guidance
envelope, but confidence in amounts this high is quite low. Given
the generally lower rainfall rates, the risk for flooding remains
low. Some minor ponding is possible where leaves or other debris
clog storm drains, but otherwise this should be a beneficial
rainfall for the region.

With plenty of cloud cover overnight and a breezy northerly wind,
there are no concerns for a particularly chilly night. It will
remain raw and wet, with lows in the upper 40s to lower 50s. Rain
shifts offshore with the front early Monday morning, coming to an
end by or before daybreak.

KEY MESSAGE 3...Showers may linger through early next week. A
coastal system is possible late week.

How long the rain lingers Monday will depend on how progressive
the system/front is. There are difference across guidance in
the speed which has led to some uncertainty in how long showers
linger around on Monday. If showers were to linger, it would
more likely effect areas more south and east (Cape/Islands or
south coast). Fall-like temperatures are likely behind the front
on Monday with breezy northerly winds. There is potential for
another system to brush southern New England Tuesday bringing
showers; however, this is lower probability as there lacking
agreement with how north this system tracks at this time.

There is good agreement across model guidance with a fairly strong
surface high shifting over Quebec Tuesday into mid-week. This will
keep a cooler than normal airmass over the northeast supporting cool
more fall-like temperatures continuing through the week.
Deterministic and ensemble guidance continues to hint at the
potential for a coastal low pressure system sometime Thursday into
Friday. However, there is still a fair amount of uncertainty in the
details of the pattern that will influence the track of this low.
Some solutions feature a low track closer to southern New England
while others well off shore. Pretty low confidence at point, but
warrants monitoring as it would bring potential for stronger winds,
rough seas for the coastal waters and potentially another round of
rainfall.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
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.

VFR through tonight. Light NE winds becoming E/ESE this afternoon.
Winds shift to the S this evening at less than 10 kt, with some
areas becoming calm overnight.

Sunday...High confidence in trends, moderate confidence in timing.

VFR to start, deteriorating to MVFR and then IFR from west to east
during the afternoon as rain overspreads the region. LLWS could
become a concern after 18z as the system moves through. Surface
winds generally SE at 5-10 kt. Chances for TS are low to near zero.

Sunday Night...High confidence in trends, moderate confidence in
timing.

IFR to LIFR with areas of 2-4SM visibility in continued RA. Winds
shift to the N at 8-12 kt.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Monday through Thursday/...

Monday: Mainly VFR, with local MVFR possible. Breezy.

Monday Night through Tuesday: VFR. Breezy.

Tuesday Night: VFR. Windy with local gusts up to 35 kt.

Wednesday: VFR. Strong winds with local gusts up to 40 kt.

Wednesday Night: Mainly VFR, with areas MVFR possible. Windy
with gusts up to 35 kt. Slight chance SHRA.

Thursday: Mainly VFR, with local MVFR possible. Strong winds
with areas of gusts up to 40 kt. Chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Through Sunday Night...High Confidence.

An area of high pressure moves east of the coastal waters overnight
and toward the Canadian Maritimes by Sunday night. With the
departure of the high, a low pressure system riding along a frontal
boundary ushers in unsettled weather by late Sunday morning, with
rain becoming widespread Sunday afternoon. There is a low chance for
a few rumbles of thunder, primarily across the southern waters. Rain
ends early Monday morning, though a few showers could linger across
the southern outer waters as the front sags to the south. Seas
throughout this period remain between 2-4 ft, with the greatest wave
heights across the outer waters. Winds are northeast through this
evening, then become southeast on Sunday. As the front pushes south,
winds shift to the north/northeast. Gusts begin to increase with
cold air advection Monday morning, which may require Small Craft
headlines.

Outlook /Monday through Thursday/...

Monday: Moderate risk for Small Craft Advisory winds with gusts
up to 30 kt. Areas of seas approaching 5 ft. Slight chance of
rain showers.

Monday Night: Low risk for Small Craft Advisory winds with
gusts up to 30 kt. Local rough seas. Slight chance of rain
showers.

Tuesday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 10 ft. Slight chance of
rain showers.

Tuesday Night: Strong winds with gusts up to 40 kt. Rough seas
up to 11 ft. Slight chance of rain showers.

Wednesday: Strong winds with local gusts up to 45 kt. Rough
seas up to 13 ft. Slight chance of rain showers.

Wednesday Night: Moderate risk for gale force winds with local
gusts up to 45 kt. Rough seas up to 16 ft. Chance of rain
showers.

Thursday: gale force winds with areas of gusts up to 45 kt.
Rough seas up to 12 ft. Chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...High Risk for Rip Currents until 8 PM EDT this evening for MAZ007-
     015-016-019-022-024.
RI...None.
MARINE...None.

&&

$$

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