BOX issues Area Forecast Discussion (AFD) at Oct 17, 4:11 AM EDT924
FXUS61 KBOX 170811
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
411 AM EDT Sat Oct 17 2026
.WHAT HAS CHANGED...
Increased probabilities for gale-force gusts in the
Monday-Wednesday timeframe.
&&
.KEY MESSAGES...
- Lingering showers this morning towards the southern coast,
Cape Cod, and the Islands. Otherwise, drier and colder today.
- Dry with a modest warmup through mid next week, but monitoring
stormy conditions near or south of the mid-Atlantic waters
which could bring periods of light rain, enhanced northeast
winds, and building waves/possible erosion to southeast New
England.
&&
.DISCUSSION...
KEY MESSAGE 1...Lingering showers this morning towards the southern
coast, Cape Cod, and the Islands. Otherwise, drier and colder today.
Showers over much of SE MA and RI continue this morning with the
cold front associated with a low pressure system now over New
Brunswick, Canada draped over the southern portion of the south
shore down into coastal RI. This front will continue eastward early
this morning, and we will find ourselves in a much colder and drier
airmass with high pressure starting to build in from the west. These
showers should remain generally over SE MA, Cape Cod, the Islands,
and parts of RI this morning, then drop off more towards the
afternoon as the drier air behind this front really sets in. Skies
will clear more towards the evening, especially with high pressure
taking more of a hold overhead by then. Gusty NW winds today as
strong cold air advection develops and the gradient between the
exiting low pressure to our northeast and the high pressure to our
west tightens, which may reach up to 35 mph in some areas this
afternoon. 925 mb temperatures fall below 0C by this evening, and
prior to that mark, they look to hover just above it. Highs today
will likely struggle to reach the low 50s across the interior and
lows Saturday night will likely dip below freezing across the
region, with the exceptions being areas closest to the coasts and
urban areas. Once the gusty NW winds diminish later this evening, we
could see some radiational cooling develop as high pressure builds
in post-FROPA, enhancing an already relatively cold night for some
locations. Areas of frost/freezing conditions are anticipated,
though because our program came to an end on October 11, there will
be no Frost/Freeze headlines issued.
KEY MESSAGE 2...Dry with a modest warmup through mid next week, but
monitoring stormy conditions near or south of the mid-Atlantic
waters which could bring periods of light rain, enhanced northeast
winds, and building waves/possible erosion to southeast New England.
High pressure continues to build in Sunday and the colder airmass
shifts out of the region. The tighter gradient between the strong
exiting low and approaching high pressure slackens, which will allow
winds to continue diminishing as well. As high pressure settles in
overhead, temperatures will moderate back to more typical levels for
this time of year as 850 mb temperatures improve from -5C today to
around +5C by Sunday evening. 925 mb temperatures steadily increase
as well, reaching around +10C towards the Monday/Tuesday
timeframe. Highs return to the 50s and 60s into early next week.
One thing we will be keeping an eye on, though, is the development
of low pressure towards the mid-Atlantic/Carolina coastal waters
Sunday into Monday. This feature appears to have detached from the
broader upper level trough that was associated with the strong low
pressure that brought yesterday's precipitation. Guidance is
indicating that a weaker spot in the surface ridge over southern New
England may allow for some showers to sneak in sometime
Monday/Tuesday over southeastern New England. Given the dry
conditions preceding these possible showers, QPF looks quite
limited, with ensemble probabilities for any measurable rainfall
mostly between 10-50%, with the GEFS and Canadian ENS skewing
slightly higher over the Cape and Islands at 50-60%. The ECMWF
ensemble is the lowest of the three, with the highest probabilities
over land being 10-30%. However, marine impacts with this
disturbance are looking a bit more impactful as it stays relatively
stationary and churns over the same waters for an extended period of
time, which will help build seas up to 15 ft offshore of Nantucket.
The gradient between this area of low pressure and the preexisting
high pressure over southern New England will tighten greatly,
increasing ENE winds over the waters and towards the Cape and
Islands, RI, and the coastal plain in SE MA. Ensembles have
continued to indicate decent probabilities of sustained winds
reaching gale-force over the southern waters, with the GEFS and
Canadian ensemble up to 30-40% (and even up to 60% in the Canadian
guidance) just south of the Islands. In terms of gale-force gusts,
probabilities have increased further from the last update, reaching
the high (80-100%) range in the ECMWF ensemble and up to 80% in the
GEFS. Persistent easterly fetch associated with these winds, along
with building rough seas, will need to be monitored as well, as
beach erosion for east- and northeast-facing beaches may become an
issue.
&&
.AVIATION /07Z SATURDAY THROUGH WEDNESDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
06z TAF Update:
Through 12z...Moderate confidence.
Another round of light showers have started to move across SE MA
and RI from SW to NE, though these are not expected to result in
any visby changes. VFR ceilings continue with some periods of
MVFR possible. Rain showers from roughly a BED/IJD line and
eastward look to continue into Sat south and east. NW winds
increase to around 13-15 kt with gusts 23-27 kt by daybreak.
Saturday: High confidence in TAF/trends, but moderate on when
SHRA clears southeast New England.
Ceilings should improve to VFR before daybreak, but rain
showers could linger until early afternoon for PVD, and
potentially into midafternoon for the Cape and Islands. North
and west from there, VFR prevails. Gusty NW winds around 13-17
kt with gusts 25-30 kt.
Saturday Night: High confidence.
VFR. Easing NW to N winds to around 5-10 kt by midnight,
continuing to ease to light NW overnight.
Sunday: High confidence.
VFR. Light N winds, though becoming NE around 8-12 kt for the
Cape and Islands.
KBOS Terminal...Moderate confidence in TAF. Timing of showers
could be slightly later than the TEMPO, though should not vary
too much from those hours.
KBDL Terminal...High confidence in TAF.
Outlook /Sunday Night through Wednesday/...
Sunday Night: VFR.
Monday: VFR. Breezy.
Monday Night: Mainly VFR, with local MVFR possible. Breezy.
Tuesday: VFR. Breezy.
Tuesday Night: VFR. Windy with areas of gusts up to 30 kt.
Wednesday: VFR. Windy with gusts up to 30 kt.
&&
.MARINE...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Through Sunday...Moderate confidence.
Gusty NW winds today following an overnight cold front.
Uncertainty remains regarding the potential for gale-force wind
gusts over the ocean zones for tonight, which currently are
forecast to remain just under gale-force. Latest guidance has
trended winds aloft tonight to generally in the mid-20 kt range
up to the 850 mb mark, which would very much keep winds below
gale criteria. Seas remain generally within small craft advisory
levels for the coastal and outer waters, though seas build to
around 8 ft by Sunday in the ocean zones after the other waters
briefly fall back to around 4 ft at most. Winds diminish greatly
Sunday, sustained up to 15 kt over the southern waters and up to
10 kt over the eastern/NE waters. Gusts remain generally below
20 kt Sunday.
Outlook /Sunday Night through Wednesday/...
Sunday Night: Winds less than 25 kt. Rough seas up to 15 ft.
Monday: Moderate risk for Small Craft Advisory winds with gusts
up to 30 kt. Rough seas up to 16 ft. Chance of rain showers.
Monday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 15 ft. Chance of rain
showers.
Tuesday: Strong winds with gusts up to 35 kt. Rough seas up to
12 ft. Chance of rain showers.
Tuesday Night: Strong winds with gusts up to 40 kt. Rough seas
up to 12 ft. Slight chance of rain showers.
Wednesday: Moderate risk for gale force winds with gusts up to
40 kt. Rough seas up to 12 ft. Slight chance of rain showers.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ230-
236.
Small Craft Advisory until 2 AM EDT Sunday for ANZ231-251.
Small Craft Advisory until 8 AM EDT Sunday for ANZ232>235-237-
250.
Small Craft Advisory until 11 AM EDT Sunday for ANZ254>256.
Gale Watch from this evening through Sunday morning for
ANZ281>283.
&&
$$
DISCUSSION...Hrencecin
AVIATION...Loconto/Hrencecin
MARINE...Hrencecin
Source:
BOX issues Area Forecast Discussion (AFD) at Oct 17, 4:11 AM EDT----------------
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