Area Forecast Discussion
National Weather Service Boston/Norton MA
717 PM EDT Mon Oct 27 2025
SYNOPSIS
Canadian high pressure will result in cool temperatures through
Wednesday. In addition, northeast winds will bring scattered
showers to areas mainly near and southeast of I-95 into
Wednesday. Strong low pressure follows with a period of heavy
windswept rain for southern New England sometime Thursday into
Thursday night. A few showers may linger into Friday, but drier
weather is likely by Saturday.
.NEAR TERM /THROUGH TUESDAY/...
Key Messages:
* Chilly again tonight with lows in the upper 20s and 30s
* Dry outside of a brief spot sprinkle/light shower across Cape
Cod and Nantucket
A large high pressure remains across Quebec, and will be the
main driver of our weather tonight. This high pressure is the
result of a pocket of colder air, which led to diurnal clouds
today, as well as some ocean-effect rain showers across portions
of southeast MA.
These clouds are anticipated to dissipate some after sunset, but
perhaps not go away completely towards the east coast of MA.
Cannot completely dismiss the idea of a stray sprinkle/shower
towards the east coast as well.
.SHORT TERM /TUESDAY NIGHT/...
Key Messages:
* Cool conditions continue with more diurnal clouds
* Risk for showers towards the east coast of MA
* NE wind gusts of 20-30 mph towards Cape/Islands
Another day with high pressure over Quebec, leading to another
day much like today. Diurnal clouds develop during the morning,
with a risk for ocean-effect showers across portions of eastern
MA, especially towards the Cape and Nantucket. NE low level flow
will be a bit breezy towards the Cape and Islands with 20-30 mph
wind gusts at times.
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Key Messages:
* Area of low pressure brings a period of heavy rainfall and gusty
winds Thu in to Thu night
* 1-3" of rain appears reasonable Thu into Thu night
* Brief nuisance street flooding & 30-50 mph gusts on the coast
* Windy with a few showers as the system departs later Friday and
Saturday
Details...
Anomalously deep shortwave digs southward over the SE CONUS and
ejects northeast Thursday morning. Continuing to see guidance
show cyclogenesis early Thursday over the Mid Atlantic. Earlier
model runs hinted at the potential for secondary cyclogenesis
near the coast but has since trended away from that outcome.
Additionally, moisture from Melissa may be transported northward
even as it appears likely that we will escape direct impacts
from the system. Forecasted integrated vapor transport from the
Center for Western Weather and Water Extremes (CW3E) shows
values approaching 1200 kg for a roughly 12-hour period Thursday
night into Friday. This efficient moisture transport combined
with ample forcing from a 50-60 kt low level jet may result in a
period of moderate to heavy rainfall Thursday night. DESI
indicates mean 6hr rainfall rates increasing to 1-1.5" for most
of the night Thursday. The saving grace is that the system does
look to be fairly progressive and with the upper level centers
passing to our west...the duration of heavy rain may be somewhat
limited.
In terms of impacts there are few changes to make from the
previous update. While the system will be progressive in nature,
most areas can expect a widespread 1-3" of rainfall. NBM 90th
percentile guidance shows a reasonable worse case scenario with
a widespread 2-4 inches of rain falling. We should note that
DESI is indicating some low probabilities of 4+ inches of rain
with this system. If we can get stronger secondary development,
that may increase that potential. So there is a low probability
of more significant flooding...but currently thinking this will
be more of the typical brief nuisance street flooding. Certainly
something to monitor over the next few days. By Thursday
afternoon, we may also see a period of 30-50 mph east southeast
wind gusts with the strongest near the coast. Thankfully we
aren't expecting a long duration strong wind event as the low
center quickly approaches from the southwest later Thursday
night.
Friday Into Saturday...
Significant mid-level dry slot moves overhead Friday as low
pressure deepens nearly overhead so any lingering showers
should come to an end fairly quickly Friday morning. A few
showers could bubble up Friday afternoon underneath a cold pool.
Outside of the showers the larger concern for Friday will be
increasing west winds behind deepening low pressure as it pulls
away to the northeast. Windy and cool conditions likely persist
into Saturday.
.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
00z Update
Tonight...High confidence.
VFR. The exception might be some brief marginal MVFR ceilings near
the Cape/Nantucket from ocean-effect clouds and perhaps a brief
passing sprinkle/light shower. N winds 5 to 10 knots except
10-15 knots across the Cape/Nantucket.
Tuesday and Tuesday Night...Moderate confidence.
Considerable cloudiness with low end VFR-MVFR ceilings. Lowest
of the conditions will be more dominant near and southeast of
I-95 in MA and RI. This is also where we expect the bulk of the
scattered ocean-effect showers. NE winds of 5 to 15 knots,
strongest towards the Cape and Islands where gusts of 20-30 kts
are expected. Some areas of mist or patchy drizzle possible by
00z Wednesday.
KBOS Terminal... High confidence in TAF.
KBDL Terminal... High confidence in TAF.
Outlook /Wednesday through Saturday/...
Wednesday through Wednesday Night: Mainly VFR, with areas MVFR
possible. Breezy. Chance SHRA.
Thursday: Mainly MVFR, with local IFR possible. Windy with
areas of gusts up to 30 kt. SHRA.
Thursday Night: Mainly IFR, with areas MVFR possible. Windy
with areas of gusts up to 30 kt. SHRA, slight chance TSRA.
Friday: Mainly VFR, with areas MVFR possible. Windy with gusts
up to 35 kt. Chance SHRA.
Friday Night: Mainly VFR, with local MVFR possible. Strong
winds with local gusts up to 40 kt. Slight chance SHRA.
Saturday: Mainly VFR, with local MVFR possible. Windy with
gusts up to 35 kt. Slight chance SHRA.
.MARINE...
Forecaster Confidence Levels...
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Tonight through Tuesday Night...High confidence.
Large high pressure anchored over Quebec will combine with a
few weak waves of low pressure passing well southeast of the
Benchmark to generate a strong enough pressure gradient to
result in NE wind gusts of 25 to 30 knots, with a few gusts up
to 35 knots possible right through Tuesday Night. Small Craft
Advisories continue for all open waters. We may briefly touch
gales, but continue to think small craft headlines are more
representative. The long NE fetch will result in rough seas as
well.
Outlook /Wednesday through Saturday/...
Wednesday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 8 ft. Chance of rain
showers.
Wednesday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of rough seas. Chance of rain showers.
Thursday: Strong winds with gusts up to 35 kt. Rough seas up to
11 ft. Chance of rain showers.
Thursday Night: Strong winds with gusts up to 35 kt. Rough seas
up to 12 ft. Rain showers, slight chance of thunderstorms.
Visibility 1 to 3 nm.
Friday: Strong winds with gusts up to 40 kt. Rough seas up to
14 ft. Chance of rain showers.
Friday Night: gale force winds with areas of gusts up to 45 kt.
Rough seas up to 15 ft. Chance of rain showers.
Saturday: Moderate risk for gale force winds with gusts up to
40 kt. Rough seas up to 15 ft. Slight chance of rain showers.
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 11 PM this evening to 8 AM EDT
Thursday for ANZ231>235-237-250-251-254>256.
SYNOPSIS...Belk/FT
NEAR TERM...Belk
SHORT TERM...Belk
LONG TERM...FT
AVIATION...FT
MARINE...Belk/FT
Forecast And Data Provided By NOAA-NWS Boston / Norton, MA