Plum Island, Massachusetts Weather Forecast Discussion

321
FXUS61 KBOX 211838
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
238 PM EDT Sun Sep 21 2025
.SYNOPSIS...
Dry weather continues until the chance for some unsettled
weather returns late Tuesday into Wednesday. Temperatures
should also average about normal this week, with the exception
of above normal temperatures Tuesday. Potential for a more
widespread rainfall event Thursday and Friday.
&&
.NEAR TERM /THROUGH TONIGHT/...
Key Messages:
* Not quite as cool tonight with some high clouds wafting by
Core of a nearby high pressure shifts more towards the Maritimes
tonight. Still expecting rather good radiational conditions,
despite some higher clouds at times. Favored the lowest
temperature guidance. Kept fog out of the forecast for now, but
thinking localized fog could develop in some of the river
valleys.
&&
.SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
Key Messages:
* Warming trend kicks off tomorrow
With the high pressure still over the North Atlantic, expecting
a general light south flow to develop across our region. Except
near the immediate east coast, where the more typical southeast
sea breeze direction should prevail from late morning into the
afternoon.
Expecting a warming trend tomorrow with continued dry weather.
&&
.LONG TERM /TUESDAY THROUGH SUNDAY/...
Key Messages:
* Warm and humid conditions peak on Tuesday
* Chance for showers and a few thunderstorms Tuesday into Wednesday
* Unsettled weather continues for the rest of the week with a chance
  for showers each day
Southwesterly return flow advects in higher moisture and warmer
temperatures Tuesday. Still thinking the the warmest temperatures
will be found the Connecticut and Merrimack River Valleys where
highs may rise as high as the lower to perhaps middle 80s.
Deterministic guidance is in agreement showing 925 mb temperatures
over the region around 20C. Dew points increase into the 60s after a
dry weekend, and ensemble mean PWAT values range between 1.5-1.7"
for the afternoon. An approaching front arrives Tuesday afternoon
and evening providing ample forcing for scattered to widespread
showers and thunderstorms. Guidance still shows MLCAPE values around
500 J/kg along with somewhat favorable shear profiles. As such,
there could be a low chance for a severe storm or two across the far
northwestern interior. Guidance has increasingly hinted at
developing a weak wave of low pressure along and just behind the
front. This wave could help increase and extend the coverage of
light to moderate rainfall Tuesday night into Wednesday especially
across the Cape and Islands.
Brief upper level ridging Wednesday afternoon won`t make much of an
impact near the surface as stiff onshore flow likely continues the
chance for low clouds and an isolated shower or two.Temperatures
will be much cooler on Wednesday, only rising into the lower to mid
60s for much of the region. Attention turns to a longwave trough as
it digs deeper into the central and midwest CONUS. A warm front
extending from surface low pressure over the Great Lakes approaches
the area Thurs. Guidance has become more bullish on periods of
showers and perhaps steady rainfall associated with this feature
Thursday. Kept chance POPs through Friday as the front will be slow
to move. Some models such as the ECMWF show the region coming into
the warm sector by Friday with dew points potentially rising into
the 60s. Such unstable air with a boundary nearby could bring
another risk for convection Friday and perhaps into the weekend.
&&
.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Through Monday Night...High Confidence.
VFR. Light E to SE winds becoming variable to calm tonight,
then light S away from the E MA coast Monday. Light SE winds
there from late Monday morning into the afternoon. Light SW
winds expected Monday night.
KBOS Terminal...High confidence in TAF.
KBDL Terminal...High confidence in TAF.
Outlook /Tuesday through Friday/...
Tuesday: VFR. Breezy. Chance SHRA, slight chance TSRA.
Tuesday Night: Mainly VFR, with local MVFR possible. Chance
SHRA, slight chance TSRA.
Wednesday: Mainly VFR, with local IFR possible. Chance SHRA.
Wednesday Night: Mainly VFR, with local MVFR possible. Chance
SHRA.
Thursday: VFR. Chance SHRA.
Thursday Night: Mainly VFR, with local MVFR possible. Chance
SHRA.
Friday: VFR. Chance SHRA.
&&
.MARINE...
Forecaster Confidence Levels...
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Through Monday Night...High Confidence.
High pressure south of the Maritimes leads to relatively light
winds and seas across the waters. Good visibility.
Outlook /Tuesday through Friday/...
Tuesday: Winds less than 25 kt. Seas up to 5 ft. Slight chance
of rain showers.
Tuesday Night: Winds less than 25 kt. Seas up to 5 ft. Chance
of rain showers, slight chance of thunderstorms.
Wednesday through Thursday: Winds less than 25 kt. Areas of
seas approaching 5 ft. Chance of rain showers.
Thursday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Chance of rain showers.
Friday: Winds less than 25 kt. Chance of rain showers.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.
&&
$$
SYNOPSIS...Belk/FT
NEAR TERM...Belk
SHORT TERM...Belk
LONG TERM...FT
AVIATION...Belk/FT
MARINE...Belk/FT

NWS box Office Area Forecast Discussion