BOX issues Area Forecast Discussion (AFD) at Sep 24, 7:54 AM EDT
767
FXUS61 KBOX 241154
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
754 AM EDT Wed Sep 24 2025
.SYNOPSIS...
A weak front moves south of the coast with NE flow bringing cooler
weather today along with the risk of showers. A period of widespread
showers and a few thunderstorms Thursday into Thursday night as
another front moves into the region. Locally heavy rainfall is
possible. Unsettled weather pattern may linger into Friday, then
gradual improvement this weekend. Above normal temperatures expected
into early next week.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Key Messages:
* A few showers or embedded thunder possible this morning near the
south coast
Widespread showers and a few embedded t-storms assocd with mid level
shortwave will move to the east before daybreak, but may see more
scattered convection develop near the south coast and Cape Cod this
morning. Scattered showers are increasing in coverage across
Long Island and HREF hitting the south coast with low probs of
brief heavy rain with convective showers and possible thunder.
Otherwise, weak cold front will stall just south of the coast today
as high pres builds south from the Maritimes. This will set up a
cooler NE flow with abundant low level moisture leading to a cloudy
and cooler day. 1.5-1.75" PWAT plume remains across SNE with
marginal elevated instability and a weak shortwave to move through
so expect scattered showers to continue, and can't rule out an
isolated t-storm this afternoon especially across CT closest to best
instability. Not much temp recovery today with NE flow and cloud
cover with temps holding in the mid-upper 60s, with lower 70s
possible in the lower CT valley and near the south coast.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY NIGHT/...
Key Messages:
* More widespread showers developing from late tonight into Thu
night. A few t-storms possible
* Localized heavy rainfall may result in minor urban and poor
drainage street flooding
There may be a lull in the shower activity this evening as shortwave
exits to the east, but more widespread showers should develop and
move in from the west late tonight into Thu evening as more
shortwave energy approaches from the west along with a modest low
level jet. PWATs forecast to increase to near 2 inches with elevated
instability and marginal surface instability so potential for
heavier convective showers and a few t-storms. It appears the window
for most active weather will be Thu into Thu evening, then cold
front moves into the region overnight with somewhat drier air moving
in from the west.
SPC has highlighted the region in a marginal risk of severe storms
for Thu and CSU machine learning probs are also indicating a low
risk for severe. Low level and deep layer shear is favorable with
low level jet moving into the region, but surface instability is
lacking. It appears best chance will be to the west where
instability is greater, but if better instability can be realized
the severe risk would increase with even a low prob of a tornado
as warm front will be in the vicinity. Something to watch.
Hi-res guidance is more robust than global guidance with heavy rain
potential and this seems reasonable given anomalous PWAT plume 2-3SD
above normal, modest low level jet and elevated instability. Looking
at 1-2 inches of rain, with heaviest likely in the interior. HREF
PMM which represents a reasonable worst case scenario offers
localized amounts up to 3 inches. If these higher amounts are
realized there could be some minor street flooding in urban and poor
drainage areas.
Warm front will be lifting north across SNE during Thu with temps
warming into the lower 70s while dewpoints climb well into the 60s
to near 70 near the south coast so there will be a rather humid feel
to the airmass. Temps Thu night will remain in the 60s.
&&
.LONG TERM /FRIDAY THROUGH TUESDAY/...
Key Messages:
* Above normal temps will prevail Fri into early next week with
potential for some 80 degree readings
* Mainly dry this weekend but watching southern stream moisture to
the south which may bring a few showers
Despite drier air moving in from the west, pattern is still somewhat
unsettled on Fri as mid level trough and shortwave move through.
Can't rule out a few showers Fri but a washout is not expected. Then
during the weekend a cut off low develops over the TN valley with
upper level confluence nearby to the north with SNE on the NW
periphery of Atlantic subtropical ridge. The uncertainty this
weekend is with the northern extent of deeper moisture from southern
stream system. Based on ensemble guidance there are low probs for
some showers, mainly Sat night into Sun, but it could remain to the
south if upper confluence holds strong. Then early next week will
have to monitor the tropics as GFS and ECMWF show a potential
tropical system approaching from the south, although GEFS and EPS
ensembles keep it well to the south through Tue.
Above normal temps are expected through the period with temps well
into the 70s into early next week. Ensembles are indicating low
probs for 80F so some 80 degree readings are possible for a few
days.
&&
.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
12z TAF Update...Low confidence.
Wide range of CIGS this morning from LIFR in the CT river valley
to VFR near Boston. CIGS in eastern MA should deteriorate to
low end MVFR/IFR by later this morning while ORH to BDL should
see improvements to IFR and possibly MVFR by this afternoon.
Areas of heavy showers across the south coast will move towards
the Cape and Islands and bring IFR to LIFR conditions.
Otherwise expect vicinity light showers for much of the day for
all terminals.
Tonight...Moderate Confidence
CIGS drop back to IFR/LIFR between 22-04z with NE winds turning
more SE. More steady moderate rain with pockets of heavy showers
likely overnight, starting between 06-09z. There could be a
rumble or two of thunder overnight as well.
Tomorrow...Low Confidence
IFR/LIFR with periods of showers and thunderstorms
KBOS Terminal...Moderate confidence in TAF.
MVFR CIGS will eventually drop to IFR by late morning with
off and on showers through much of the day. Overnight, CIGS
should drop to IFR/LIFR with NE winds, but may see improvements
towards day break as winds turn more SE and moderate to heavy
rain moves in.
KBDL Terminal...Moderate confidence in TAF.
LIFR turning IFR/MVFR by mid morning. Off and on showers this
morning, with heavy showers or thunderstorms possible this
afternoon. CIGS remain IFR tonight with moderate to heavy rain
after 06z
Outlook /Friday through Sunday/...
Friday: VFR. Slight chance SHRA.
Friday Night: VFR.
Saturday through Sunday: VFR. Slight chance SHRA.
&&
.MARINE...
Forecaster Confidence Levels...
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Through Thursday...High Confidence.
Winds below SCA thresholds with NE flow today shifting to S during
Thu. As low level jet moves into the region, some risk for gusts
approaching 25 kt Thu afternoon. 5 ft seas over the outer waters
slowly subside today into tonight.
Outlook /Friday through Sunday/...
Friday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Chance of rain showers.
Friday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain showers.
Saturday: Winds less than 25 kt. Slight chance of rain showers.
Saturday Night: Winds less than 25 kt. Chance of rain showers.
Sunday: Winds less than 25 kt. Slight chance of rain showers.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 2 AM EDT Thursday for ANZ250.
Small Craft Advisory until 2 PM EDT this afternoon for ANZ254.
Small Craft Advisory until 9 AM EDT this morning for ANZ255-
256.
&&
$$
SYNOPSIS...KJC
NEAR TERM...KJC
SHORT TERM...KJC
LONG TERM...KJC
AVIATION...KJC/KP
MARINE...KJC
Source: BOX issues Area Forecast Discussion (AFD) at Sep 24, 7:54 AM EDT (https://mesonet.agron.iastate.edu/p.php?pid=202509241154-KBOX-FXUS61-AFDBOX)
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