Mendon, Massachusetts Weather Forecast Discussion

528
FXUS61 KBOX 241901
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
301 PM EDT Wed Sep 24 2025
.SYNOPSIS...
A period of widespread showers and a few thunderstorms Thursday
morning into Thursday night as another front moves into the
region. Locally heavy rainfall is possible as well as an
isolated stronger storm or two. Unsettled weather pattern may
linger into Friday, then gradual improvement this weekend. Above
normal temperatures expected into early next week.
&&
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Key Messages:
* Below average temps and scattered showers today
* Another round of beneficial rain with embedded thunderstorms
  tonight
Weak stationary boundary still stalled just south of the coast today
as high pres holds firm over the Canadian Maritimes. NE flow has
kept things cool with most stations reporting temperatures in the
middle and upper 60s, especially near the coast. Lingering showers
and embedded heavier elements should continue to move away from the
Cape and Islands as the afternoon goes on. High res guidance shows a
lull in the shower activity this afternoon and the first part of
this evening as shortwave exits to the east. More widespread showers
should develop and move in from after 04z 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
(nearly 3 STD above climatology!).
As an upper level disturbance approaches from the west there will
likely be two distinct windows for active weather. The first arrives
overnight into late Thursday morning as a warm from approaches from
the southwest and the second possibly occurs Thursday evening as a
surface cold front and upper level disturbance approaches from the
Great Lakes region. For tonight into early Thursday, BUFKIT
soundings show warm cloud depths increasing to >12kft with elevated
instability and marginal surface instability. Deep warm clouds and
efficient rainfall processes will likely result in a broad shield of
rain with embedded tropical downpours. A rumble or two of thunder is
possible, but severe weather will be limited as MLCAPE values only
rise to 100-200 J/kg.
&&
.SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
Key Messages:
* Low risk of severe weather Thursday morning into the early
  afternoon before a lull in the afternoon and early evening
* Localized heavy rainfall may result in minor urban and poor
  drainage street flooding
Active day of weather expected on Thursday with heavy rain and a
risk for an isolated severe storm or two. Heavy rain will likely be
ongoing for much of the area Thursday morning which may affect the
morning commute. HREF shows a period of rainfall rates between 0.5-
0.75" per hour between 6 and 9 am. HREF PMM 6hr QPF forecasts still
show a broad 1.5-2 inches of rainfall with locally higher totals
where heavier echoes can train. Thus, will need to keep an eye out
for localized street and poor drainage flooding.
Other threat tomorrow will be an isolated severe storm or two and
the SPC has a marginal risk for severe storms just to the SW of our
CWA where a narrow axis of greater surface instability is more
likely. Guidance shows an increasing low-level jet near and just
behind the warm front Thursday morning. As a result, the HRRR has 0-
3km SRH increasing to between 150 and 250 m2/s2 between 13 and 17z
Thursday. While there will be plenty of cloud cover to temper
instability, models show a brief window where values of 0-3km CAPE
climb to >120 J/kg. Should this instability overlap with the
elevated effective shear and helicity values, we could see brief
instances of rotating updrafts and stronger storms. The threat will
be short lived as the warm front moves well to the north of the
region after noon or so. Thursday afternoon will be quite warm and
humid for late September as the entire CWA finds itself in the warm
sector. With limited forcing, POP chances fall off, and most of the
area may have a drier period outside of a few areas of drizzle
during the afternoon. Another round of storms approaches from the
west later Thursday afternoon into the evening as a cold front moves
in. Could see a stronger storm or two within the line, but mostly
expecting downpours as instability wanes.
Temps warm 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 with a
decreasing risk for showers going into Friday morning.
&&
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Key Messages:
* High temperatures near 80F continue to be likely through at least
  Friday.
* Mainly dry this weekend, but watching shower potential Sat
  Night/Sun Morning.
Friday continues to look unsettled as a quick shortwave moves
through. Some light showers are possible, but not expecting an all-
day event. High temperatures will likely remain close to 80 across
southern New England with dewpoints in the low to mid 60s.
A cut off low develops over the TN Valley over the weekend, but
ensemble guidance remains uncertain with how far north the deep
moisture from the south with travel. Opted to keep low-end chance
for showers Saturday night into Sunday morning, but given the
uncertainty in the guidance, unsure of how far north those shower
chances will impact.
We are continuing to monitor the tropics as the GFS and ECMWF show a
potential tropical system approaching from the south early next
week, although GEFS and EPS ensembles keep it well to the south
through Tue.
&&
.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
18z TAF Update...Moderate confidence.
MVFR/IFR CIGS will continue to deteriorate this afternoon with
pop up showers and drizzle. Winds remain out of the east at 5-10
knots
Tonight...Moderate Confidence
IFR/LIFR esspically near coastal terminals. It will likely take
rain to clear out LIFR fog, and guidance is in disagreement on
its arrival, from as early as 08z to as late as 14z.
Tomorrow...Low Confidence
IFR with perhaps some pockets of MVFR where rain can help clear
low visibility out. Rain will continue off and on through much
of the day with embedded thunder possibly esspically in the
afternoon.
Tomorrow night...Low Confidence
Even behind the cold front, CIGS may struggle to improve as
ground fog forms due to the antecedent wet conditions.
KBOS Terminal...Moderate confidence in TAF.
MVFR CIGS will eventually drop to IFR this afternoon 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.
Off and on showers this afternoon with perhaps a rumble or two
of thunder. CIGS remain IFR tonight with moderate to heavy rain
moving in sometime between 06z-10z tonight and continuing into
much of tomorrow. Low chance for severe weather tomorrow
afternoon, but thunder probs remain low due to low topped nature
of convection.
Outlook /Friday through Monday/...
Friday: Mainly VFR, with local MVFR possible. Slight chance
SHRA.
Friday Night through Saturday: VFR.
Saturday Night through Sunday: VFR. Slight chance SHRA.
Sunday Night: VFR.
Monday:
&&
.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 Monday/...
Friday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Chance of rain showers, patchy fog.
Friday Night: Winds less than 25 kt. Seas locally approaching
5 ft.
Saturday: Winds less than 25 kt.
Saturday Night through Monday: 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.
&&
$$
SYNOPSIS...McMinn/FT
NEAR TERM...FT
SHORT TERM...FT
LONG TERM...McMinn
AVIATION...KP
MARINE...KJC/FT

NWS BOX Office Area Forecast Discussion