Hopkinton, Massachusetts Weather Forecast Discussion

173
FXUS61 KBOX 051910
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
310 PM EDT Fri Sep 5 2025
.SYNOPSIS...
A warm and humid day is on tap for Saturday ahead of an approaching
cold front. This front will bring scattered severe thunderstorms
with localized torrential rainfall Saturday afternoon and evening
across interior southern New England. This activity will weaken some
on approach the Boston to Providence corridor Saturday evening.
However...an anafrontal wave will bring a period of widespread
showers Sunday morning which may linger int the afternoon towards
the coast. Otherwise...much of the work week looks dry and very
pleasant outside the risk for a few brief showers around mid-
week.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Key Messages:
* Increasingly warm and muggy conditions this afternoon
* Breezy conditions with gusts as high as 30 mph
Weakening frontal boundary continues to move offshore this afternoon.
Thankfully, most of the area received some beneficial rainfall from
the disturbance with COCORAHS observations ranging from 0.10-0.20"
across eastern Massachusetts to as high as 0.50" for much of central
Massachusetts and Connecticut. Additional rainfall chances are quite
limited over the next 12-18 hours with a transient area of high
pressure and drier air aloft moving in. Temperatures will be
somewhat warmer than what we saw yesterday, generally rising into
the lower to mid 80s. More noticeable will be the higher dewpoints
with values climbing into the mid and upper 60s for most of us.
Should see winds increase fairly quickly this afternoon as low level
cloud cover mixes out.
Dry weather continues overnight with increasing low level moisture.
Could see some low stratus and fog develop along the south coast as
dew points increase. Will be quite warm with lows in the lower to
mid 60s.
SATURDAY AND SATURDAY NIGHT
Key Messages:
* Scattered severe weather possible across the interior tomorrow
  afternoon. Biggest threats include damaging winds, heavy rain, and
  frequent lightning. A tornado or two is possible.
* Anafrontal wave brings continued showers into Sunday morning
A final taste of summer heat and humidity on Saturday as strong WAA
ahead of an approaching cold front brings anomalous moisture and
warmer temperatures. Temperatures on Saturday soar into the lower to
mid 80s and dewpoints will be on either side of 70 for much of the
area. The rich moist environment will set the stage for likely
scattered strong and severe storms across much of interior New
England tomorrow afternoon. Increased confidence in severe
convection has allowed for the SPC to increase the Day 2 severe
weather outlook to a slight risk across much of the interior.
Biggest change with this update is to reflect trends in CAMs which
have all increased the amount of forecasted CAPE for the region. Any
clearing tomorrow will allow for CAPE values to climb to between
1500 and perhaps as high as 2000 J/kg. Wind field progs continue to
impress with somewhat unusually high amounts of 0-6km shear on the
order of 45-50kts. Also noteworthy are elongated and curved
hodographs indicative of stronger low and mid level winds. Poor mid-
level lapse rates on the order of 5.5-6.0 C/km will help to cap the
overall spatial extent of activity. On the other hand, robust values
of 0-3km CAPE on the order of 150-180 J/kg will support strong and
efficient updrafts. The somewhat unusually high amounts of low-level
instability may also help to locally enhance any low-level spin and
result in a tornado or two. Case in point, the HREF has 0-1km SRH
value approaching 130 m2/s2 across the Connecticut river valley. The
other threat will be damaging winds as low-level lapse rates
approach 8 C/km and DCAPE values rise to around 1000 J/kg. CAMs
suggest that the initial storm mode could be linear segments with
embedded supercells. Eventually, storms will likely congeal into a
line with bowing segments and areas of damaging winds. HREF
helicity swaths even suggest a brief period of QLCS-like activity
before the main severe threat transitions into damaging straight-
line winds.
In addition to the severe threat there may also be some localized
flash flooding concerns. Despite strong winds aloft, the mean flow
will be parallel to the front and result in the potential for
training storms. Ensemble guidance shows PWATS rising to between 1.5
and 1.8", a full 2 STD above climatology. Convection that does form
will result in efficient rain production as CAPE will be on the
skinnier side and warm cloud heights are forecast to rise above 10
kft. In essence, with thermodynamic profiles like this, we`ve traded
a large, damaging hail threat for a local flash flood threat. Best
chance for flash flooding will be across urban areas in western and
central southern New England.
The biggest fly in the ointment will the timing of clearing. HREF
mean low level cloud cover shows a narrow window of clearing later
Saturday morning with the majority of the day being cloudy. As is
usually the case with these events, the timing and extent of
clearing will be a determining factor in the intensity and extent of
severe convection.
Thankfully it looks like storms will be quick to wind down after
sunset Saturday. Expecting rain showers to continue especially
across eastern portions of the CWA Saturday night into Sunday. High
res guidance suggests an anafrontal wave develops during the predawn
hours Sunday morning. The wave could help to focus more of a steady
rain mainly southeast of I-95.
&&
.LONG TERM /SUNDAY THROUGH FRIDAY/...
Key Messages...
* Cooler with showers Sun am, which linger into afternoon on coast
* Mainly dry/pleasant for much of next week...cool nights/mild days
* Offshore low may briefly graze the coast with a few showers Wed
Details...
Sunday...
An anafrontal wave will result in a wet Sunday morning for much of
southern New England given persistent southwest flow aloft. We still
need to sort out the axis of the most significant rain...but there
is often a narrow area that can receive quite the soaking in these
setups. Some elevated instability around too...so there will be an
isolated t-storm risk in the morning especially southeast of I-95.
We should see things dry out across the interior Sunday
afternoon...but showers may linger into the afternoon along and
southeast of the I-95 corridor. High temps will probably be held in
the middle 60s to the lower 70s given the clouds and rain.
Monday through Friday...
Dry/very pleasant weather is in store for much of the upcoming work
week...outside of an offshore low may briefly graze the coast with a
few showers mid-week. High pressure building in behind the cold
front will for the first half of next week will result in cool
nights and mild days. Low temps will probably be in the 40s to the
lower 50s with highs mainly in the 70-75 degree range. In fact...on
the coast and high terrain may see highs in the upper 60s at times.
This might occur near mid-week when a distant offshore low may
briefly graze the coast with a few showers. We may see a a brief
warm up on Thursday with perhaps highs approaching 80. However...a
cold front will likely bring the return to slightly cooler than
normal temps by Friday.
&&
.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
18z TAF Update...
Today... High Confidence. Moderate on timing of improvements to
VFR.
IFR cigs scatter out this morning bemusing VFR for the
afternoon. Breezy, SSW wind 10-15 knots with gusts around 25
knots. A few brief gusts approaching 30 knots are also possible
during the afternoon.
Tonight... High Confidence.
VFR, areas of MVFR-IFR are possible across south coast, Cape
Cod, and the Islands. SW wind 8-12 knots.
Saturday... Moderate Confidence.
VFR, becoming MVFR with afternoon thunderstorms. Area of greatest
risk for strong to severe storms are interior southern New England
terminals. Storms likely develop into a squall line after 19z
and move west. Gusty SSW wind 10-15 knots, gusting 25 knots.
KBOS Terminal...Moderate confidence in TAF.
Likely VFR through the overnight and into tomorrow morning.
Gusty SSW winds, 15-20 knots, gusting to 30 knots. Possible
-SHRA and -TSRA activity after 22z as a line of storms moves
 from west to east.
KBDL Terminal...High confidence in TAF.
Outlook /Sunday through Wednesday/...
Sunday: Mainly VFR, with areas MVFR possible. Breezy. Chance
SHRA, slight chance TSRA.
Sunday Night: VFR. Breezy. Slight chance SHRA.
Monday: VFR. Breezy.
Monday Night: VFR.
Tuesday through Tuesday Night: VFR. Breezy.
Wednesday: Breezy. Slight chance SHRA.
&&
.MARINE...
Forecaster Confidence Levels...
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
* A Small Craft Advisory is in effect into Saturday evening
Tonight and  Saturday... High Confidence.
SSW for continue tonight and Saturday ahead of a cold front with
gusts between 20 and 30 knots. Strongest of those winds will
be nearshore Saturday afternoon. Seas on the outer waters are
building 4-5 feet and near shore waters are 3-4 feet. A strong
cold front will move across the waters late Saturday into Sunday
morning, rain and thunderstorms are possible.
Outlook /Sunday through Wednesday/...
Sunday: Winds less than 25 kt. Seas locally approaching 5 ft.
Rain showers, isolated thunderstorms. Local visibility 1 to
3 nm.
Sunday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain showers.
Monday: Winds less than 25 kt. Seas locally approaching 5 ft.
Monday Night through Tuesday: Winds less than 25 kt.
Tuesday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain showers.
Wednesday: Low risk for Small Craft Advisory winds with gusts
up to 25 kt. Areas of seas approaching 5 ft. Chance of rain
showers.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 7 PM EDT this evening for ANZ230-
     236.
     Small Craft Advisory until 8 PM EDT Saturday for ANZ231>235-
     237-250-251-254>256.
&&
$$
SYNOPSIS...Frank
NEAR TERM...FT
SHORT TERM...FT
LONG TERM...Frank
AVIATION...Frank/FT
MARINE...Frank/FT

NWS BOX Office Area Forecast Discussion