Charlestown, Rhode Island 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

417
FXUS61 KBOX 201112
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
712 AM EDT Sun Jul 20 2025

.SYNOPSIS...
Warm and humid today with two rounds of showers and thunderstorms
expected ahead of a cold front. The first round will be this
morning near the south coast and especially the Cape and Islands
with locally heavy rainfall possible. The second round of
potentially severe storms with damaging winds will be from mid
afternoon into the evening, especially across the interior.
Behind the front, it will turn cooler and much less humid Monday
and Tuesday. A warming trend begins Wednesday, with heat and
humidity returning for Thursday and especially Friday when highs
may reach well into the 90s.

&&

.NEAR TERM /THROUGH TONIGHT/...
Key Messages:

* Scattered showers and a few t-storms impacting the south coast
  between 6-10 am, but through midday over Cape/Islands. Best chance
  of locally heavy rainfall over the Cape and Islands

* A second round of scattered strong to severe t-storms expected to
  move through SNE between 4-10 pm. Greatest risk in the interior.

* Main threat is damaging wind gusts with a secondary threat for
  large hail and locally heavy rainfall

This morning...

Area of showers south of Long Island expected to increase in
coverage as they lift northward toward the south coast this morning,
with scattered showers expected along the south coast 6-10 am, but
lingering through midday over the Cape/Islands. Showers are
accompanying a warm front ahead of a mid level shortwave with
decreasing stability and increasing moisture plume moving in from
the west. MUCAPES increase to around 500 J/kg this morning so expect
a few t-storms will develop and given PWATs nearing 2 inches, any
storms will contain locally heavy rainfall. However, recent hi-res
guidance has continued to trend south with heavy rainfall potential
focused over the south coastal waters and possibly impacting Cape
Cod and especially the Islands. HREF still showing low probs (10%)
of 3" in 3 hours over Nantucket with higher probs of 1+ inch in 3
hours over Cape/Islands. So we think there will be some heavy
downpours over the Cape/Islands this morning, mainly after 8 am but
flash flooding not anticipated. May see localized rainfall
approaching 2 inches. 0-6km shear is near 35 kt this morning so
there is a low risk for a strong storm over the Cape/Islands and
HREF is showing some weak updraft helicity swaths around Nantucket
so will have to monitor this closely, but 0-3km CAPE is forecast to
be rather meager.

This afternoon and evening...

The mid level shortwave moves to the east by late morning and expect
showers and t-storms will be exiting the Cape/Islands by midday with
subsidence leading to some clearing this afternoon. Warm and humid
airmass will lead to increasing instability with CAPES 1000-2000
J/kg ahead of an approaching cold front so expect scattered t-storms
will develop and move southward into SNE. While mid level lapse
rates are poor, favorable 0-6km shear 35-40 kt and modest forcing
along the cold front will lead to storm organization and potential
for scattered severe t-storms this afternoon, with best chance in
the interior where updraft helicities are greatest. CSU ML probs and
Nadocast both increased severe probs for this afternoon. Given
linear forcing along the cold front and shear vectors mostly
parallel to the cold front, expect mostly line segments and clusters
with damaging wind the primary threat, but can`t rule out hail with
with any mid level rotators. We think tornado risk is rather low as
low level winds/shear are weak but any discrete storm early on will
have to be monitored. Timing of strongest storms will be mostly 4-8
pm, with weakening convection approaching the south coast this
evening 8-10 pm.

Tonight...

After cold front passage and wind shift to NW, drier moves in with
clearing skies overnight. Lows will drop into the 60s with some
upper 50s over northern MA higher terrain.

&&

.SHORT TERM /MONDAY/...
Key Messages:

*  Sunny and pleasant with low humidity

Post-frontal airmass Monday with dry NW flow and subsidence
behind upper trough over the Maritimes as PWATs drop to around
0.5". The column is dry so it will be a sunny day, and well
mixed BL will support gusty NW winds to 25 mph at times,
diminishing mid- late afternoon as gradient relaxes. 925 mb
temps 16-17C support highs upper 70s to near 80F, except 70-75
interior higher terrain. It will be rather dry with low
humidity as dewpoints fall through the 50s and into the 40s
interior in the afternoon.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Key Messages:

* Very pleasant Tue with sunshine, low humidity and light winds

* Warming trend begins Wed with increasing heat and humidity Thu and
  especially Fri when temps expected to reach into the 90s across
  much of SNE

* Mainly dry through Thu, then risk for showers and t-storms
  increase Fri

* Hot and humid conditions may persist into next weekend

Temperatures...

Core of the coldest air aloft will be over New Eng early Tue before
moderation begins. After a chilly night Mon night by July standards
with lows in the 40s and 50s, temps will recover to 75-80 followed
by another chilly night Tue night with dry airmass in place. Then
midwest subtropical ridge will build eastward to the mid Atlc coast
Wed through Fri with SNE on the periphery of the ridge with nearby
polar jet to the north. This will lead to warming trend beginning
Wed with temps returning to normal for late July, then increasing
heat and humidity building Thu and especially Fri when warmest temps
aloft will be over New Eng. Will likely see some 90+ temps by Thu
but mostly confined to the interior with gusty SW flow keeping
coastal plain a bit cooler. Then more of a W flow Fri and 850 mb
temps around 20C will support widespread highs in the 90s across
much of SNE, except perhaps along the immediate south coast. With
dewpoints climbing to 70+ heat advisories will likely be needed. It
appears heat will continue into next Sat but not as hot as Fri
as only slight cooling noted at 925 and 850 mb. GEFS and EPS
still showing at least moderate probs (50-70%) of 90+ on Sat.

Precipitation...

Dry weather will prevail through Thu. Even as heat and humidity
begin to increase on Thu, moisture is shallow with best instability
and deeper moisture likely confined to the west. Best chance for
showers and t-storms will come on Fri as deeper tropical moisture
axis and instability axis moves over SNE with polar jet dropping
south into New Eng along with a weak cold front or trough. But
uncertainty with timing of weak shortwaves within the flow lining up
with diurnal instability. Low confidence for Sat due to uncertainty
with where moisture axis will be located.

&&

.AVIATION /11Z SUNDAY THROUGH THURSDAY/...
Forecaster Confidence Levels...

Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

12z TAF Update: Moderate confidence. Uncertainty with timing of
ceilings today.

Expecting MVFR cigs to become more widespread this morning with
areas of IFR, especially near South Coast. Showers and embedded
TS will lift NE from Long Island and should reach Cape Cod and
Islands later this morning with brief downpours.

Should see some improvement to lower end VFR cigs from later
this morning into early afternoon, except Cape Cod and Islands
where IFR cigs are likely to develop. Attention then turns to
potential line of TS tracking NW to SE from late afternoon
through early evening, probably weakening before reaching Cape
Cod and Islands. Potential for gusts to 45kt and brief IFR in
downpours.

Clearing follows as winds shift to NW with VFR tonight and Mon.

KBOS terminal...Moderate confidence in TAF due to timing of
ceiling changes. More confident on TS timing within an hour or
so of 00z Mon.

KBDL terminal...Moderate confidence in TAF due to timing of
ceiling changes. More confident on TS timing within an hour or
so of 23z.

Outlook /Monday Night through Thursday/...

Monday Night through Tuesday Night: VFR.

Wednesday through Thursday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels...

Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.

Through Monday...High confidence.

Southerly winds 10-20 kt today shifting to NW tonight with a few 20-
25 kt post-frontal gusts developing late tonight into Mon. Showers
and scattered t-storms will impact the south coastal waters this
morning. Another round of weakening storms expected late afternoon
and evening.

Outlook /Monday Night through Thursday/...

Monday through Wednesday Night: Winds less than 25 kt.

Thursday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Seas locally approaching 5 ft.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

$$

SYNOPSIS...KJC
NEAR TERM...KJC
SHORT TERM...KJC
LONG TERM...KJC
AVIATION...JWD
MARINE...KJC