142
FXUS61 KBOX 182346
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
746 PM EDT Fri Jul 18 2025

.SYNOPSIS...
Dry and pleasant weather with comfortable humidity levels continues
tonight into Saturday. Another cold front may bring scattered
showers and a few thunderstorms to the region toward daybreak Sunday
with perhaps another round sometime late Sunday into Sunday evening.
Much less humid along with cooler than normal temperatures
and dry weather for early next week. Warming trend then begins
around the middle of next week, with heat and humidity returning
for Thursday and Friday.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Key Messages...

* Mostly clear & cool tonight with lows mainly in the 50s

Details...

A ridge of high pressure builds over the region tonight. This will
allow for mainly clear skies...light/calm winds and a good night of
radiational cooling given the dry airmass in place for July
standards. Low temps will bottom out mainly in the 50s with perhaps
even some upper 40s in the normally coolest outlying locations of
western MA. Meanwhile...the Urban Heat Islands of Boston/Providence
only bottom out in the lower to middle 60s.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
Key Messages...

* Mostly Sunny Sat...Highs mainly in the middle to upper 80s

* Milder Sat night with lows in the upper 60s to the lower 70s along
  with scattered showers & a few t-storms possible after midnight

Details...

Saturday...

High pressure slides east of the region on Sat. This will allow a
warmer airmass to begin to overspread the region...but with
comfortable humidity levels. High temps should reach mainly in the
middle to upper 80s with a few spots in the lower CT River Valley
perhaps flirting with 90. It will be a few degrees cooler along
portions of the immediate eastern MA coast with sea breezes.

Saturday night...

Dry weather should prevail Sat evening...but clouds will be on the
increase ahead of an approaching shortwave and associated mid-level
warm front. There is a pretty good elevated instability burst ahead
of this warm front as Showalter indices  quickly drop from over 10
to below zero overnight. Therefore...expect scattered showers and a
few thunderstorms to be possible after midnight and especially
toward daybreak Sunday. There also might be pockets of heavy
rainfall as Pwats climb into the 1.50 to 2 inches. Low temps will be
much milder than tonight...only bottoming out in the upper 60s to
the lower 70s.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Key Messages:

* Showers/embedded storms early-day Sunday, possibly a second
  round of storms later in the day.

* Drie, cooler than normal and low humidity levels for Mon and
  Tue.

* Warming trend mid to late next week, with heat and humidity
  Thu/Fri. Daily chances for showers/storms Thu and Fri.

Sunday looks more active, with early-day showers and embedded
thunderstorms carrying over from the Saturday-overnight period.
Then a slowly-sagging cold front will be moving southward during
the afternoon to early evening hours, in association with a
seasonably- strong upper level trough. That could lead to a risk
for scattered stronger storms, although with a couple of
potential limiting factors: (1) weak mid-level lapse rates, (2)
best deep layer shear of 35-40 kt for more persistent storms
lies behind the cold front and (3) the extent to which we can
clear out from early-day shower and embedded storm activity.
Currently view the severe weather risk as on the lower side but
it isn`t zero. Given the very humid, higher PWAT airmass and
that the surface front is nearly or becomes nearly parallel to
the 500 mb heights, it could favor slow- moving heavy rainers,
but it is conditional on thunderstorms developing. Clearing then
takes place from north to south late Sun aftn to early evening,
and with it will come a substantial change in airmass as we
open the workweek.

Mon and Tues then trend dry as a strong 1020+ mb high pressure
area extends ridging through Southern New England. The bigger
story for this period is cooler temperatures and substantially
lower humidity levels. 850 mb temps could slip below 10C, and it
may feel closer to conditions more typical of early to mid
September than late July with highs in the 70s to low 80s and
dewpoints in the low 50s. Temps to run some 5-10 degrees cooler
than late-July normals. Not exactly summerlike but still overall
ideal for outdoor activities.

High pressure then moves offshore for mid to late in the
workweek, which will allow for warming temps and rising humidity
levels back to summerlike levels. This is especially the case as
we move into Thu/Fri with moderately high probs of highs
reaching 90 or above. While generally dry on Wed, the risk for
showers and thunderstorms will also increase into Thu and Fri;
but in a quasi-zonal flow pattern, the coverage and strength of
this activity will hinge on the strength of upstream trough
energy, which varies fairly substantially across the ensemble
systems.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
Forecaster Confidence Levels...

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

00z TAF Update:

Tonight: High confidence.

VFR. Seabreezes along the eastern coast of MA turn
offshore/light SW by 01z; winds remainder of the evening and
overnight are light out of the NW.

Saturday...High confidence.

VFR. SSW winds around 10 knots except for localized sea breezes
developing along portions of the immediate coast.

Saturday night...Moderate confidence.

VFR during the evening...but some MVFR cigs may develop across parts
of the region after midnight. In addition...the risk for scattered
showers and a few t-storms will increase after midnight and
especially by daybreak. SSW winds 5-10 knots.

KBOS terminal...High confidence in TAF.

KBDL terminal...High confidence in TAF.

Outlook /Sunday through Wednesday/...

Sunday: Mainly VFR, with areas MVFR possible. Breezy. Chance
SHRA, chance TSRA.

Sunday Night: VFR. Chance SHRA.

Monday through Tuesday Night: VFR.

Wednesday: Breezy.

&&

.MARINE...
Forecaster Confidence Levels...

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

Tonight through Saturday night...High confidence.

High pressure moves off the waters tonight and then pushes east of
the waters Sat as a warm front approaches by Sat night. Winds will
be light tonight into Sat morning...with sustained speeds generally
under 15 knots. S winds may gust to 20+ knots and perhaps briefly up
to 25 knots Sat night across our northern outer-waters. Later shifts
may need to consider a marginal small craft advisory for the
northern outer-waters...but other than that not expecting any marine
headlines over this time period.

Outlook /Sunday through Wednesday/...

Sunday: Winds less than 25 kt. Chance of rain showers, chance
of thunderstorms.

Sunday Night: Winds less than 25 kt. Slight chance of rain
showers, slight chance of thunderstorms.

Monday through Wednesday: Winds less than 25 kt.

&&

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

&&

$$

SYNOPSIS...Frank/Loconto
NEAR TERM...Frank
SHORT TERM...Frank
LONG TERM...Loconto
AVIATION...Frank/Loconto
MARINE...Frank/Loconto