883
FXUS61 KBOX 171141
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
741 AM EDT Thu Jul 17 2025

.SYNOPSIS...
One more day of dangerous heat and humidity is in store for the
region today. An approaching cold front may bring hit or miss
showers and thunderstorms today, but much of the day will be dry.
The cold front will bring and end to the heat and humidity later
tonight with beautiful dry weather Friday and Saturday. Another cold
front will likely bring a round of showers and embedded
thunderstorms to the region late Saturday night and/or Sunday along
with the return of some humidity. This will be short-lived though as
a dry and very pleasant airmass moves back in time for the start of
the next work week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Key Messages...

* Hit or miss showers/t-storms today...but much of the day is dry
* One more day of dangerous heat/humidity...Heat Indices 95-100
* Any Severe weather threat today should be isolated/localized

Details...

Today...

A shortwave and its associated cluster of showers & t-storms across
the mid-Atlantic states early this morning will lift northeast. The
guidance indicates that the convection may weaken as it moves
northeastward into lingering mid-level ridging. However...diurnal
heating may try to offset that later this morning into the mid-
afternoon. Therefore...hit or miss showers and thunderstorms may
cross the region this morning and into the mid afternoon. We then
will need to watch for the approaching cold front and perhaps
another risk for isolated/widely scattered convection late in the
afternoon and evening. However...subsidence behind initial shortwave
and a lot of mid level dry air will probably keep this as an
isolated convective threat. Modest instability will quickly develop
with Capes on the order of 1500 to 2500+ J/kg along with 25 to 30
knots of effective shear. A fair amount of 0-1 KM helicity will also
develop on the order of 100 to 200+ units.

Despite a lot of favorable parameters for severe weather...there is
a significant limiting factor. The mid level lapse rates are poor
and the forcing is quite limited in our region with the better of it
across northern New England. The HREF is also showing rather limited
2-5 KM UH swaths which might be a red flag. That being said...given
the parameters in place if some mesoscale processes can come into
play there will be an isolated/localized severe wind threat and even
a low risk for a weak tornado given the 0-1 KM helicity. But any
severe weather threat should be isolated/localized given the limited
forcing. We also should mention that with Pwats near 2"...brief
torrential rainfall will also be possible with any thunderstorm.

Outside the convective threat...the majority of the day will feature
heat and humidity. High temps will be in the upper 80s to lower 90s
allowing heat indices to reach into the 95 to 100 degree range. Heat
Advisories remain in place through 7 pm this evening.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
Key Messages...

* Relief from heat & humidity later tonight with a NW breeze
* Mostly sunny Fri with low humidity and highs 80-85

Details...

Tonight and Friday...

Any isolated shower & thunderstorm activity this evening will come
to an end later tonight. Otherwise...the main story will be relief
from the heat and humidity behind the cold front later tonight and
Friday. This much drier air will be ushered in on a northwest breeze
which may gust to around 25 mph later tonight into Friday morning.
Low temps tonight will be in the upper 60s to the lower 70s...but
with relief from the humidity. This will be followed by mostly sunny
& beautiful weather for Fri with highs mainly between 80 and 85 and
very comfortable humidity levels. Quite the change from the last few
days.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Key Messages...

* Dry & very pleasant Fri night and Sat with comfortable humidity

* More humid with a round of showers & embedded t-storms sometime
  late Sat night and/or Sun with locally heavy rainfall

* Dry pleasant weather returns Mon/Tue/Wed with comfortable humidity

Details...

Friday night and Saturday...

A ridge of high pressure builds over the region resulting in very
pleasant weather Fri night into Sat. Low temps Fri night will
probably drop into the lower to middle 50s in the outlying locations
given light winds/mainly clear skies and a dry airmass in place.
Highs on Sat will be in the 80s with very comfortable humidity.

Saturday night and Sunday...

The next shortwave/cold front will approach southern New England
from the west late Sat night into Sun. This will be associated with
the return of some humidity and Pwats increasing to around 2 inches.
The forcing with this system looks quite impressive for July
standards...so we may see a round of fairly widespread showers and
embedded t-storms sometime late Sat night and/or Sun.

Monday through Wednesday...

A ridge of high pressure builds in behind the latest cold front for
the start of the next work week. This will bring mainly dry and very
pleasant weather to the region. Highs will mainly be in the upper
70s to the middle 80s although by next Wed may be on the warmer side
of those numbers.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
Forecaster Confidence Levels...

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

12z TAF Update...

Today...Moderate confidence.

Deep moist southerly flow was allowing IFR-LIFR in mainly low clouds
with some fog near the Cape/Islands to overspread much of the region
early this morning. These low clouds should mix out later this
morning and afternoon allowing many locales to improve to
VFR...although lower cigs may flirt with the Cape/Islands at times
through the day. Otherwise...we may have a few brief showers & t-
storms cross the region in two waves. The first wave arrives
this morning, but activity will be weak and widely scattered.
Greater chances for TSRA this afternoon and early evening. The
eastward extent of storm activity is uncertain, with greatest
chances for TSRA west of ORH. SW winds may gust to between 20
and 25 knots by afternoon.

Tonight and Friday...High confidence.

Any isolated shower & t-storm activity should come to an end this
evening. Otherwise...VFR conditions as a dry NW flow of air takes
over later tonight into Friday. NW winds may gust between 20 and 25
knots behind the cold frontal passage overnight into the first half
of Friday before diminishing.

KBOS Terminal...Moderate confidence in TAF.

KBDL Terminal...Moderate confidence in TAF.

Outlook /Friday Night through Monday/...

Friday Night: VFR.

Saturday: VFR. Breezy.

Saturday Night: Mainly VFR, with local MVFR possible. Breezy.
Chance SHRA, chance TSRA.

Sunday: Mainly VFR, with local IFR possible. Breezy. Chance
SHRA, chance TSRA.

Sunday Night through Monday: VFR.

&&

.MARINE...
Forecaster Confidence Levels...

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

Today through Friday...High confidence.

Gusty southwest winds near 25 knots develop across our near shore
southern waters this afternoon given good mixing ahead of an
approaching cold front. We opted to issue a small craft advisory for
those near shore southern waters given it is peak boating season. We
also expect marginal SCA seas to develop with long southerly fetch
across the southern outer-waters by this evening into Friday so we
have headlines for that too. Lastly...behind the cold expect a round
of NW wind gusts of 25 knots overnight into Fri morning across our
northern waters...where we will have additional small craft
headlines.

Outlook /Friday Night through Monday/...

Friday Night through Saturday: Winds less than 25 kt.

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

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

Monday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory until 7 PM EDT this evening for CTZ002>004.
MA...Heat Advisory until 7 PM EDT this evening for MAZ003>007-
     010>021-026.
RI...Heat Advisory until 7 PM EDT this evening for RIZ001>007.
MARINE...Small Craft Advisory from midnight tonight to 2 PM EDT Friday
     for ANZ230-250-251.
     Small Craft Advisory from noon today to 8 PM EDT this evening
     for ANZ231>237.
     Small Craft Advisory from 2 PM this afternoon to 2 PM EDT
     Friday for ANZ254>256.

&&

$$

SYNOPSIS...Frank
NEAR TERM...Frank
SHORT TERM...Frank
LONG TERM...Frank
AVIATION...FT/Nash
MARINE...Frank