610
FXUS61 KBOX 191808
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
208 PM EDT Wed Aug 19 2026

.WHAT HAS CHANGED...
Aviation section updated, but no significant changes to the
forecast.

&&

.KEY MESSAGES...

- Dry today through tonight.

- Unsettled weather returning Thursday with a front passing
  through, followed by a brief tranquil period Friday.

- Another round of unsettled weather possible for the weekend.

&&

.DISCUSSION...
KEY MESSAGE 1...Dry today through tonight.

With the low earlier this week now off the coast of Nova Scotia,
high pressure has been able to build in over southern New England in
its place. Notably aloft, a trough well to our north and west in
Canada continues shifting eastward over the southern portion of the
Hudson Bay. With where we are in context of this trough, strong SW-
ly flow aloft develops today through the column. Diurnal mixing
should also aid in mixing down this SW flow, which may inhibit sea
breeze development despite the presence of high pressure centered
just off to our east. Any early morning fog and lower clouds will
diminish shortly after sunrise. 925 mb temperatures will likely
remain in the 20-23C range for the afternoon, encouraging highs into
the mid to upper 80s.

KEY MESSAGE 2...Unsettled weather returning Thursday with a front
passing through, followed by a brief tranquil period Friday.

A shortwave within this slightly SW flow makes its way towards
southern New England heading into tomorrow, bringing with it more
favorable dynamics and moisture for showers as the jet aloft also
becomes more SW and cyclonic. With better ascent and forcing, will
need to keep an eye on where the best moisture tracks. The
differences between the CAMs and the global guidance remain quite
significant, with the NAM showing greater moisture through the
column across the whole region, while the Canadian, ECMWF, and GFS
all indicate layers of dry air in the lower to mid levels that would
greatly affect precipitation. Given the signal for dry air limiting
rainfall, I kept the chances for precipitation to around 30% or less
and total QPF to up to 0.15". This is in line with what most of the
ensemble guidance is indicating as well, as the greater
concentration of moisture is shown in this guidance to remain just
to our southwest.

Following the passage of this front, much drier air files in behind
it. Dew points are expected to drop into the 50s across the region
and remain generally in the upper 50s and low 60s Thursday night
into Friday. High pressure makes its return Friday as a brief
respite from this unsettled pattern, with onshore breezes and highs
in the low 80s and upper 70s, with mid 70s along the immediate
coastal areas.

KEY MESSAGE 3...Another round of unsettled weather possible for the
weekend.

A much larger shortwave moves in from the Great Lakes Saturday into
Sunday, greatly amplifying the SW flow aloft. Guidance signals at
the possibility of a series of waves tracking NE along within this
SW flow, and a surface low may pass along the east coast up into
southern New England. Track is still somewhat uncertain, but this
would likely bring the return of showers. Depending on the timing of
these waves and low pressure, thunderstorms could be possible if
they can take advantage of daytime heat.

Heading into the start of next week, it`s also worth noting that the
troughing associated with the leading shortwave cutting south
through the Great Lakes could end up more as a closed off low aloft.
Deterministic guidance keys in more on this possibility, but the
Canadian ensemble notes the possibility along with the ECMWF
ensemble hinting at it slightly; the GEFS keeps it a bit more open
as of the 00z run. We may find ourselves in the low`s post-frontal
airmass for Monday with more W-ly flow keeping the region slightly
cooler; 850 mb temps may fall to near 10C. Will be something to
continue monitoring in future updates.

&&

.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 - Overall high confidence

Today and Tonight...High confidence overall.

Primarily VFR conditions with the exception of the Cape and
Islands with periods of MVFR ceilings possible. Light -SHRA
possible 19-22Z for Islands, mainly ACK. Otherwise SW flow 8-12
kts with an occasional gust to 18 kts. Very low chance at a sea
breeze sneaking into BOS, but if it were to it would be between
18-20Z.

Mainly VFR tonight. May see patchy MVFR cigs and FG for Cape
and Islands after midnight. Low chance of an isolated shower
overnight. Light WSW winds.

Thursday...High confidence.

VFR. Scattered showers arrive from west to east after 18Z with a
few thunderstorms possible. Confidence not high enough to
include TSRA in TAF, but SHRA included as PROB30 for now.


KBOS Terminal...Moderate confidence with respect to the sea
breeze. Sea breeze remains just off the terminal at BOS this
afternoon. Kept prevailing as SW for remainder of afternoon.
There is a low chance (<15%) for the sea breeze to make it in
18-20Z.

KBDL Terminal...High confidence in TAF.

Outlook /Thursday Night through Monday/...

Friday: VFR.

Friday Night: VFR. Slight chance SHRA.

Saturday: VFR. Chance SHRA.

Saturday Night: Mainly VFR, with local IFR possible. Chance
SHRA.

Sunday: VFR. Chance SHRA, slight chance TSRA.

Sunday Night: VFR. Chance SHRA.

Monday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels...

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

Through Thursday...High confidence.

Light winds generally from the SW, though gusts nearing 20 kt
are possible for this afternoon in the eastern waters. Showers
possible over the waters Thursday into Thursday night. Patchy
fog also a possible tonight, particularly for the southern
waters. Seas to 2-3 ft.

Outlook /Thursday Night through Monday/...

Friday through Friday Night: Winds less than 25 kt. Chance of
rain showers.

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

Saturday Night: Winds less than 25 kt. Rain showers likely,
slight chance of thunderstorms.

Sunday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain showers, slight chance of thunderstorms.

Sunday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain showers, slight chance of thunderstorms.

Monday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Slight chance of rain showers.

&&

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

&&

$$

DISCUSSION...Hrencecin
AVIATION...Mensch
MARINE...Hrencecin