241
FXUS61 KBOX 270559
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
159 AM EDT Mon Jul 27 2026

.WHAT HAS CHANGED...
Refined shower chances and flash flood potential through the
upcoming week.

&&

.KEY MESSAGES...

- Low-impact weather through Monday night. A few thunderstorms
  are possible Monday afternoon across western portions of
  southern New England.

- Temperatures on the lower end of seasonable as chances for
  prolonged rainfall return through Wed (possibly into Thurs).
  Monitoring for increasing chances of localized heavy rainfall
  and potentially flash flooding.

&&

.DISCUSSION...
KEY MESSAGE 1...Low-impact weather through Monday night. A few
thunderstorms are possible Monday afternoon across western portions
of southern New England.

A weak area of low pressure continues to spin southeast of
Nantucket, maintaining low clouds and occasional light precipitation
across the outer Cape and Islands. While not the best beach day
there, a High Risk for rip currents continues through this evening
for east-facing beaches of Cape Cod and Nantucket. Elsewhere, most
of southern New England enjoys sunshine and comfortable conditions.
The remainder of today through tonight will be relatively quiet.
Lingering low-level moisture from northeasterly flow combined with
light winds and mostly clear skies overnight may allow for patchy
fog to develop in the typical low-lying and river valley locations
of eastern Massachusetts. Overnight lows fall into the 50s inland
and the lower 60s along the immediate coast, which is seasonably
cool for late July.

Monday will feature seasonable temperatures, with highs in the lower
to middle 80s inland and upper 70s along the coast. A shortwave
trough dropping into the Northeast, along with an embedded 850-700mb
disturbance, will provide enough forcing for isolated to scattered
showers and thunderstorms during the mid to late afternoon,
primarily west of the Connecticut River Valley. PWATs increase to
around 1.3 inches, near to slightly above climatological normals but
not especially anomalous. While a few thunderstorms may produce
locally heavy downpours, rainfall amounts should generally remain
modest, with isolated localized totals approaching one-half inch.
Flash flooding is not anticipated, as 3-hour flash flood guidance
remains around 2.5 to 3.0 inches. Instability increases to around
800-1200 J/kg Monday afternoon, but weak deep-layer shear (generally
less than 30 kt) should limit storm organization. As a result,
convection is expected to remain isolated and pulse-like, with many
locations remaining dry. The highest PoPs therefore remain focused
west of the Connecticut River. CSU machine-learning guidance also
keeps the better severe-weather signal west of eastern New York.
While severe weather appears unlikely, the primary hazards with any
storms will be cloud-to-ground lightning and brief, locally heavy
rainfall.

Monday night, any lingering convection will diminish during the
evening. Southwesterly flow aloft then increases moisture, with
PWATs climbing toward 1.5 inches. Low clouds become more widespread
overnight, and scattered light showers may begin to develop ahead of
a more unsettled pattern on Tuesday. Overnight temperatures remain
mild, holding in the 60s.

KEY MESSAGE 2...Temperatures on the lower end of seasonable as
chances for prolonged rainfall return through Wed (possibly into
Thurs). Monitoring for increasing chances of localized heavy
rainfall and potentially flash flooding.

Guidance continues to hone in on a low pressure system pushing
into New England by Wednesday, but a mid-level trough
accompanied by several embedded shortwaves will brings chances
for prolonged rainfall later Tuesday into Wednesday... possibly
lingering into Thursday. There continues to be a strong signal
for PWATs 120-170 percent of normal to advect into the region by
Tuesday, with deterministic guidance on the extreme high end of
that range. The ECMWF and it`s ensemble continue to be the most
aggressive of the guidance suite. Not only is it favoring a
slower progression of the low as well as favoring more of the
near-shore/coastal track, but it`s also indicating the low could
deepen much further than the GFS or CMC ensembles are
indicating. Soundings continue to exhibit the textbook
environment for efficient rain processes with deep warm cloud
depths aligned with instability and slower mid-level wind
speeds, which would create an environment for training storms.
ECMWF ensemble probabilities show 50-80% chance for 1.0"+/24
hours Tue into Wed across southern New England and 10-30% for
2.0"+/24 hours across the CT River Valley, and the deterministic
ECMWF mirrors those locations with around 2.0"/24 hours as
well. Combined with the enhanced forcing of the low, the higher
PWATs and potential for training, the threats for localized
heavy rainfall and potentially flash flooding are continuing to
be monitored. Unfortunately, there still remains some
uncertainty in the guidance regarding where exactly the low
could track, with the Canadian and GFS (and their ensembles)
indicating the low moving further south near NYC and/or off our
southern waters. Another large question that remains is where
the heaviest rain bands will set up given the timeframe is still
too far out to utilize the hi-res guidance.

Otherwise, high temperatures are expected to remain on the
lower end of seasonable, even dipping to slightly below normal
at times given 850mb temperatures hovering around +12C to +14C
through mid- week.

&&

.AVIATION /06Z MONDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...

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

06z TAF Update:

Through 12Z...Moderate confidence (ceilings on Cape and patchy
fog location)

Mainly VFR conditions with the exception of the Cape and Islands
where there are still low clouds resulting in IFR cigs and patchy
fog. Patchy fog possible around the eastern terminals with a
risk for it to reach PVD after 08Z. Fog should dissipate around
sunrise or just after sunrise. Lower cloud likely scatter/exit
the Cape/Islands 12-15Z. Light and variable winds for interior
and N/NNE less than 8 kts for east terminals.

Monday...High confidence. (moderate for timing of VFR for Cape
terminals)

Lower IFR ceilings should be scattered out for Cape and Islands
by 15Z otherwise VFR today. ESE to SE winds 5-10 kts. Low chance
(< 25%) for an isolated shower or thunderstorm after 18Z for
western terminals (BDL). Too low in coverage to have anything
more than a VCSH in there right now.

Monday Night...Moderate confidence.

VFR conditions to start with the general trend being
deteriorating ceilings toward low end VFR/MVFR, with localized
IFR/LIFR ceilings possible. Still lower confidence in the
timing of the lower ceilings. Widely scattered showers possible
overnight. Potential for widespread precipitation increases for
Tuesday. Light S winds.

KBOS Terminal...High confidence.

KBDL Terminal...High confidence.

Outlook /Tuesday through Friday/...

Tuesday: Mainly VFR, with areas MVFR possible. Breezy.
Scattered SHRA, isolated TSRA.

Tuesday Night: Mainly VFR, with local IFR possible. Breezy.
Scattered SHRA, isolated TSRA, patchy BR.

Wednesday: Mainly MVFR, with areas IFR possible. Breezy. SHRA,
slight chance TSRA, patchy BR.

Wednesday Night: Mainly VFR, with areas MVFR possible. Breezy.
SHRA likely, chance TSRA.

Thursday: VFR. Breezy. Chance SHRA, slight chance TSRA.

Thursday Night: VFR. Chance SHRA, slight chance TSRA.

Friday: VFR. Slight chance SHRA, slight chance TSRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Through Tuesday...High confidence.

Light winds and seas 1-4 ft through Monday. Increasing winds
and seas for Sunday; however, below SCA. NE winds 10-15 kts
with gusts to 20 kts. Light NE to SE winds Monday.

Seas increase late Tuesday into Wednesday with SCA conditions
becoming more likely from winds and increased seas.

Increased risk for rip currents today with the greatest risk
for the east-facing beaches/coastline.

Outlook /Tuesday through Friday/...

Tuesday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain showers, chance of thunderstorms, patchy fog.
Local visibility 1 to 3 nm.

Tuesday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of seas approaching 5 ft. Scattered
rain showers.

Wednesday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Seas up to 5 ft. Rain showers likely, slight
chance of thunderstorms, patchy fog.

Wednesday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas up to 5 ft. Rain showers likely, slight
chance of thunderstorms.

Thursday: Winds less than 25 kt. Areas of rough seas. Chance of
rain showers, slight chance of thunderstorms.

Thursday Night: Winds less than 25 kt. Areas of rough seas.
Slight chance of rain showers, slight chance of thunderstorms.

Friday: Winds less than 25 kt. Seas up to 5 ft.

&&

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

&&

$$

DISCUSSION...Dooley/McMinn
AVIATION...Mensch
MARINE...Dooley/McMinn