Old Res Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 261126
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
726 AM EDT Sun Jul 26 2026

.WHAT HAS CHANGED...
Aviation discussion updated.

&&

.KEY MESSAGES...

- Mainly dry conditions expected today. Increased risk for rip 
  currents today, mainly for Cape Cod and Nantucket. 

- Periodic chances of scattered showers and thunderstorms early
  to mid week next week, potentially lingering into Thursday. 
  Increasing potential for heavy rain late Tuesday through 
  Wednesday with at least localized flash flooding possible.

&&

.DISCUSSION...
KEY MESSAGE 1...Mainly dry conditions expected today. Increased 
risk for rip currents today, mainly for Cape Cod and Nantucket. 


Mainly dry conditions expected today with weak high pressure 
overhead. Aloft, heights continue to fall today as a mid-level 
trough works into the region while a low pressure system passes well 
offshore. The only "impact" this system will have the region is 
bringing a stream of moisture brushing across mainly the southeast 
portions of MA. This has been prevalent in the low level moisture 
fields with easterly flow to reinforce it. Model soundings indicate 
a shallow layer of moisture at the surface with dry air above. 
Indicator for low clouds and perhaps some patchy drizzle in the 
highest coverage spots. The area that has the greater risk for 
seeing this is Nantucket and perhaps the outer most portion of the 
Cape. Aside from the clouds in some areas, it will be a mainly dry 
day with a northeasterly breeze for the eastern coastal areas. 
Temperatures lean slightly below normal in the upper 70s to low 80s 
for the interior and mid to upper 70s in the eastern and coastal 
areas. Areas such as Nantucket may struggle to get out of the low 
70s today if the clouds stay persistent. 

Prolonged easterly component flow will lead to an increased risk for 
rip currents today. The greatest risk will be for the east-facing 
beaches on Cape Cod and Nantucket; however, there is also an 
elevated risk for the south coast and remaining east-facing beaches. 
Nantucket was added to the current Rip Current Statement. 

KEY MESSAGE 2...Periodic chances of scattered showers and 
thunderstorms early to mid week next week, potentially 
lingering into Thursday. Increasing potential for heavy rain 
late Tuesday through Wednesday with at least localized flash 
flooding possible.

A mid-level trough positions across the region through much of the 
week. A series of shortwaves embedded in the flow are expected to 
progress across the region through the week supporting periodic 
chances for showers and thunderstorms. 

The first embedded shortwave likely moves through late Monday into 
Tuesday. WAA and moist advection occur ahead of the shortwave during 
the day Monday resulting in a warmer day in the low to mid 80s and 
upper 70s for coastal areas. There is still potential for scattered 
showers and thunderstorms late afternoon/evening though guidance is 
still lacking agreement on the coverage and convective potential. 
This keeps us at probabilities less than 40% still with west/central 
southern New England being more favored. 

Model guidance has remained generally consistent with a deepening 
trough into Tue/Wed with a strong signal for above normal moisture 
(120-170% of normal) advecting into the region by Tuesday. Most 
deterministic and ensemble solutions have now come on board with the 
development of a low pressure system. In many solutions now, the low 
pressure is quite anomalous in magnitude for late-July. Combined 
with the enhanced forcing from the low, this is a set-up for heavy 
rain potential. However, some model guidance has been more 
aggressive than others. The ECMWF and its ensemble members have 
shown the strongest signal for heavy rain/flash flooding potential 
with a stronger low pressure system tracking in the vicinity of Long 
Island, toward eastern MA/Cape Cod in many of its solutions. It also 
leans on a slower progression of the trough as well. Soundings 
exhibit the textbook environment for efficient rain processes with 
deep warm cloud depths aligned with instability. ECMWF ens probs 
show 40-75% probability for 1+ of rainfall later Tue into Wed and 10-
40% for 2"+ across a good portion of southern New England. The 
deterministic guidance over the last 24 hours of runs has showed a 
large footprint of 2"+ amounts across the region in that same 
timeframe. With weak steering flow this support slow storm motions 
of embedded heavy rain and thunderstorms. This combined with 
potential for training for training will increase the risk for flash 
flooding with more "scattered" occurrences as opposed to an 
isolated case or two. While the recent deterministic runs of the
Canadian and GFS have gone more on board with the heavy rain 
potential, their ensemble guidance still have shown solutions 
leaning toward a weaker low and differing track resulting 
leading to lesser rainfall amounts. There is still a signal for 
localized heavy rain/flash flooding within these solutions; 
however, they are more isolated or localized. There is still 
uncertainty; however, we are at least seeing increasing 
confidence for widespread rain with at least localized heavy 
downpours/flash flooding possible in spots, particularly later 
Tue through Wed. Depending on the track of the low, showers may 
linger through Thurs. 

Temperatures lean seasonably cool to slightly below normal at times 
through the week ranging in the mid 70s to low 80s.

&&

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

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

12z TAF Update...

Today...High confidence overall (Moderate for cigs in east).

VFR for most. A stream of moisture has started to brush across 
the Cape and Nantucket today resulting increased cloud cover.
MVFR ceilings have already developed at ACK, and these will
likely continue to spread onto the Cape. Confidence is
relatively moderate with regards to how far on the Cape these
ceilings get, along with the potential development of IFR
ceilings there and on ACK. Consistent with the previous
forecast, though, is that the risk for IFR is higher at ACK than
the Cape terminals.

E winds for the interior at 5-10 kts. NE winds for east coast 
terminals 8-12 kts, few gusts to 20 kts possible for 
Cape/Islands.

Tonight...High confidence overall (Moderate for cigs for
Cape/Islands).

As ceilings have already lowered for ACK, we will continue to
watch ceilings for the rest of the Cape/Islands terminals. If
these lower today, expect MVFR/IFR cigs to continue overnight 
for those areas. Greatest risk for IFR cigs continues to be at 
ACK with patchy FG possible. VFR elsewhere. Light northerly to 
VRB winds.

KBOS Terminal...Moderate Confidence in TAF. 

Only moderate confidence due to the low end potential for a
patch of lower MVFR cigs to develop offshore of the BOS 
terminal through 14Z this morning. This is very low probability
as it has still not shown up on satellite as of this 12z TAF update.
Will have to keep an eye out for development this morning.

KBDL Terminal...High confidence in TAF.

Outlook /Monday through Thursday/...

Monday: VFR. 

Monday Night: VFR. Slight chance SHRA.

Tuesday: Breezy. Chance SHRA, slight chance TSRA.

Tuesday Night through Wednesday: Breezy. SHRA, chance TSRA.

Wednesday Night: MVFR/IFR conditions possible. Breezy. SHRA
likely, slight chance TSRA.

Thursday: Mainly VFR, with local MVFR possible. Breezy. 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 /Monday

Monday through Monday Night: Winds less than 25 kt. 

Tuesday: Winds less than 25 kt. Seas locally approaching 5 ft. 

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

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

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

Thursday: Winds less than 25 kt. Areas of rough seas. Chance of
rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...High Risk for Rip Currents through Monday morning for MAZ022-024.
RI...None.
MARINE...None.

&&

$$

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