Old Res Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 291823
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
223 PM EDT Fri May 29 2026

.WHAT HAS CHANGED...
Upgraded the Wind Advisory to a High Wind Warning for Cape Cod and 
Nantucket. Expanded the Wind Advisory to include all of Eastern 
Massachusetts and Rhode Island.

&&

.KEY MESSAGES...

- Low pressure system brings rain and areas of strong to damaging 
  winds tonight and Saturday. 

- Cooler than normal temperatures early next week with hit-or-
  miss shower/thundershower chances during the daytime hours 
  Monday and Tuesday. 

- Monitoring possible offshore low development around midweek,
  which could pass far enough south to allow for warming
  temperatures, or lead to a continuation of cooler than normal
  temperatures and possible rains with a closer pass.


&&

.DISCUSSION...
KEY MESSAGE 1...Low pressure system brings rain and areas of strong 
to damaging winds tonight and Saturday. 

Highly amplified pattern results in an anomalously strong albeit 
quick-hitting storm system tonight and Saturday. System will bring 
periods of heavy rain and showers, but the bigger issue will be a 
period of strong winds on Saturday.

A period of strong to damaging winds continues to be of greatest 
concern with this system. Synoptically, strong winds will stem from 
a deepening area of low pressure and associated pressure rises as it 
pulls away. Guidance shows 3hr pressure rise values of 5-7 mb/3hr as 
the system winds up and pulls off the coast of MA Saturday 
afternoon. The latest HREF ensemble guidance greatly expanded the 
area of gusts 35-45 mph and now shows the potential isolated higher 
gusts (45-55 mph) well into the I-95 corridor. This seems reasonable 
given that the LLJ jet more likely shifts across east southern New 
England through the day. The degree of mixing has come into much 
better agreement among guidance with 1000-950mb lapse rates likely 
increasing to 8-10C/km Saturday afternoon! For these reasons, the 
Wind Advisory has been expanded further inland. Part of the 
rationale in expanding the advisories inland is increasing 
confidence in an apparent trend towards greater mixing in the lowest 
100mb. Somewhat unusually, the core of the LLJ will be fairly close 
to the surface (between 925 and 850mb). Thus, the mixed layer won't 
have to be as deep to tap into the strong winds. The other 
change was to issue a High Wind Warning for the Cape and 
Nantucket where the LLJ will slightly stronger on the order of 
55-65kt. 

In terms of precipitation with this system we're looking at 
periods of showers that become more widespread after the evening
commute into this evening and tonight. There could be a few 
embedded weak storms or downpours with some meager mid-level 
instability. Quick lull in the activity gives way to more 
widespread rainfall Saturday morning as low pressure rotates 
through. Showers slowly diminish as the low exits further 
offshore mid to late afternoon. It's possible for showers to 
linger as late as the evening for the outer Cape/Islands. 

For rain totals, ensembles range rain totals 0.20" to 1.1" across 
the 25th to 75th percentile range with the higher amounts favored in 
northeast MA. While we are already in cool troughy flow, the passage 
of this deep upper low will shift a core of anomalously cold air 
aloft across the region Saturday. This will bring us a fairly cool 
day for late-May with highs in the upper 40s and low 50s. With the 
timing of the colder air and the showers, some model guidance hints 
at potential for a few snowflakes mixing in at the higher 
elevations. If the cold air arrives in a similar period of better 
precip rates some spots may cool enough to mix in some wet flakes. 
The NAM has shown the strongest signal for this, but also shows a 
colder airmass in place with a wider footprint compared to other 
guidance (Temps - upper 30s). So overall, can't rule out a wintry 
mix in the highest elevations of the interior although little impact 
expected. 

KEY MESSAGE 2...Cooler than normal temperatures early next week
with hit-or-miss shower/thundershower chances during the 
daytime hours Monday and Tuesday. 

Ensemble means continue to point to 500 mb troughing governing 
Southern New England's weather late this weekend into a good portion 
of next week, in a slow-evolving, blocky 500 mb pattern. There are a 
couple of upper level lows that will be moving into and/or 
meandering around Southern New England.

The first of these closed upper lows settles in Sunday night and 
into Monday, before moving offshore into Tuesday. Really not much 
change in terms of sensible weather each day, with diurnally-driven, 
hit-or-mostly-miss showers or low-topped thundershowers popping up 
with the cool pocket of air aloft associated with the closed low. 
This type of showery pattern also means no one area can be 
guaranteed to be rain-free, but there will be several dry periods in 
between. Temperatures trend slightly cooler than early-June normals, 
with values in the mid 60s to mid 70s with comfortable humidity 
levels. Climatological normals run around the mid/upper 70s for 
highs.

KEY MESSAGE 3...Monitoring possible offshore low development 
around midweek, which could pass far enough south to allow for 
warming temperatures, or lead to a continuation of cooler than 
normal temperatures and possible rains with a closer pass.

More uncertainty during the mid to latter part of the upcoming 
workweek with regard to the next surge of vort energy diving 
southward from the Canadian Maritimes. This feature digs south/south-
southwest to a position generally south of 40N/70W into a wound-up, 
closed mid/upper circulation and associated surface low. The 
placement of this cyclone, when it begins to exit further offshore 
and if we see any rainy conditions associated with its 
north/northeast passage are all unclear at this time. Besides just 
rain chances, this feature's location will also dictate temperatures 
as some of the further-offshore/drier solutions bring in shortwave 
ridging aloft north of it extending into New England, with potential 
for drier weather and a considerable warmup in temps for at least 
interior Southern New England. On the other hand, a closer pass to 
Southern New England would bring cooler than normal temperatures and 
perhaps some light rains. We offered to not make many changes to NBM 
at this point and let trends dictate subsequent adjustments to the 
forecast.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
Forecaster Confidence Levels...

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

18z TAF Update... 

Today...High confidence.

Mainly VFR today outside the risk for a few showers mainly
after 20z/21z. NW winds may gust to around 20 knots or so into
mid afternoon...But sea breezes should kick in by mid afternoon
along portions of the immediate coast. 

Tonight and Saturday...Moderate confidence.

VFR this evening outside scattered showers especially east of 
the CT River and particularly eastern MA. Low risk for a rumble 
or two of thunder. We should then have a lull in the activity 
after midnight before the upper level low drops south. A shield 
of rain will drop south with the focus east of the CT River 
Valley in the 9z to 15z Sat time frame. Conditions will lower to
MVFR with pockets of IFR conditions possible. too. N-NE winds 
will increase with gusts on the order 30-45 knots with the 
strongest of those along the coast. We may even briefly see some wet
snow flakes mix in across the highest terrain. Gradual
improvement expected Saturday afternoon and evening from west to
east. 

KBOS...High confidence in TAF but some uncertainty lingers on 
the specific timing of the sea breeze... likely between
1730-18z.

KBDL...High confidence in TAF.

Outlook /Saturday through Wednesday/...

Saturday: Mainly VFR, with local IFR possible. Strong winds
with gusts up to 45 kt. Chance RA.

Saturday Night: VFR. Windy with local gusts up to 30 kt. 

Sunday: VFR. 

Sunday Night: VFR. Chance SHRA.

Monday: VFR. SHRA likely, chance TSRA.

Monday Night: VFR. Slight chance SHRA.

Tuesday through Tuesday Night: VFR. Chance SHRA.

Wednesday: VFR. Breezy. Chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Tonight...

Generally tranquil with wave heights between 1 and 3 feet for 
most of the waters. Winds from the NW between 5 and 15 mph with
gusts up to 20 mph. Winds and seas increasing from the north
early Saturday morning. 

Saturday into Saturday Night... 

Storm warning for all the waters except Narragansett Bay and
Boston Harbor where Gale Warnings are in effect on Saturday. A
a strong area of low pressure system tracks across the region 
bringing gusty N-NE winds.

Outlook /Saturday through Wednesday/...

Saturday: Moderate risk for storm force winds with gusts up to 
45 kt. Rough seas up to 13 ft. Chance of rain. 

Saturday Night: Low risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 12 ft. 

Sunday: Winds less than 25 kt. Local rough seas. 

Sunday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of
rain showers. 

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

Monday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain showers. 

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

Tuesday Night: Winds less than 25 kt. Local rough seas. Chance
of rain showers. 

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Wind Advisory from 8 AM to 8 PM EDT Saturday for MAZ004>007-
     012>021-023-026.
     High Wind Warning from 8 AM to 8 PM EDT Saturday for MAZ022-
     024.
RI...Wind Advisory from 8 AM to 8 PM EDT Saturday for RIZ001>008.
MARINE...Gale Warning from 2 AM to 8 PM EDT Saturday for ANZ230-236.
     Storm Warning from 2 AM to 8 PM EDT Saturday for ANZ231>235-
     237-250-251-254>256-280>283.

&&

$$

DISCUSSION...Loconto/FT
AVIATION...Frank/McMinn
MARINE...FT