Old Res Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 012032
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
432 PM EDT Sat Aug 1 2026

.WHAT HAS CHANGED...
Introduced a slight chance of showers/t-storms this afternoon though 
most will stay dry.

&&

.KEY MESSAGES...

- Mainly dry conditions through Sunday with the exception of an
  isolated shower or storm today. Unsettled weather arrives 
  Sunday night.

- Cold front brings showers and thunderstorms with heavy rain Monday.
  Street flooding is possible. A brief break on Tuesday before 
  turning active and unsettled again Wednesday.

- Still unsettled late in the week with periods of showers and 
  storms. 


&&

.DISCUSSION...
KEY MESSAGE 1...Mainly dry conditions through Sunday with the 
exception of an isolated shower or storm today. Unsettled weather 
arrives Sunday night.

Day Cloud Phase satellite imagery shows development of shallow 
cumulus this afternoon with a few isolated showers driven by 
the diurnal heating. Expect any showers to diminish around 
sunset. Quiet weather overnight with weak high pressure 
overhead. Moisture advects in within the southerly flow tonight 
similar to last night. Model soundings show a signal for 
moisture in the low levels under an inversion with the strongest
signal for the south coast and Cape/Islands. This will increase
the potential for stratus and perhaps some fog. HREF has shown 
potential for the stratus to push northward after midnight 
although there is lower confidence how far north it extends. 
Patch fog is also possible in the CT Valley overnight. 

Similar pattern for Sunday with the mid-level ridge and surface high 
offshore as a shortwave trough to the west of the region. Weak high 
pressure stays put over the area keeping conditions mainly dry. 
Can't rule out an isolated shower or storm in the afternoon, mainly 
in western MA. High temperatures range in the low to mid 80s for 
most with southerly winds. Skies will be mainly cloudy. 

A low pressure system moves through the Ohio Valley as the mid-level 
trough pushes further east across western southern New England 
Sunday night. An accompanying LLJ pushes northward into the 
region. This will help advect in a plume of above normal 
moisture into the region ahead of the approaching trough. A mix 
of isentropic lift and jet dynamics will provide synoptic 
support for rain developing Sunday night. There is a signal for 
marginal instability which may support a few embedded moderate 
showers or brief downpours in localized areas with the higher 
risk for western MA/CT. The higher risk for the heavier rainfall
will be Monday (see next key message). 

KEY MESSAGE 2...Cold front brings showers and thunderstorms with heavy rain 
Monday. Street flooding is possible. A brief break on Tuesday before 
turning active and unsettled again Wednesday.

Still monitoring the potential for heavy rain into the early and 
possibly into the middle portion of next week. This rain and 
embedded thunderstorms looks to be forced by an injection of 
subtropical moisture on SWly low-level jet maxima of upwards of 45 
kt Monday, ahead of an anomalously strong mid-level low stalling 
over the lower OH Valley Monday and remaining more-or-less in place 
into early next week. This strong meridional flow of air brings 
precipitable water values to 2-2.25", corresponding to anomalies 
which are 2 to 2.5 standard deviations above normal! A slow-moving 
south-to-north surface cold frontal boundary will interact with this 
subtropical moisture plume and favor rounds of showers and 
thunderstorms. Monday looks to be a washout with moderate (40-60%) 
model-ensemble probabilities of 24-hr rainfall totals at/over 
1", with very low (<10%) chances of 24-hr rain totals at/over 
over 2". Will have to watch for possible street and poor 
drainage flooding in heavy downpours, as well as rises on 
rivers, creeks and streams as USGS streamflow data over the last
7 days (e.g. coming out of the very wet stretch we've had of 
late) show most rivers running above- to well-above normal. 
WPC's excessive rainfall outlook shows as much as a Level 2 of 4
(Slight) Risk for Excessive Rainfall for Monday. While not a 
zero-risk, severe weather potential looks to be a more limited, 
secondary risk in the form of water-loaded downdrafts given the 
juiced airmass. 

It looks like on Tuesday that the northern end of the frontal 
boundary shifts the axis of highest PWAT values offshore, and allows 
for weak subsidence to return - put another way, it looks like 
Tuesday is a general minimum in rain chances, but it's still 
unsettled as the mid-level low to our south could still allow for 
northward-moving showers and storms in the northern Mid-Atlantic to 
clip portions of western Southern New England. A better chance for 
another round of showers and storms mainly into western/central 
Southern New England returns by Wednesday. All told a pretty muggy 
and unsettled weather pattern with several opportunities for 
showers and storms. 

Temperatures should run above normal, especially with regard to the 
low temps in a humid, muggy airmass. 


KEY MESSAGE 3...Still unsettled late in the week with periods of 
showers and storms. 

The mid-level low over the Ohio Valley weakens and washes out into 
Thursday. Unfortunately an active northern stream portion of the jet 
continues, so it still ends up looking unsettled with showers/storms 
which are too difficult to provide more distinct periods when they 
become more likely. With stronger mid-level westerly flow associated 
with the stronger northern stream, there could be the potential for 
some storms to become strong but whether or not this comes to 
fruition remains to be seen. Temperatures continue to run above 
normal as we move into late week. 

&&

.AVIATION /20Z SATURDAY THROUGH THURSDAY/...
Forecaster Confidence Levels...

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

18Z TAF Update: 

This Afternoon: High confidence. 

VFR. SW winds around 5-10 kt and sea breeze around 10 kts at 
BOS. Low chance for an isolated shower or weak storm through
00Z. Sea breeze kicks out of BOS 23-00Z returning to SSW flow. 

Tonight: Moderate confidence. 

VFR to start. Main challenge for tonight will be ceilings. There
is potential for re-development of a stratus deck across the
Cape/Islands potentially extending to the south coast closer to
03Z. This could bring a range of LIFR to IFR ceilings with FG
possible for the Cape/Islands. There is considerable 
uncertainty in the northward extent of this stratus deck. There 
is a low end potential for this deck to extend northward close 
to BOS after 09Z. Low ceilings appear in TAFs with higher 
confidence for the stratus (Cape/Islands) while the other 
terminals have either FEW/SCT decks hinting at the lower cigs 
for now. Will have to re-assess for the 00Z TAF. 

KBOS Terminal...Moderate confidence in TAF. 
Sea breeze this afternoon around 10 kts. Kicks out 23-00Z to SSW
flow less than 10 kts for remainder of night. SCT 4000-5000ft
decks this afternoon with an isolated shower possible. If a
shower were to develop it would more likely be west of the
terminal.

There is low probability for a stratus deck to extend north
enough to bring lower MVFR/IFR ceilings to or near BOS 09-13Z.
Confidence too low to include in TAF. Messaged as a FEW deck
at this time. Will need to monitor for a stronger signal for 00Z
TAF.


KBDL Terminal...Moderate confidence in TAF.

Potential for MVFR/IFR ceilings after 06Z through around 12Z
with BR. Confidence lower in the extent/coverage of a low 
stratus deck.

Outlook /Sunday through Thursday/...

Sunday: Mainly VFR, with local MVFR possible. Breezy. 

Sunday Night: MVFR/IFR conditions possible. Breezy. SHRA
likely, slight chance TSRA, patchy BR.

Monday: MVFR/IFR conditions possible. Windy with local gusts up
to 30 kt. SHRA, chance TSRA.

Monday Night: VFR. Breezy. Chance SHRA, slight chance TSRA.

Tuesday through Tuesday Night: VFR. Slight chance SHRA.

Wednesday: VFR. Chance SHRA, slight chance TSRA.

Wednesday Night: VFR. Slight chance SHRA, slight chance TSRA.

Thursday: VFR. 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.

Winds and seas below small craft advisory levels through
Sunday. Winds and seas increase late Sunday night into early
Monday morning across the southern and eastern waters. Seas
5-8 ft for the outer coastal waters, especially south. 5-7 ft
seas stretch into portions of the inner souther waters. SW winds
15-20 kts with gusts around 30 kts. SCAs have been issued for 
the southern and eastern waters included the Buzzards Bay, 
Vineyard Sound, and Nantucket Sound starting early Monday 
morning. Elevated seas will keep SCAs around through Tuesday for
the southern waters. 

Outlook /Sunday through Thursday/...

Sunday: Winds less than 25 kt. 

Sunday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Local rough seas. Chance of rain showers,
slight chance of thunderstorms, patchy fog. 

Monday: Moderate risk for Small Craft Advisory winds with gusts
up to 30 kt. Rough seas up to 9 ft. Rain showers likely, slight
chance of thunderstorms. 

Monday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Rough seas up to 8 ft. Rain showers likely,
slight chance of thunderstorms. 

Tuesday: Winds less than 25 kt. Local rough seas. Slight chance
of rain showers. 

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

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

Wednesday Night: Winds less than 25 kt. 

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 8 AM Monday to 2 AM EDT Tuesday for 
     ANZ232>234.
     Small Craft Advisory from 8 AM Monday to 2 PM EDT Tuesday for 
     ANZ235-237-254.
     Small Craft Advisory from 5 AM Monday to 8 PM EDT Tuesday for 
     ANZ255-256.

&&

$$

DISCUSSION...Loconto/Mensch
AVIATION...Mensch
MARINE...Loconto/Mensch