Old Res Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 022001
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
401 PM EDT Sun Aug 2 2026

.WHAT HAS CHANGED...
No significant changes.

&&

.KEY MESSAGES...

- A cold front brings the return of heavy rain and gusty winds
  Sunday night and Monday. Localized flash flooding possible
  Monday. 

- Dry and less humid weather returns Tuesday 

- Weather pattern quickly becomes unsettled again by later Wednesday,
  continuing late week and into the weekend, with periods of 
  showers and storms, noticeably more humid as well. 


&&

.DISCUSSION...
KEY MESSAGE 1...A cold front brings the return of heavy rain and 
gusty winds Sunday night and Monday. Localized flash flooding
possible Monday. 

A potent shortwave trough and anomalous low track across the Ohio 
Valley toward the northeast. A strong 30-45 kt LLJ pushes northward 
into the region tonight helping facilitate lift and advection of an 
anomalous plume of moisture (2-2.5 SD above normal). Positioning 
under the upper level jet, an incoming cold front, and marginal 
instability will provide ample support for widespread heavy rainfall 
Monday. 

Tonight, expect a scattered showers perhaps a weak 
thunderstorm as synoptic ascent/moisture increases ahead of the 
approaching system. Majority of the rain will fall Monday morning 
through Monday evening. This can be divided into two "rounds", 
categorized by timing and prominent hazard. The first "round" will 
be showers and embedded thunderstorms pushing across southern New 
England in the morning through mid-afternoon timeframe. The heaviest 
rain rates will be driven by the location of embedded thunderstorms; 
therefore, the location of the heaviest rainfall will be less 
certain. The HREF shows some isolated low probabilities for rain 
rates 1" or greater during the day Wednesday. The HREF PMM 3 hour 
amounts range from 0.75 to 1.75". With deep moisture/lift efficient 
rainfall is supported. This is where localized to scattered 
flash flooding will be a concern, especially in our areas that 
are still fairly saturated from last week's rain event and the
usual poor drainage areas. The second "round" will be the 
potential for a round of scattered thunderstorms pushing from 
west to east mid afternoon through the evening. There is lower 
confidence in this as it will depend on how much clearing we get
after the first round of showers and thunderstorms. If we can 
get a period of clearing with breaks of sun this will allow the 
atmosphere to destabilize. The unstable/moisture environment 
combined with the incoming cold front and sufficient shear from 
the LLJ would provide an environment support of even a few 
strong to severe thunderstorms if the atmosphere can recover 
from the first round of rain. The primary hazards within any 
stronger storms will be strong downdrafts/gusts and brief heavy 
downpours.

In terms of rain totals, the specific locations of the heaviest 
rainfall will highly depend on where the heavier rates/thunderstorms 
track. Based on global and high-resolution ensemble guidance, many 
areas will see a range of 0.75-2.0" with potential for localized 3". 
HREF ensemble maxes even show potential for close to 4" in localized 
spots. These higher values will be quite localized and will be 
driven by the location of embedded thunderstorms.  

The last thing to address is the gusty winds. With strong winds not 
far from the surface within the strong 30-45 kt LLJ, gusty SW winds 
are likely Monday. Ensemble means show gusts in the 20-35 mph 
range. With the core of the stronger winds positioned across 
east and especially southeast MA, these areas will have the 
greater risk of seeing the higher end of that range. However, 
there is an increasing risk for higher gusts in recent guidance.
A big factor will be if we clear enough from the first push of 
rain to promote mixing, especially in the east/southeast areas 
under the strong core of winds aloft. If winds mix efficiently, 
40 mph gusts are possible in the afternoon in areas (E/SE MA).  

KEY MESSAGE 2...Dry and less humid weather returns Tuesday 

Post frontal airmass overspreads the region Tue with good column 
drying, as PWATs plummet to less than an inch. Dry weather, plenty 
of sunshine, dew pts 55-60 and seasonably warm highs of 80-85 
expected. Easily the pick of the week, enjoy! 

KEY MESSAGE 3...Weather pattern quickly becomes unsettled again by 
later Wednesday, continuing late week and into the weekend, with 
periods of showers and storms, noticeably more humid as well. 

Remnant mid level closed low and sub-tropical moisture over the 
southeast states, begins to advect up the eastern seaboard into SNE 
beginning late Wed/Wed night. This moist flow into SNE may persist 
into late week and the weekend, as subtropical ridge develops across 
the western Atlantic, in concert with upstream trough across the 
western Great Lakes. This will translate to an unsettled weather 
pattern for SNE, in the form of periodic showers and thunderstorms 
chances through the period, probably greatest during the 
afternoon/early evening, in response to max heating. 


&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...

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

18z TAF Update: 

Today: High confidence.

VFR conditions with SCT to BKN cloud decks this afternoon. SSW 
winds around 8-12 kts with occasional gusts to 20 kt.


Sunday Night: Moderate confidence. 

Ceilings fall to IFR from south to north after 00Z with LIFR
possible in areas after 03Z. Scattered -SHRA develop 00-02z 
with potential for a band of more moderate showers to push from 
south to north between 06-10Z. Embedded thunder is possible, but
too low confidence to include in TAF at this time. LLJ pushes 
in from the south after 06Z, so added wind shear to Cape 
terminals, BOS, and PVD. 

Monday: Moderate confidence. 

IFR/LIFR in RA/+RA through the day. Embedded storms possible 
within the first few rounds of rain 12-21Z. Included in TAFs as
PROB30s until we have higher confidence in the
timing/probability of storms. Another round of scattered
thunderstorms likely pushes through from west to east 19Z-02Z
ahead of the approaching cold front. Wind shear likely continues
in the east/southeast terminals during the day. SW winds 10-20 
kts with gusts 20-30 kts. Could see period in the afternoon 
that winds gust 25-35 kts for the east and especially SE 
terminals if we clear out before the early evening round of 
storms.

KBOS Terminal...Moderate confidence in TAF. 

KBDL Terminal...Moderate confidence in TAF.

Outlook /Monday Night through Friday/...

Tuesday through Tuesday Night: VFR. 

Wednesday through Wednesday Night: VFR. Slight chance SHRA.

Thursday through Thursday Night: VFR. Breezy. Slight chance
SHRA, slight chance TSRA.

Friday: VFR. Breezy. Chance SHRA, chance TSRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Winds and seas increase late tonight into early Monday morning 
across the southern and eastern waters eventually increasing
across the northern waters. Seas 5-9 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. Can't rule out a few isolated gusts near Gale-force late
morning-afternoon if winds mix down from the low level jet 
overhead. SCAs are in effect for all the coastal marine zones. 
Elevated seas will keep SCAs around through Tuesday for the 
southern waters.

A high surf advisory has been issued for the south coast and
islands Monday. A strong 35-45 kt southerly low level jet will
help build waves 5-9 ft across the waters of RI and south of
MVY-ACK Monday. Rough surf and strong rips are likely to linger
into Tuesday. Will have to watch this as Tuesday is shaping up
to be an ideal beach day. 

Outlook /Monday Night through Friday/...

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

Tuesday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. 

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.

Thursday Night through Friday: Winds less than 25 kt. Areas of
seas approaching 5 ft. 

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...High Surf Advisory from 7 AM to 9 PM EDT Monday for MAZ023-024.
RI...High Surf Advisory from 7 AM to 9 PM EDT Monday for RIZ006>008.
MARINE...Small Craft Advisory from 5 AM to 5 PM EDT Monday for ANZ230-
     236.
     Small Craft Advisory from 8 AM to 5 PM EDT Monday for ANZ231-
     251.
     Small Craft Advisory from 8 AM Monday to 2 AM EDT Tuesday for 
     ANZ232>234.
     Small Craft Advisory from 5 AM Monday to 2 PM EDT Tuesday for 
     ANZ235-237.
     Small Craft Advisory from 8 AM Monday to 2 PM EDT Tuesday for 
     ANZ250-254.
     Small Craft Advisory from 5 AM Monday to 8 PM EDT Tuesday for 
     ANZ255-256.

&&

$$

DISCUSSION...Mensch/Nocera
AVIATION...Mensch
MARINE...Mensch/Nocera