BOX issues Area Forecast Discussion (AFD) at Aug 3, 7:28 AM EDT965
FXUS61 KBOX 031128
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
728 AM EDT Mon Aug 3 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.
- After a quiet Tuesday unsettled weather returns mid week through
the weekend with periods of showers and storms.
&&
.DISCUSSION...
KEY MESSAGE 1...A cold front brings the return of heavy rain and
gusty winds Monday.
An anomalously deep upper trough digging into the Ohio Valley will
become cutoff as the broader longwave trough axis works its way
slowly east. Its trough axis will cross over southern New England
Monday night into Tuesday ushering in a much quiet and drier period.
Before that, however, we'll be dealing with a very moist and dynamic
system for the next 18-24 hours. This, as the shortwave and surface
reflection pull copious amounts of moisture north into New England
on strengthening SW flow (PWATs 2+ inches) with a 40-55 kt LLJ
strengthening as it's core moves over the Cape and islands.
Fortunately, even though BUFKIT soundings show 55kts down to about
925mb, the low level inversion should keep the worst aloft.
Regardless, it will be a gusty day, especially over southeast MA.
While some brief stronger gusts can't be ruled out, they are more
than likely to top out around 40 mph on Cape Cod.
Regardless of its impact at the surface, said LLJ will certainly act
as a strong forcing mechanism for our heavy rain. This together with
divergence aloft/placement beneath the RRQ of an upper jet will lead
to broad, deep layer ascent and widespread rain showers and
thunderstorms. Continuing to expect an initial round of moderate to
heavy rain showers this morning into the afternoon which has already
begun to materialize. The atmosphere is primed for some heavy
downpours and while we can't nail down exactly who will see these
downpours, any convection would lead to a better chance of those
higher rain rates hinted at by the HREF (low probability of as much
as 1+/hr).
There's unlikely to be a real break in the showers and embedded
thunderstorms but any pockets of clearing skies between showers may
lead to increased instability parameters and a better chance for one
of these thunderstorms to become severe as a final source of forcing
arrives in the evening in the form of a cold front. Any storms that
do get going will be in an environment with 30-45 kts of 0-6km bulk
shear meaning potential for organization and some damaging wind
potential.
When all is said and done (ending in western MA by 8pm, eastern MA
by midnight) a widespread 0.5 to 1.5 inches of rain is expected.
That being said, convective enhancement and potential for training
thanks to boundary-parallel mean flow mean that localized areas
could see significantly more, on the order of 3-4 inches. This
amount, especially if it falls in a short period, may lead to street
flooding and even isolated flash flooding situations. However, we
don't expect a widespread flash flooding risk with this system.
KEY MESSAGE 2...After a quiet Tuesday unsettled weather returns mid
week through the weekend with periods of showers and storms.
After a beautiful, mostly sunny, less humid day on Tuesday under
high pressure ridging, unsettled weather returns Wednesday into the
weekend. A broad mid level trough sets up over the eastern U.S. with
several shortwaves rotating through the base of the broader trough
and this will bring periodic rain and thunderstorm chances each day,
especially in the afternoon/evening.
&&
.AVIATION /12Z MONDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
12Z TAF Update:
Today: Moderate confidence.
IFR/LIFR in RA/+RA through the day. Embedded storms possible
within the first few rounds of rain 12-21Z. Another round of
scattered thunderstorms likely pushes through from west to east
19Z-00Z 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.
Monday night: High confidence.
SHRA/TSRA will be pushing out of eastern terminals between 00-03Z
leaving VFR conditions with light W wind.
Tuesday: High confidence.
VFR. Winds 5-10 kts, first W then becoming SW after 18Z.
KBOS Terminal...Moderate confidence in TAF.
Expect steadiest precipitation between 14-18Z with intermittent
SHRA thereafter. Low confidence in TSRA, but thunder will be
possible for the duration of the day.
KBDL Terminal...Moderate confidence in TAF.
Outlook /Tuesday 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 into early this 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 is in effect for the south coast and
islands Tuesday. 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 /Tuesday 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 until 9 PM EDT this evening for MAZ023-024.
RI...High Surf Advisory until 9 PM EDT this evening for RIZ006>008.
MARINE...Small Craft Advisory until 5 PM EDT this afternoon for ANZ230-
236.
Small Craft Advisory until 5 PM EDT this afternoon for ANZ231-
251.
Small Craft Advisory until 2 AM EDT Tuesday for ANZ232>234.
Small Craft Advisory until 2 PM EDT Tuesday for ANZ235-237.
Small Craft Advisory until 2 PM EDT Tuesday for ANZ250-254.
Small Craft Advisory until 8 PM EDT Tuesday for ANZ255-256.
&&
$$
DISCUSSION...BW
AVIATION...BW/RM
MARINE...BW
Source:
BOX issues Area Forecast Discussion (AFD) at Aug 3, 7:28 AM EDT----------------
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