Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 150300
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1100 PM EDT Sat Sep 14 2019

.SYNOPSIS...
Line of light to moderate showers sweeping S New England this
afternoon. Expect additional shower activity to persist into
this evening preceding a cold front which will sweep offshore
into Sunday morning. Dry Sunday, pleasant, while some showers
are possible Monday. Thereafter, looking dry into the week with
pleasant weather, mild days and cool nights. By late in the
week a gradual warming trend develops.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...

1030 PM Update...

A band of showers continues from about Cape Ann SWwd across S
central Mass into N RI and NE and N central CT at 0230Z NE
regional 88D radar imagery. Also had some isolated
thunderstorms over the last couple of hours due to elevated
instability as noted on previous discussion, including at
KBOX around 0045Z.

With the best deep moisture in place along the S coast, should
see more showers/isolated thunder develop ahead of the
approaching cold front, so kept LKLY POPs mainly along S coastal
areas through daybreak, with some leftover showers lingering
into SE Mass and E central CT. Cold front looks to cross into NE
and central Mass into NW CT by around 12Z.

Temps will fall back a bit in the somewhat drier air as winds
slowly veer to W across N central/NW Mass during the pre dawn
hours, down to the mid 50s to around 60, ranging to the lower-
mid 60s elsewhere.

Have updated near term to bring conditions current.

Previous Discussion...

ThetaE axis collocated with deep layer moisture all the way
through H5 undergoing weak of moderate ascent courtesy of a
stretched mid-level vortmax. But just the initial wave. As
surmised earlier, still a fairly low level moist environment
beneath falling heights, cyclonic flow, some low level
convergent wind tendencies, and orographic support, all of which
preceding the main cold front over the E Great Lakes
accompanied by additional stretched mid-level vortmax energy,
there remains the chance of light to moderate showers going into
this evening. Keep with chance to likely PoPs. Some places have
already seeing upwards of a two to three tenths, not ruling
that out for other locations.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...

2 pm update...

Sunday into Sunday night...

Pleasant and dry Sunday, perhaps the return of light shower activity
overnight. Washing out with drier air, subsidence building from the
N with an associated 1020+ high. Surface cold front lingers SE just
offshore, some spot shower activity for Nantucket especially, will
go with Sunday morning chance PoPs then drying. Otherwise, pleasant
and dry, light W winds which should allow near-shore sea-breezes as
highs warm into the mid to upper 70s (the airmass aloft relatively
unchanged other than being drier). Mixing up to H9, some draw down
of faster winds, lower dewpoints especially into the 50s.

Amplifying H5 trof late into the overnight period with accompanying
vortmax dropping S, cyclonically rotating through. CAMs a bit more
robust on outcomes versus global guidance. Given the modest lift and
forcing along a reinforcing cold front, any continental-moist air-
mass to which consensus of guidance signal in some variation of
magnitude should squeeze out some light shower activity. Suggestion
of slight chance PoPs towards Monday morning seems warranted. High
confidence on cloud cover that should keep overnight lows mild in
the upper 50s to low 60s.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...

Highlights...

* Chance of showers Monday with a cooler start to the week
* Dry Tuesday through Friday
* Cooler than normal Tue-Thur, warming Friday into the weekend

Details...

Monday...

Low and mid level moisture associated with a passing
shortwave/front during the day Monday will bringing increased
cloud cover and the chance for rain showers. Some guidance
suggesting less coverage, keeping things mainly inland, but
we`ll stick with a slight chance of rain showers in the interior
early, shifting to the southeast coast by late afternoon and
evening. It`ll be the last we see of PWATs >1" until Friday.
Temperatures take a dip as mid level flow turns northerly. Highs
only reach into the upper 60s/low 70s. This starts off a string
of cooler days ahead.

Tuesday through Thursday...

Very pleasant, fall-like stretch of weather coming up for much of
the week. This is thanks to surface high pressure setting up
over New England with mid level ridging to our west. Dry NE/N
flow continues at the mid levels and the column dries out with
time...PWATs dropping below 0.5" by Thursday. Temperatures will
be quite cool, compared to average (highs 70-75, lows 54-59),
with H85 temps 3-5C and N/NE surface winds around that high.
Dropped the forecast highs a few degrees with this latest update
based on newest guidance; expecting highs in the 60s Tue/Wed,
warming a few degrees Thursday. Onshore flow along the east
coast will keep things a bit cooler there.

Friday and Saturday...

Forecast remains dry into next weekend, with temperatures warming
back into the 70s. This as the ridge shifts east over top of us.
Only wrinkle may be a slight chance for showers over the
interior sometime late Fri/Sat as a shortwave rotates around top
of the ridge. However, not thinking its a likely outcome at
this point, just something to monitor.

&&

.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
Forecaster Confidence Levels...

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

Short Term /through Sunday Night/...High confidence.

Overnight...

Noting mainly VFR conditions across RI into SE Mass at 02Z, but
CIGS/VSBYS lowering to MVFR-IFR further N and W just ahead of
the approaching cold front. Lower conditions appear to be
associated with approach band of showers/isolated thunder from
near KBVY to just S of KORH to KIJD and SWwd with the pre-
frontal trough. Best shot for showers/thunderstorms will
continue through 06Z from NE CT/RI/SE Mass, then will shift to
the S coast overnight.

May see areas of MVFR-IFR CIGS/VSBYS across most areas after 05Z
or so, though may slowly improve across N central/NE Mass after
09Z or so. SW winds 5-10 kt with some gusts to around 15-20 kt
across S RI/S coastal Mass terminals.

Sunday...
Lower MVFR possible IFR CIGs pushing SE with S-W wind shift. ACK
could see lingering -SHRA through midday. W winds potentially light
enough to allow near-shore sea-breezes during the day.

Sunday night...
Increasing clouds overnight potentially getting down as low as low-
end VFR especially for the high terrain. Spot -SHRA possible.
Continued W winds albeit light.

KBOS Terminal...High confidence in TAF trends.

KBDL Terminal...High confidence in TAF trends.

Outlook /Monday through Thursday/...High confidence.

Monday: VFR. Chance SHRA.

Monday Night through Thursday: VFR.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Sunday Night/...High confidence.

Small Craft Advisories ended this evening. S-SW winds in place,
with some gusts up to 20 kt. May see similar gusts ahead of the
cold front toward daybreak around Cape Ann area. Seas mainly 4
ft or less.

Expect winds to diminish after frontal passage into Sunday
morning, with a light W wind and near shore sea breezes, should
allow for good boating weather the remainder of the day.

Shower activity moving into the waters overnight and lingering
as late as midday Sunday more so over the S waters. Some
visibility restrictions at times.

Outlook /Monday through Thursday/...Moderate confidence.

Monday: Winds less than 25 kt. Slight chance of rain showers.

Monday Night: Winds less than 25 kt.

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

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

$$
SYNOPSIS...Sipprell/BW
NEAR TERM...EVT/BW
SHORT TERM...Sipprell
LONG TERM...BW
AVIATION...Sipprell/EVT/BW
MARINE...Sipprell/EVT/BW


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