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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KBOX 081056
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
656 AM EDT Sat May 8 2021

.SYNOPSIS...
A few showers are possible today, but most of the day should be
dry, as a coastal low passes offshore and another weak low
pressure moves into the Great Lakes. A brief period of fair and
seasonable weather for Sunday beneath high pressure. A wave of
low pressure likely brings a period of appreciable rainfall
Sunday night into Monday morning, followed by a dry but cooling
trend Tue and Wed. Dry and seasonable weather is possible
Thursday, before yet another round of rain is possible Thursday
night into Friday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

-- Changed Discussion --
7 am update...

Cloudy skies prevail this morning and will continue through the
day. Satellite shows the offshore low well displaced enough
that we shouldn`t see any precip from it. Could see a few
sprinkles in western MA this morning, but the appreciable
showers don`t appear until the afternoon. No significant changes
to the forecast.

Previous Discussion...

A mishmash of weather features today. Nothing particularly
strong, which would make this forecast a little easier. Starting
out the day with a weak surface ridge, along with a weak mid
level inverted trough extending back to the Great Lakes.
Expecting yet another weak mid level shortwave to arrive later
this afternoon. Put it all together, and there is a risk for
some showers, but not likely a widespread rainfall. The greatest
risk for showers will be from late morning into this afternoon.


Yet another day of onshore flow and clouds. Below normal
temperatures continue.
-- End Changed Discussion --

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
Weak surface ridging should slowly develop across southern New
England tonight into early Sunday. Some mid level drying with
the corresponding subsidence should mean showers end near or
shortly after sunset. These drier conditions should hold into
Sunday morning, and perhaps last all day for most of our region.
Another low pressure will approach from the southwest late in
the day. Thinking an increasing risk for rainfall during the
late afternoon and evening hours. This will be mainly across the
western half of southern New England. It is possible this timing
may change with later forecasts. Gut feeling is precipitation
arrival timing may be slower than current forecast.

Below normal temperatures continue.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Highlights...

* Seasonable to slightly cooler than normal temperatures through
  next week

* Rain returns late Sunday into Monday

* A few scattered showers Tuesday then drier through at least
  Thursday

Details...

Sunday night and Monday...

A mid level shortwave and surface low approach from the Ohio
Valley on Sunday night into Monday bringing the returns of
widespread rain chances, mainly Sunday night into Monday
morning. The warm front lifts north after sunset on Sunday
bringing isentropically forced rain showers to much of southern
New England. This front together with a PWAT plume ~1 inch and
40-50 kt low level jet will bring a widespread decent soaking on
the order of 0.25 to 0.75 inches under the heavier bands.
Whether the heavier rain falls over the south shore or further
north will be honed in on in future updates, heavily dependent
on the exact track of the low and surface warm front. For now,
most guidance would suggest we remain on the cool side of the
low. After 12-15Z, drier air pushes in above 800 mb bringing the
widespread rain to an end, so the second half of Monday should
be drier; could even see some breaks of sun. Temperature- wise
highs won`t get out of the low 60s.

Tuesday through Thursday...

This will be a mainly dry stretch, with a few scattered showers
mixed in, mainly on Tuesday. Behind the departing system from
Monday a cool and drier northwest flow kicks in with a 30 kt low
level jet between the departing low and incoming highs. So,
should see a breezy day, gusting 15 to 20 mph. The upper level
trough and cold pool move overhead, so should see some widely
scattered instability showers. This cold airmass (-3 to -4 C at
850 mb) will be brief, but passing overhead Tuesday night into
Wednesday. Thus, low temps will take a dip back into the 30s for
much of the interior; low to mid 30s at higher elevations.
Drier air brings clearer skies Wednesday, so sunshine together
with a rapidly moderating airmass will bring quickly rebounding
temps, back into the 60s. Thursday a high pressure ridge moves
in with a much warmer airmass. 850 mb temps return to +3 to 4 C,
allowing for highs in the upper 60s.

Friday into the weekend...

Our next shot at some rain comes around next Friday with an
approaching shortwave, but confidence is low.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
Forecaster Confidence Levels.

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

12Z update...

High confidence.

Mostly VFR through Sunday. Increasing risk for showers today.
Scattered MVFR in SHRA is possible across the western half of
southern New England late this morning and afternoon. Relatively
light onshore flow becomes variable this evening, then
generally light westerly flow late tonight through Sunday.

KBOS TAF...High confidence.

KBDL TAF...High confidence.

Outlook /Sunday Night through Wednesday/...

Sunday Night: Mainly VFR, with local IFR possible. Breezy. RA.

Monday: Mainly VFR, with local IFR possible. Breezy. Chance RA.

Monday Night: VFR. Slight chance RA.

Tuesday through Wednesday: VFR. Breezy.
-- End Changed Discussion --

&&

.MARINE...
Weak high pressure near the Maritimes will maintain relatively
light winds and seas across the waters through today. There is a
small chance for 5 foot seas across the southern outer coastal
waters today, especially south and east of Nantucket. While it
is marginal, will be issuing a Small Craft Advisory for the
southern outer coastal waters as seas should build, especially
tonight into Sunday.

Outlook /Sunday Night through Wednesday/...

Sunday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of seas approaching 5 ft. Rain.

Monday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of rough seas. Chance of rain.

Monday Night: Winds less than 25 kt. Areas of rough seas.

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

Tuesday Night: Low risk for Small Craft Advisory winds with
gusts up to 20 kt. Seas up to 5 ft.

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 PM EDT Sunday for ANZ254-255.
     Small Craft Advisory from 5 AM to 8 PM EDT Sunday for ANZ256.
-- End Changed Discussion --

&&

$$
SYNOPSIS...Belk/BW
NEAR TERM...Belk/BW
SHORT TERM...Belk
LONG TERM...BW
AVIATION...Belk/BW
MARINE...Belk/BW