Area Forecast Discussion
Issued by NWS Boston, MA

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901
FXUS61 KBOX 240846
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
446 AM EDT Sat Aug 24 2019

.SYNOPSIS...
High pressure from the Great Lakes will move across Eastern
Canada to the Maritimes. This high will maintain dry conditions
over much of the region today, then bring low clouds, showers
and drizzle Sunday, especially across Eastern Massachusetts and
Rhode Island. The high lingers over the Maritimes for Monday and
Tuesday with dry conditions and seasonably mild temperatures
for Southern New England. A potential tropical system may
develop, tracking from the Bahamas to well south of New England
around the middle of next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
High pressure centered north of the Great Lakes will build over
the Northeast USA today. This will bring dry air at the surface
and subsidence overall. At the same time, an upper trough will
move across Southern New England with small cold advection at
mid levels. This will try to destabilize the airmass. Cross
sections show a layer of 850 mb moisture with the trough.

Put it together, it suggests fair weather with diurnal cumulus
but no showers. Temps at the top of the mixed layer, about 8-9C,
would support max sfc temps in the 70s. Dew points in the upper
40s and 50s mean comfortable humidity levels. As the surface
high moves east across Canada, the pressure gradient projects
north winds this morning turning from the northeast by midday or
early afternoon.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
As the Canadian high moves into the Maritimes, the pressure
gradient continues to support northeast wind. The gradient is
low enough for relatively light winds in northern/western
sections, but the northeast wind should increase in speed.
Expect winds to be trending stronger along the coasts and
especially along the South Coast and Islands tonight and Sunday.

Moisture advection off the Gulf of Maine will spread low clouds
over parts of Southern New England late tonight and Sunday. With
limited lift, expect the clouds to produce drizzle and possible
a few light showers. The area most in line to be affected would
be Eastern Mass and RI and especially SE Mass. The remainder of
Southern New England should experience partly to mostly sunny
skies.

With skies partly to mostly clear tonight and dew points in the
50s, expect min temps generally in the 50s, with low 60s
possible where the wind is coming off the water. Temps aloft
Sunday will be similar to today, so afternoon potential will
again be in the 70s. Areas with more clouds and a wind off the
water, such as near the Eastern MA coastline, may struggle to
cross 70 for a high temp.

&&

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

Highlights...

* Cooler than normal temperatures early next week especially
  across eastern Massachusetts into Rhode Island
* Onshore winds will bring spotty light rain or showers at
  times into mid week
* Temperatures return to near normal levels around mid week,
  becoming warmer than normal by Friday
* Another chance for showers late Wednesday through Thursday

Details...

Sunday night through Tuesday...

The center of the large high to the N will slowly cross
southern Quebec into the Maritimes by early Sunday night. With
the long easterly fetch around the E-W elongated high, will see
temps below seasonal levels both Monday and Tuesday with the
coolest temps along the immediate E coast where readings may not
break 70 on Sunday and possibly even Monday.

The long fetch will also allow low level moisture to continue
to increase, so have kept slight CHC POPs across E Mass into RI
through part of Monday before the winds diminish as the center
of the high tries to shift a bit further S. Chances for spotty
showers and possibly even some drizzle return on Tuesday.
Further inland, skies should be partly to mostly sunny.

The easterly winds may become gusty as the pressure gradient
increases around the southern section of the high from Monday
into Tuesday. May see gusts up to 20 to as high as 30 mph,
highest across Cape Cod and the islands.

Wednesday through Friday...

As the large high slowly exits to the western Atlc, another
cold front begins to approach later Wed, but will tend to stall
across E NY state as the potential tropical system passes well
SE of Nantucket around the late Wed night or Thu timeframe.
Light E-SE winds should eventually shift to SE or even S as the
front approaches, but this will depend upon the timing of the
passing tropical system.

Will also see marginal instability as the front approaches, so
can not rule out isolated thunderstorms mainly from late Wed
through Thu. By Thu, highs will reach up to the lower-mid 80s,
which will also assist in any developing convection. As the
potential tropical system exits to the western Atlc, showers
should push offshore, but some question on the timing of this
front as model solution spread increases. At this point, have
kept slight chance POPs going into Friday as yet another front
may approach in the fast flow aloft.

&&

.AVIATION /09Z SATURDAY THROUGH WEDNESDAY/...
Forecaster Confidence Levels...

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

Short Term /through Sunday/...Moderate confidence.

Early this Morning ... VFR with NNW winds under 10 kt.

Today ... VFR with N winds becoming NE. Dry weather continues.

Tonight ... VFR. Clouds spreading across the region from
Massachusetts Bay after midnight. Becoming MVFR in Eastern MA
and RI after midnight. Light showers develop along the east MA
coast late. NE wind 10 kt with gusts near 20 kt Cape Cod and
islands.

Sunday... VFR, except MVFR cigs/vsbys in showers RI and Eastern
MA. NE wind continues.

KBOS Terminal...High confidence in TAF

KBDL Terminal...High confidence in TAF.

Outlook /Sunday Night through Wednesday/...Moderate to high
confidence.

Sunday Night: Mainly VFR, with local MVFR possible. Breezy.
Slight chance SHRA.

Monday through Tuesday: VFR. Breezy.

Tuesday Night: Mainly VFR, with local IFR possible. Slight
chance SHRA, patchy BR.

Wednesday: Mainly VFR, with areas MVFR possible. Slight chance
SHRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

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

Today ...

Large high pressure moves from Ontario to Quebec with modest
north-northwest winds turning from the northeast during the day.
Dry weather and good visibility.

Tonight...

The persisting northeast wind will bring low clouds and
fog/drizzle over the waters, especially in areas south of
Boston Harbor. Scattered showers may lower vsby at times. A
building pressure gradient south of New England will bring gusts
around 25 kt to the southern waters, with winds progressively
lighter farther north. A Small Craft Advisory will be issued for
these waters.

Sunday...

Persistent northeast winds will continue to bring gusts of
25-30 kt to the southern waters. Seas in all areas will build,
with 5 foot seas developing on all outer waters.
Clouds/fog/drizzle/scattered light rain showers will lower vsbys
at times, especially on the waters south of Boston Harbor.

Outlook /Sunday Night through Wednesday/...Moderate confidence.

Sunday Night through Monday: Low risk for Small Craft Advisory
winds with gusts up to 25 kt. Seas up to 5 ft. Slight chance of
rain showers.

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

Tuesday through Tuesday Night: Winds less than 25 kt. Seas up
to 5 ft. Slight chance of rain showers.

Wednesday: Winds less than 25 kt. Seas up to 5 ft. Slight
chance of rain showers, isolated thunderstorms.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 6 AM Sunday to 6 AM EDT Monday for
     ANZ232>235-237.
     Small Craft Advisory from 2 AM Sunday to 6 AM EDT Monday for
     ANZ250-254.
     Small Craft Advisory from 5 AM Sunday to 6 AM EDT Monday for
     ANZ255-256.

&&

$$
SYNOPSIS...WTB/EVT
NEAR TERM...WTB
SHORT TERM...WTB
LONG TERM...EVT
AVIATION...WTB/EVT
MARINE...WTB/EVT



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