Area Forecast Discussion
Issued by NWS Boston, MA

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237
FXUS61 KBOX 212008
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
408 PM EDT Mon Aug 21 2017

.SYNOPSIS...
High pressure moves farther offshore tonight. Southwest winds
bring warm humid air Tuesday night, which will feed developing
showers and thunderstorms. The wet weather will continue into
Wednesday, until a cold front sweeps across Southern New
England. High pressure brings dry weather Thursday through
Sunday.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Rather quiet weather continues tonight as a high pressure moves
farther offshore. Increasing south to southwest winds, along
with increasing clouds, will result in above normal low
temperatures.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
A cold front will approach our region from the west Tuesday.
With a strong high pressure off to the east, thinking this
front will be delayed from entering our region until Tuesday
night. This front should not move off the coast until sometime
after daybreak Wednesday morning.

Despite the expected timing of this front, our region should see
an increasing risk for showers and thunderstorms from west to
east through Tuesday morning into the afternoon. Latest
guidance suite continues to CAPE values of 1,000-1,600 J/kg
during the afternoon and evening, with mid level wind speeds of
40-50 kt. These values are supportive of the risk for a few
strong to sever storms. The greatest threat is across western
and central MA, and northern CT.

Showers and a few thunderstorms should continue into Tuesday
night as a cold front pushes across southern New England.
Precipitable water values are anticipated to be around 2.00
inches. Locally heavy rainfall is possible within any
thunderstorms.

Above normal temperatures continue through this period.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Big Picture...

Long term starts off with an upper trough centered over Quebec on
Wednesday. Although the upper trough center pulls somewhat
northeastward on Thu, cyclonic flow remains over our region thru
this weekend. Expecting temperatures to trend seasonably cool thru
the period.

During early next week GFS and ECMWF show signs of the upper trough
moving east, placing us in upper level ridging. Thus we could see a
warmup for next Mon.

Details...

Wednesday...

Upper level short wave will push a cold front eastward during
Wednesday. Depending on the exact timing of the cold front, western
portions of the area could start the day off dry. However to the
east and ahead of the cold front, precipitable water is 1.5 to 2
inches, allowing for locally heavy rain. Instability ahead of the
cold front with LIs 0 to -2 and Cape generally 500 to 1000 J/kg,
accompanied by the right entrance region of the upper jet. So some
rumbles of thunder are probable ahead of the cold front Wed morning.

Wed afternoon expected to bring a drying trend as the deeper
moisture and better dynamics move offshore. Increasing sunshine
anticipated, allowing high temps to reach the upper 70s to low 80s
for most locales. Dew points will gradually dip into the 50s during
the day and evening.

Wednesday night...

Surface ridging starts to build into southern New England and quite
dry airmass in place. Thus mostly clear skies are expected.

Thursday through Sunday...

High pressure builds in at the surface, while upper trough lingers
over southeast Canada and into our area. Not much available moisture
thru this period except mainly between 700 and 850 mb. So cold pool
aloft will likely allow for partly cloudy skies and mainly dry
conditions. Short wave crossing the base of the trough Thu night/Fri
could bring some additional clouds. Could see a few showers here or
there during the long term timeframe, but again moisture looks quite
limited.

Temps will range from near normal to several degrees below normal.
High temps ranging mainly from 70 to 80 degrees F. Dew points range
mainly from the upper 40s to mid 50s, so quite comfortable from a
humidity standpoint. With light winds each night, min temps in the
50s to low 60s are expected, with the warmest overnight temps near
the shoreline, coolest in sheltered valleys.

The light wind flow will allow sea breezes to develop each late
morning and afternoon Friday through Sunday.

Monday...

Models indicate weak upper level ridging in our area, while surface
high pressure lingers. Should be a dry day accompanied by warmer
temps.

&&

.AVIATION /20Z MONDAY THROUGH SATURDAY/...
Forecaster Confidence Levels...

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

Short Term /through Tuesday Night/...

Tonight...High confidence. Mainly VFR. Low confidence in IFR
stratus developing along the south coast late tonight.

Tuesday...Moderate confidence. Mainly VFR through the day. Any
morning IFR stratus should slowly lift to VFR by mid morning.
Scattered thunderstorms are possible in the afternoon across
interior, mainly near Berkshires.

Tuesday night...Moderate confidence. Mainly VFR with scattered
MVFR is SHRA/TSRA.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Wednesday through Saturday/...

Areas of MVFR cigs/vsbys in showers/thunderstorms Wednesday morning.

Otherwise, VFR all areas thru Saturday, with patchy IFR
cigs/vsbys in fog Wednesday night/early Thursday and Thursday
night/early Friday.

&&

.MARINE...
Forecaster Confidence Levels...

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

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

Small Craft Advisories remain posted from late Tuesday morning
into Tuesday night for south coastal and outer coastal waters.
Gusts should reach 25 kt, to perhaps 30 kt, along with building
seas up to 6-7 ft offshore.

After some more thought, decided to expand the Small Craft
Advisory into Massachusetts Bay. It possible we might need an
advisory in Boston Harbor, but don`t have enough confidence just
yet.

Winds diminish Tuesday night, although seas may take a bit
longer into Wednesday morning to subside, particularly across
the outer coastal waters.

Outlook /Wednesday through Saturday/...

Wednesday...

Cold front moves across the waters, turning winds from the west-
northwest. Gusts to 25 kt possible early in the day. Seas 3 to
5 ft on the coastal waters gradually subside during the day.

Thursday through Saturday...

High pressure then builds in with W/NW winds diminishing to less
than 20 kt. Winds become north on Friday. Diminishing winds
will bring diminishing seas, generally 3 ft or less through
this period.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 11 AM Tuesday to 6 AM EDT Wednesday
     for ANZ231>234-250-254>256.
     Small Craft Advisory from 2 PM Tuesday to 2 AM EDT Wednesday
     for ANZ236.
     Small Craft Advisory from 2 PM Tuesday to 6 AM EDT Wednesday
     for ANZ235-237.
     Small Craft Advisory from 2 PM Tuesday to 4 AM EDT Wednesday
     for ANZ251.

&&

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



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