Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 301354
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
954 AM EDT TUE AUG 30 2016

.SYNOPSIS...
High pressure over New England will move offshore by tonight. Warm
and humid weather returns Wednesday. A cold front moves through
Wednesday night and Thursday, which will bring scattered showers
and a few thunderstorms. Large high pressure will build out of
central Canada, bringing dry, seasonable conditions into the
upcoming holiday weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
950 AM update...
High pres in control and forecast on track. Lots of sun with
comfortable humidity and warm temps. Light winds will result in
coastal seabreezes developing.

Previous discussion...
High pressure over the Northeast USA will mean lots of sun today
along with light wind. Mixing profiles suggest a layer up to 850
mb, where temps will be 13-14C. That supports high temps in the
low to mid 80s. The light flow will allow sea breezes to develop,
which will keep high temps a little cooler along the coast.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
Tonight...

High pressure moves offshore, bringing a slow increase in surface
flow from the west-southwest. This suggests increasing dew points,
which will hold temperatures a little milder than tonight. The
light flow will also allow areas of fog to develop. We are using
the dew point range to forecast min temps, in the upper 50s and
60s.

Wednesday...

Upper shortwave dives southeast from central Canada, driving a
cold front over the Eastern Great Lakes. This shortwave will also
move a 90-knot jet south through New England. The ECMWF shows
this more than the GFS. The ECMWF is also less distinct with
dynamically favored locations along the jet, while the GFS is more
distinct and shows favorable dynamics across Northern New England.

Moisture fields are rather thin most of the day, increasing a
little during late afternoon. CAPEs climb to around 500 J/Kg and
Totals to the upper 40s. Much of this is concentrated over Western
MA. We also should consider the ongoing drought, which works
against confidence for measurable precip. We will continue with
low-end chance pops late-day in Western and North-central MA, and
slight chance across Nrn CT and the remainder of Northern MA.
Temps at 850 mb climb to 16-17C, suggesting max temps in the mid
to upper 80s.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
HIGHLIGHTS...

* Cold front brings showers and thunderstorms Wed night into Thu
* Dry weather and seasonable temps through much of the holiday
  weekend
* Rough surf and rip currents could occur mid to late week due to SE
  swells from distant Hurricane Gaston

While the 00Z model guidance is in overall good agreement on the
general synoptic pattern throughout the long term portion of the
forecast, there are a few complicating factors.  Namely, Tropical
Depression Eight and Tropical Depression Nine, and to a lesser
extent Hurricane Gaston.

TD 8 is off the Carolina coastline currently and is expected to
become a tropical storm sometime later today and pass well to the SE
of southern New England.  While it is something to keep an eye on,
the only impacts to southern New England are expected to be on the
waters.

TD 9 is in the Gulf of Mexico currently and is forecast to move
through the eastern part of the Gulf before crossing northern
Florida back into the Atlantic late in the week.  This is the main
potential complicating factor.  At this point, the ensemble runs of
both the ECMWF and the GFS build an upper ridge/high pressure well
into southern New England through early next week, keeping TD 9 well
south of the area.  This lines up well with previous forecasts
including the National Hurricane Center`s forecast.  However, the
00Z operational GFS run keeps the upper ridge a bit farther west and
weakens the high pressure allowing it to move eastward away from the
east coast.  This would allow TD 9 to make a much closer approach to
southern New England.  While this solution is an outlier currently,
we will need to keep an eye on future guidance trends.

Finally, Hurricane Gaston is hanging out in the middle of the
Atlantic and is forecast to stay well out to sea.  However, it will
push higher swells into the southern New England coastline,
resulting in rough surf, rip currents, and choppy seas just in time
for the holiday weekend.

Overall, the weather will be fairly quiet through the long term. The
main exception to this will be Wednesday night into Thursday when
low pressure in Quebec will bring a cold front through southern New
England.  This may result in scattered showers and a few
thunderstorms.  While ingredients are there for this to occur, given
the trends in the region towards drought, have less confidence in
the much higher PoPs given in the models.  Therefore, have lowered
PoPs to low end chance, but kept the possibility of a few scattered
showers and storms.  Definitely won`t be a washout, but a few areas
may see some much needed rain.

Otherwise, until we see what the tropics end up doing, expecting
seasonable temperatures and dry weather through the end of the week
and warming temperatures through the weekend.

&&

.AVIATION /14Z TUESDAY THROUGH SATURDAY/...
Forecaster Confidence Levels.

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

Through Wednesday...High confidence.

Mainly VFR outside of a few patches of fog early this morning and
again early Wednesday morning at typically prone locations.

Light variable winds today will give way to sea breezes on all
coasts. Winds then pick up a little from the west-southwest
Wednesday.

KBOS Terminal...High confidence in TAF. A NE-SE sea Breeze
develops starting around 14z.

KBDL Terminal...High confidence in TAF.

Outlook /Wednesday Night through Saturday/...

Wednesday night and Thursday...High confidence.  Mainly VFR
conditions.  Low probability of SCT -SHRA/ISOLD TSRA, resulting in
brief MVFR conditions.

Friday and Saturday...High confidence. VFR.

&&

.MARINE...
Forecaster Confidence Levels.

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

Short Term /through Wednesday/...High confidence.

Today...

North to northeast winds become variable. Sea breezes will develop
late morning and afternoon. Continued swell from Tropical Storm
Gaston and Tropical Depression 8 will continue to bring 5 foot
seas to the outer coastal waters.

Tonight and Wednesday...

With high pressure departing, winds will pick up from the
southwest but remain below 20 knots. Swell from the tropical
systems will diminish on the Southern Outer Waters but increase on
the Eastern Waters, near the Gulf of Maine. Small craft advisories
will move as this focus moves east.

Outlook /Wednesday Night through Saturday/...

Wednesday night and Thursday...High confidence.  Winds and seas
remain below SCA criteria for the most part.  There is a possibility
of a few 5 foot seas on the outer waters.  There is also a low
probability of a few scattered showers and thunderstorms over the
waters.

Friday and Saturday...Moderate confidence.  Winds and seas expected
to remain below SCA criteria.  However, SE swell starts to increase
in response to distant Hurricane Gaston.  This may result in rough
surf and an increase in rip currents.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory for hazardous seas until 4 PM EDT
     Wednesday for ANZ250-254.
     Small Craft Advisory for hazardous seas until 6 AM EDT
     Wednesday for ANZ255-256.

&&

$$
SYNOPSIS...WTB/RLG
NEAR TERM...WTB/KJC
SHORT TERM...WTB
LONG TERM...RLG
AVIATION...WTB/RLG
MARINE...WTB/RLG



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