Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 160209

Area Forecast Discussion
National Weather Service Taunton MA
1009 PM EDT Tue Aug 15 2017

Light rain will linger mainly along south coastal areas through
the evening, giving way to dry weather which will linger
tomorrow and Thursday along with plenty of sunshine. A weather
system from the Plains will bring showers and scattered thunder
with locally heavy rainfall possible Friday and Saturday. A
drying trend likely follows for Sunday into early next week
along with seasonable temperatures.



1000 PM Update...

Overall trend in the forecast remains on track for this evening.
Showers have come to an end as clouds are clearing out across
the interior. As prev forecaster mentioned a lot of low level
moisture is around, so have noticed some stratus developing and
moving to portions of southern New England. Fog is also another
issue as sites across CT are starting to drop as well as KTAN.
Have updated the forecast to account for more clouds and fog,
but otherwise the forecast remains dry for tonight.


WV imagery shows modest mid lvl shortwave moving through central
portions of the forecast area, with deep layer dry air already
beginning to filter across NY state in its wake. Meanwhile along
with this small vort-max, slight strengthening of LLJ is
occurring within the deepens moisture plume, mainly 1.5-2.0
inches, along the immediate S coast. Will continue to focus POPs
through this area through 00Z, but thereafter, a combination of
AVA and dry air should bring this S coastal rain to an end.

Do note some low lvl moisture trapped beneath the subsidence and
dry air building aloft through the late evening and early
overnight hours, this could allow for some evening and early
overnight fog development, as well as low clouds building mainly
in the same areas (SE MA/RI) as last night. However, with a
weakening cold front swinging through around midnight or just
after, the shift to a more W component to the wind may scour
these out toward the morning except areas where winds remain
mostly calm and radiational fog develops. These will be in
typically prone locations.

Overnight mins remain a bit mild, mainly in the low-mid 60s as
sfc dwpts are likely to remain elevated until mixing can scour
these out tomorrow by day.


Gert makes its closest pass during the early AM hours, just as
it swings more to the E about 400sm S of Nantucket, captured by
the weak front as it shifts offshore. The usurping of moisture
and net gradient will yield NW flow across New England and,
aside from some remnant wisps of CI. Although H85 temps will be
dropping through the day, as well as mixing out of sfc dwpts,
temps are likely to actually be above seasonal normals
especially where the downsloping W component of the flow can be
maximized. There for, looking at highs around 80 in the coolest
spots to the upper 80s elsewhere. Leaned most heavily on the
bias-corrected guidance which provided these warmer numbers. The
main impacts from Gert will be felt on some area beaches...

Beach Forecast:
We still expect areas of high surf along with a high risk for
rip currents along primarily south facing beaches which are open
to the ocean. This extends from Watch Hill all the way across to
the outer arm of Cape Cod and includes all Islands. A building
swell into tomorrow morning, from Gert, will reach a 14 second
period and nearly 8 ft offshore. This will create a potentially
life-threatening situation due to high seas and rip currents.
Will maintain the current High Surf Advisory as it stands.

Tomorrow night...
Pleasant sleeping weather as sfc dwpts will continue to drop
even after mixing diminishes through the overnight hours. Weak
gradient and mainly SKC conditions should promote some
radiational cooling suggesting some min temps could dip into the
low 50s. In fact, where radiational cooling is typically
maximized, would not be surprised to see a few upper 40s for min
temps, in the coldest valleys.



* Very pleasant Thu with dry weather and low humidity
* Scattered showers/T-storms with locally heavy rain Fri-Sat
* Drying trend Sunday into early next week w/seasonable temps

Synoptic Overview...

Active northern stream jet along the Canadian/US border continues
this period and will result in the risk for scattered showers/T-
storms Fri and Sat. Although with the upper air pattern progressive
there will also be dry weather days as well including Thu followed
by a drying trend Sun into early next week. This active northern
stream jet will also suppress the subtropical ridge and its
excessive heat and humidity to the southern states this period.


Residual post frontal airmass combined with 1018 mb surface high
overhead will provide seasonable temperatures (U70s-L80s) and very
pleasant humidity across the region Thu. Cooler Fri (70s) with
overcast conditions and scattered showers/T-storms and warm sector
airmass remaining west of New England. Saturday will be a warm and
muggy day ahead of an approaching cold front with highs in the low
80s and dew pts in the low 70s.  Behind the frontal passage,
trending less humid Sunday into early next week but temperatures
will be seasonably warm (highs low to mid 80s).


Dry pleasant weather lingers into Thu. Then an airmass change Fri
ahead of next short wave trough with PWATs jumping up to 2+ inches
Friday. Warm sector remains west of New England so any instability
will be elevated. Nonetheless scattered showers and T-storms with
locally heavy rainfall possible Fri/Fri night. By Saturday cold
front is over or entering the region. Cyclonic flow aloft, frontal
convergence and at least marginal instability should be sufficient
for another round of scattered showers/T-storms. Drier air begins to
work in from the best so the highest risk for storms may be across
RI and eastern MA. Instability and wind fields aloft appear marginal
for severe weather so heavy rain/downpours may be the main concern.
Trailing short wave trough arrives Sunday but less moisture and
instability to work with per ensembles and deterministic guidance.
Thus shower/T-storm coverage likely less than Sat. So not expecting
a washout Sunday. Short wave ridging and associated dry weather
appears to arrive early next as trough exits later Sunday.


Forecaster Confidence Levels...

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

Short Term /through Wednesday Night/...

Through tonight...moderate confidence.
VFR through early evening, then after another round of MVFR
(occasional IFR on Cape/Islands) will spill across SE MA and RI
through about 04Z. Some patchy ground fog this evening as well,
although with winds shifting to the west, improvement to VFR
also possible. Ground fog possible at typically prone airports
in the morning if winds go calm.

Tomorrow and tomorrow night...high confidence.
Any fog burns off within a couple hours after sunrise. Mainly
VFR with NW winds. Gusts to around 15 kt at times through the
daylight hours.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...Moderate confidence in TAF. Issue at hand is
whether a period of MVFR fog will impact the terminal during the
overnight hours.

Outlook /Thursday through Sunday/...

Thursday...VFR, dry runways and light winds with seabreezes along
the coast. High forecast confidence.

Friday...VFR to start but trending toward MVFR/IFR as showers and
isolated T-storms overspread the region from west to east. High
confidence on trends but lower on details.

Saturday...MVFR/IFR in morning fog/low clouds likely improves to VFR-
MVFR during the day however scattered afternoon showers/T-storms
possible esp eastern MA/RI. High confidence on trends but lower on

Sunday...low risk of IFR/MVFR in morning fog/low clouds but then
improving to VFR by midday. Spot shower/T-storm possible. Moderate


Forecaster Confidence Levels...

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

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

Through tomorrow night...
Building southerly swell overnight. Reaching as high as 7-9 ft
in the open ocean waters well south of Nantucket, meanwhile seas
could reach 5-7 ft in nearer to the shore as this long period
swell peaks toward the morning hours Wed. Small Craft Advisories
will continue, and have been hoisted even for some of the area
bays and sounds (Buzzards Bay, Nantucket and Vineyard Sounds) as
some near 5 ft seas are possible on the periphery of these
zones, especially thanks to some tidal influences. These seas will
gradually subside tomorrow night.

Meanwhile, an area of rain/fog will linger through the overnight
hours tonight mainly across the S waters, leading to visibility

Outlook /Thursday through Sunday/...

Thursday...fine boating weather with high pres over the region.
Southerly swells from Gert may linger across the ocean waters. Dry
weather and good vsby. High forecast confidence.

Friday...a warm front lifts across the area with SE winds becoming
SW late. Showers and TSTMS limit vsby. Moderate confidence.

Saturday...southwest winds ahead of an approaching cold front along
with scattered showers/T-storms. Vsby will be restrict in fog in the
morning and showers/T-storms much of the day. Moderate confidence.

Sunday...main cold front pushes offshore providing an improving
trend in vsby and drier conditions. However a secondary front may
trigger an isolated shower/T-storm in the afternoon near shore.
Moderate confidence.


MA...High Surf Advisory from 9 AM to 8 PM EDT Wednesday for MAZ020-
RI...High Surf Advisory from 9 AM to 8 PM EDT Wednesday for
MARINE...Small Craft Advisory for hazardous seas from 5 AM to 8 PM EDT
     Wednesday for ANZ232>234.
     Small Craft Advisory for hazardous seas until midnight EDT
     Wednesday night for ANZ235-237.
     Small Craft Advisory for hazardous seas until 5 AM EDT
     Thursday for ANZ254.
     Small Craft Advisory for hazardous seas until 5 AM EDT
     Thursday for ANZ255-256.


NEAR TERM...Doody/Dunten
LONG TERM...Nocera
MARINE...Nocera/Doody is the U.S. government's official web portal to all federal, state and local government web resources and services.