Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 281356

Area Forecast Discussion
National Weather Service Taunton MA
956 AM EDT SUN AUG 28 2016

High pressure centered over the Canadian Maritimes brings dry
weather through today. A cold front moves south into New England
tonight and then exits later Monday, which may be accompanied by a
spot shower or thunderstorm. Weak high pressure brings dry and
less humid conditions Tuesday. Warm and humid weather returns
Wed ahead of another cold front, which will bring the chance for
showers and thunderstorms Wednesday into early Thursday. Large
Canadian high pressure will bring dry, fall like weather late this
week into the weekend, with mild days and cool nights.



10 AM Update...

Deep layer ridge over the Northeast this morning yielding plenty
of subsidence and resulting in mostly sunny conditions. SPC
mesoanalysis indicates higher dew pt air at 925 mb and 850 mb
remain well to the west of New England. Thus any convection from
upstream short wave energy will remain west of New England. Hence
dry forecast remains intact.

As for temps...weak pres gradient over the area with 1027 mb
surface high centered over the maritimes will promote cooling
seabreezes for the shoreline. Previous forecast captures this
nicely...thus no major changes with this forecast update. Earlier
discussion below.

Previous Discussion...

Not much change from previous thinking. Ridge aloft shifts east
by this evening. High pressure at the surface will move out of
the Maritimes and out to sea. Dry weather still expected though,
as not much lift or moisture to work with during the day.
Generally light south winds today. Sea breezes develop again on
both coasts. Max temperatures similar to Saturday.


A mid level shortwave from the Plains moves east to Quebec
tonight, then moves south across New England Monday. The best
dynamics, in the form of a 100+ knot upper level jet, still looks
like it will stay mainly to our north. That means most of the
forcing for rainfall will be from a shortwave, a weak cold front,
and whatever convective instability can be generated. Given that
most of this will occur at night into the morning hours, not
expecting strong thunderstorms. These attributes should also keep
areal coverage of any storms isolated or widely scattered. Thus
not a washout expected.




* Expect mainly warm and dry conditions on Tuesday, with more
  humidity returning on Wednesday
* A cold front brings the chance for showers/thunderstorms
  Wednesday afternoon into early Thursday
* Fall like conditions move in for Friday and Saturday with mild
  days and cool nights

Overview and model preferences...

Models and ensembles remain in good agreement in the overall mid
level steering pattern across North America with an amplified
northern stream extending across central and southern Canada early
this week. However, noting changes by mid week, as H5 heights fall
as long wave trough digs across New England in response to large
H5 ridge building from the Plains states northward into Nunavut
and the Northwest Territories of N central Canada toward the
Arctic Circle. The high amplitude pattern does remain progressive,
so will see the large ridge building slowly but steadily eastward
through the remainder of the week.

Will see another H5 short wave in the flow approach during late
Wednesday night/Thursday in the NW flow. Will see some showers/
thunderstorms move across with rather weak surface front. Not a
lot of support with this, but a pretty sharp temperature
difference behind the front. Will see a batch of cooler air work
in late this week as the cold front pushes offshore, feeling more
fall like by the upcoming holiday weekend.

Have rather good confidence for the overall timing of this
forecast package, though somewhat lower confidence from Wednesday
night onward on specific details. Used a blend of available
guidance through Wednesday, then leaned more toward the model
ensemble guidance for the latter portion of the forecast.


Monday night...The cold front will push offshore without much
fanfare. Cooler air works in across the region, with H85 temps
falling to +10C to +12C by daybreak. With mainly clear skies and
light N-NW winds, expect temps to fall back to near seasonal
levels. Readings will bottom out in the mid-upper 50s across
inland valley locations to the mid-upper 660s along the immediate

Tuesday...High pressure ridge builds across, bringing dry
conditions and low humidities. With a light pressure gradient
across the region thanks to the passing high, sea breezes will
bring slightly cooler temperatures along the shoreline.

Wednesday...Another cold front begins to approach N and W Mass
Wed afternoon, then will steadily move SE. Will see warm and more
humid conditions ahead of this system as SW winds pick up. Noting
the PWATs do increase by Wednesday evening to 1.6 inches, so could
see some brief heavy downpours with any thunderstorms across
central and southern areas toward evening.

Wednesday night-Thursday...Scattered showers and a few
thunderstorms may linger across N CT/RI into SE Mass early
Wednesday night as the cold front passes. The front may even slow
down near the south coast by Thursday morning, so some showers may
linger there for a part of the day. Will still see mild
temperatures as the cooler air does not work into the region until
later in the day, but dewpts will be falling so it will be mild
but more comfortable as the day progresses on Thursday.

Friday and Saturday...Large high pressure will build SE out of
north central Canada across the Great Lakes, bringing cool temps
especially Friday morning. H85 temps will drop to +5C to +8C by
12Z Friday, which will linger through the day. Expect highs on
Friday to run up to 5 degrees below seasonal normals. May see some
overnight lows early Saturday morning into the upper 40s well
inland, but will recover with mainly clear skies and temperatures
reaching close to or a bit above normal for early September.


Forecaster Confidence Levels.

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

Short Term /through Monday/...High Confidence.

10 am update ...

Not much change from 12z TAFs...VFR along with dry weather and
light onshore winds. Earlier discussion below.


VFR with light winds increasing out of the south. Some increase
in high thin clouds during the afternoon. Seabreezes redevelop.

VFR. Increasing mid and high clouds. Areas of 5000 foot ceiling
bases with widely scattered MVFR in a shower or thunderstorm.
Patchy fog with local IFR vsbys after midnight.

Mainly VFR, with isolated SHRA/TSRA yielding brief MVFR which
shifts into CT/RI and southeast MA during the afternoon.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Monday Night through Thursday/...

Monday night...Moderate to high confidence. Mainly VFR. May see a
few leftover SHRA with brief MVFR conditions along the S coast
Monday evening. Light W-NW winds early shift to N after midnight.
Patchy fog after midnight with local MVFR-IFR VSBYS.

Tuesday...High confidence. VFR. Expect dry conditions. Light W-SW
winds inland. Sea breezes along both coasts likely. Patchy fog
late Tuesday night with local MVFR-IFR VSBYS.

Wednesday...Moderate confidence. Mainly VFR. May see local MVFR
conditions in scattered SHRA/TSRA across N central and W Mass
during the afternoon.

Wednesday night-Thursday...Moderate confidence. Mainly VFR. Local
MVFR-IFR CIGS/VSBYS in scattered SHRA/TSRA as cold front crosses
the region Wednesday night. The front may slow down along the S
coast Thursday morning, so a few showers may linger until around
midday Thursday before improving.


Forecaster Confidence Levels.

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

Short Term /through Monday/...High confidence.

Seabreezes will return late this morning and continue through
this afternoon. Seas trend slowly higher into Monday in response
to southeast swell from distant Hurricane Gaston.

A widely scattered shower or thunderstorm possible late tonight
into Monday as a cold front crosses the waters.

Outlook /Monday Night through Thursday/...

Monday night...Moderate to high confidence. W-SW winds early
shift to NW as cold front pushes offshore. May see a few leftover
showers Monday evening across the southern waters with briefly
reduced visibilities. S-SE swells will increase across the outer
waters from distant Hurricane Gaston.

Tuesday...High confidence. Light N-NE winds shift to SE during
the day. May see briefly reduced visibilities late Tuesday night
in patchy fog on the near shore waters. S-SE swells from Hurricane
Gaston continue on the outer waters.

Wednesday...Moderate to high confidence. SW winds increase, with
gusts up to 20 kt mainly across the eastern waters where seas will
increase to around 5 ft. Local visibility restrictions in
scattered showers/thunderstorms may approach the eastern waters
Wednesday afternoon.

Wednesday night-Thursday...Moderate confidence. A cold front
crosses the waters with scattered showers/thunderstorms Wednesday
night into early Thursday morning. A few showers may linger
through midday across the southern waters. Winds shift from SW to
W-NW by Thursday morning, then N-NE on the eastern waters Thursday
afternoon. Seas may occasional reach 5 ft on the eastern outer
waters Thu into Thu night.




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