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Area forecast discussion 
National Weather Service Taunton Massachusetts
321 PM EDT Tuesday Sep 1 2015

Synopsis...
hot and humid weather prevails beneath high pressure tonight and
Wednesday. A weak cold front will sweep across New England on
Thursday. High pressure from Canada moves over New England for the
Labor Day weekend. Another cold front approaches New England next
Tuesday night.

&&

Near term /until 6 am Wednesday morning/...
middle-level ridging prevalent beneath which winds will be light over-
night. Stout dry-subsidence inversion in place yields the potential
for surface moisture-pooling. Looking at a low-cloud / fog potential
as the combination of light winds and mostly clear conditions net an
environment favorable for radiational cooling. Got a few degrees
cooler into Tuesday morning than initially thought...so will go a
degree or two cooler than MOS with lows around the low-60s and a
higher fog potential across the interior.

&&

Short term /6 am Wednesday morning through Wednesday night/...
Wednesday...

Certainly hot and humid with several locales seeing temperatures
into the low-90s beneath influential middle-level ridging and dry-air
subsidence and a 850 mb airmass aloft of +18-20c. A mostly clear day
with some scattered cumulus out to the west parent with increasing low-
to middle-level thetae. Echoing the previous forecaster...moisture and
instability appear interesting beneath favorable lapse rates more to
the north. But absent are the forcing mechanisms. BUFKIT profiles show a
strong warm-dry cap around 850 mb with parent deep-layer subsidence. So
looking to remain dry. Light winds overall with sea-breezes along
the shores.

Wednesday night...

Noteworthy middle-Atlantic low pushing east and offshore to our S as a
cold front approaches from the north. Look to be in The Squeeze-play of
the two with more dominant subsidence and dry air associated with
ridging of lingering high pressure. Will keep with a dry forecast
with light winds. Another night of low clouds / patchy dense fog is
possible as moisture pools again beneath a decoupling boundary-layer
and dry-subsidence inversion. Otherwise increasing middle-high level
clouds working in towards morning.

&&

Long term /Thursday through Tuesday/...

Big picture... long wave pattern shows an upper ridge over the
eastern USA with troughs over the Maritimes and Pacific coast. These
features slowly migrate west over the forecast period. At shorter
scales...upper shortwave sweeps through New England Thursday. High
pressure rebuilds over the Holiday weekend but with a prevailing
north-northwest flow. The flow turns more west-southwest Sunday-
Monday. The upper ridge then erodes as a shortwave moves east across
Canada next Tuesday.

The GFS and European model (ecmwf) are similar through next Tuesday. The overnight
models diverged in their handling of the shortwave next week...but
the 12z runs have now come more into accord.

The dailies...

Thursday... shortwave moves over the top of the eastern ridge and
crosses the northeast USA. Most of the jet dynamics with this system
moves from Quebec across Maine into the Maritimes...but there is
enough oomph with this shortwave to push a cold front through
southern New England and turn our upper flow northwest. Wind fields
will be light...but stability will be favorable with convective available potential energy around
1000 j/kg and totals around 50. Moisture fields will be modest and
concentrated below 750 mb. This should be enough for scattered
showers/tstms.

Friday through Monday...Canadian high pressure in control through
the period with subsidence and dry air. A prevailing northeast flow
Friday as the high approaches...this may limit mixing a little
especially in eastern mass. On Saturday and Sunday light winds
under the high may allow afternoon sea breezes. Mixing profiles
reach 825 mb Thursday...900 mb Friday and Saturday...roughly 850 mb
Sunday and Monday. Here are the equivalent 850 mb temperatures and surface temperature
forecasts... Thursday 17c u80-l90/Friday 8-10c m70s-around 80/Sat 11c
around 80-l80s/sun 16-17c m80-u80/Monday 17-18c u80-l90.

Tuesday...approaching upper shortwave and surface cold front. Model
timing for cold frontal passage is either next Tuesday night or Wednesday.
Timing uncertainty abounds this far out in time. For now with a cold
front approaching we will have fair warm weather during the day and
then include a chance of showers next Tuesday night. With 850 mb
temperatures around 18c expect maximum daytime temperatures in the upper 80s and lower
90s...cooler near the South Coast.

&&

Aviation /19z Tuesday through Sunday/...
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.

VFR. Onshore flow diminishes overnight. Light winds and sky clear allow
for IFR fog development in sheltered / low-lying terminals across
interior New England. Burning off during the morning...light west/light snow shower
flow returns with sea-breezes along the shores for Wednesday. Scattered
5 kft ceilings to the west. A return of MVFR-IFR ceilings / visibilities for the
Wednesday overnight period into Thursday morning.

Kbos terminal...high confidence in taf. Sea breeze possible albeit
later for Wednesday.

Kbdl terminal...high confidence in taf.

Outlook...Thursday through Sunday...high confidence.

Thursday...mainly VFR. Brief MVFR ceilings/visibilities in afternoon/evening
showers/tstms. Patchy IFR in early morning fog.

Friday through Sunday...VFR. Patchy IFR in early morning fog.

&&

Marine...
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.

Seas at or below 4-feet. Only issues are west/SW-winds over the waters
with gusts up to around 15 kts across the east-outer waters for a
majority of the period...perhaps some patchy dense fog along the
shores with onshore flow during the day. Mainly quiet boating
weather prevails through Wednesday.

Outlook...Thursday through Sunday...moderate to high confidence.

Cold front moves across the waters late Thursday or Thursday night.
Winds turn northeast behind the front and climb to 20-25 knots for
Friday. The northeast winds may also bring a period of 5 foot
seas...best chance on the waters east of Massachusetts. A Small
Craft Advisory may be needed Friday. High pressure then moves
overhead and brings light wind and seas over the weekend.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...none.

&&

$$
Synopsis...wtb/sipprell
near term...sipprell
short term...sipprell
long term...wtb
aviation...wtb/sipprell
marine...wtb/sipprell

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