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Area forecast discussion 
National Weather Service Taunton Massachusetts
412 am EDT Wednesday Sep 3 2014

Synopsis...
drier air moves into the region today as a cold front moves
offshore. Warm weather continues...but the humidity will be low.
Very warm to hot weather expected on Friday as humidity
increases...but it will remain dry. An approaching cold front will
bring scattered showers/thunderstorms with locally heavy rainfall
Sat into Sat night. A few showers may linger Sun morning across
eastern New England...otherwise dry weather along with
significantly cooler/less humid conditions expected early next
week.

&&

Near term /through this evening/...
a combination of both surface observation and available msas data suggests
the cold front is currently draped from westerly Rhode Island NE into Essex
CT Massachusetts as of 07z. The front is moving east rapidly and should be
offshore of even the cape/islands by about 10-11z. Also noting
that cloud cover continues to dissipate across the region as the
best energy and moisture shifts to the north and S of the region and
away from an inflection point in the front.

Given that infrared imagery continues to show the dissipation of area
cloud cover...it/S possible that many locations see the sunrise in
the next couple of hours...but even if that isn/T the case...the
rapid decrease in column dewpoints /including at the surface/ should allow
for rapid clearing with increased diurnal mixing. Therefore...many
locations should be in nearly full sunshine by middle morning to middle
day. With this sunshine...mixing should have little trouble
reaching 850 mb where temperatures are expected to average about
+13c. Therefore...at least low-middle 80s are expected for
highs...but with west-northwest flow behind the front...downsloping is
likely to make areas of the coastal plain and CT valleys in the
middle-upper 80s. The best news is...that mixing of the drier air
should let dewpoints fall back into the middle 50s...so humidity much
lower today.

A little be breezy following the front...may see some gusts of
15-20 miles per hour at times at peak heating. Even though pressure gradient will
be gradually slackening through the day...feel it will likely be a
bit too late for any sea breezes to move onshore.

&&

Short term /tonight through Thursday/...
tonight...
high pressure and attendant middle level ridging will be cresting over the
region during the overnight hours. With a dry column...expect
little in the way of cloud cover and a weakened pressure gradient
supports light to near calm flow. Therefore...expect plenty of
room for radiational cooling...especially with the drier air in
place and dewpoints starting already in the low-middle 50s.
Therefore...likely see several locations with mins in the low-middle
50s as well. One caveat is likely to be the normally cooler
valleys of northwest Massachusetts and SW New Hampshire where cold air drainage is usually
maximized...40s are possible there. The other caveat are the
typically warmer heat islands...where temperatures may remain somewhat
closer to the 60 degree mark.

Thursday...
high pressure slides to the southeast of the region but remains in control.
Therefore...outside of maybe some diurnal cumulus across the interior
and maybe a few wisps of cirrus from the north mostly sunny conditions
remain. Return flow allows surface and middle level temperatures to increase
somewhat...so may see more widespread middle-upper 80s although dewpoints
remain in the 50s. The only caveat are near shorelines...where sea
breezes are likely to keep highs down...mainly in the low 80s.

&&

Long term /Thursday night through Tuesday/...
highlights:

* dry but very warm/hot with increasing humidity on Friday
* scattered showers/storms Sat into Sat night with locally heavy rain
* dry and significantly cooler/less humid weather early next week

Details:

Thursday night...

High pressure nearby will result in a dry and tranquil night. Low
temperatures will bottom out mainly in the 50s...to the middle 60s. Patchy
fog is expected to develop in the typically prone locations.

Friday...

High pressure moving off the coast will allow southwest flow to pump
an unseasonably warm to hot airmass into southern New England.
Given 850 mb temperatures rise to between +16c and +18c...high temperatures should
top out mainly in the upper 80s to possibly near 90 under at least
partly sunny skies. Upper level riding and lack of synoptic forcing
should keep the weather dry. Humidity will also increase...but it
will not be as oppressive as what we saw yesterday.

Friday night...

An unseasonably mild and muggy night anticipated with southwest winds
ahead of an approaching cold front. While we can/T rule out a spot
shower/thunderstorm after midnight in the warm air advection
pattern...mainly dry weather expected with forcing well to our west.
Low temperatures will only bottom out in the upper 60s to the lower 70s.
Areas of fog may also develop...especially near the South Coast.

Saturday and Saturday night...

A humid day on Saturday with dewpoints near 70 ahead of an
approaching cold front. Plenty of low level moisture/forcing and
enough instability will be available for scattered showers and
thunderstorms sometime Saturday into Saturday night. As is usually
the case...timing is uncertain so not expecting the entire day to be
a washout. The most likely timeframe for the bulk of the
activity appears to be Saturday afternoon and night.

Given precipitable waters near 2 inches...the main concern will be heavy rain and
perhaps localized flash flood flooding if activity can train. In
addition...while wind fields aloft are not ideal for severe weather
they do increase a bit towards 00z. Despite weak middle level lapse
rates...70 dewpoints may allow enough instability develop for a few
strong to severe thunderstorms. The main threat would be isolated
strong to damaging wind gusts.

Sunday through Tuesday...

The cold front should be offshore by daybreak. However...some
showers may linger into Sunday morning across eastern New England.
Otherwise...strong high pressure will build in from the west
bringing dry weather through early next week. Temperatures will be
noticeably cooler along with much lower humidity values. High temperatures
will mainly be in the 70s.

&&

Aviation /07z Wednesday through Sunday/...
forecaster confidence levels...

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

Short term /through Thursday/...high confidence.

Outside of some early morning thunderstorms this morning across
mainly extreme northern Massachusetts and S New Hampshire and some brief fog in east Massachusetts.
Conditions should be mainly VFR through the day on Thursday. This is
thanks to a cold front which will move across the region this
morning. With this front...winds shift from S-SW to west-northwest and may
briefly gust to 20 knots. The front is offshore after 12z.

Kbos terminal...high confidence.

Kbdl terminal...high confidence.

Outlook...Thursday night through Sunday...

Thursday night and Friday...high confidence. Mainly VFR conditions
other than late night/early morning patchy ground fog in the
typically prone locations.

Saturday and Saturday night...moderate confidence. A period of MVFR-
IFR conditions expected in low clouds/fog patches and scattered
showers/thunderstorms. Timing uncertain at this point...but best
chance for scattered showers/thunderstorms will be Saturday
afternoon and evening.

Sunday...moderate confidence. MVFR conditions may linger across
eastern New England into the morning. Otherwise...VFR conditions
expected.

&&

Marine...
forecaster confidence levels...

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

High confidence through the period Wednesday night.

A cold front crosses the waters early this morning...with the
possibility of a brief gust to around 20 knots as it moves
through. These gusts will be associated with a wind shift to the
W-NW. These west-northwest winds continue into the day today with a few
gusts to around 15 knots possible. Otherwise...conditions remain
below Small Craft Advisory thresholds through the period.

Winds shift back to the SW tomorrow...with seas generally
remaining at 3 feet or less through Thursday.

Outlook...Thursday night through Sunday...

Thursday night...high confidence. High pressure nearby will keep
winds/seas below Small Craft Advisory thresholds.

Friday...moderate to high confidence. Near shore southwest wind
gusts around 20 knots should develop in the afternoon with good
mixing over the land. SW wind waves/choppy seas should develop
Friday afternoon especially near shore.

Friday night and Saturday...moderate confidence. Areas of fog may
affect the southern waters. Southwest wind gusts around 20 knots
are expected ahead of an approaching cold front. There will be the
risk of scattered showers and thunderstorms Sat afternoon and evening with
a few strong storms possible. Locally strong wind gusts will be the
primary concern.

Sunday...front begins to move offshore slowly but showers may linger
especially in the morning. Winds will be from the north northeast.

&&

Climate...
Boston Logan Airport reached 93 degrees yesterday. This is the
warmest temperature in Boston so far this Summer.

&&

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

&&

$$
Synopsis...Frank/doody
near term...doody
short term...doody
long term...Frank
aviation...Frank/doody
marine...Frank/doody
climate...staff

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