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Area forecast discussion 
National Weather Service Taunton Massachusetts
134 PM EDT Tuesday Jun 30 2015

Synopsis...
warmer temperatures move in Tuesday ahead of an approaching cold
front. This front will bring showers/scattered thunderstorms very
late Tuesday night and Wednesday. The front stalls near the South
Coast into Thursday...with a few more showers or thunderstorms
possible. This front pushes south of the coast Friday...with weak
high pressure bringing mainly dry and seasonable weather through
this weekend.

&&

Near term /until 6 PM this evening/...
130 PM update... only minor adjustments mainly to bring
temperatures/dewpoints up to current trends. Otherwise forecast is on track.

Previous discussion...

A partly sunny and pleasant day in store for the region.
Seabreezes will develop once again. A middle level shortwave will
result in showers and thunderstorms developing to our west this
afternoon. The issue at hand will be to see how much instability
develops over the western half of southern New England. Cannot
completely rule out the possibility of a thunderstorm...so will
continue to mention isolated thunderstorms this afternoon. At this
time...the greatest risk appears to be across northwest Massachusetts.

&&

Short term /6 PM this evening through 6 PM Wednesday/...
other than isolated to scattered showers/thunderstorms this
evening across the western half of southern New England...dry
weather will dominate through midnight. A potent shortwave and its
associated cold pool aloft will approach from the west toward
daybreak. The timing remains uncertain...but the consensus
indicates an increasing risk for rainfall after midnight...with
most of the area likely seeing a risk for showers between 09z and
12z.

Lots of shear projected to be in place. The main question will be
the amount of instability. The current timing is climatologically
unfavored...but not without precedent. The latest guidance does
generate cape of 700-1500 j/kg by early afternoon. With strong
shear already in place...we still cannot rule out a few strong to
severe thunderstorms Wednesday morning into Wednesday afternoon...
should enough instability generate fast enough.

Heavy rainfall will also be a threat. The main question for later
Wednesday afternoon is if a second round of showers/thunderstorms can
develop across the interior ahead of a cold front. Models continue
to dry the column late in the day...so there is limited window
for a second round of convection. The deeper layer shear is
projected to also weaken in the afternoon as well.

&&

Long term /Wednesday night through Tuesday/...
highlights...

* continued threat of showers and thunderstorms Thursday
* looking mainly dry and seasonable Friday through the 4th of July
weekend with confidence increasing somewhat.

Overview and model preferences...
persistent east Pacific block remains in play through the long term.
However...shortwave energy will be moving out of northern
Canada...shifting the longwave trough over the Great Lakes
NE...leading to mainly zonal flow across the area toward the end
of the week. There is actually reasonable agreement between 30.00z
model guidance. While this zonal flow does suggest lower
confidence in timing of any specific feature...it also suggests
that anything that develops will be weakened and mainly open.
Given the generally good agreement...and lack of significant
differences a blend of the operational runs with the previous
forecast should work well for this update.

Details...

Wednesday night into Thursday...
a cold front will be slowly crossing the region Wednesday night...stalling
in vicinity of of the S coast as it becomes parallel to the upper steering
flow. Column still has enough moisture...shear and moderate middle
level lapse rates during the overnight hours to maintain at least
some risk of ts/rain showers as the front moves through. However...with
the lack of a surface connection...will likely see a drying trend
toward the morning hours. By daylight on Thursday...a pocket of steep
upper level lapse rates in place...and with the front stalling
nearby combining with one last upper level shortwave rotating
through to yield yet another round of diurnal -shra and possibly a
ts. As previous forecaster noted...shear remains elevated as well.

Friday...
with upper level zonal flow in place...a weak ridge and attendant
high pressure will be moving across the area...forcing the weak front
further to the S. Mainly dry day as available BUFKIT data shows a
dry column and subsidence. A slight increase in 850 mb temperatures suggest
highs are slightly on the warmer increased sky cover a bit
in the west as well on the periphery of the deepening wave well west of
the region. Side of normal away from the
coastlines where sea breeze will dominate.

The weekend...
confidence in the forecast begins to wain here mainly due to the
development of a weak warm wave to the S of the upper level ridge
which could generate enough lift for -shra development Sat or sun.
However...at the same time...the Bermuda looks to gain
strength...amplifying the ridge upstream of a stronger wave in
central Canada. Therefore...it/S a battle between this ridging and
the weak wave to the S. Given the robust nature of the ridge and
amplification of the Bermuda high...will lean toward the
drier...high pressure solution at this time. But there is room for a
shower should the weak wave to the S shift a bit further north within
the weak flow regime to the S of the ridge. Building ridge and
increasing middle level temperatures suggest temperatures mainly above normal.

Early next week...
the robust shortwave to the west across southern Canada will be moving east
and could lead to a more unsettled pattern however...this will be
dependent on the final amplitude of the ridge in place across the
region.

&&

Aviation /18z Tuesday through Sunday/...
forecaster confidence levels...

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

Through 00z...high confidence. VFR. Very low chance for a brief
shower/T-storm in northwest Massachusetts late today. Sea breezes continue at
coastlines.

Tonight...moderate confidence. VFR this evening. May see some low
clouds develop late at some locations...with the greatest risk for
this along the southeast New England coast. May also see an area
of showers and thunderstorms work into western New England toward
daybreak. Confidence in the timing at a particular location is the
lowest confidence part.

Wednesday...high probability for widespread thunderstorms and rain. Risk for a few
strong storms and heavy rainfall. IFR and MVFR conditions likely
in shra/tsra.

Kbos terminal...high confidence in taf.

Kbdl terminal...high confidence in taf.

Outlook...Thursday through Saturday...

Thursday...moderate confidence.
Mostly VFR...but scattered showers/thunderstorms possible in the afternoon with
MVFR conditions.

Friday and Sat...moderate confidence.
Mainly VFR with high pressure...but still a bit of uncertainty
regarding a shower risk Fri-Sat.

&&

Marine...
forecaster confidence levels...

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

Short term /tonight into Wednesday/...high confidence.

Today and tonight...weak pressure gradient will keep winds/seas
below Small Craft Advisory thresholds. Some fog may develop toward
daybreak Wednesday across the southern coastal waters.

Wednesday...high confidence. SW wind gusts up to 20 knots...with
Small Craft Advisory seas over southern waters. Visibilities limited in
showers and scattered thunderstorms...along with areas of fog.

Outlook...Thursday through Saturday...

Thursday...high confidence.
Winds weakening and shift to the west. Lingering swell remains across
the waters...with wave heights averaging 5-7 feet. Small craft
advisories remain for this swell. Some showers and thunderstorms
linger...especially across the southern waters.

Friday and Sat...high confidence.
High pressure over the waters leads to a period of mainly quiet
boating weather.

&&

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

&&

$$
Synopsis...Belk/doody
near term...Belk/doody/rlg
short term...Belk
long term...doody
aviation...Belk/doody/rlg
marine...Belk/doody

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