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Area forecast discussion 
National Weather Service Taunton Massachusetts
742 am EDT Wednesday Jul 1 2015

Synopsis...
a frontal system will bring showers...and a chance for strong to
severe thunderstorms...into this afternoon. This front stalls
near the South Coast Thursday...before moving offshore Thursday
night. Aside from a spot shower possible Saturday...mainly dry and
seasonable weather is expected into early next week.

&&

Near term /until 6 PM this evening/...
740 am update...

Nose of the low level jet is combining with middle level instability
to generate some thunderstorms this morning. These storms are
racing northeast about 45 miles per hour. The main concern will be for urban/poor
drainage flooding. Noted a fairly strong surface-based inversion
in the model soundings. That means it will be tough to get the
stronger winds aloft down to the ground.

Made minor tweaks to forecast to reflect the latest observed
trends.

Previous discussion...

A potent middle level shortwave and its associated cold pool aloft will
approach southern New England early this morning. This will be
enough to initiate some showers. Surface instability remains lacking
during this time. However...there is some elevated instability
leading to a few thunderstorms across western New England. Recent
trends have been for these thunderstorms to weaken as the move
farther east.

The larger question will be how quickly deeper instability can be
developed this morning. Guidance continues to advertise a quick
increase of cape to around 1000 j/kg. We also noted the arrival of
rather strong low level shear...which will only help to focus this
energy. That said...we do not seem to maximize the shear and
instability at the same time. Thus...not expecting widespread
severe weather at this time. Thinking is for a few strong to
severe thunderstorms...with the main threat being damaging winds
and/or hail.

Precipitable water values remain near 2.0 inches into early
afternoon. Coupled with the strong low level jet...this is a
recipe for heavy rainfall within the showers and thunderstorms. A
quick inch of rain in less than an hour is not unreasonable. This
could result in poor drainage and urban flooding. The benefit of
the strong low level jet is storms should move along at a fairly
good speed. This will reduce the likelihood of flooding somewhat.
Main flooding threat will be with any training thunderstorms.

&&

Short term /6 PM this evening through 6 PM Thursday/...
a few leftover showers...and perhaps a thunderstorm or two...are
still possible early this evening. Otherwise expecting dry
conditions for most of tonight. A cold front will be slowly
crossing our region tonight...likely stalling near the South Coast
of New England for a time late tonight into Thursday. Latest
guidance continues to advertise a dry atmosphere...so expecting
most of Thursday.

&&

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

* seasonable to slightly above seasonable temperatures expected.
* Low chance of a shower mainly on the 4th.

Overview and model preferences...models continue to indicate a shift
in the overall pattern from a highly amplified regime to one that is
more progressive and zonal. This is in spite of the fairly robust
ridges in place across the east Pacific and the Bermuda high north of the
Antilles. Although this more zonal flow pattern does take on a
longwave trough feature between the two ridges...it is not overly
deep/sharp. This allows the ridging associated with the Bermuda
high to become the dominant player for our sensible weather into early
next week. At this point a much deeper northern stream vortex will be in
play...and will transition the drier and more stable regime across
the NE Continental U.S. To a more unsettled pattern. The only fly in the
ointment is on the 4th unfortunately...but more on that below.

Details...

Thursday night into Friday...the first in a series of middle level ridges will
be moving through the zonal flow pattern during this period. This
introduces a mainly dry period with weak high pressure in place across
southern New England. There remains a front stalled to the S...with
some upper level moisture suggesting some partly cloudy conditions.
Otherwise...850 mb temperatures between +10c and +12c suggest highs near to
slightly above seasonal normals across the region away from the
coast were sea breezes are likely.

Friday night into Sat night...with this nearly zonal flow in
place...it/S not just ridging...but weak shortwaves to concern
ourselves with. Models continue to indicate a weak packet of
energy passing through the region during the early weekend. The
overall column is relatively dry...with precipitable waters near normal for
early July. However...with the front stalled to the S...the
development of a weak wave of low pressure could bring about modest
lift along the southern tier of southern New England during the day Sat.
There are two camps here...GFS and some ensemble members with quantitative precipitation forecast
across the region...and the European model (ecmwf) and other ensemble members
without. Therefore...confidence not high on precipitation chances...but
it is likely to not be a washout in either case given how weak the
wave is and the lack of moisture. Just a few passing showers to
contend with.

Sun into Monday...as deep er wave forms across the Canadian prairie
lands...a secondary ridge will amplify in response to warm
advection from the Bermuda high to the southeast. This will yield another
period of drier and warmer conditions across southern New England.
Better chances for temperatures inching above normal during this
stretch...thanks to more influence from the southeast.

Toward middle week...the aforementioned wave will begin a slide to
the east. This particular feature is more robust than previous
waves...so it/S likely a period of wetter and unsettled weather will
return by the middle portion of next week. Uncertainty in exact
timing.

&&

Aviation /12z Wednesday through Sunday/...
forecaster confidence levels...

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

Today...high probability for widespread rain showers and scattered thunderstorms and rain.
Risk for a few strong storms and heavy rainfall. IFR and MVFR
conditions likely in shra/tsra. Conditions improving to VFR during
this afternoon...but scattered thunderstorms and rain may redevelop later this afternoon.

Tonight...moderate confidence. Patchy MVFR/IFR stratus and fog
developing...otherwise VFR.

Thursday...high confidence. VFR.

Kbos terminal...high confidence in taf trends. Moderate confidence
in timing.

Kbdl terminal...high confidence in taf trends. Moderate confidence
in timing.

Outlook...Thursday night through Sunday...

High confidence. Mainly VFR. A few showers possible on Sat...but
mainly dry otherwise. Sea breezes likely most days.

&&

Marine...
forecaster confidence levels...

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

Winds and seas will increase in response to a frontal system
approaching the waters later today. Small craft advisories have
been extended for the southern outer waters and Rhode Island and
Block Island sounds.

Outlook...Thursday night through Sunday...

Thursday night into Friday...high confidence. Weak ridge of high pressure will
be moving over the waters through the period. Any lingering swell
above 5 feet will recede overnight with quiet boating weather expected
through the rest of Friday.

Sat and Sunday...moderate confidence. This period will be
dependent on how closely a weak wave of low pressure passes to the S
coast on Sat. If it passes close enough...a period of swells
exceeding 5 feet is possible. Otherwise...mainly quiet boating
weather will continue especially as high pressure returns Sunday.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...Small Craft Advisory from noon today to 6 PM EDT Thursday for
anz254>256.
Small Craft Advisory from 8 PM this evening to 3 PM EDT
Thursday for anz235-237.

&&

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

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