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Area forecast discussion 
National Weather Service Taunton Massachusetts
404 am EDT Tuesday Apr 21 2015

Synopsis...
scattered showers and isolated thunderstorms along with mild
temperatures this morning...gives way to a drying trend this
afternoon. A cold front will bring scattered showers...and perhaps
even an isolated thunderstorm or two...Wednesday afternoon and
evening. Unseasonably cool weather follows Thursday through this
weekend with just a spot shower from time to time.

&&

Near term /until 6 PM this evening/...
latest runs of the hrrr look to have a very good handle on the
forecast for the next several hours this morning. Lots of elevated
convection across the western half of southern New England already
this morning. So far...the main hazards have been the lightning
and briefly torrential rainfall. These storms were moving along at
35-45 miles per hour...so am not overly concerned about significant
widespread flooding at this time. Some poor drainage areas could
experience nuisance flooding for a time this morning. We will
continue to monitor rainfall rates though.

Expecting rapid clearing behind a warm front later this morning
with temperatures soaring into the upper 60s to near 70 most
locations. Westerly winds will allow even the coastal locations to
get in on the warm temperatures...unlike this past Saturday.

&&

Short term /6 PM this evening through 6 am Wednesday/...
a shortwave will be approaching from the west...bringing a chance
for some showers to portions of western Massachusetts by daybreak Wednesday.
With a cold front having already passed through our region late
this afternoon...models do not show much rainfall as instability
is rather limited. Much of tonight should remain dry across
southern New England with seasonable minimum temperatures.

&&

Long term /Wednesday through Monday/...

Highlights...

* scattered showers Wednesday with a low risk of thunder/small hail
* seasonably mild temperatures Wednesday
* unseasonably cool Thursday-sun with a spot shower or two at times

Overview...

Overall the 12z guidance is in good agreement within the medium and
long range. However exact timing and strength of each system still
needs to be worked out. Upper level low will continue to dominate
the region through the extended...pinwheeling between the Great
Lakes and New England. This system will yield to a more showery and
cooler forecast for the rest of the week and into the weekend.

Details...

* Wednesday and Wednesday night...moderate confidence.

Strong shortwave will move through the flow on Wednesday developing
a surface low across Hudson River valley and into southern New
England. This low will bring scattered rain showers and isolated thunder
to the area by the afternoon hours. Appears we may try to warm
sector allowing surface temperatures to reach into the low to middle 60s. This
will steepen the lapse rates to around 7-8 c/km as 500 mb temperatures are
-24c. Model guidance is also indicating that some surface Cape May
develop which will help in thunderstorm development. In fact we
could see small hail/graupel as freezing heights will be low
thanks to the cold pool. Still a lot of details to work out but
something to watch in the coming day.



* Thursday into Monday...moderate confidence.

Strong cut off low will continue to spin over the northeast during
this time period. New England could see a several waves develop and
push through the region. However may see a lot of diurnal cumulus and
diurnal showers developing rather than widespread rain. These
showers will be diurnally driven as cold pool aloft will be overhead
steepening the lapse rates. Areas that have the best chance for
any precipitation will be north of the Pike...closer to the low pressure.

Lastly expect temperatures to be about 5-10 f below average for the week
thanks to the cooler temperatures aloft via the cold pool. In fact some
areas may not see the 60s for the rest of the week and into the
weekend.

&&

Aviation /08z Tuesday through Saturday/...
forecaster confidence levels...

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

Short-term /through Tuesday/...

Through 12z...line of elevated thunderstorms moves into the
central and eastern sections of southern New England. Brief gusty
winds and torrential rainfall are the biggest threats.

Today...conditions improving to VFR by midday. Cold front moves
through with winds shifting west/SW this afternoon.

Tonight...high confidence in mainly VFR conditions despite the
risk for a spot shower or two.

Kbos taf...high confidence in trends. Moderate confidence in
timing. Morning push likely to be affected. Also low risk of a
thunderstorm between 08z and 12z.

Kbdl taf...high confidence in trends. Moderate confidence in
timing. Risk for thunderstorms has likely moved east of the
terminal for the rest of this morning.

Outlook...Wednesday through Saturday...

Wednesday...moderate confidence. A cold front will bring a round of
scattered showers mainly Wednesday afternoon/early evening. Low risk for
even a few rumbles of thunder and perhaps small hail/graupel with
the heaviest showers.

Thu/Fri/Sat...high confidence. Mainly VFR. Conditions could lower to
MVFR quickly in a brief diurnally driven shower or two.

&&

Marine...
forecaster confidence levels...

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

Short term /through tonight/...

Will likely be able to convert the rest of the gale warnings for
the outer southern New England waters to small craft advisories.
Still need to watch for thunderstorms this morning...some of which
could produce brief gusts up to 35 knots. Visibility improves later
today with winds and seas continuing to diminish tonight.

Visibilities may be limited at times.

Outlook...Wednesday through Saturday...

Wednesday...high confidence. Modest west to southwest flow expected
ahead of a cold front...but speeds will be near Small Craft Advisory especially across the
near shore waters. A few showers Wednesday afternoon and evening with a
low risk of an isolated thunderstorm with small hail.

Thursday through Saturday...high confidence. Modest westerly flow
as a result of closed low pressure across Quebec. Enough cold
advection over the waters will be present to generate periods of 25
knot wind gusts. Marginal Small Craft Advisory seas expected across the outer-waters
at times...but with good visibility.

&&

Tides/coastal flooding...
east to southeast winds will increase through tonight. Guidance
continues to track strongest winds across New England early this
evening...before high tide occurs along the South Coast /around
03z/ and East Coast /about 06z/. This results in winds beginning
to slacken as high tide approaches. Also system is fairly
progressive so duration of onshore winds is limited.

Estofs continues to be more robust and realistic than etss with
surge values 1.0-1.5 feet at the time of high tide. Seas also building
to 10-15 feet just offshore. This should be sufficient to generate
areas of minor coastal flooding and splash over. Thus will continue
with a coastal Flood Advisory for these locations during this
evening and early Tuesday morning high tides.

Winds do not look strong enough at the time of high tide for a
moderate coastal flood event.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...Small Craft Advisory until 6 PM EDT Wednesday for anz235-237-
250-254>256.
Small Craft Advisory until noon EDT Wednesday for anz251.

&&

$$
Synopsis...Belk/dunten
near term...Belk
short term...Belk
long term...dunten
aviation...Belk/dunten
marine...Belk/dunten
tides/coastal flooding...staff

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