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Area forecast discussion 
National Weather Service Taunton Massachusetts
321 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 /through today/...
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 /tonight/...

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

Details...

Wednesday and Wednesday night...

A fairly strong shortwave and associated cold front will cross the
region Wednesday afternoon and evening. High temperatures should still reach
into into the upper 50s to middle 60s ahead of the front. We will
see scattered showers with the front given decent forcing and some
marginal instability. Most likely time frame is Wednesday afternoon and
early evening. Its quite cold aloft and middle level lapse rates are
very impressive around 8c/km! If we can muster a few hundred j/kg
of Cape...May even see an embedded thunderstorm or two. Confidence
on thunder is low at this point...but given cold pool aloft there is
at least this risk for some graupel/small hail and perhaps even
gusty winds in the heaviest showers. This activity should wind down
by Wednesday evening.



Thursday through Monday...

Anomalous closed upper level low sets up across northern New England
and into Quebec. The result will be below normal heights and cooler
than normal temperatures in southern New England. Overall...high temperatures
will range from the upper 40s to middle 50s much of the time but
some moderation is possible by Monday. As for precipitation chances...the
vast majority of the time should feature dry weather.
However...given cold pool aloft a few spot showers will be possible
at times...especially in northern sections during the afternoon
hours. Low risk for even a few wet snow flakes to mix in for
a time across the higher terrain...but would be of no impact.

There is one fly in the ointment. We will have to watch a more
significant low pressure system Sat night/sun. Most of the model
guidance keeps that system well to our south. The 12z European model (ecmwf) is a
bit closer then the rest of the guidance...but even that would keep
US dry. Again...odds strongly favor keeping this system south or
our region given anomalous closed low sitting just to our north.

&&

Aviation /07z 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 despite the risk for 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 should remain below
small craft thresholds. 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...coastal Flood Advisory until 4 am EDT early this morning for
maz007-015-016-019-022-024.
Rhode Island...none.
Marine...Small Craft Advisory until 5 am EDT early this morning for
anz231>234.
Small Craft Advisory until 4 am EDT early this morning for
anz230-236.
Small Craft Advisory until midnight EDT tonight for anz235-237-
251.
Gale Warning until 4 am EDT early this morning for anz250-
254>256.

&&

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

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