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Area forecast discussion 
National Weather Service Taunton Massachusetts
1005 PM EDT Tuesday may 26 2015

Synopsis...
warm and muggy conditions will increase through tomorrow.
Scattered showers and thunderstorms are expected each day...
with Wednesday and Thursday having the higher potential for
strong storms.

&&

Near term /until 6 am Wednesday morning/...

1000 PM update...

Any left over showers have dissipated this evening. Southern New
England continues to remain in the warm moist sector as warm front
is well north with a cold front well to the west. We have already
started to tap into the Gulf moisture so precipitable waters are on the increase
as well. Low confidence if any shower will develop overnight as
we do have some elevated instability...but lack the trigger
mechanism.

Temperatures are slow to drop this evening with many sites still
in the 70s away from the South Coast/cape and islands. Biggest
question is the potential for fog. Visibilities are slowly dropping
across ack and mvy...but feel that stratus may be the biggest
issue overnight. Will wait and see latest forecast soundings to
determine fog potential...but right now have a low confidence.

Previous discussion...

Tonight...the upper ridge over the eastern Seaboard will start to
break down which will allow for better moisture and instability over
southern New England. This could lead to a few sprinkles or light
rain showers overnight. Most of the model guidance was dry but the
GFS has been indicating not just sprinkles but a good two tenths of
an inch of precipitation. Feel this may be some convective feedback from
the convection over New York and PA this evening.

Otherwise...expect some cloudiness and that with the moist
southwesterly winds will keep temperatures from falling too much.
Expect low temperatures mainly in the 60s. That warm...moist air
flowing over the colder ocean will likely result in areas of dense
fog over the ocean and bleeding onto the South Coast...cape...and
islands.

&&

Short term /6 am Wednesday morning through Wednesday night/...
Wednesday...another warm and muggy day for southern New England with
temperatures topping out in the upper 80s in the Connecticut and
Merrimack valleys with middle 80s elsewhere. Exception to this is
along the South Coast...cape...and islands where both onshore winds
and perhaps lingering marine stratus and fog will keep temperatures
from climbing. Expect high temperatures in the 60s in these
locations.

This looks like the better day for some showers and thunderstorms to
affect southern New England. However...this doesn/T appear to occur
until late afternoon and evening. Instability is a bit better than
it was today but is still somewhat lacking and middle level lapse rates
leave plenty to be desired. The main focus for storms will be over
New York and Pennsylvania where the better instability and focusing
will be. These storms...much like today...will likely move into the
western part of the County Warning Area towards the late afternoon/early evening.
While these storms have the potential to be strong to severe...the
most likely threats with these storms are heavy downpours and gusty
winds.

Wednesday night...showers and thunderstorms are expected to last
into the evening as wind shear increases with a strong low level jet
moving over southern New England. Another warm night in store with
lows in the 60s.

&&

Long term /Thursday through Tuesday/...
overview and model preferences...

To start off...medium range models and ensembles keep overall upper
level pattern in place across the lower 48...with ridging along or
just east of the eastern Seaboard and troughing across The Rockies into
the southwest. Model trends continue to signal slow deamplification
of the upper pattern going into this weekend...with ridge axis
flattening out across the northeast as a surface front that tries to
work across the region washes out during Friday. Bermuda high re-
establishes for early this weekend while another front works southeast out
of Quebec. This front looks strong enough to work slowly southeast as the
western Atlantic ridge shifts S and upper troughing takes over across
the northern stream. Big question will be whether the front will
clear off the S coast early next week or will it stall closer to or
over southern areas.

Used a blend of available guidance for this forecast package...
though did lean toward more toward the ensembles from this weekend
Onward due to timing differences with the approaching front. For the
latter timeframe...leaned closer to the slower European model (ecmwf) and ecens
means.

Details...

Thursday...will see leftover scattered showers/thunderstorms across western areas
Thursday morning with precipitable waters on order of around 1.5 inches. The front
shifts S taking the higher precipitable water air with it...so expect the precipitation
to tend to weaken though will linger where milder temperatures are thanks
to diurnal influences. Instability also shifts offshore and weakens
so expect any thunderstorms to taper off by around midday. Best shot
for precipitation will be from the Merrimack valley southeast across central Massachusetts to
the middle and lower CT valley. Can not rule out a few quick downpours
through midday with the higher precipitable water airmass. Will see areas of
fog...locally dense...develop across S coastal areas Thursday night into
Friday morning.

Friday...models started to signal drier air working in on Monday...
but most of the model suite has high pressure ridge building S out of
Quebec so expect a dry but mild day. Dewpoints drop a bit...down to the
50s...but will begin to rise again Friday night. Will see a light east-southeast
wind flow so will be cooler along the coast...highs mainly in the
70s except 65-70 across coastal areas...ranging to the lower to middle
80s across the CT valley.

Saturday...high pressure repositions off the eastern Seaboard so SW
winds kick in again bringing a return to more humid air. Another
cold front start to approach out of Great Lakes and western Quebec.
Also noting increasing instability parameters ahead of the front...
with k indices rising to the Lower-Middle 30s and tq values in the
upper teens so could see some elevated convection which could last
into Sat night. Best lift moves closer during late Sat/Sat night so
will see scattered showers/thunderstorms develop. A precipitable water swath of 1.6 to
1.75 inches pushes out ahead of the front...so may see some heavier
downpours with any convection. Will see quite a bit of sunshine
early Saturday...so temperatures will rebound to the 80s for most locations
except the Lower-Middle 70s along S coastal areas.

Sunday...cold front slowly across the region Sunday morning...then
reaches the S coast by Sunday night. Expect chance showers and
thunderstorms. Still some timing issues between the GFS and European model (ecmwf)
but a bit better for this timeframe. With the slow movement of the
front...expect scattered precipitation to continue through Sun night.

Monday-Tuesday...somewhat lower confidence due to timing and
placement differences with the front and whether it stalls near the
S coast or offshore. At this point...kept chance probability of precipitation across central
and southern areas through midday then should push just offshore but
may linger across the islands through most of the day Sunday. May
see some thunderstorms early...then instability works offshore but
could still see some showers while high pressure moves across northern
New England.

Have kept slight chance probability of precipitation going for southern areas into Tuesday
as front looks to linger...then may try to make a run back NE as the
high pushes off into the Gulf of Maine.

&&

Aviation /02z Wednesday through Sunday/...
forecaster confidence levels...

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

Tonight...moderate confidence. Any leftover showers across northwest Massachusetts
should dissipate by 03z...but may produce brief MVFR cigs/vsbys.
Otherwise...mainly VFR to start...then deteriorating to MVFR-IFR
in areas of fog along the South Coast...cape...and islands. Could
see passing shower overnight.

Wednesday...moderate confidence. IFR along the South Coast during
the morning should push offshore. Anticipate VFR conditions across
the interior... dropping to MVFR within any -shra/-tsra that
develops. Expect SW winds to gust up to 20-25 knots at times mainly
across Rhode Island/southeast Massachusetts.

Wednesday night...moderate confidence. Conditions deteriorate to
IFR along the South Coast...cape...and islands as maritime fog and
stratus rolls back in.

Kbos terminal...high confidence in taf.

Kbdl terminal...high confidence in taf. Could see conditions drop
to MVFR within a pop-up thunderstorm today.

Outlook...Thursday through Sunday...moderate confidence.

Thursday...mainly VFR. Will see scattered -shra/thunderstorms and rain with local MVFR-IFR
conditions. Expect areas of fog develop during the late night/early
morning period with IFR-LIFR visibilities.

Friday...VFR. May see local MVFR-IFR conditions early Friday morning
along S coast in patchy fog...then will lower again late Friday
night/Sat morning to MVFR-IFR.

Saturday...patchy fog early Sat morning with MVFR-IFR conditions
will improve. Scattered rain showers/thunderstorms and rain Sat through Sat night with local MVFR-
IFR conditions. SW winds gusting to 20-25 knots mainly along the coast
Sat afternoon/evening.

Sunday...scattered showers thunderstorms linger through Sunday...but should end
Sun night. May see brief MVFR conditions.

&&

Marine...
forecaster confidence levels...

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

Short term /through Wednesday night/...high confidence.

Small craft advisories are up through tonight...mainly on the
outer waters for seas and southwesterly winds. Seas will climb to
5 feet and remain there through the period. Small craft advisories
will expire at midnight for the inner waters. Southwesterly winds
will diminish...but may linger for a few hours after sunset.

In addition...areas of dense fog are likely to develop on the
waters tonight...substantially reducing visibilities.

Outlook...Thursday through Sunday...moderate confidence.

Thursday...expect SW winds gusting to around 20 knots. Seas build to
around 5 feet across the southern waters to the outer waters east of Cape
Cod...but should subside below 5 feet Thursday night. Visibilities reduced in
areas of fog...locally dense offshore both Thursday and Friday nights.

Friday...light north-NE winds become east during the day...then shift to
S-SW Friday night. Expect winds and seas below small craft criteria.

Saturday-Sunday...SW winds may briefly gust to 25 knots during Sat on
the eastern waters...otherwise expect gusts up to 20 knots seas build
again to around 5 feet across the outer waters...which will slowly
subside late sun or Sun night.

&&

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

&&

$$
Synopsis...rlg/evt
near term...dunten/rlg
short term...rlg
long term...evt
aviation...rlg/evt
marine...rlg/evt

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