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Area forecast discussion
National Weather Service Taunton Massachusetts
947 PM EDT Tue Jun 27 2017

Synopsis...
a frontal passage will usher in drier air across the region
overnight. High pressure builds fair and dry weather for
Wednesday. A warming trend begins for the latter half of the
week. Expect Summer heat and humidity from Friday through the
weekend. A warm front passes Thursday night, bringing scattered
showers and thunderstorms. More showers and thunderstorms are
possible from Friday through the weekend. A cold front tries to
shift toward the region early next week.

&&

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

10 PM update...

Convection now offshore with frontal passage/wind shift back
from Oregon-bdl-hfd and will continue moving east ushering in drier
air across the region overnight. More of a early fall airmass
tonight with lows in the upper 40s across northwest Massachusetts with 50s
elsewhere.

Previous discussion...
once the convection dies down, expect dry weather the remainder
of the night. Light winds and mostly clear skies will allow fog
to form in some spots, especially parts of the CT valley.

Dew points in the upper 40s and 50s should leave room for temps
to cool down into the 50s most places by early morning.

&&

Short term /6 am Wednesday morning through Wednesday night/...
the upper trough is overhead along with its cold pool. So
continued support for lift. But the airmass will be much drier
with a moist layer limited to the 750-850 mb layer. Expect
diurnal clouds but precip is unlikely. Temps aloft will be
equivalent to 8-10c at 850 mb, supporting Max temps 75-80.

High pressure maintains mostly clear skies and light wind should
allow overnight temps to reach the 50s, with lower 60s in the
urban areas.

&&

Long term /Thursday through Tuesday/...

Highlights...

* scattered showers/thunderstorms from Thursday night through
Sunday night
* very warm, humid conditions return Friday, lasting through
the weekend

Overview...

12z medium range models and ensembles continue same theme for
Summer conditions. Active northern stream in place with a broad
mid level fast flow that looks to continue through the upcoming
weekend at least.

500 mb short wave/cutoff low moves out of Saskatchewan and Manitoba
on Thursday, which will push across southern Canada into the
northern Great Lakes through this weekend, then into Quebec
Monday. Weak short waves will move along in the general west-SW
steering flow around the base of the cutoff low through the
broad trough to its S and SW. Will see rounds of scattered
showers/thunderstorms as each short wave moves across. Very
sultry airmass in place thanks to Bermuda high sitting off the
Carolina coast. Will see dewpts rising to the mid-upper 60s late
this week through the weekend. The offshore high and western
Atlantic mid level ridging will cause an approaching cold front
to stall west of the region.

Question will be when the 500 mb trough will move across the region
early next week. Model solution spread leading to lower
confidence on timing of cold front that may approach around
Monday or the 4th of July.

Details...

Thursday-Thursday night...
high pressure off the mid Atlantic/southeast U.S. Coast will keep dry
conditions across the region through about midday Thursday. A
warm front will start to approach, with some showers that may
develop across north and west mass, mainly north of the Mass Pike around or
after 21z. Will see some more instability start to work into west
mass/north central CT Thu night as the warm front moves across, so
have included chance thunder from W-E.

Highs Thursday will mainly be in the lower-mid 80s away from
the S coast, only in the 70s along the S coast. Overnight lows
will be in the mid-upper 60s.

Friday through Sunday...
with the ridge in place off the coast, continued SW flow
through this period. Typical summertime airmass in place, with
dewpts up to the mid and upper 60s with a few spots that may
touch 70, along with 850 mb temps rising to +16c to +18c Fri-Sat.
With the soupy airmass, will likely see nighttime fog develop
mainly around or after midnight as temps fall back close to the
higher dewpts.

Will see scattered showers and thunderstorms from the midday
through evening hours each day, especially across the interior.
Looks like best shot for convection will occur Friday
afternoon/evening, then again Saturday especially over western
areas. The ridge offshore may allow for somewhat drier air and
subsidence to move into coastal areas on Saturday, so could be
drier during the daylight hours. Approaching cold front on
Sunday will trigger another round of convection as well.

Will likely see some brief heavy downpours in some activity
thanks to pwats increasing to 1.5 to 1.8 inches, especially
Friday afternoon/evening and again Sat night-Sunday.

Some question as to whether some stronger storms will develop
during this timeframe. Will continue to monitor this aspect.

One other issue is possible heat headlines on Fri and Sat, due
to combination of high temps (lower 90s) and dewpts (up to 70
degs). Could reach high indices close to 95, which would trigger
possible advisories. Current forecast suggests lower 90s. Will
monitor this as well.

Monday-Tuesday...
low confidence on this portion of the forecast due to model
solution spread, mainly with frontal passage. Some question on
frontal passage late Sun night or Mon morning which will wash
out rather quickly as winds shift back to SW during Mon
afternoon. Another front may approach during Tue which may
trigger more convection.

&&

Aviation /02z Wednesday through Sunday/...
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.

Tonight...

Updated 10 PM...

T-storms now offshore with frontal passage/wind shift to the west-northwest
from Oregon- bdl-hfd and continuing to move east, ushering in
dry/stable airmass overnight. Earlier discussion below.

=====================================================================

Areas of fog possible after midnight with the best chance in
the CT River Valley north of Springfield.

Wednesday...

VFR and drier weather. Showers/tstms will fire again north of
mass, but all quiet in southern New England. West-northwest
winds.

Wednesday night...

VFR. Light winds and clearing skies. Patchy fog possible late at
night.

Kbos terminal...high confidence in taf. Showers and T-storms
likely this evening. A few of the stronger storms may contain
small hail and gusty winds.

Kbdl terminal...high confidence in taf. Showers and T-storms
diminish this evening.

Outlook /Thursday through Sunday/...

Thursday...high confidence.
Mainly VFR. Dry through midday, then scattered afternoon/
evening showers across north and west mass mainly north of the Mass Pike.
Showers/ thunderstorms possible entire region Thu night. Gusty
SW winds to 20- 30 kt developing along the S coast late Thu/Thu
night.

Friday through Sunday...moderate confidence.
Patchy early morning fog each day with local MVFR-IFR
conditions. Otherwise mainly VFR. Local MVFR-IFR in possible
strong thunderstorms, mainly during the midday through evening
hours.

&&

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.

Tonight...

Updated 750 PM...

Showers and thunderstorms over land will move over parts of the
waters this evening. Best chance will be along the Massachusetts
North Shore.

Have ended the small craft for the nearshore waters as S-SW
winds have diminished. Expect gusts up to 20 kt through around
04z or so. Seas generally 3 feet or less.

Wednesday and Wednesday night...

Winds become west-northwest at modest speeds. Seas 3 feet or less.

Outlook /Thursday through Sunday/...

Thursday...moderate confidence.
Small craft advisories will likely be needed. SW winds will
increase, with gusts to 25-30 kt highest across the southern
outer waters. Seas build to 6 to 8 ft over southern waters Thu
night.

Friday...moderate confidence.
SW winds continue, gusting to around 25 kt, diminishing after
midnight Fri night. Seas up to 5 to 7 ft. Scattered
thunderstorms, some with reduced visibilities and strong gusty
winds. Patchy late night fog.

Saturday-Sunday...moderate confidence.
SW winds continue, though diminishing. Seas around 5 ft on the
outer waters Sat, then slowly subside. Patchy late night fog
each night with reduced visibilities. Chance of
showers/thunderstorms.

&&

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

&&

$$
Synopsis...wtb/evt
near term...wtb/nocera/evt

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