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Area forecast discussion
National Weather Service Taunton Massachusetts
208 am EDT Thu Jun 29 2017

Synopsis...
high pressure brings dry and cool conditions early this morning.
A warm front moves through the region this afternoon with a few
showers and thunderstorms tonight as more humid air moves in.
Summer heat and humidity arrives Fri and continues into the
weekend. A cold front likely breaks the heat and humidity later
Sunday and will be accompanied by thunderstorms. Not as warm or
humid early next week including the Fourth of July Holiday.

&&

Near term /until 5 am this morning/...

2 am update...

Tranquil/dry and seasonable weather continues early this morning
across southern New England, with temps in the 50s away from the
coast and outside of the urban areas where temps were in the
60s. Cirrus canopy continues to stream across the region in
response to the warm air advection regime beginning to overspread the area.

Previous discussion...

Dry weather tonight with high pres south of new eng. Weak
shortwave will spread some mid/high clouds into new eng with
clouds increasing later tonight. Another cool night with dry
airmass in place and light winds. Lows in the 50s.

&&

Short term /5 am this morning through 6 PM Friday/...

Thursday...

Warm front lifts north across southern New England to near the Massachusetts/New Hampshire border late
in the day. No instability across southern New England and main focus for showers
will be to the north assocd with deeper moisture and mid level
Omega north of the warm front along with the nose of the 850 mb
jet. Can't rule out a few showers spilling into northern Massachusetts in
the afternoon but it should be a mostly dry day. Most sunshine
will be found toward the South Coast with most clouds north of
the Pike. Rather gusty S/SW winds developing in the afternoon
as the low level jet strengthens across southern New England. Gusts to 25-35 mph
expected, strongest in the coastal plain. Shallow mixing will
limit high temps to the upper 70s and lower 80s. While dewpoints
will be increasing, very humid air will remain to the west.
Expect dewpoints increasing to 55-60.

Thursday night...

Warm sector airmass in place. Increasing ki and elevated
instability as a piece of the low level jet shifts south into
southern New England will result in a few showers and isold T-storms moving
through. Milder night with lows remaining in the 60s as higher
Theta-E air moves into the region with increasing dewpoints.
This may lead to fog patches developing overnight.

&&

Long term /Friday night through Wednesday/...

Highlights...

* hot and humid conditions return Friday and continue into
Sunday
* increasing risk for scattered showers/thunder Friday into
Sunday
* cooler and less humid Monday and Tuesday

Overview...
12z model suite over the medium range period continues to
feature nearly zonal northern stream mid level flow, which keeps
systems moving along into this weekend. The big question
continues to be the timing of the approaching cold front out of
south central Canada and the Great Lakes, pushing far enough S
to bring cooler, drier conditions.

With each run, models continue to keep the front further north and west of
the region. Could see enough instability for diurnal convection to
develop across the interior Fri into Sat, while tending to be drier
closer to the coast as some residual subsidence building northwest across
coastal areas from the east-west elongated high pressure from Virginia/NC to the
western Atlantic.

By late this weekend, models continue to dig 500 mb trough over the
western Great Lakes/northern plains states, with responding mid
level flow becomes more SW across the northeast U.S. All short
range models signaling a short wave in the 500 mb flow moving
steadily southeast sun/Sun night, which will allow the pre-frontal
trough to move slowly southeast late Sat into sun. Models in fair
agreement on timing of this feature, pushing off the S coast
Sunday morning. Trailing cold front follows Sun night-early Mon,
then tends to stall along the northwest periphery of the Bermuda high,
while another 500 mb short wave moves east. Timing issues come into
play with this feature, as well as placement of the stalled
front and subsequent potential for precip during the 4th of July
Holiday into Wed.

Leaned toward a blend of available model guidance as well as
ensemble means through around 12z Mon, then transitioned to
ensemble means beyond this due to the timing and placement
systems amongst the individual models.

Details...

Friday-Friday night...
expect very warm temps and high humidities during this
timeframe. Dewpts rise to the mid-upper 60s with a few spots
briefly touching 70 during the afternoon/evening hours. As
approaching pre-frontal trough slows in the parallel SW wind
flow aloft, will see scattered showers/thunderstorms mainly from
Cape Ann across to central and west mass into north central CT Fri
afternoon/evening, then orienting west-east Fri night, running from
about the Mass Pike northward.

Could see some heavier downpours with some thunderstorms across
the interior Fri afternoon/evening as signaled by both the GFS
and ggem. CAPES are in the 1000-1200 j/kg range, along with k
indices in the lower-mid 30s into Fri evening. However, may see
some capping as 850 mb temps rise to +16c to +18c. 500 mb heights
slowly rise during the day as well, up to 5820-5840 M by around
00z Sat, which could also limit the potential for stronger
storms.

Expect friday's highs in the mid-upper 80s away from the S
coast, a bit cooler along the S coast and the higher inland
terrain. Can not rule out a few spots reaching 90.

Saturday-Sunday...
best instability/lift associated with the pre-frontal trough
moves across the region during this timeframe. Have likely pops
with this feature. Have mentioned scattered thunderstorms as
well. Also noted slis below zero, k indices in the lower 30s and
tq values up to 20 as this feature passes. Can not rule out
some gusty SW winds with some of the storms as well.

Signal from the 12z ggem that there could be some heavier
rainfall as the trough moves across late Sat into Sat night,
especially across NE CT/RI/se mass. Noting pwats up to 1.8 to 2
inches overnight Sat night, so could see some downpours that may
cause local street and poor drainage flooding.

Another aspect will be the very sultry conditions with dewpts
in the 65-70 degree range. A few spots may see heat indices in
the lower 90s during Sat afternoon.

Sunday night-Monday...
trailing cold front moves across Sun night, moving near or just
S of the South Coast Mon morning. Any leftover showers/
thunderstorms should push offshore by around midnight or so Sun
night, but could linger across the cape and islands into early
Mon morning. Will also see some patchy fog develop as higher
dewpts linger there.

Winds shift to light west Sun night, except SW at around 5-10 kt
along the S coast. This will delay the drier air from moving in
until Monday. Dewpts drop back to the mid-upper 50s across the
interior Monday, but linger in the lower-mid 60s along the S
coast.

Skies will become partly cloudy from northwest-southeast Sun night, but
clouds may linger across the Outer Cape and Nantucket closer to
the stalling front into Monday.

Monday night through Wednesday...low confidence.
Flat 500 mb trough across the NE U.S. Looks to lift into northern
New England and Quebec. For now, have forecasted mainly dry
conditions Mon night and Tue, even as front stalls close to or S
of the South Coast. A weak wave may move along this front
sometime late Tue through Wed, but quite a bit of spread amongst
the model guidance. Did mention chance pops for this period, as
suggested by blended guidance.

&&

Aviation /06z Thursday through Monday/...
forecaster confidence levels...

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

Short term /through Friday/...high confidence.

2 am update...

Thru 12z...

VFR and dry weather continue with light west-southwest winds.

After 12z...

VFR cigs and vsbys continue with low risk of light rain late in
the day across northern Massachusetts to the New Hampshire border. SW winds increase
this afternoon with gusts up to 25 kt across Rhode Island and southeast
Massachusetts.

Tonight...

VFR and mainly dry across CT/Rhode Island and southeast Massachusetts. Chance of
scattered showers and T-storms mainly across northern Massachusetts. MVFR
vsbys possible across the interior in patchy fog. Modest SW
winds 15-20kt likely along the South Coast of MA/RI.

Friday...

Mainly VFR with low risk of a few T-storms mainly across the
interior during the afternoon. Gusty SW winds continue 15-20 kt
with gusts up to 25 kt possible.

Kbos terminal...high confidence. Mainly dry thru 00z with low
risk of a few showers/T-storms thereafter.

Kbdl terminal...high confidence.

Outlook /Friday night through Monday/...

Friday night through Saturday...moderate confidence.
Patchy late night/early morning fog each day. Otherwise mainly
VFR, except local IFR in scattered showers/thunderstorms, mainly
during the afternoon and evening hours through the period. A
few storms may be strong, with gusty winds. SW winds through the
period with gusts around 20 kt, highest along the S coast.

Sunday-Sunday night...moderate confidence.
Mainly VFR. Periods of MVFR-IFR conditions in scattered
rain showers/thunderstorms and rain Sunday into Sunday evening. Patchy late night and
early morning fog with local IFR cigs/vsbys. Winds shift to S-SW
Sunday to west Sunday night from N-S.

Monday...low to moderate confidence.
Mainly VFR. May see isolated showers move into north central and west
mass Mon afternoon/evening. Winds back to SW again across Rhode Island/east
mass Mon afternoon.

&&

Marine...
forecaster confidence levels...

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

Short term /through Friday/...high confidence.

Tonight...high pres south of New England. SW winds 10 kt or less
and seas 3 ft or less.

Thursday...increasing S/SW flow as low level jet develops.
Enough mixing to support gusts to 25-30 kt in the afternoon over
nearshore south coastal waters and particularly Narragansett
Bay and Boston Harbor. Less wind over outer waters due to low
level inversion. Small Craft Advisory issued for south coastal waters and Boston
Harbor.

Thursday night...low level jet remains across the region
resulting in Small Craft Advisory SW gusts and building seas.

Outlook /Friday night through Monday/...

Friday...moderate confidence.
Small craft advisories will likely be needed. SW winds gusting
up to 25-30 kt likely, especially across the waters east of Cape
Cod and southern waters. Seas up to 6-8 feet, highest on the
southern outer waters, but may start subsiding Fri night.

Saturday and Sunday...moderate confidence.
SW winds continue, gusting up to 25-30 kt on the southern outer
waters. Seas lingering at around 5 ft, but should subside
during Sat night into sun. Scattered showers and thunderstorms,
some with reduced visibilities and strong gusty winds especially
on Sunday. Patchy late night/early morning fog with reduced
visibilities.

Sunday night and Monday...moderate confidence.
Winds briefly shift to west Sunday night into Monday morning, but
back to S-SW again by midday Monday. Seas up to 4 ft on the
outer waters. Leftover showers/thunderstorms linger across the
southern waters along with patchy late night/early morning fog
reducing visibilities.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...Small Craft Advisory from 1 PM this afternoon to 8 am EDT
Friday for anz231>235-237-255-256.
Small Craft Advisory from 3 PM this afternoon to 2 am EDT
Friday for anz230.
Small Craft Advisory from 1 PM this afternoon to 4 am EDT
Friday for anz236.

&&

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

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