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Area forecast discussion 
National Weather Service Taunton Massachusetts
1032 am EDT Sat Jul 4 2015

Synopsis...
low pressure races south of New England this afternoon bringing
scattered pockets of light rain. High pressure returns Sunday and
lingers through Monday. A transition period is likely middle next
week...with a chance for showers and thunderstorms.

&&

Near term /until 6 PM this evening/...

Two areas of concern...one over Cape Cod and islands and the
second over western mass. Low pressure offshore has spread
scattered showers over the islands and could similarly effect Cape
Cod this morning. Scattered showers will be over or just south of
the islands through afternoon. The second area is moving northeast
from New York into western mass and western CT. Observed precipitation
upstream has been light...roughly .01 to .10 inches. Dew points
have moistened in New England but will be dry enough to eat away
at the precipitation. Right entrance region of upper jet is moving into the
region...which should support rain/showers for a few hours. The
chance of .01 inches in western mass is reasonably high...enough
to boost probability of precipitation to 65-70 percent for the afternoon. Parts of northern CT
may also be affected. Back edge of the light rain trends across
western mass around 3-4 PM.

Late morning temperatures are running about 2-4f lower than forecast. We
have made adjustments lower by a couple of degrees for the hourly
temperatures and in overall maximum surface temperature for the day.

&&

Short term /6 PM this evening through 6 PM Sunday/...
the coastal low moves farther offshore this evening...moving south
of Nova Scotia late tonight. This should bring any rainfall to an
end late this evening. The supporting upper trough moves east of
US by morning. This should bring a clearing trend after midnight
with winds turning northwest.

Weak high pressure moves into southern New England from the south
Sunday. This should mean dry weather with higher temperatures.

&&

Long term /Sunday night through Friday/...
highlights...

* high pressure and warming conditions into early next week.
* Unsettled conditions return middle-late next week.

Overview and model preferences...with 04.00z model guidance
coming in...there is better agreement with the middle and long term
than previous runs...although typical uncertainty remains in the
long term. Strong ridging early in the week will give way to
mainly zonal flow on the SW quadrant of a strong northern stream vortex
developing across north central Canada. The flattening wave will
arrive middle week...with high precipitable waters and instability in Tow which may
need to be watched. There are timing issues...especially regarding
the influence of the ridge of high pressure for Tuesday...but with better
agreement in this round of guidance a blend of operational models
will work well as a baseline.

Details...

Sun night into Monday night...warm ridging builds across southern New
England with high pressure at the surface. Mainly dry weather prevails with
moderating highs/lows as 850 mb temperatures increase to between +12c and
+14c by late Monday. This suggests highs mainly in 80s across the
region.

Tuesday...upper level wave will be approaching from the west. Models
indicate increasing moisture as precipitable waters approach 2 Standard deviations
above normal with k-values over 30. A warm front will be the
initial surface reflection of this wave. However...soundings support
the possibility of high pressure remaining in control through much of
Tuesday. Therefore...chance for afternoon rain showers/T-storm with the warm
frontal approach may be quite low to near zero the further east one
GOES. In fact...the best axis of surface cape/Theta-E ridge is mainly
west of the Massachusetts/New York border. Therefore...chance probability of precipitation west will be lowered
to slight chance to none probability of precipitation further east. Will include thunder with
this forecast given the favorable parameters.

Wednesday...as previous forecaster noted...this is where the model
solution divergence begins to show more significantly. Mainly with
the timing of a cold frontal passage. GFS remains progressive
while European model (ecmwf)/CMC continues to linger as the front begins to
parallel the zonal flow developing aloft. Will continue with the
chance and slight chance probability of precipitation from the the previous forecast since
the convergent boundary remains in place. Soundings do support
some surface based cape exceeding 1000j/kg and high k-values...so will
continue to include ts...but given the lacking shear...remain
somewhat dubious of severe chances at this time.

Thursday...the uncertainty remains as the cold front continues to push
further southeast...albeit slowly. Will gradually reduce probability of precipitation from
north-S during the day...but will have to wait before we can nail down
timing for the late week.

Friday and Sat...uncertainty remains but with zonal flow...a series
of ridge/trough Couplets is likely to yield periods of
dry/potentially wet periods are likely. Interestingly...with southern
New England on the ridge periphery may need to monitor for mesoscale convective system
steering flow as well. Still way too many variables to nail
anything down...but seasonable temperatures and low to none probability of precipitation should
cover the spread.

&&

Aviation /15z Saturday through Wednesday/...
forecaster confidence levels...

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

Short-term /through Friday night/...

Today...high confidence.
Mainly VFR. A spot shower is possible through early evening...with
the highest risk being along the immediate S coast later today.
Very low chance of brief MVFR conditions in these showers. Winds
will be generally light...with sea breezes likely on coastlines.

Tonight...high confidence.
Rain over southeast mass/Rhode Island should taper off during the first
part of the night. MVFR conditions possible in any areas of
rain/fog...otherwise VFR with cloud bases lifting/clearing.

Sunday...high confidence. VFR.

Kbos terminal...high confidence in taf.

Kbdl terminal...high confidence in taf.

Outlook /Sunday night through Wednesday/...

Sun night into Monday...high confidence. VFR with high pressure. Sea
breezes likely Monday.

Tuesday and Wednesday...moderate confidence. First a warm front Tuesday...then a
cold front Wednesday may provide a focus for occasional showers and
thunderstorms each day with periodic MVFR or lower conditions.
Otherwise VFR. Some fog possible during the overnights.

&&

Marine...
forecaster confidence levels...

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

Moderate confidence today and tonight...high confidence Sunday.

Low pressure developing along the middle Atlantic coast will pass
over or south of the southern outer waters this afternoon and
evening. This will bring lower visibilities in rain to the southern
waters with east winds increasing to 15-20 knots. Farther north
the winds will become east...but with lighter speeds. As this low
pressure moves off to the east...winds will diminish and turn
north overnight. Weak high pressure builds over the waters
Sunday.

Persistent winds will build seas across the outer southern coastal
waters. There has been a persistent signal the past few days for 5
feet seas. While marginal...decided to issue a Small Craft Advisory
due to this persistent signal.

Outlook /Sunday night through Wednesday/...

Sun night into Monday...high confidence. Any lingering swell recedes
below 5 feet Sun night. High pressure then brings quiet boating weather
to the waters through Monday.

Tuesday and Wednesday...moderate confidence. A warm front on Tuesday...then a cold
front on Wednesday will be approaching from the west. While winds should
generally remain out of the S-se...wind speeds should remain below
Small Craft Advisory thresholds. Seas is also likely to remain
below small craft thresholds. Some showers/thunderstorms and/or
fog are possible over the waters.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...Small Craft Advisory for hazardous seas from 2 am to 5 PM EDT
Sunday for anz254.
Small Craft Advisory for hazardous seas from 8 PM this evening
to 5 PM EDT Sunday for anz255.
Small Craft Advisory for hazardous seas from 5 PM this
afternoon to 5 PM EDT Sunday for anz256.

&&

$$
Synopsis...wtb/Belk/doody
near term...wtb/Belk/doody
short term...Belk
long term...doody
aviation...Belk/doody
marine...wtb/Belk/doody

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