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Area forecast discussion 
National Weather Service Taunton Massachusetts
712 PM EDT Sat Jul 4 2015

Synopsis...
low pressure races south of New England this afternoon and evening
bringing scattered pockets of light rain. High pressure returns
Sunday and lingers through Monday. Becoming more humid Tuesday and
Wednesday. A chance of showers and thunderstorms along and west
of the Connecticut River valley on Tuesday and more generally
across the area on Wednesday. Local heavy downpours possible on
Wednesday. Becoming dry the rest of the week.

&&

Near term /until 6 am Sunday morning/...
7 PM update...
band of light showers will continue to diminish and move offshore
this evening. A few clusters of showers and possible thunderstorms in
upstate New York should run into an unfavorable thermodynamic
environment well before reaching southern New England. May just
see some scattered middle and high debris clouds. Satellite imagery
indicates partial clearing continuing to cape and islands this
evening. Mass of lower clouds across southern tier New York state and PA
appears to be eroding on the NE side. Winds are relatively light
behind departing short wave trough and surface wave crossing Georges
Bank but not enough rain fell to come close to saturating lower
layers of atmosphere. Thus...it seems at this time unlikely that
any stratus will form given not enough moisture to be trapped.
Light and variable surface winds may tend to be from north or northwest most
locations except may become locally offshore as light land breeze
overnight. Temperatures running a little cooler than forecast and so have
tweaked downward a tad...especially western sections.

Prior discussion for tonight...
coastal low pressure moves out to sea. Upper shortwave swings
over New England with the best dynamical support moving offshore
early. Expect a diminishing trend for any remaining showers as
they move offshore...followed by a clearing trend after midnight.
Dew points upstream are in the 50s...this should allow min surface
temperatures in the 50s and lower 60s.

&&

Short term /6 am Sunday morning through Sunday night/...
high pressure from the plains builds east over New England Sunday.
Cross sections of relative humidity show dry air above 800 mb...and a moist layer
at 800-850 mb. Mixing should reach above 850 mb. This suggests
some diurnal cumulus developing Sunday and dissipating Sunday
evening. Tempertures at the top of the mixed layer would support
maximum surface temperatures of 80-85.

Fair skies Sunday night with light winds and radiational cooling.
Dew points rise a little to around 60. Expect min surface temperatures in
the upper 50s and lower 60s. This may support patches of fog
developing late at night...especially in western mass.

&&

Long term /Monday through Saturday/...
highlights...

* warm front may trigger scattered showers/thunderstorms in west Tuesday
* locally excessive rain possible with showers/thunderstorms on Wednesday

Overview...several players influence the weather pattern affecting southern
New England this coming week. Our area will be susceptible to short
wave energy rotating about strong eastward moving trough across north
central Canada and ejecting from closed low slowly approaching California.
As is typical for this time of year...h50 heights are relatively
high...but at the same time the large scale flow is characterized
by broad cyclonic flow with susceptibility for troughing across
the east central Continental U.S.. main focus for this forecast period is on the
middle week period when a slow moving cold front through a high
precipitable water or precipitable water environment may set the stage for
convective heavy rain bands. Models have come into better
agreement for this period. The latter part of the week into the
weekend will probably feature ridging and dry conditions...but
confidence is lower due to challenge of resolving short wave troughs
in the large scale flow that far out. Also...as noted in the prior
forecast discussion...New England may at some point by next
weekend or a little beyond be situated on the peripery of a ridge
across the southern/central Continental U.S. And be susceptible to any mesoscale convective system
activity on that periphery.

Details...

Monday...high confidence of dry conditions as models agree upon
short wave ridging both aloft and at the surface. 850 mb temperature
projections combined with ample sunshine support current forecasts
of temperatures in the middle to upper 80s across the interior.

Tuesday...short wave trough and warm front usher in higher dewpoint air
and much higher precipitable waters . Will indicate chance probability of precipitation roughly west of an
afn-orh-ijd line on Tuesday where k indices rise to above 30 for a
time and suggestive for scattered showers/tstms. Air mass looks
drier and more stable further east where will continue with slight
chance or less probability of precipitation. In deference to some instability noted on the
latest GFS...will indicate some slight chance probability of precipitation Tuesday night near
the Vermont and New Hampshire borders.

Wednesday...there is a concern of one or bands of significant to excessive
rafl setting up as cold front deaccelerates across the region with precipitable waters
over 2 inches. Model consensus also indicates k indices in the middle 30s.
Isobars become baggy at the surface as a weak wave attempts to form
along the front near the South Coast of New England...and the h70 and
h50 flows are parallel during the afternoon and evening. There is even
a hint of divergence with the 1000-500 mb thickness. All of this in
the synoptic pattern suggest a potential for heavy downpours and possibly
training of cells. The instabiliy and wind shear look quite modest and
so the severe potential looks low. The signal for localized heavy/excessive
rain looks strong enough...however...to mention in the severe weather potential statement.

Thursday...models have changed positions from 24 hours ago with
the GFS hanging rafl over the area for a time with a wave whereas
the European model (ecmwf) is now more progressive. For the probability of precipitation have gone with a
model blend with a slight leaning toward the GFS which seems to
have been demonstrating a little more run to run continuity than
the European model (ecmwf). Anticipating lower dewpoints and seasonable temperatures.

Friday through Saturday...confidence lower since difficult to
resolve short wave troughs days 6 and 7 especially in the warm
season. Model consensus is for a dry forecast for this part of
the forecast period with temperatures not too far from the long term
averages for this time of year.

&&

Aviation /23z Saturday through Thursday/...
forecaster confidence levels...

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

Short-term /through Friday night/...

Tonight...high confidence. Expecting VFR conditions to hold with
scattered occasional broken middle clouds. See only a slight risk for patches
of MVFR conditions. Light winds are expected to trend to
west/northwest toward morning.

Sunday...high confidence. VFR

Sunday night...high confidence. VFR. Patches of IFR in late night
fog possible in the CT valley of Massachusetts.

Kbos terminal...high confidence in taf.

Kbdl terminal...high confidence in taf.

Outlook /Monday through Thursday/...

Monday...high confidence. VFR expected.

Tuesday...moderate to high confidence. Mostly VFR conditions
except areas of MVFR in scattered showers/thunderstorms west of afn-orh-ijd line.

Tuesday night...moderate confidence. MVFR ceilings/visibilities with areas of
IFR ceilings/visibilities in fog along the S coast. Elsewhere...mostly VFR.

Wednesday...moderate confidence. Areas of MVFR ceilings/visibilities in showers/tstms.
Pockets of IFR conditions possible in heavier showers/thunderstorms as
well as in fog patches along the S coast.

Wednesday night...moderate confidence. Improving to VFR except MVFR
ceilings/visibilities may persist in showers and fog along southeast coastal areas.

Thursday...moderate confidence. VFR or becoming VFR.

&&

Marine...
forecaster confidence levels...

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

7 PM update...
continuing with prior forecast. Noted recent gusts to near 25 knots
in northwest flow behind departing low pressure and seas now 5 feet at
Nantucket Shoals buoy. Thus...will continue with headline for now
but suspect it may be able to be lowered sooner than currently
advertised.

Prior discussion for tonight...high confidence. Low pressure
passes south of the waters and moves off south of Nova Scotia
tonight. Winds shift from east to north after the passage of the
low...but will remain below 25 knots. Expect seas to build a
little with heights around 5 feet on the southern outer waters.
Timing on the advisory has been adjusted to a later start time but
otherwise the headline remains the same.

Sunday and Sunday night...high confidence. High pressure builds
over the waters with light wind and diminishing swell. The Small
Craft Advisory will end around midday.

Outlook /Monday through Thursday/...

Moderate to high confidence.

Winds and seas expected to remain below Small Craft Advisory thresholds
through the period. Areas of fog with pockects of visibility a mile
or less possible Tuesday night and Wednesday morning...mainly along south coastal
waters. Possibly areas of fog again Wednesday night along the S coast.
Scattered thunderstorms may occur late Wednesday afternoon and evening 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 anz255-256.

&&

$$
Synopsis...wtb/Thompson
near term...wtb/Thompson
short term...wtb
long term...Thompson
aviation...wtb/Thompson
marine...wtb/Thompson

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