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Area forecast discussion 
National Weather Service Taunton Massachusetts
456 am EDT Tuesday Aug 4 2015

Synopsis...
thunderstorms are once again expected today...but mainly across
the eastern half of the area. Some of these may become severe.
Dry...warm and less humid weather arrives Thursday. A period of
unsettled weather is possible Thursday night into Saturday...but
confidence is low regarding the timing and coverage of any
potential wet weather.

&&

Near term /through Wednesday/...
convection developing in PA and southeast New York continues to diminish as it
approaches the NE...where dry air and some subsidence continues to
limit the convection as it approaches. Only some showers just now
entering the lower CT valley. Stronger storms are staying to the
S...mainly where the highest cape values are per latest mesoscale-
analysis. Therefore...outside of a shower...or mainly an isolated
rumble of thunder in the west suspect most of the morning to remain
quiet.

The rest of the day...still remains somewhat uncertain. At odds is
the ability to generate surface instability as a cold front sweeps
through from about 14z - 22z. Upper level instability is likely
somewhere between the moist NAM and the drier GFS...but with a
modified eml and 6.0-7.0c/km lapse rates and around 2000j/kg of mu
cape...there is plenty available. Shear increases as the front
approaches as well. Sref probs continue to highlight greater than
50 percent probability of MUCAPES greater thank 2000/shear greater
than 40 knots...especially across the eastern 2/3 of the region...where
Storm Prediction Center has upgraded to a slight risk. The surface connection...will be
based on the amount of cloud cover that remains over the area from
the weakened convection this morning and low stratus across southeast
mass. Latest quantitative precipitation forecast on mesoscale guidance is higher than previous
runs...which increases confidence that better destabilization will
occur later in the day in spite of the early cloud
cover...therefore...will increase afternoon/evening probability of precipitation...and be
adding enhanced/severe wording with this update.

Some dry air at the surface...and shear suggest that strong winds and
downdrafts are the primary concern. Some hail possible especially
given NAM shows hail convective available potential energy approaching 500+. Precipitable waters increasing to
near 2.0 inches will once again support heavy rain...but storms
should be moving. Shear also high enough to support the risk of a
weak tornado...reflecting current thinking by Storm Prediction Center.
Therefore...stay tuned to updates through the day.

Otherwise...heat and humidity remains today ahead of the
front...with dewpoints in the upper 6os to near 70. Highs mainly in
the middle-upper 80s.

&&

Short term /Wednesday night through 6 PM Wednesday/...
overnight...
cold front will be slowing to a near stall between 00z and 04z
this evening just offshore. This will allow a continuation of
T-storm risk mainly across coastal regions until drier air moves
in from the northwest and convection shifts S toward better instability.
Therefore...gradual improvement expected. Some fog possible where
rainfall occurs. Otherwise...temperatures a little cooler...mainly in
the lower 60s across the area...or even in the 50s across northwest Massachusetts.

Wednesday...
cyclonically curved flow remains in place across the region
combined with 500 mb temperatures abnormally cold...around -13c. Stalled
frontal boundary remains to the S...but one final shortwave will
be rotating through to the north. This may lead to some scattered
showers/T-storms mainly north of the Mass Pike. With the very cold 500 mb
temperatures...there is a risk for hail as well. Key will be how
much dry air builds through the column. Not expecting
showers/storms to be as widespread as today...but some low chance
or at least slight chance probability of precipitation are needed to reflect the risk.
Warmer temperatures remain in place...mainly the low-middle 80s.

&&

Long term /Wednesday night through Monday/...
highlights...

* unsettled weather possible Friday
* temperatures trending below normal during this period

Overall...the models continue to have rather poor agreement on
the details through this portion of the forecast. There is some
agreement on the overall pattern trend...with a closed middle level
low over eastern Canada...moving into the Maritimes late this
week. Looking at a period of unsettled weather with temperatures
trending below normal through much of this time period.

Thursday...much of the day looks to be dry with high pressure
building into the area.

Thursday night through Saturday...this looks to be the most
unsettled time with a low pressure moving into the Middle Atlantic
States...then possibly up the East Coast over the 40/70 benchmark
southeast of southern New England. The European model (ecmwf) remains more bullish
than the GFS...and has a faster timing as well. The GFS also has a
more southern track than the GFS. Given the uncertainty in the
details...will keep at least a chance of rainfall...with the
greatest probability of precipitation toward the South Coast of New England. With mostly
cloudy to overcast skies for much of this time...expecting below
normal temperatures.

Sunday and Monday...much of this forecast will depend on how the
pattern for Friday and Saturday develop. In general though...
expecting drier weather with rebounding temperatures.

&&

Aviation /08z Tuesday through Saturday/...
forecaster confidence levels...

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

Short-term /through Wednesday/...

Through 12z...moderate confidence.
Mainly VFR...will have to watch some leftover rain showers/thunderstorms moving
through New York/PA which may impact mainly CT during the early morning
hours.

Today...moderate confidence.
Depending on sunshine...expect some thunderstorms and showers to
develop middle day and continue...from west-east into the evening hours.
Some of these storms may be severe...with strong winds and
hail...as well as brief MVFR/IFR conditions.

Tonight into Wednesday...high confidence.
After storms/rain sweeps offshore late this evening...expect
improvement to VFR which will linger into the daylight hours on
Wednesday. An isolated shower or thunderstorm is then possible mainly north
of the Mass Pike on Wednesday...but not as widespread as Tuesday.

Kbos terminal...high confidence in taf. Lower confidence in timing
of any afternoon storms.

Kbdl terminal...high confidence in taf. Lower confidence in timing
of any afternoon storms.

Outlook /Wednesday night through Saturday/...

Wednesday night through Thursday...high confidence. VFR. Low
probability of a few showers/storms across northwest Massachusetts Wednesday. Any
storms that develop may have MVFR/IFR conditions.

Thursday night through Saturday...low confidence on timing...higher
confidence on trends. MVFR/IFR conditions in widespread rain likely
sometime during this period. VFR before and after periods of rain.

&&

Marine...
forecaster confidence levels...

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

Short-term /through Tuesday night/...

Through today...moderate confidence.
SW winds remain in place and with some gusts potentially
approaching 25-30 knots at times. This will allow seas...which are
already running around 5 feet on the S waters to increase...possibly
increasing to as high as 7 feet by the evening. Small craft
advisories currently out reflect this...so no changes.

Tonight into Wednesday...moderate confidence.
Front moves further offshore...outside of any
storms/showers...winds and seas will gradually diminish...so
expect these small craft advisories to gradually be dropped
through the period.

Outlook /Wednesday night through Saturday/...moderate confidence.

Wednesday night through Friday...high confidence. Quiet boating
weather with light winds and seas below 5 feet expected. Rain is
likely at times Thursday night through Friday...limiting
visibilities at times.

Friday night and Saturday...moderate confidence. Easterly winds
and seas increase as low pressure passes south of the waters.
Small craft advisories will likely be needed for the outer waters.
Rain is likely Friday night into Saturday...limiting visibilities
at times.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...Small Craft Advisory until 8 PM EDT this evening for
anz230>234-236-250-251.
Small Craft Advisory until 8 am EDT Wednesday for anz235-237-
254>256.

&&

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

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