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

showers and thunderstorms are expected to develop towards Tuesday
morning...continuing through the day into the evening hours. Some
of these storms could become strong to severe. Dry...warm and less
humid weather arrives Wednesday and continues into Thursday. A
period of unsettled weather is possible Thursday night into Saturday
but confidence is low on the timing of potential wet weather.


Near term /until 6 am this morning/...
10 PM update...
we continue to watch bulk of active convection roll northwest of the
region along the periphery of the first in a series of weak
shortwaves and a pre-frontal trough which continues to diminish. The
next round to watch will be the developing convection colocated
with a secondary trough across PA and southeast New York. With the modified eml
settling further east and increasing moisture through the column
/something we were lacking most of the day/ a slight up-
tick in shear will need to watch this development as it moves east
into New York/southern New England during the early morning hours. Some mesoscale
guidance suggests the typical right-turn as the convection dives
S toward better instability while others leave the steering flow
in control...taking it across CT/southeast mass. Have increased probability of precipitation in
this area primarily while lowering them somewhat elsewhere. It
will be interesting to observe through the overnight hour
convection survives with little surface based support.
Otherwise...mild...min temperatures in the middle 60s to around 70.

Previous discussion...


Potential convective weather outcomes into southeast New England towards
Tuesday morning. Forecast guidance consensus notes an instability
burst elevated and maintained by a S/SW warm-moist plume of higher
Theta-E air above a subsequent inversion. Precipitable waters of 1.50-1.75 inches.
Activity looks to originate along the nose of a h925-85 jet within a
850 mb-7 environment of 6-7c/km lapse rates. Yet there is a lack of
deep-layer forcing as the better area of positive vorticity advection / middle-level trough /
surface cold front remain to the west.

Thinking is that we may see a widespread area of activity of showers
and thunderstorms collocated with the convergent low-level plume.
Uncertainty if any thunderstorms become strong to severe. Heavy rain
looks to be the main threat along with lightning. Thinking low risk
severe and potential for some of the storms to become strong. Will
see collocated Uni-directional SW-NE 0-6 km bulk shear exceeding 40
kts and freezing levels of around 11 kft. Some evidence of turning
within the 0-1/0-3 km layer. Sref does denote decent probabilities
of instability exceeding 2k j/kg in addition to the aforementioned
shear and turning environment. Though sref probs not so much helpful
with respect to precipitation accumulations...thus confidence with respect
to possible flooding is low despite the anticipated outcomes that
were discussed above. Will avoid enhanced wording with the forecast
for the time being.

Should better forcing and venting aloft with the 300 mb jet shift east...
there would be greater impetus upon the environment to generate
greater and likely stronger convective weather. Interesting as to
whether convective remnants west from earlier in the day shift east and
act as a crux of forcing via low- to middle-level convergence. Overall
individual models continue to wobble and there is just an underlying
level of uncertainty other than the focus being on southeast New England.
It may be quiet throughout as the present dry subsiding wedge of
air across the region maintains.

Otherwise SW-flow continues overnight ushering higher dewpoint air
across interior New England. Should remain breezy along the S/se-
coast. Increasing cloud cover should yield mild low temperatures
around the middle- to upper-60s and may subsequently limit patchy dense
fog to just across S/southeast New England in higher dewpoint air.


Short term /6 am this morning through 6 PM Wednesday/...

A combination of rising heights within the middle-levels combined with
drier air aloft could subdue the potential convective environment.
Beneath cyclonic flow aloft through which additional middle-level impulses
and accompanying jet-streaks reside...the overall question is as to
whether a surface frontal boundary can become the focus for showers
and thunderstorms. Sweeping through an environment of robust Theta-E
air and instability on the order of 2k j/kg in which lapse rates are
steep especially 850 mb-7 and shear profiles are moderate to strong to
50 kts with slight turning within the 0-1/0-3 km profile...there
appears to be mechanisms for forcing...but should middle-level ridging
proceed...this seems to squash the possibility for convection. There
is also the possibility that should activity develop towards morning
over southeast New England as noted earlier it could subdue the environment
from becoming convective /I.E. Cloud cover/. A very complicated

But still can not rule out the possibility of something popping
across the interior. Am somewhat concerned noting the cips analog
guidance in where several of the analogs witnessed substantial wind
and hail impacts over north- and west-portions of S New England. The strong
to severe weather potential is seemingly there though there is some
level of doubt. Even Storm Prediction Center will wait on how the environment develops
with respect to their convective weather outlooks...whether the
environment will destabilize. Can not rule it out completely and
will prepare for the potential accordingly. Focus of a heavy rain
threat along with potential hail and strong to damaging wind
possibilities. Can not rule out the possibility of a tornado. But
not enough confidence at this time to go with enhanced wording in
the forecast.

While forecast guidance seems mixed with an uncertain evolution of
synoptics...there is greater confidence of shower and thunderstorm
activity around the vicinity of southeast New England and adjacent waters
where the SW-NE plume of higher Theta-E air resides as well as both
a stronger and convergent SW-NE h925-85 wind profile. Would expect a
continuation beginning in the morning as outlined in the earlier
discussion of scattered showers and thunderstorms...some of which
also could be strong and possibly severe.

Overall...a mild and muggy day with highs into the middle- to upper-80s
as dewpoints range around the middle- to upper-60s.

Tuesday night...

Frontal boundary pushes the higher Theta-E / instability out to sea
into the overnight period. So anticipating a drying trend. West-flow
proceeding ushering lower dewpoint air across the interior. As
conditions gradually clear...temperatures drop into the low- to middle-


Long term /Wednesday night through Monday/...

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

Overall...the models have rather poor agreement on the general
pattern and timing through the long term. In some time periods it
seems that the GFS may just be slower than the European model (ecmwf). In others...
they are just completely different. The ensembles are not much
help in that the European model (ecmwf) ensembles look very similar to the operational
model and the gefs is very similar to the GFS. Basically have two
fairly different solutions for much of the long term. However...
general trends are similar. Looking at a period of unsettled
weather with temperatures trending below normal through much of
the week.

Wednesday...looks to be the warmest day of the period with
temperatures around or just above normal. Despite the potential for
a few showers or thunderstorms across the northwestern zones as a
shortwave pushes into the region...expect much of the day and much
of the area to remain dry.

Thursday...much of the day looks to be dry with high pressure
building into the area. This is one of those times the timing is
off between the European model (ecmwf) and the GFS. The European model (ecmwf) is quick to move the
high pressure out of the region...pushed by low pressure moving
into the middle-Atlantic from the Great Lakes. The GFS keeps that
high pressure over southern New England and the low pressure in
the Great Lakes.

Thursday night through Saturday...this looks to be the most
unsettled time with low pressure moving into the middle-Atlantic and
then possibly up the East Coast over the 40/70 benchmark southeast
of southern New England. The European model (ecmwf) is the most bullish with this...
tracking the low directly over the benchmark and bringing an
extended period of rain to much of southern New England. The GFS
develops some sort of boundary along which several areas of low
pressure travel...bringing periods of rain to the region. Below
normal temperatures are a given with lowering heights/temperatures aloft
and mostly cloudy to overcast skies for much of this time.
Wouldn/T be surprised to see temperatures top out in the upper 60s to
lower 70s on Friday.

Sunday and Monday...much of this forecast will depend on how Friday
and Saturday shake out...but in general the weather looks drier and
quieter with rebounding temperatures.


Aviation /06z 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

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 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 period of rain.


forecaster confidence levels...

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

Short-term /through Tuesday night/...

Tonight...moderate confidence.
SW-winds continue with gusts around 20 kts...stronger over the S-
waters at 25 kts. Waves building to 5 feet. Perhaps some patchy
fog issues. Increasing areal coverage of showers and possible
thunder- storms towards morning. Storms may be strong to severe.

Tuesday...moderate confidence.
SW-winds with gusts 20-25 kts. Waves at 5-6 feet. Continued
shower and thunderstorm activity with some of those storms being
strong to severe.

Tuesday night...moderate confidence.
SW-winds backing west through the night. Gusts subsiding. Waves at
5-6 feet. Shower / thunderstorm chances conclude west to east towards

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

Wednesday through Friday...high confidence. Quiet boating weather
with light winds and seas below 5 feet expected. Rain is likely
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...
Rhode Island...none.
Marine...Small Craft Advisory until 8 PM EDT this evening for
Small Craft Advisory until 2 am EDT Wednesday for anz235-237-


near term...doody/sipprell
short term...sipprell
long term...rlg

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