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Area forecast discussion 
National Weather Service Taunton Massachusetts
648 PM EDT Tuesday Aug 4 2015

Synopsis...

Thunderstorms continuing into the evening hours mainly pushing east.
Continued strong to severe threats. Dry...warm and less humid
weather arrives Thursday. A period of unsettled weather is
possible Friday into this weekend...but confidence remains low
regarding the timing and coverage of any potential wet weather.

&&

Near term /through Wednesday/...

Into this evening...

Stretched middle-level impulses through the broader cyclonic flow kicking
off scattered showers and thunderstorms in a lingering decent
environment of steep lapse rates and marginal instability. Not
thinking as much umpf as earlier storms...environment has been
worked over to some degree and weaker/stretched middle-level impulses
through a more zonal flow not invoking more vigorous forcing as
the wave earlier today. Still effective shear in excess of 50 kts
with MUCAPES/instability on the order of 1k j/kg. While a downward
trend is evident...still can not rule out a storm here or there
kicking off but remaining sub-severe.

Think the hrrr has the right idea...focus along the Massachusetts/RI/CT border
where middle-level energy is being stretched and along the north-periphery
of drier air discerned per water vapor imagery. Thus likely probability of precipitation
for those locales...chance to slight chance probability of precipitation for S/central CT
and Rhode Island as well as southeast Massachusetts including the cape/islands...welcoming as
they took the brunt earlier this morning.

Tonight...

Middle-level impulse and accompanying trough push east subsequently easing
the surface frontal boundary offshore along with deeper moisture and
higher Theta-E air. Will see showers / thunderstorms push out to sea
with some of the storms strong to severe lingering longest over the
cape and islands within a low-level convergent environment of higher
Theta-E air. Anticipated conclusion shortly after midnight of
wet- weather. Light west-winds prevailing and drier air working in.
Expect it to clear out west to east accordingly. Lows dropping in and
around the low-60s with spots north/west into the upper-50s as there is
an opportunity for radiational cooling to proceed. With that there
is the potential for patchy dense fog...especially those areas
which observed rain during the day.

&&

Short term /Wednesday night/...

Wednesday...

Middle-level impulse sweeps through the broad cyclonic flow followed by
the middle-level trough. Robust forcing of an environment slightly
drier but cooler aloft. Enough moisture present. While lesser
instability...freezing level heights will be lower. The middle-level
ascent through the column upon a boundary layer which is likely to
become well-mixed with daytime heating as initial conditions will
be mostly clear is likely to lead to scattered shower activity...
some thunderstorms...storms in which could produce small hail.
Perhaps even a gusty wind threat with inverted-v soundings but
have low confidence as moisture is limited. Will go with chance
probability of precipitation as it is difficult to pin down exactly where weather will
make an impact. Certain though there is a threat across the
interior away from the coast. A tad cooler. Highs around the low
80s. Seasonable.

Wednesday night...

Behind the trough it looks to remain a bit breezy west. Can not rule
out a few locales experiencing light winds overnight. Should see
quiet weather and clear conditions. All factors combined...there is
some potential for radiational cooling and highest confidence is to
the north/west within sheltered valley regimes. Lows down into the middle- to
upper-50s while low-60s along the coast. Dewpoints in the low-50s.
An end to the heat and humidity and quite refreshing.

&&

Long term /Thursday through Tuesday/...

Highlights...

* unsettled weather remains possible Friday into the weekend
* temperatures trending below normal through most if not the entire
period

Overview and model preferences...

Noting fairly good agreement with 12z operational models runs into
Friday...then each GOES on their merry own way which lends to low
confidence beyond Friday. One big question will be how the 500 mb cutoff
low across Quebec and Maritimes flattens out...which also flattens
out the flow across most of the northern stream. Depending upon
whether this upper level system flattens out will determine how far
S the large high pressure ridge builds out of central Canada. Also
noting a stalled front S of the region which has a short wave moving
along it...which could push some moisture into portions of southern
New England. Another fly in the ointment is the possible
amplification of long wave trough across the middle Atlantic region this
weekend.

Needless to say...low confidence forecast beyond Friday due to the
wide variance of op model run solutions. Went along with most
available guidance /except GFS/ through Friday...then transitioned
over to an ensemble model blend similar to wpc guidance from
Saturday Onward.

Details...

Thursday...high pressure builds out of central Canada into upstate
New York. Weak short wave moves across northern New England and...with
lack of available moisture in the general west-northwest flow...expect dry
conditions. Highs look to run around 80 degrees...slightly below
seasonal norms.

Thursday night through Saturday...short wave moving along stalled
front from the Ohio Valley. Could start to see some moisture moving
NE into north CT/RI/se Massachusetts overnight Thursday night then push further north during
Friday. Still a lot of question on how far this rain will push into the
region...if at all. For now...kept continuity going from the
previous forecast with mainly chance probability of precipitation...though low likely in
place across S coastal areas Friday into Friday night.

Have lowered probability of precipitation to chance for early Saturday then should push east
during the afternoon into Sat evening.

Sunday through Wednesday...much of this forecast continues to
depend upon the Friday-Sat pattern sets up. At this point...looks like
it should be mainly dry but cool on Sunday. Models signaling another
500 mb long wave trough digging across eastern Great Lakes as 500 mb low
trying to cut off again across Hudson Bay. May see periods of widely
scattered showers from time to time during this timeframe...but low
confidence on timing and placement.

&&

Aviation /22z Tuesday through Sunday/...

Forecaster confidence levels...

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

Short-term /through Wednesday night/...

Into this evening...high confidence.
Scattered rain showers/thunderstorms and rain around the Massachusetts-CT-RI border. Sub-severe. Tempo MVFR
with +ra. Should see this activity dissipate...begin to refocus southeast
offshore around Nantucket into the overnight hours along and ahead
of an outflow pushing S. Winds shifting SW to north with passage.

Tonight...moderate confidence.
Rain showers/thunderstorms and rain linger over the far southeast terminals till around 6-9z.
Tempo MVFR-IFR conditions focused towards the cape / islands.
Otherwise light winds and VFR...though terminals which experienced
rain during the day may see MVFR-LIFR patchy dense fog.

Wednesday...high confidence.
Scattered rain showers with lower possibility of thunderstorms and rain. Low risk of small hail.
Breezy west-winds with gusts upwards of 20 kts. Scattered-broken low-end VFR
ceilings.

Wednesday night...high confidence.
West-winds diminishing. VFR. Sky clear. Low confidence patchy dense fog.

Kbos terminal...moderate confidence. Enough confidence that storms
will impact the terminal with significant impact...but uncertain
on the exact timing.

Kbdl terminal...moderate confidence. Watching closely for storm
impact. Storms could potentially hold off to the north.

Outlook /Thursday through Sunday/...

Thursday...high confidence. VFR.

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

Sunday...low confidence mainly for timing. May see leftover showers
with brief MVFR conditions early...then VFR.

&&

Marine...

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.
Showers and thunderstorms linger over the southeast waters along with
breezy SW-winds. Subsequent 5-6 foot seas beginning to diminish
into morning as the wet-weather ahead of a frontal boundary pushes
out to sea behind which winds back west.

Wednesday...high confidence.
West-winds continuing perhaps breezy with gusts upwards of 20 kts.
Seas will gradually diminish through the period. There is the
possibility of some renewed shower activity though likely closer
to the shore.

Wednesday night...high confidence.
West-winds diminishing allowing seas to relax. Should see quiet
boating weather.

Outlook /Thursday through Sunday/...

Thursday-Thursday night...high confidence. Winds and seas below
small craft criteria. Locally reduced visibilities in light rain Thursday night.

Friday through Sunday...moderate confidence. Easterly winds gusting
up to 20 knots. With onshore winds...seas look to build up to 5-6 feet
highest across the eastern outer waters. Rain likely Friday night
through Saturday night...limiting visibilities at times...then
should improve during Sunday.

&&

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...sipprell/evt
near term...sipprell
short term...sipprell
long term...evt
aviation...sipprell/evt
marine...sipprell/evt

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