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Area forecast discussion 
National Weather Service Taunton Massachusetts
714 PM EDT Thursday Aug 25 2016

Synopsis...

High pressure offshore brings warm and humid conditions tonight. A
cold front swings through the region Friday, bringing showers and
a few thunderstorms later tonight and Friday. Seasonable and dry
for the weekend. Chance of scattered showers and thunderstorms
for Monday. Thereafter dry weather Tuesday into Wednesday. From
then on possibly into the Labor Day weekend a more disturbed, wet-
weather pattern is forecast. Continue to monitor the latest with
invest-99l but the long-term track forecast remains uncertain.

&&

Near term /until 6 am Friday morning/...

730 PM update...

Looking at the broad picture across the NE Continental U.S.. low to mid level
heights lowering with the influx of mid-level energy across the NE
Continental U.S.. still some component of anticyclonic flow aloft. Per BUFKIT
profiles, majority of forcing is confined at or below h5, mainly
within the low-levels with some association with mid-level weak
vortex energy.

Isallobaric response of S/SW winds gusting upwards of 25 mph ahead
of a surface cold frontal feature presently into the east Great Lakes,
plenty of moisture within the low-levels beneath 700 mb. Precipitable
waters up to 2 inches with surface dewpoints rising into the upper
60s to the 70 degree mark. Weak shear in an otherwise weakly
unstable environment as lapse rates are poor aloft.

Pre-frontal trough sweeping across the Hudson presently into New
England, expect overnight chances of showers, with the greater
likelihood of low clouds and possibly fog. Have gone ahead and
removed the mention of thunder given the environment noted above.
Have greater confidence of thunder chances into Friday as the cold
front approaches ahead of which there is an opportunity for the
boundary-layer to destabilize. Still, will have to keep an eye on
activity emerging out of the east Great Lakes region. With boundary-
layer decoupling, expecting winds to drop off but maintain a S/SW
flow.

Low temperatures limited by cloud cover and rising dewpoints.
Values in the upper 60s to low 70s. But will have to monitor the
possibility of clearing between the present pre-frontal trough and
activity over the Great Lakes. If radiational cooling is allowed
to proceed, especially for the interior sheltered valleys, could
be contending with some fog given the higher dewpoints.

&&

Short term /6 am Friday morning through Friday night/...

Friday...

First plume of moisture moves through in the morning. A second
plume crosses in the afternoon along with the cold front. Shear
continues marginal, with brief 35 knots at 500 mb midday.
Instability builds with a couple of models showing 1000 j/kg
CAPES. Li remains sub-zero. Continue showers/scattered thunder
during the day. The high precip water values will allow for
locally heavy downpours.

Friday night...

Cold front moves offshore Friday evening. The high precip water
values decrease noticeably behind the cold front, as does the
cloud-level moisture. Expect clearing skies and winds shifting
from the northwest.

&&

Long term /Saturday through Thursday/...

*/ highlights...

- seasonable and dry weekend, fantastic weather!
- Shower and thunderstorm chances for Monday
- banking dry weather for early-mid week, wet-weather mid-late week
- low confidence forecast for next week especially with invest-99l

*/ discussion...

Forecast hinges upon the morphology of synoptic features towards the
later-half of the week into Labor Day weekend with respect to invest-
99l (al99). Continued struggles with forecast model performance in
handling North/East Pacific disturbances into the west Continental U.S. Is subsequently
leading to alterations in the ridge-trough-ridge pattern extending
from the Gulf of Alaska region into the central and east Continental U.S.. notably
atmospheric teleconnections have exhibited some waffling within the
last few model runs, especially into the beginning of September. Do
still believe through the complications that the 500 mb high presently
across S/east Continental U.S. And mid-Atlantic will only shift and perhaps weaken
with the presence of al99. This yields the opportunity for Pacific-
origin energy through the consensus forecast of near-zonal flow for
the early- to mid-week period to have a greater influence S across
the north Continental U.S. As al99 makes its approach. Then it becomes a question
of how such energy from the north interacts with the consensus forecast
of al99 into the southeast Continental U.S. Towards the mid-Atlantic.

After a certainly pleasant, comfortable weekend with seasonably dry
weather with likely onshore influences, looking at wet-weather for
Monday with scattered showers and thunderstorms. Not overwhelming
confident. Timing of associated cold frontal passage in question as
is both the availability of moisture and instability. Weak shear
profiles as lapse rates are poor. Seemingly still dealing with the
lingering influence of high pressure. But if synoptic forcing can
come together along with a destabilizing boundary-layer, outcomes
are plausible, especially Monday afternoon. Will hold with chance
pops over much of S New England.

Continued low confidence forecast hereafter as deterministic models
struggle with individual waves and accompanying influences through
the ensemble-weighted near-zonal flow with favorable troughing in
the vicinity of the west Continental U.S.. content with earlier thinking that
beyond Monday will be a brief period of high pressure followed by
periods of disturbed weather for the mid-late week period. Crucial
is whether al99 is wrapped into expected disturbed weather and north-
stream energy late week into Labor Day weekend to which the majority
of guidance keeps offshore. But with some ensemble members that is
not the case, and the consensus forecast has exhibited some wobbling
as of late, so overall forecast outcomes remain uncertain.

&&

Aviation /00z Friday through Tuesday/...

Forecaster confidence levels.

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

Short term /through Friday night/...

0z update...

Tonight...moderate confidence.

Low-end VFR cigs with MVFR likely. Highest confidence MVFR across
high terrain (i.E., Orh). Lot of moisture in the air, so will have
to monitor for potential fog as well, perhaps after scattered rain showers
sweep northwest to southeast during the overnight period. Potential sky clear behind
the line could yield fog. Not expecting thunderstorms and rain. S/SW winds gusting
initially 20 to 25 kts will diminish during the evening period.

Friday...moderate confidence.

Scattered rain showers/tsra, with higher confidence over S/east interior S New
England terminals. S/SW winds continue with gusts up to 20 kts
before shifting out of the northwest late. Low-end VFR cigs but can not
rule out MVFR, with tempo MVFR-IFR conditions with any thunderstorms and rain and/or
+ra.

Friday night...moderate confidence.

SW winds shifting out of the west/NW, 10 kts or less. VFR with the
possibility of IFR conditions prior to the wind shift over S/east
coastal terminals. Will also need to monitor whether light winds
and radiational cooling can yield interior fog issues.

Kbos terminal...prevail -shra overnight. Towards 15z onwards will
be closely watching areas short wave for thunderstorms and rain development. SW winds
overall with gusts around 20 kts during midday Friday into afternoon.

Kbdl terminal...low-end VFR to MVFR possible overnight. Clearing
into Friday morning, potentially, will be monitoring for thunderstorms and rain
development around and east of the terminal midday into afternoon.

Outlook /Saturday through Tuesday/...

Saturday into Sunday...high confidence.

VFR. Light winds. Likely sea-breezes. Winds turning east/southeast Sunday,
potentially breezy late with scattered mid-high cloud.

Monday...moderate confidence.

Chance of shra/tsra. Timing of outcomes remains unclear at this
time, could see some morning activity followed by afternoon storm
development. S/SW winds, breezy with gusts up to 20 kts, backing out
of the west/northwest towards morning.

Tuesday...moderate confidence.

Will prevail VFR with winds turning out of the W/NW.

&&

Marine...

Forecaster confidence levels.

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

Short term /through Friday night/...high confidence.

730 PM update...no major changes to the forecast.

Tonight...

Winds 20 to 25 knots this evening should diminish during the
night. Seas will remain below 5 feet. A Small Craft Advisory
remains in effect through the evening due to the wind potential
being near 25 knots.

Friday...

Cold front approaches late tonight and Friday with potential for
showers and scattered thunderstorms. This will bring briefly lower
vsbys. Also areas of fog possible early Friday with lower vsbys.
Winds below 20 knots or less, seas 4 feet or less.

Friday night...moderate confidence.
SW winds 10-15 kt Friday evening, with gusts up to 20 kt on the
southern waters, shifting to north-northwest overnight as a cold front sweeps
the waters. Seas 4 ft or less. Patchy fog on the S near shore
waters with visibility restrictions.

Outlook /Saturday through Tuesday/...

Saturday into Sunday...high confidence.

High pressure, light winds, gradually veering out of the S/southeast into
Sunday, becoming breezy late. Waves remaining below 5 feet.

Monday...moderate confidence.

Winds turning out of the S/SW ahead of a sweeping cold front. There
is the potential for gusts up to 20 kts. This in addition to shower
and thunderstorm activity, mainly considering the near-shore waters.
Expect the cold front to sweep the waters towards the later half of
the day, into evening, at latest overnight. Wave influence per
weather may be minimal, but of greater concern is swell associated
with Gaston. Waves in excess of 5 feet by evening.

Tuesday...moderate confidence.

Cold front pushing out to sea as winds back W/NW. Swell continuing
from Gaston with wave heights up to 6 feet on the outer waters.

&&

Box watches/warnings/advisories...

CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...Small Craft Advisory until 11 PM EDT this evening for
anz231>235-237-250-251-254>256.
Small Craft Advisory until 10 PM EDT this evening for anz236.

&&

$$

Synopsis...wtb/sipprell
near term...wtb/sipprell
short term...wtb
long term...sipprell
aviation...wtb/sipprell
marine...wtb/sipprell

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