Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 262318
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
718 PM EDT FRI AUG 26 2016

.SYNOPSIS...

A cold front moves off the New England coast this evening. High
pressure then builds over Northern New England, bringing dry weather
for much of the weekend. As we go Sunday into Monday there is the
chance of showers and thunderstorms ahead of a sweeping cold front.
A brief period of high pressure follows for Tuesday prior to another
cold front for Wednesday with again the chance of wet-weather. Low
confidence forecast from Thursday onward as competing airmasses
present the double-sided possibility of either wet- weather or
remaining completely dry.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...

715 pm update...

Cold front offshore by midnight. Dewpoints are in the 70s ahead
of the front and mid 60s behind, so expect the air to become a
little more comfortable. But drier air is still well N/W of the
region. Conditions clear if not already so through the night.
Winds to become light in the interior. All told, expect lows to
bottom out in the mid and upper 60s most places, and low 70s
Cape/Islands and urban spots.

There is an opportunity for radiational cooling, and given dewpoints
are still modest, and wherever it may have rained earlier in the
day, there is an opportunity for patchy dense fog. Something we`ll
need to watch closely this evening. It is perhaps that high-res
guidance is not capturing the potential well. Lows are forecast to
get down to if not lower than the cross-over threshold, but again
there is drier air being advected into the region. Again, just got
to keep an eye on it.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...

High pressure builds over New England with center along the
Canadian border. This will bring a light wind inland and sea
breezes along the coast. Dew points will continue to lower with
readings near 60.  Temps at 850 mb will be in the mid teens, so
max sfc temps should reach the mid to upper 80s, with coolest
temps along the coastline.

The center of high pressure shifts east a little Saturday night,
but fair skies and light winds remain in place over Southern New
England through the night. With light wind and dew points
lingering near 60, expect min temps roughly 60 to 65.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...

*/ Highlights...

 - Shower and Thunderstorm chances Sunday into Monday
 - Keeping it dry for Tuesday
 - Another cold front and chances of wet-weather for Wednesday
 - Low confidence forecast from Thursday onward
 - Keeping Invest-99L out of the picture and out to sea

*/ Discussion...

Interpreting the N Hemispheric pattern. Atmospheric teleconnections
continuing a -WPO/-EPO trend through the beginning of September with
a waffling PNA. Of certainty, we`re seeing a buckling in the height
pattern across the N Pacific in concert with a -WPO/-EPO yielding a
high latitude block and stronger than normal Pacific jet within the
deepening troughs. Given the PNA trend, there is no clear signal as
to outcomes downstream. Nevertheless, during -EPO/-WPO trends it is
noted that anomalous cyclonic circulations can occur over E portions
of N America, drawing cooler air S. So while the late-August early-
September cyclone in vicinity of the NE CONUS per deterministic
guidance may seem erroneous, it can not entirely be rule out. Will
for the sake of simplicity keep with an ensemble-weighted forecast.
Inclined to believe per ensemble members and deterministic forecasts
that at this point whatever becomes of Invest-99L (AL99) will sweep
out N/E ahead of preferred troughing prior to and during the Labor
Day Holiday Weekend.

So will lean with the following forecast: Sunday into Monday a
deamplifying disturbance which will introduce lower heights and
cyclonic flow, a slight kink to the near-zonal flow. Surface cold-
frontal feature, there is the chance of showers and thunderstorms.
Prefer to keep it dry for Tuesday. Another cold front for Wednesday
and the chance of showers and thunderstorms. Thursday and Friday
remain up in the air. If a deep cyclone does develop and remains in
the vicinity of the NE CONUS, then the combination of cooler air
aloft and daytime heating/destabilizing boundary layer below, along
with continued impulses through the cyclonic flow, could yield a
setup for diurnally-forced storms. But it is possible that drier air
and high pressure win out. Toss up at this point and subsequently a
low confidence forecast. For Labor Day Weekend, going by ensemble
means, it does appear the trough-ridge-trough pattern across the
CONUS shifts subtly E thereby putting the NE CONUS at least the
influence of high pressure. As to airmass depends on the preferred
wind flow aloft (i.e., NW vs. SW). No threats or impacts just yet to
speak of throughout the long-term forecast, as well as no end in
sight with regards to current drought conditions.

&&

.AVIATION /23Z FRIDAY THROUGH WEDNESDAY/...

Forecaster Confidence Levels.

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

Short Term /through Saturday Night/...

0z update...

Tonight...High Confidence.

VFR. SKC. Just a few MVFR-IFR clouds lingering over ACK for an
hour or two with VCSH. Otherwise a potential risk of patchy MVFR-
IFR fog in the CT River Valley towards early morning Saturday.
Light NW winds.

Saturday...High Confidence.

VFR. Light north winds, with sea-breezes developing along both
coasts.

Saturday night...High Confidence.

VFR. Light variable wind. Patchy fog after midnight in the usual
prone locations with IFR/LIFR cigs/vsbys through sunrise.

KBOS Terminal...VFR. Sea breeze likely around 15Z Saturday. High
confidence in TAF.

KBDL Terminal...VFR. High confidence in TAF.

Outlook /Sunday through Wednesday/...Moderate Confidence.

Sunday...

Will keep it VFR with winds turning S becoming breezy. Increasing
mid-high cloud across the region with the possibility of SHRA N/W
late in the period.

Monday...

Chance of SHRA/TSRA. S/SW winds, breezy with gusts up to 20 kts,
backing out of the W/NW towards Monday evening.

Tuesday...

Will prevail VFR with W/NW winds initially veering out of the S/SW.
Anticipating increasing mid to high cloud late in the period.

Wednesday...

Chance of SHRA/TSRA. S/SW winds, breezy with gusts up to 20 kts,
backing out of the W/NW during the evening into overnight period.

&&

.MARINE...

Forecaster Confidence Levels.

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

Short Term /through Saturday Night/...High confidence.

715 pm update...not major changes to the forecast.

Cold front pushing SE out to sea overnight. Light NW winds to
follow. High pressure builds over New England Saturday. Winds and
seas expected to remain below small craft advisory thresholds
through Saturday night.

Gusty southwest winds early tonight shift northwest, then become
light north Saturday. Local seabreezes likely Saturday near shore.
Light variable wind Saturday night. Seas 4 feet or less through
the period.

Outlook /Sunday through Wednesday/...

Sunday...

High pressure departing E. Winds turning S becoming breezy with
gusts up to 20 kts. Will keep wave heights below 5 feet even with
the swell associated with Gaston.

Monday...

Chance of showers and thunderstorms, mainly over the near-shore
waters. S/SW winds, breezy with gusts up to 20 kts continuing,
backing out of the W/NW towards Monday evening with a cold frontal
passage. Persistent wind stress plus swell associated with Gaston,
will introduce 5 foot seas on the outer waters.

Tuesday...

W/NW winds initially, fairly benign, veering out of the S/SW through
the day. Will keep it dry. Continued swell from Gaston, will keep
with 5 foot seas on the outer waters.

Wednesday...

Another cold front and another chance of showers and thunderstorms.
S/SW winds ahead of the front with gusts up to 20 kts, backing out
of the W/NW into the evening and overnight period.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...

CT...None.
MA...None.
RI...None.
MARINE...None.

&&

$$

SYNOPSIS...WTB/Sipprell
NEAR TERM...WTB/Sipprell
SHORT TERM...WTB
LONG TERM...Sipprell
AVIATION...WTB/Sipprell
MARINE...WTB/Sipprell



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