Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 310133
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
933 PM EDT SAT JUL 30 2016

.SYNOPSIS...
An area of low pressure will move slowly eastward from the lower
Great Lakes Region towards southern New England. The warm front
extending from this low is expected to remain to our south during
tonight and Sunday, which will allow for scattered showers and
isolated thunderstorms across our area. This low will pass south
of New England during Sunday night and Monday, then move offshore
during Tuesday. High pressure will build out of northern New
England during Wednesday through Friday, bringing dry conditions.
Temperatures will warm up toward the end of next week.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
930 pm Update...

Rainfall rates have decreased over past hour and were no more than
1"/hour across parts of CT Valley. This activity formed in an area
of marginal instability (CAPES up to 500 j/kg) but on nose of
moisture axis which extends from mid Atlantic states into central
MA. High-res models keep showers around southern New England overnight,
and want to weaken activity as it passes E of Worcester Hills,
focusing most of it near the Berkshires after midnight. This looks
reasonable based upon radar trends so have adjusted PoPs
accordingly (highest in W New England). That`s not to say there
won`t be a stray shower or two farther E as well.

Warm/muggy night ahead with lows in 60s to around 70 and patchy
fog, which will be dense in spots near South Coast.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
During Sunday the warm front is expected to remain draped just south
of our area, as the weak low pressure gradually moves eastward. Thus
a continued modest overrunning setup is anticipated. For Sunday
have the highest (likely) POPs in the western MA/north central CT
where the models suggest better forcing. Chance pops to the east.
With K indices in the lower 30s, cannot rule out isolated thunder
during Sunday. Skies are expected to be mainly cloudy through the
day. The combination of clouds and generally onshore flow is
expected to keep temperatures in the mid to upper 70s on Sunday.

During Sunday night models show the weak low pressure passing south
of New England. This will bring continued cloudiness to the area,
along with scattered showers/isolated t-storms. Lows mainly in the
60s are expected. With abundant low level moisture expecting some
areas of fog.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Highlights...

* Unsettled weather through early Tuesday with scattered showers,
  mainly over northern and western areas
* Isolated thunderstorms possible across central and western
  areas Monday afternoon/evening
* Mostly dry weather expected Tuesday afternoon through Friday,
  with a warming trend toward the end of next week

Overview and model preferences...

30/12z guidance continues to shower decent overall agreement with
synoptic trends over this portion of the forecast. Agreement on
some of the more significant details, not so much.

Latest guidance continues to show an open wave of energy in the
mid levels passing the northeast USA early next week. Then the mid
level flow transitions to a nearly zonal flow for the second half
of next week. One question which still needs to be answered is how
close does another mid level open wave get to southern New England
toward next weekend. This nearly zonal flow should lead to much
quieter weather during the middle of next week.

At the surface, there is some disagreement at how close a pair of
low pressures get to our region early next week. This will be key
to determining how quickly the risk for showers winds down
Tuesday. The majority of the guidance keeps these low pressures to
our south Monday into Tuesday. So while not expecting a washout,
have low confidence with this portion of the forecast, especially
with timing.

Used a blend of available model and ensemble guidance for this
portion of the forecast.

Details...

Monday through early Tuesday...

Expect a couple of low pressures to slowly ride along a stalled
front just off the southern New England coast into early Tuesday.
This will keep a good low to mid level moisture feed across the
region thanks to an E-SE wind flow that will slowly back to NE
late Monday night into Tuesday as the final low pressure pushes
offshore.

The greatest risk for showers still appears to be Monday,
gradually diminishing Monday night into Tuesday. Greatest risk
for showers should be across the interior, but really anywhere in
southern New England has a shot at some showers or thunderstorms.

Will see the final low push offshore early Tuesday as it becomes
better organized. The last of the showers should start to
dissipate during the morning.

With the mainly onshore flow, expecting temperatures to run
several degrees below seasonal normals, especially toward the
coasts.

Tuesday afternoon through Friday...

This still looks like a mainly dry period of the forecast. Cannot
rule out a stray, isolated shower. There may be just enough
instability and moisture to generate one or two, especially across
the higher terrain of interior southern New England.

Temperatures should return to seasonal levels Wednesday, then
will warm further as winds become more S-SW as the high crests
across the region, then slowly pushes offshore. Humidity levels
will also slowly increase.

Saturday...A cold front is currently expected to cross our region.
This should lead to a chance of showers. Still lots of time to
work out the timing details.

&&

.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
Forecaster Confidence Levels.

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

Short Term /through Sunday Night/...

Tonight...Moderate confidence. Mainly VFR ceilings are expected
to start, except localized IFR cigs/vsbys in fog possible
Cape/Islands. Then areas of MVFR cigs/vsbys developing overnight
in scattered showers and areas of fog. Localized IFR cigs/vsbys
possible.

Sunday...Moderate confidence. MVFR ceilings/vsbys to start with
scattered showers and patchy fog. There is a chance for IFR
ceilings/vsbys in stratus/fog near the coastline. Ceilings should
become mostly VFR for afternoon although some MVFR ceilings will
be possible in vicinity of showers.

Sunday night...Moderate confidence. MVFR/IFR cigs/vsbys with
scattered showers and areas of fog.

KBOS TAF...Moderate confidence through Sunday. VFR conditions
expected through this evening. Occasional MVFR ceilings possible
in vicinity of showers and fog late tonight/Sunday. Weakening
thundershower south of the terminal through 01Z.

KBDL TAF...Moderate confidence through Sunday. VFR conditions
expected through this evening, except brief MVFR cigs/vsbys
possible in an isolated shower or t-storm. Occasional MVFR
ceilings possible in vicinity of showers and fog late
tonight/Sunday.

Outlook /Monday through Thursday/...

Monday through Monday night...Moderate confidence. Mainly VFR.
Scattered showers possible at any time. Cannot rule out a heavier
shower or thunderstorm with local MVFR-IFR conditions, mainly from
central Mass into N Connecticut Monday afternoon and evening.
Areas of late night/early morning fog with IFR CIGS/VSBYS Monday
night.

Tuesday...High confidence in trends. Moderate confidence in
timing. Mainly VFR. Scattered showers across the CT Valley through
north central and northeast MA Tuesday morning, then improving.
May see brief local MVFR conditions in any showers. Patchy late
night/early morning fog with MVFR-IFR conditions Tuesday night in
the normally prone areas.

Wednesday and Thursday...High confidence.
VFR. Just a few areas of MVFR possible in patchy late night/early
morning valley fog and in the usual fog prone locations.

&&

.MARINE...
Forecaster Confidence Levels.

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

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

Winds and seas are expected to remain below Small Craft Advisory
thresholds through Sunday Night. Areas of visibilities 1 to 3 nm in
areas of fog are possible at times tonight along the waters around
Nantucket, and isolated to scattered showers are possible over the
waters later tonight and Sunday.  For Sunday night, visibility
restrictions possible in scattered showers and fog
patches.

Outlook /Monday through Thursday/...High confidence.

Monday through Tuesday...Relatively light winds and seas.
Visibility restrictions in patchy late night/early morning fog
both nights, and in scattered showers Monday and Monday night,
slowly improving on Tuesday. Isolated thunderstorms possible off
the RI coast Monday into Monday evening.

Tuesday night through Wednesday...Persistent onshore winds
continue. A passing low pressure may generate rough seas across
the eastern coastal waters. Local visibility restrictions continue
Tuesday night in patchy fog, mainly after midnight through mid
morning Wednesday.

Thursday...Tranquil boating conditions with light winds and seas
expected.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

$$
SYNOPSIS...Belk/NMB
NEAR TERM...JWD
SHORT TERM...NMB
LONG TERM...Belk
AVIATION...Belk/NMB
MARINE...Belk/NMB


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