Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 251915
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
315 PM EDT Sun Jun 25 2017

.SYNOPSIS...
Scattered showers and isolated thunderstorms will diminish early
tonight. Additional upper level disturbances move across New
England on Monday and Tuesday, bringing a few showers or
isolated thunderstorm. Then a warming trend begins for the
latter half of the week with a return to summer heat and
humidity by Friday. A warm front may bring some showers Thursday
with more showers and thunderstorms possible Friday and
Saturday. A backdoor front may drop south into the region
Saturday.

&&

.NEAR TERM /THROUGH TONIGHT/...

Lingering instability along with the right entrance region of
the upper jet...this may support a few showers/tstms through the
first hours of the night. Upper shortweave moving along the
Canadian border moves off to the northeast tonight. The
instability will diminish and the upper jet will shift southeast
during the night, so expect any showers to end and skies clear.

Clearing skies and light wind will allow some radiational
cooling. With dew points in the 50s, expect min temps mainly in
the 50s...except low 60s in some urban centers.

&&

.SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...

Upper flow remains cyclonic. A weak shortwave moves through the
flow and across New England on Monday. Temps aloft will be a
couple of degrees cooler, with solar heating working on the
surface temperatures. The resulting lapse rates should be
favorable for a few showers/tstms.

Mixing will again reach high, up to 800 mb or a little higher.
Temps at that level, equivalent to 11C at 850 mb, will support
max temps in the upper 70s and the low 80s.

Convection will again diminish after sunset with clearing skies
and light wind. With dew points in the 50s, expect min temps in
the 50s and low 60s.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Highlights...

* A few showers/isold t-storm possible Tue/Wed
* Warming trend toward end of the week with return to summer
  heat/humidity by Fri
* A few showers possible Thu with sct showers/t-storms Fri/Sat
* Backdoor front possible Sat but low confidence

Overview...

Mid level trof will begin to exit the northeast Wed, followed by
building heights as subtropical ridge builds over the western
Atlantic. Polar jet will be in the vicinity of New Eng late in the
week into the weekend which will leave us susceptible to weak
shortwave passages and bouts of showers and t-storms. Temps starting
out slightly below normal Tue then warming through the end of the
week. Will have to watch a backdoor front for next Sat.

Details...

Tuesday and Wednesday...

Fairly robust shortwave lifts NE from the Gt Lakes Tue with mid
level trof moving into New Eng by Tue evening before exiting on Wed.
Increasing dynamic forcing and 500 mb temps cooling to -18 to -20C
will bring sct showers and isold t-storms to SNE Tue into Tue
evening with best chance in the interior. ECMWF is showing a more
amplified trof with a second shortwave rotating around and inducing
a coastal low south of New Eng Tue night with area of rain for SE
New Eng. This does not have support of other global models so we
have discounted for now but something to watch in later forecasts.
On Wed, mid level trof begins to exit the region but 500 mb temps
around -21C through 18z before warming toward evening. Moisture is
limited but can`t rule out a few showers given the rather cold temps
aloft. Temps mid/upper 70s Tue and a few degrees warmer on Wed.

Thursday...

Increasing warm advection pattern as warm front approaches from the
SW will lead to increasing clouds. GFS and ECMWF differ on the
positioning of the warm front which impacts sensible weather and
temps. GFS lifts the front to the north with main focus for
showers/t-storms to the north and west. ECMWF holds the front to the
south with wetter and much cooler conditions. A low confidence
forecast this far out so minimal changes were made to PoPs and temps
and will have chc pops in the interior. Higher theta-e air and
better instability remains to the west where best t-storm chances
are. Gusty SW winds developing, especially in the coastal plain as
low level jet develops. The risk for t-storms will increase Thu
night as higher theta-e air moves in.

Friday...

Warm sector airmass with low level theta-e ridge axis across the
region and decent instability so expect sct showers and t-storms
developing. Difficult to pinpoint shear profiles this far out but it
does appear the region will be on the southern edge of stronger deep
layer shear so severe weather is possible. Temps should reach well
into the 80s to near 90 degrees but cloud cover could have some
impact. Very humid with dewpoints near 70.

Saturday...

Tricky forecast as we may be dealing with a backdoor front close to
New Eng. Impossible to know where this front will be but there is
potential for a sharp temp gradient across the region depending on
where the front is located. Very warm/humid south of the front with
temps well into the 80s but much cooler to the north of the boundary
with 60s possible. It will all depend on where the front is.
Continued risk for showers/t-storms, mainly south and west of the
boundary.

&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...

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

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

Tonight...

VFR. Evening showers and scattered thunderstorms, especially in
Western and Central Mass, will diminish. Brief MVFR vsbys in any
showers. Clearing skies overnight with light winds.

Monday into Monday night...

VFR. Daytime heating will develop cumulus clouds with bases
4000-5000 feet. These will lead to scattered showers and a few
thunderstorms. Brief vsbys below 5 miles in any showers.

Clouds and showers dissipate after sunset.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday through Friday/...

Tuesday and Wednesday...High confidence.
Mainly VFR. A few showers and isold t-storm possible Tue and still
can`t rule out a shower on Wed.

Thursday...Moderate confidence.
Mainly VFR with cigs lowering from NW to SE. Afternoon showers
possible in the interior with showers/t-storms possible all SNE Thu
night. Gusty SW winds developing, especially coastal plain.

&&

.MARINE...
Forecaster Confidence Levels...

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

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

High pressure offshore with west to southwest winds. Speeds
should remain 20 knots or less. Seas have diminished, and should
remain at 4 feet or less through the period.

Outlook /Tuesday through Friday/...

Tuesday and Wednesday...High confidence. Quiet boating weather with
winds and seas below SCA. Gusts to 20 kt possible nearshore waters.

Thursday...Moderate confidence. Increasing SW winds with gusts to
25+ kt likely, especially over nearshore waters. Building seas may
reach 8 ft over southern waters Thu night. Chance of showers and
thunderstorms Thursday night.

&&

.TIDES/COASTAL FLOODING...

High astronomical tides have peaked at most spots, but still at
high levels for at least one more cycle. The overnight tide
cycle will be the one of concern, with Boston reaching 12.2 feet
after midnight tonight. Tidal departures will be around 0.3 to
0.4 feet along the Massachusetts East Coast. This means
conditions will be high enough along the Mass East coast for at
least some minor splashover at high tide.

Subsequent high tides will be trending lower, and thus less of a
risk for splashover concerns.

&&

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

&&

$$
SYNOPSIS...WTB/KJC
NEAR TERM...WTB/KJC
SHORT TERM...WTB
LONG TERM...KJC
AVIATION...WTB/KJC
MARINE...WTB/KJC
TIDES/COASTAL FLOODING...



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