Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 270810
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
410 AM EDT Tue Jun 27 2017

.SYNOPSIS...
A strong jet stream will result in widespread afternoon showers
and thunderstorms across Massachusetts, Rhode Island and
Connecticut. A few of the storms may contain gusty winds and
small hail. A warming trend begins for the latter half of the
week with a return to summer heat and humidity Friday and
Saturday. A warm front may bring some showers and some
thunderstorms Thursday night, with more showers and
thunderstorms possible Friday through the weekend.&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

4 AM Update...

*** A Few Strong Thunderstorms Possible This Afternoon With Gusty
Winds and Small Hail ***

Mostly clear skies during the predawn hours across southern New
England along with comfortable temperatures in the 50s. High clouds
streaming across western sections of MA/CT in the southwest flow
aloft. Thus duration of sunshine later this morning will be greatest
across RI and eastern MA.

By this afternoon will be watching a potent short wave trough over
the eastern Great Lakes early this morning. Anomalous wind fields
and cold temps aloft associated with this feature will move across
southern New England this afternoon. The combination of synoptic
scale lift and modest deep layer moisture will likely result in
widespread showers and T-storms this afternoon.

Showers currently across southeast PA into NJ showing signs of
intensifying as cloud tops cool in this region. This activity will
enter western CT/MA between 8 am and 11 am. As short wave over
eastern Great Lakes approaches showers and T-storms will become more
widespread this afternoon. Cold temps aloft -18C to -20C at 500 mb
will result in steep mid level lapse rates. This combined with
anomalous wind fields aloft will likely result in at least a few
strong storms with a hail and wind threat. One limiting factor will
be dew pts only in the 50s which will result in SBCAPES of less than
1000 J/KG. Nevertheless, expecting a few strong storms this
afternoon with risk highest across interior MA and lowest risk over
southeast MA, where it may not even rain at all.

As for temps, highs likely in the 75-80 deg range. Not excessively
humid with dew pts only in the 50s today.

Regarding winds, modest low level southwest jet moves across the
area this afternoon with winds gusting up to 25-30 mph over RI and
southeast MA.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...

Tonight...

Cyclonic flow continues along with cold temps aloft and 40-45 kt of
deep layer shear. This will support leftover showers and isolated T-
storms to persist into the evening (especially over RI and eastern
MA) before taping off after midnight. Patchy fog possible given
leftover low level moisture from earlier storms

Wednesday...

Mid level flow is still cyclonic however flow becomes more WNW which
results in column drying out along with surface dew pts falling into
the 40s. Cyclonic flow aloft combined with cold temps will yield
plenty of diurnal clouds and the risk of an isolated shower/T-storm.
However given lack of moisture areal coverage should be limited to
isolated. Otherwise a fairly nice day by late June standards with a
mix of sun and clouds, highs 75-80 along with comfortable humidity
with dew pts in the upper 40s and low 50s!

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...

Highlights...

* Thunderstorm chances increase Thursday night through Sunday
* Heat and Humidity return Friday, lasting into the weekend

Pattern Details...

00z guidance is in general agreement synoptically with some
difference in strength and timing for each wave late in the week.
Upper level trough axis will begin to push offshore on Wednesday
resulting in a quasi-zonal flow for the region beginning on
Thursday. The upper level pattern will become more amplified by the
weekend resulting in a broad trough over the Great Lakes with sub-
tropical ridge building over the weekend. Because of the ridging
over the East Coast and the Midwest trough, a cold front will be
come nearly stationary with very little eastward progress this
weekend. Ridging out West by Sunday will push towards the Great
Lakes by early next week, pushing the broad upper level trough over
the Northeast.

Details...

Wednesday night into Thursday...

Surface high pressure over the region Wednesday night will help keep
winds light and skies clear. Overnight lows will drop into the mid
to upper 50s with metro regions in the 60s.

Dry day to start on Thursday as high pressure will slide offshore.
The flow will turn more active with zonal flow aloft and a few weak
waves passing through. Impressive warming aloft as surface warm
front pushes through the region. This will push southern New England
in the warm sector resulting in increasingly warm and humid
temperatures.

A weak shortwave will move through the flow Thursday evening/night.
With zonal pattern and both 850mb isotherms and winds becoming
parallel, appears that anything the fires across upstate NY will
ride through the flow moving into the area. In fact, guidance is
indicating a lingering MCS will move through the flow late in the
afternoon/evening which could result in a few strong storms, esp
north of the Pike. However, new convection could refire along its
southern edge given the strong low level jet and moisture over the
area. Trends will have to be watched.

Depending on the outcome of convection and cloud cover,
temperatures will remain in the low 80s. But it will feel warmer as
humidity will be on the rise. Showers and thunderstorms will
continue during the overnight hours keeping temps in the upper 60s.

Friday into Sunday...

Unsettled weather pattern for this time period as southern New
England remains in the warm sector with heat and humidity. 850 mb
temps warming to 17-18C as well as southwesterly flow, will allow
for the summer heat to returns to the region. Appears that the
potential for 90 degrees is possible on Friday and Saturday as the
back door cold front continues to remain well north of the region.
Heat headlines may be needed as 70F dewpoints beginning to pool into
the area.

There remains a chance for showers and thunderstorms each day, but
difficult to place the exact timing and location of any strong
storms due to lack of surface boundary. Daytime heating will allow
for scattered showers and thunderstorms to develop on Friday.
Another shot for scattered showers and thunderstorms will develop on
Saturday, but western locations have the better shot thanks to
approaching pre-frontal trough. Lower confidence for eastern
locations as subtropical ridge will build in pushing a dry slot into
the area on Saturday. Cold front will approach on Sunday triggering
another round of showers and thunderstorms for southern New England.

Through this period, the potential for strong to severe weather
appears possible as the region remains in the warm sector. Plenty of
instability and moisture will continue to pool into the area with 0-
6 km shear values around 30 kts. Main risk will be strong gusty
winds as well as heavy downpours as PWATs will be above 1.5 inches.
Still uncertainty with this portion of the forecast so stay tuned
for updates.

Monday...

Cold front will slowly pass through the region on Monday, however is
appears that it may get hung up. Cyclonic flow aloft with southwest
flow in the mid-levels may trigger another round of showers for the
area. Low confidence on this portion of the forecast as there is
still a spread in the guidance.

&&

.AVIATION /08Z TUESDAY THROUGH SATURDAY/...
Forecaster Confidence Levels...

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

2 AM update...

Short Term /through Wednesday/...High confidence.

Thru 12z...

VFR and dry weather. Patchy MVFR possible briefly in areas of
fog toward sunrise. Showers and T-storms over southeast PA near
Philly will enter western CT/MA 12z-15z.

After 12z...

VFR becoming marginal VFR-MVFR in Widespread showers and
embedded T-storms develop from southwest to northeast with
T-storms becoming more numerous this afternoon. A few of the
stronger storms may contain gusty winds and small hail across
the interior. Increasing pressure gradient will result in gusty
SSW winds even in the absence of T-storms.

Tonight...

Marginal VFR-MVFR in scattered showers and T-storms during the
evening, especially across eastern MA and RI. Activity should
diminish after midnight.

Wednesday...

VFR and drier weather. Although can/t rule out an isolated
shower/T-storm during the afternoon. Modest WNW winds.

KBOS Terminal...High confidence in TAF. Showers and T-storms
likely this afternoon. A few of the stronger storms may contain
small hail and gusty winds.

KBDL Terminal...High confidence in TAF. Showers and T-storms
overspread KBDL 12z-15z and continuing into the afternoon. A few
of the stronger storms may contain small hail and gusty winds.

Outlook /Wednesday Night through Saturday/...

Thursday...High confidence. Mainly VFR. Afternoon/evening showers
possible in the interior with showers/t-storms possible all SNE Thu
night. Gusty SW winds to 25-30 kt developing, especially coastal
plain.

Friday into Saturday...Moderate confidence.  Patchy early morning fog
each day. Otherwise mainly VFR, except local IFR in possible strong
thunderstorms, mainly during the afternoon and evening hours
through the period.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Wednesday/...High confidence.

Today...

SSW winds increase up to 25 kt along the RI and MA coastline.
Strongest winds near shore and occurring from noon to 6 pm. SCA
posted for all the near shore waters. Showers and T-storms develop
this afternoon. A few strong storms possible especially north shore
of Boston.

Tonight...

Showers and thunderstorms most numerous during the evening hours. A
few strong storms possible with gusty winds and small hail. SSW
winds may yield patchy fog especially during the evening. Improving
after midnight.

Wednesday...

Winds become WNW at modest speeds. This results in good vsby and
mainly dry weather, other than an isolated shower or T-storm.

Outlook /Wednesday Night through Saturday/...

Thursday...Moderate confidence. Small craft advisories will likely
be needed. Increasing SW winds with gusts to 25+ kt likely,
especially over nearshore waters. Building seas may reach 6 to 8 ft
over southern waters Thu night.

Friday into Saturday...Moderate confidence. SW winds continue,
mainly 20-25 kt with building seas. Scattered thunderstorms, some
with reduced visibilities and strong gusty winds for each day.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from noon today to 8 PM EDT this evening
     for ANZ230>237-251.

&&

$$
SYNOPSIS...Nocera/Dunten
NEAR TERM...Nocera
SHORT TERM...Nocera
LONG TERM...Dunten
AVIATION...Nocera/Dunten
MARINE...Nocera/Dunten



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