Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 291701
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
101 PM EDT SUN MAY 29 2016

.SYNOPSIS...
A backdoor cold front will bring much cooler temperatures today
along the eastern MA coast, but another hot afternoon is in store
farther inland where hit and miss showers and thunderstorms are
expected. Mainly dry weather is expected this evening, but bands
of torrential rain showers along with isolated thunderstorms are
expected very late tonight and Memorial Day. Dry conditions with
warm afternoons follow Tuesday into Wednesday. Unsettled weather
may return by the end of next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
100 pm Update...

Low clouds are holding their own across eastern MA but have been
eroding on southern and western edge across western and south
central MA and northern RI. Expect this to continue through late
afternoon while some breaks begin to appear across eastern MA.

Temperatures have certainly been a challenge with backdoor front
essentially splitting SNE in half: Coolest temps were across NE MA
where onshore flow was keeping readings in 50s, while it has
soared well into 80s around Hartford.

Airmass has begun to destabilize across much of western New
England early this afternoon, where ML CAPES were approaching
1000-2000 j/kg near Berkshires. While most of activity has
developed under more favorable conditions in upstate NY, we have
also begun to see some scattered showers form over Berkshires
during past hour. We should see additional scattered
showers/storms develop through late afternoon in MA, primarily
west of Worcester Hills. Potential for organized severe weather
remains low given very marginal 0-6km shear of 20-25kt and meager
mid level lapse rates (less than 6C/km). Main hazards are brief
downpours and lightning, and perhaps one or two storms that
produce 40 mph gusts.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
***Bands of torrential rain showers with isolated thunderstorms
   develop very late tonight and continue through Memorial Day***

***Potential for localized flash flooding***

Tonight and Memorial Day...

Convection across the interior will quickly dissipate early this
evening with the loss of daytime heating/instability.  Otherwise,
much of the evening should be dry with perhaps just a spot shower or
two.  May see some patchy fog develop especially near the south
coast.

Things then become interesting very late tonight and Memorial Day.
Tropical Storm Bonnie off the South Carolina coast will remain well
to the south of our region.  While Bonnie will not directly impact
us, its plume of tropical moisture will get pulled northward out
ahead of an approaching cold front. PWATs will approach or even
exceed 2 inches, which is near record high levels for this time of
year based on historical climatological upper air data. These
extremely high PWATs will combine with some elevated instability
coupled with a low level jet of 30 to 40 knots. The result will be
bands of rain showers with torrential rainfall along with isolated
thunderstorms.

This is one of those scenarios that has the potential to result in
very localized 2+ inch rainfall amounts in less than one hour.
This will bring the potential for localized flash flooding,
particularly if the heaviest bands move across our more vulnerable
urban centers. The problem is that this will come down to a lot of
mesoscale processes and its uncertain where the highest risk for
this will occur. We actually may see two main areas with the
heaviest rainfall. The first may occur with the shortwave that
moves across interior southern New England overnight into Monday
morning. There is also the potential for a second area across
RI/southeastern MA on the nose of the low level jet.

Depending on how the timing works out, may see bulk of heavy rain
threat shift to the coastal plain by mid to late Monday afternoon.
If this occurs there may be a small window for destabilization and a
few surface based thunderstorms to move into far western MA early
Monday evening.  Instability/shear do not look to be enough for
severe weather, but low risk for an isolated strong storm.

So to sum up, main concern will be bands of torrential rain
showers/isolated thunderstorms with a localized flash flood
threat, particularly if torrential rain bands setup across our
more vulnerable urban centers.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Highlights...
  * Lingering showers & thunderstorms SE MA & RI Mon Night
  * Mainly dry with above normal temperatures Tue/Wed
  * Unsettled weather may return toward next weekend

Medium range models are in good agreement on the overall synoptic
pattern.  There are points of uncertainty, including how Tropical
Storm Bonnie and her remnants interact with the pattern at large as
well as the usual uncertainties further out in time.  A mid-level
ridge will move over southern New England Tuesday and then move
offshore Wednesday.  Mid-level troughing then moves into Quebec
towards the end of the work week and starts influencing our weather
with several shortwaves working around the base of the trough.  This
will result in more unsettled weather towards the end of the week.

Monday night...Showers and isolated thunderstorms will linger across
southeastern Massachusetts and Rhode Island through the evening
hours before they diminish or move offshore.  Clearing conditions
are expected through the remainder of the night.

Tuesday and Wednesday...Mid-level ridge moves over southern New
England.  This will bring dry weather to much of the area.  A dry
cold front will move through southern New England Tuesday, resulting
in a wind shift to the north.  This is followed by a backdoor cold
front on Wednesday.  Temperatures will be above normal through both
days.

Thursday through Saturday...Mid-level trough moves into Quebec
allowing several shortwaves rotating through the base of the trough
to move through southern New England.  This will result in periods
of showers throughout this period.  Thus have continued with chance
PoPs through this period.  Temperatures will be around or just below
normal for much of the time.

&&

.AVIATION /18Z 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/...Moderate Confidence.

Eastern MA and RI through this evening...
IFR ceilings along E MA coast will continue to slowly lift and
should improve to MVFR for a few hours this afternoon, except
around Cape Ann where ceilings probably won`t improve much. VFR
conditions elsewhere will persist through late afternoon, but an
approaching fog bank from the south will quickly bring IFR and
even LIFR to Cape Cod and the Islands toward sunset.

Western/Central MA and northern CT through this evening...
VFR will give way to scattered showers/storms, especially in
western MA near the Berkshires through 23z. Storms may bring IFR
visibilities for a brief time and possibly gusts to 35kt.

All areas tonight, Monday, and Monday Night...
IFR and even LIFR becomes widespread as bands of showers/isolated
storms approach from the south. Activity should be more numerous
09z-18z Mon, especially closer to the South Coast, before it
begins to push offshore later Mon. It is also possible that a few
showers or storms reach western New England from eastern NY late
Mon afternoon or evening, but confidence is low.

KBOS TAF...Moderate confidence. Should see ceilings lift to MVFR
for a few hours before IFR ceilings return around 00z Mon.

KBDL TAF...High confidence. Any storms should remain well to the
north and west, but an isolated storm is possible through 21z.

Outlook /Tuesday through Thursday/...

Tuesday and Wednesday...Moderate confidence. VFR.

Thursday...Moderate confidence.  Mainly VFR conditions expected.
Increasing clouds with diminishing conditions through the night,
particularly along the south coast.

&&

.MARINE...
Forecaster Confidence Levels.

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

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

Winds and seas should generally remain below small craft advisory
thresholds through Monday, but seas may approach 5 feet across
our far outer-waters by Monday afternoon. Main concern though for
mariners will be for areas of fog, particularly tonight into
Monday across our southern waters. In addition, heavy showers and
isolated thunderstorms will result in poor visibility.

Outlook /Monday Night through Thursday/...

Monday night and Tuesday...Moderate confidence.  Some uncertainty on
wave heights with swell from Tropical Storm Bonnie potentially
moving up into the coastal waters.  At this point there is potential
for 5 foot seas, especially on the outer waters.  Southwesterly
winds remain below 20 kts, shifting to the north Tuesday night.
Visibilities may be limited at times Monday night in both fog and
showers and thunderstorms.

Wednesday...Moderate confidence.  Northeasterly winds and seas will
remain below Small Craft Advisory criteria.

Thursday...Moderate confidence.  Easterly winds and seas increase.
Seas may rise above 5 feet, especially on the outer waters.

&&

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

&&

$$
SYNOPSIS...Frank/RLG
NEAR TERM...JWD
SHORT TERM...Frank
LONG TERM...RLG
AVIATION...JWD
MARINE...Frank/RLG


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