Area Forecast Discussion
Issued by NWS Boston, MA

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498
FXUS61 KBOX 260803
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
403 AM EDT Wed Apr 26 2017

.SYNOPSIS...
Low pressure will slowly track up the east coast this morning
bringing periods of rain. Low clouds along with some drizzle and fog
are expected to linger tonight into Thursday especially along the
coast. Very mild to warm afternoons should return Friday and
Saturday with the low risk for a few showers/thunderstorms. Much
cooler weather follows Sunday especially on the coast. Another cold
front will likely bring more showers to the region sometime Monday
into Tuesday.

&&

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

400 AM Update....

Overall trend in the forecast remains on track for early this
morning. Next batch of precip is beginning to make its way onto the
south coast as of 330 AM. This bulk of precip could drop near a half
of an inch of QPF. Many areas across RI have already seen over 1.5
inches of rain so this will just continue to add. Will have to
closely watch for nuisance flooding in the typically prone regions
of Cranston/Warwick and eventually Fall River and New Bedford.

Cannot rule out a rumble of thunder with the rain as models continue
to show elevated instability with showalters dropping to below 0.
However haven`t seen a bolt on the lightning tracker for quite some
time, so confidence is low in a rumble of thunder. If convection
does develop early this morning, then this will enhance the rainfall
amounts for the morning commute.

Today...

Stacked surface low pressure system near the Mid-Atlantic will move
towards southern New England today. Continuous southerly flow aloft
will continue to pump moisture into the region through the day.
Appears that surface warm front will try to move in, or may just
stall across the area. This will result in difference in
temperatures. For now continued with a blend in the guidance.

The main bulk of precip will lift this morning. However, still some
weak lift and with a very saturated moisture profile, anticipate on
and off showers late this morning and into the afternoon hours.

Increasing dewpoints across the south coast could lead to patchy fog
development. Low confidence on how low vsbys will go, but something
to watch through the day.


&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/...

Wednesday night...

Stacked low pressure system will begin to move south and east of the
region. 850 mb becomes more of a open wave resulting in a more
weaken system.

Upper levels appear to begin to dry out as the low begins to move,
however, at the surface and mid-levels, the profile is quite
saturated. Anticipate a soupy mess with low clouds and fog. Will
have to watch for vsbys dropping below a quarter of a mile which
would result in a dense fog advisory. Confidence is low at this
time, but something to watch.

Continuous easterly flow overnight combined with some weak lift will
result in areas of drizzle especially across eastern locations.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Highlights...

* Low clouds/spotty drizzle Wed night+Thu with cool temps on coast
* Mild to warm afternoons Fri/Sat with a low risk for a few t-storms
* Backdoor cold front brings much cooler temps by Sun
* Period of showers which may be briefly heavy sometime Mon/Tue

Details...

Wednesday night and Thursday...

Closed upper level low will linger off the southern New England
coast Wed night into Thu.  Model cross sections indicate a fair
amount of low level moisture lingering below the subsidence
inversion.  Given overall setup and time of year, feel low clouds
will linger Wed night into Thu afternoon even across much of the
interior.  There also should be areas of fog and drizzle, especially
on the coast Wed night and Thu am along with the risk for a spot
shower or two.

With that said, guidance is probably too warm with forecasted high
temps on Thu given expected low cloud cover.  High probably remain
in the 60s for most of the region and perhaps stuck in the mid to
upper 50s along the coast. Now if more sun is realized than expected
it still would be possible for portions of the interior to break 70,
but hedging cooler for now.

Friday and Saturday...

Upper level ridge of high pressure building off the southeast coast
will be pumping higher height fields into southern New England.
Decent shot for high temps to reach the 70s to lower 80s away from
any marine influence along the coastline, especially the south coast
with south to southwest flow.  Most of this time should feature dry
weather, but a few shortwaves will result in the low risk for a
couple of showers/t-storms. Greater chance of development would
occur if energy moves through closer to the time of peak
heating on Fri and Sat.

Saturday night and Sunday...

Despite abnormally high height fields, strong high pressure will be
building across eastern Canada.  This will likely send a backdoor
cold front south of the region late Sat or Sat night.  Much cooler
temps are likely for Sunday especially along the coast where they
should remain in the 50s. Perhaps a few spot showers, but high
pressure may suppress most of the activity to our southwest.

Monday and Tuesday...

Timing uncertain, but an approaching cold front will likely bring a
period of showers.  GEFS anomalies signaling decent low level jet
coupled with fairly high Pwats so the showers may be heavy for a
brief period of time. Again, timing uncertain and not expecting
both days to be total washouts. Temperatures also uncertain
given timing/wind direction.

&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels...

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

Short Term /through Tonight/...

Before 12z...High confidence. Mainly IFR conditions persist in
widespread rain showers. Heaviest rain and greatest risk for
isolated t-storms will be now through 12z Wednesday. LLWS will be a
concern especially across the Cape and Islands.

Today...Moderate confidence. MVFR-IFR CIGS continue with areas of -
RA/RA and patchy fog, especially across the eastern half of southern
New England. Reduced VSBYS likely, down to IFR in spots. May see
areas of LIFR CIGS across the higher inland terrain and along the
coast. SE winds gusting up to around 25 kt across Cape Cod and the
islands. LLWS impacts for the Cape and islands, and possibly as far
north as BOS, during the morning hours.

Tonight...Moderate confidence. MVFR-IFR conditions continue in areas
of fog and drizzle. A few showers are possible.

KBOS TAF...High confidence in TAF, moderate confidence on trends.

KBDL TAF...High confidence in TAF, moderate confidence on trends.

Outlook /Thursday through Sunday/...

Wednesday night into Thursday...Moderate to high confidence.  IFR to
even LIFR conditions likely Wed night into part of Thu am along with
some fog, drizzle and a spot shower.  Lower conditions most likely
on the coast. Conditions may improve to mainly MVFR by late Thu
morning and afternoon.

Thursday night and Friday...Moderate confidence.  MVFR/IFR
conditions likely in areas of low clouds and fog patches Thu night
into early Fri am.  Improvement to VFR likely by Fri afternoon with
the low risk for a few showers and perhaps a t-storm.

Saturday and Sunday...Moderate confidence.  VFR conditions probably
dominate.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Tonight/...High confidence.

Small Craft Advisories are in effect for all waters expect Boston
Harbor and Narragansett Bay. Seas will remain above 5 feet with
winds gusts near 20-25 kts into the afternoon. As the coastal low
begins to move eastward, winds gusts will begin to subside and seas
will relax. SCA will still be needed for ocean waters, but overall
trend will be improvement. Could see vsbys restrictions across the
waters tonight in dense fog.

Outlook /Thursday through Sunday/...

Wednesday night through Friday...Moderate to high confidence.
Despite wind gusts mainly 20 knots or less, left over southeast
swell will result in small craft seas persisting through Friday
across many of our outer and southern waters.  In addition, areas of
fog may result in poor vsbys for mariners especially during the
overnight and early morning hours.

Saturday and Sunday...Moderate to high confidence.  West to
southwest wind gusts to 20 knots Saturday will shift to the
northeast by late Sat or Sat night behind a backdoor cold front.
Overall, expect winds and seas to remain below small craft advisory
thresholds.

&&

.TIDES/COASTAL FLOODING...

* Isolated minor coastal flooding impacts during astronomically
  high tides through tonight along the east and south coasts

We are entering a spring tide cycle with high tides that are
astronomically high. This combined with an anticipated storm surge
of around 1 foot may set the stage for isolated pockets of minor
coastal flooding along both south and east coasts around the time of
high tide this morning and again tonight. Went ahead an issued a new
coastal flood statement for potential for splashover. There is
also the combination of runoff from heavy rain and elevated
water levels near high tide this morning which could exacerbate
drainage of fresh water in some coastal urban areas and near
the mouths of streams and small rivers.

We will need to continue to monitor the tides through at least
Wednesday night as there is not a significant offshore flow or
pressure rises to help evacuate a lingering surge. The astronomical
high tides remain very elevated through the end of the week.

Due to the breadth of the fetch, we may encounter enough wave action
with lengthening periods on top of an elevated tide to cause pockets
of erosion tonight through tonight along the Martha`s Vineyard south
coast, Nantucket south and east coasts, and the outer Cape ocean
side from Truro to Chatham.

Boston High Tides (flood stage at Boston 12.5 feet)...

11.47 feet / Tuesday 11:20 pm
11.15 feet / Wednesday 11:50 am
11.92 feet / Thursday 12:07 am

Providence High Tides (flood stage at Providence 7 feet)...

5.98 feet / Tuesday 8:11 pm
5.53 feet / Wednesday 8:41 am
6.21 feet / Wednesday 9:00 pm

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 3 PM EDT this afternoon for
     ANZ231>234.
     Small Craft Advisory until 9 AM EDT Thursday for ANZ235-237-
     250-251-254>256.

&&

$$
SYNOPSIS...Belk/Dunten
NEAR TERM...Dunten
SHORT TERM...Dunten
LONG TERM...Belk
AVIATION...Belk/Dunten
MARINE...Belk/Dunten
TIDES/COASTAL FLOODING...staff



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