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Area forecast discussion
National Weather Service Taunton Massachusetts
715 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 a 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/...

No major changes to the forecast this morning. Tweaked pops
slightly to update the timing. Thinking the last couple runs of
the hrrr have a good timing for moving the heaviest rainfall out
of our region later today. Also made minor tweaks to
temperatures to reflect observed trends.

Not really being reported in surface obs, but thinking areas of
drizzle are likely in between the heavier rainfall echoes. Kept
that mention in the forecast.

Previous discussion....

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 quantitative precipitation forecast. Many areas across Rhode Island 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 Thursday with cooler temps on coast
* mild to warm afternoons Fri/Sat with a low risk for a few
thunderstorms
* backdoor cold front brings much lower temperatures by Sunday
* period of showers, which may be briefly heavy, sometime Mon/Tue

Details...

Thursday...

Still dealing with a persistent mid level low near Nantucket
Thursday morning, while the surface low pressure is slightly
farther northeast. This will mean light onshore flow with lots
of low level moisture. Expecting cloudy skies with areas of
drizzle and fog, particularly across eastern Massachusetts. As noted by the
previous forecaster, MOS guidance is likely a little too high
with Max temperatures Thursday. Used the lower consensus of raw
model 2 meter temperatures for Max temperatures.

Friday and Saturday...this will be a tricky portion of the
forecast. An approaching cold front should become parallel to
the mid level flow, stalling somewhere just west of our region.
This should mean a persistent southwest flow, and much higher
temperatures than the past couple of days. Expecting Max
temperatures in the 70s degrees away from the south coastal
areas on both days.

However, these higher temperatures will combine with decent mid
level lapse rates to produce a low risk for thunderstorms. Right
now, Friday appears to have the greater risk of these two days,
as mid level dry air may be in place for Saturday. This could
all change should the stalled front shift closer to southern New
England.

Saturday night and Sunday...

A strong high pressure moves over eastern Canada, dominating
the blocking high pressure to our southeast. This push from the
northwest should be enough to drive the stalled front just to
our south, resulting in much lower temperatures, on the order of
15-20 degrees lower Sunday afternoon.

Monday and Tuesday...

A stalled front to our south should return as a warm front
sometime Monday into Tuesday as a low pressure moves from WI
into southeast Canada. The timing is still uncertain, as a
strong high pressure should be over Labrador. Should this high
linger longer than currently forecast, then the precipitation
timing will be also off. Still looking like another prolonged
window for periodic showers. Rainfall could be moderate to heavy
at times.

&&

Aviation /12z 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/...

Today...moderate confidence. Mainly IFR cigs, with local MVFR
cigs, continue with areas of -ra/rain and patchy fog, especially
across the eastern half of southern New England. Reduced visibilities
likely, down to IFR in spots. May see areas of LIFR ceilings across
the higher inland terrain and along the coast. Southeast winds gusting
up to around 25 kt across Cape Cod and the islands. Low level wind shear impacts
for the cape and islands, and possibly as far north as bos,
during this morning.

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 in timing.

Kbdl taf...high confidence in taf, moderate confidence in timing.

Outlook /Thursday through Sunday/...

Thursday...moderate to high confidence. IFR to even LIFR
conditions likely into the morning 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 into
early Friday morning. Improvement to VFR likely by Friday
afternoon, with the low risk for a few showers and perhaps a
thunderstorm.

Saturday and Sunday...moderate confidence. VFR conditions.

&&

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 a coastal low
begins to move eastward, winds gusts will begin to subside and
seas will relax. Small craft advisories will still be needed
for ocean waters, but overall trend will be improvement. Could
see visibility restrictions across the waters tonight in dense
fog.



Outlook /Thursday through Sunday/...moderate confidence.

Winds are not expected to be be a concern through this portion
of the forecast, generally remaining less than 20 kt. The main
issue will be how long it takes for lingering swell from the
persistent low pressure near the waters to diminish. Small craft
advisories are likely to be needed across the outer coastal
waters.

In addition, areas of drizzle, fog or rain will lead to some
visibility restrictions on the coastal waters into Friday.

&&

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 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.
Massachusetts...none.
Rhode Island...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...Belk/dunten
short term...dunten

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