Area Forecast Discussion
Issued by NWS Boston, MA

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201
FXUS61 KBOX 262013
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
413 PM EDT Wed Apr 26 2017

.SYNOPSIS...
A few showers, along with areas of drizzle and fog will persist
tonight into Thursday, especially along the coast.  A fast
moving disturbance may bring a few more rain showers and perhaps
an isolated thunderstorm very late Thursday night into mid
morning Friday, with mainly dry and warm weather for Friday and
Saturday afternoons. A backdoor cold front crosses the region
Saturday night, bringing much cooler weather on Sunday
especially along the coast. Another cold front will likely bring
a period of showers sometime Monday into early Tuesday.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
4 pm Update...

Weakening stacked low pressure center was centered south of Long
Island at 20Z, drifting northeastward. Warm front extended from
coastal RI/Newport to north of Marshfield MA. Surface dewpoints near
and on the warm side of the front were in the 55 to 60. The stronger
winds noted on the south side of the front will continue to diminish
this evening, becoming light tonight.

HRRR shows the front should remain nearly stationary late this
afternoon before becoming less discernible this evening. Moisture
convergence along the front will allow for continued chances for
showers late this afternoon and into this evening, especially within
RI and eastern MA. Abundant low level moisture will also allow for
areas of fog and drizzle. Fog will be locally dense this evening and
tonight along eastern MA and RI as well as some of the higher
terrain of the Worcester Hills, with visibility below 1/2 mile at
times.

With surface dewpoints so high, temps won`t have much room to fall.
Overnight lows mainly in in the low 50s expected.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
Weak surface low washes out as it lifts northeast of our area, but
still have the mid level low passing near the Cape/Islands during
the day. Will continue to have weak onshore flow. Areas of fog in
the morning, with visibility gradually improving. Cloudy skies
anticipated thru the day, with lingering drizzle eastern MA/RI.
Can`t rule out some patchy measurable light rain in eastern MA and
RI. Continuing to think that MOS guidance is likely a little too
high with max temperatures Thursday, so will utilize the lower
consensus of raw model 2 meter temperatures for max
temperatures.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Highlights...

* Brief scattered showers and perhaps an isolated t-storm possible
  very late Thu night into mid morning Fri

* Dry/very mild to warm temps expected by Friday afternoon

* Warm on Sat away from the south coast with the low risk for a few
  afternoon/early evening t-storms

* Turning much cooler Sat night and Sun especially on the coast

* Period of showers likely sometime Mon into early Tue

Details...

Thursday night and Friday morning...

Still a lot of lingering low level moisture trapped beneath the
subsidence inversion based on model cross sections Thu night.
Therefore, feel there will be an abundance of low clouds and fog
patches with even some drizzle possible.  The clouds and low level
moisture should keep low temperatures mainly in the lower to middle
50s. The majority of Thu night will be dry, other than perhaps some
drizzle.  However, a fast moving shortwave approaches the region
toward daybreak Friday with a burst of elevated instability. This
will probably result in a brief band of scattered showers and
perhaps a few embedded thunderstorms. Activity should be scattered
and short-lived with it mainly coming to an end by mid to late
Friday morning.

Friday afternoon...

Steep mid level lapse rates along with decent instability/shear
develop by Friday afternoon as temps warm with dewpoints in the 50s.
However, subsidence behind the morning shortwave and very dry mid
levels of the atmosphere should result prevent convection from
developing Friday afternoon.  Therefore, expect dry weather and with
plenty of sun Friday afternoon.  Highs should recover in the 70s to
near 80 away from the marine influence of the south coast.

Friday night...

Upper level ridge off the southeast coast will pump unseasonably
mild air into southern New England.  Low temps should only drop into
the middle to upper 50s in most locations.  May also see some patchy
fog develop given relatively high dewpoints in place.

Saturday...

A rather warm day appears to be in the cards away from the south
coast, Cape and Islands.  Given west to southwest flow out ahead of
an approaching pre-frontal trough/cold front, should see high temps
reach 80 to 85 in many locations.  At the same time, a pre-frontal
trough will be dropping south into the region but it is uncertain if
it will trigger a few thunderstorms during the afternoon. While
there are impressive wind fields along with some instability,
forcing will be limited. The models actually show subtle height
field rises during the afternoon, which is not normally a good sign
for convection. Much of the guidance also pushes the plume of
steeper mid level lapse rates south of the region by Saturday
afternoon. Nonetheless, "If" a few thunderstorms are able to develop
the risk for an isolated strong to severe t-storm or two would exist
given impressive wind fields. Currently, we will consider this a low
risk given limiting factors stated above, but certainly something
will have to watch with pre-frontal trough.

Saturday night and Sunday...

Despite upper level ridging, a strong high pressure system will
build into eastern Canada.  This will send a backdoor cold front
south of the region Sat night and result in much cooler temps on
Sun. Highs Sunday will probably only in the 50s along the coast with
60s further inland.  May see a spot shower or two Sat night/Sun, but
the vast majority of the time will feature dry weather given lack of
forcing.

Monday into Tuesday morning...

Low pressure across the central Plains will lift northeast across
the Great Lakes Monday and then into eastern Canada Tue.  Some over
running showers are possible early Monday, but a period of steadier
showers with even brief heavy rainfall will be possible later Mon
into early Tue with the cold front.  Temps highly uncertain on Mon
as a frontal boundary may be jammed up across the region.  Overall,
coolest temps probably in northeast MA and mildest in our CT zones.

Tuesday afternoon into Wednesday...

Low confidence given the time range, but most guidance suggests
mainly dry and pleasant weather as a weak ridge of high pressure
builds in from the west.

&&

.AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
Forecaster Confidence Levels...

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

Short Term /through Thursday/...

Remainder of this afternoon...Moderate confidence. Mainly IFR/LIFR
CIGS/VSBYS in low clouds, drizzle, areas of light rain and fog.
Exception may be BDL/BAF and vicinity, with MVFR conditions for a
period of time late this afternoon. Fog locally dense within east
coastal MA and south coastal RI, with localized vsbys 1/2 mile or
less at times.

Tonight...Moderate confidence. IFR/LIFR conditions continue in areas
of fog and drizzle, and some light rain. Areas of dense fog
anticipated along eastern MA and RI.

KBOS TAF...Moderate confidence in TAF, moderate confidence in
timing.

KBDL TAF...Moderate confidence in TAF, moderate confidence in
timing.

Outlook /Thursday Night through Monday/...

Thursday night into mid morning Friday...Moderate confidence. Mainly
MVFR/IFR conditions in low clouds and fog patches Thursday night and
early Fri morning.  Also, a brief period of scattered showers and
perhaps an isolated t-storm are possible very late Thu night into
mid morning Fri.

Late Friday morning and afternoon.  Moderate to high confidence in
mainly VFR conditions.

Saturday and Sunday...Moderate confidence in mainly VFR conditions.

Monday...Moderate confidence.  MVFR/IFR conditions possible in lower
clouds and some showers, particularly late Mon/Mon night.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Thursday/...High confidence.

4 pm update...

Tonight...

Low pressure continues to weaken as it lifts from south of Long
Island northeastward into the southern New England coastal waters
tonight. Gale Warning that was previously in effect for the
southeastern coastal waters has been allowed to expire. Small Craft
Advisory is in effect until 8 pm for Cape Cod Bay/Buzzards
Bay/Vineyard and Nantucket Sounds for gusts to 25 kts, with winds
diminishing.  For the remainder of the coastal waters excluding
Boston Harbor and Narragansett Bay, a Small Craft Advisory continues
thru tonight. Visibility restrictions at times across the waters
thru tonight in locally dense fog.

Thursday...

Low pressure weakens further as it lifts northeast of the waters.
Winds will expected to be around 10 kt or less. However due to
lingering swell, Small Craft Advisories will continue to be needed
across the outer coastal waters as well as RI and BI Sounds.
In addition, areas of drizzle, fog or patchy rain will lead to some
visibility restrictions on the coastal waters.

Outlook /Thursday Night through Monday/...

Thursday night and Friday...Moderate to high confidence.  Despite
winds 20 knots or less, lingering southeast swell will result in
marginal small craft seas persisting across the outer-waters and
western sounds.  Areas of fog may result in poor visibility for
mariners Thu night into mid morning Friday.

Saturday and Sunday...Moderate to high confidence.  Winds and seas
mainly below small craft thresholds, but some marginal small craft
seas for a time on Saturday across our southern waters.  May also
see some near shore southwest wind gusts of 20 to 25 knots Sat
afternoon.

Monday...Moderate confidence.  Winds and seas will probably increase
to small craft thresholds on gusty southerly winds late Mon and
especially Mon night ahead of the next cold front.

&&

.TIDES/COASTAL FLOODING...
* Isolated minor coastal flooding impacts during astronomically
  high tide tonight along the east and south coasts

We are in 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 tonight.

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 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)...

11.92 feet / Thursday 12:07 am

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

6.21 feet / Wednesday 9:00 pm

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Dense Fog Advisory until 9 AM EDT Thursday for MAZ007-014>016-
     019>024.
     Dense Fog Advisory until 9 AM EDT Thursday for MAZ005-006-012-
     013-017-018.
RI...Dense Fog Advisory until 9 AM EDT Thursday for RIZ005>008.
     Dense Fog Advisory until 9 AM EDT Thursday for RIZ001>004.
MARINE...Small Craft Advisory until 8 PM EDT this evening for
     ANZ231>234.
     Small Craft Advisory until 6 AM EDT Friday for ANZ235-237-250-
     254>256.
     Small Craft Advisory until 9 AM EDT Thursday for ANZ251.

&&

$$
SYNOPSIS...Frank/NMB
NEAR TERM...NMB
SHORT TERM...NMB
LONG TERM...Frank
AVIATION...Frank/NMB
MARINE...Frank/NMB
TIDES/COASTAL FLOODING...



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