Area Forecast Discussion
Issued by NWS Boston, MA

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486
FXUS61 KBOX 290846
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
446 AM EDT Sat Apr 29 2017

.SYNOPSIS...
Mild start for today with showers and isolated thunderstorms
moving through a portion of the area in the morning. Warm
conditions follow once again for the daytime. After a cold
frontal passage tonight, high pressure builds over New England
Sunday with dry but cooler air. A sprawling low pressure in the
Plains will push a warm front through our area Monday, then
swing a cold front through on Tuesday. Another storm moves
toward southern New England late Thursday or Friday, and could
linger nearby into Saturday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
400 AM update....

Mild start this morning with many spots still in the 60s. Showers
are beginning to move across western portion of the area. Main focus
is on the overnight convection moving into NJ. This area of
thunderstorms will most likely maintain itself and move across the
south coast including the southern waters. This area of convection
is in line with an area 850 mb divergence and upper level jet
streaks and is moving along the 925 mb moisture line. Guidance and
SPC meso analysis continues to show that there is still enough
instability as well as steep mid-level lapse rates across the
southern half of the region to maintain the convection. Will have to
watch this area closely for the potential for a few strong storms
with heavy downpours as PWATs increase to 1.5 inches.

This afternoon...

Cold front will sweep across the region this afternoon turning the
flow to a more westerly direction.  Still some lingering moisture in
the mid-levels will result in just clouds moving through. Still need
to keep an eye on the potential for a pop-up shower/t-storm ahead of
the cold front. Best are for this to occur is across the south coast
where guidance is hinting as some surface instability as well as
dewpoints in the 60s before the front pushes through. Lapse rates
are also somewhat steep.

Aside from clouds as the potential for a rogue storms, westerly
winds aloft will increase between passing shortwave in southern
Canada and Bermuda high to the south. Anticipate gusty winds near 20
MPH during the afternoon. Cooler temps aloft will also lag behind
the front, so another warm day will be in store across the region
with highs back into the 80s.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
Tonight and Sunday...

Stalled front to the south of the region with zonal flow aloft. Some
of the models including the NAM are showing another decaying
MCS/thunderstorms moving across PA into southern NY tonight. Believe
that these storms will follow along the stalled boundary and should
stay south of the region.

High pressure to the north will begin to slide down into southern
New England. This will switch the winds from the west to a more
northerly direction and eventually east by Sunday. Dry air will spill
in the area resulting in the potential for radiational cooling.
Temps overnight will drop into the mid 40s to low 50s. During the
day, large temperature spread is possible with high temps in the mid
60s for the CT river valley to low 50s along the MA east coast.
Depending on cloud cover temps out west could be to optimistic.

Approaching warm front south and west of the region may result in
some overrunning precip during the later half of the day on Sunday.
Low confidence if this will occur as model soundings are quite dry
at the low levels. Heights aloft are also building which will lowers
chances. However, if this were to occur then the wester half of the
region has the best shot, but for now kept pops low on Sunday.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Overview...

29/00Z guidance remains in rather good agreement through
Wednesday, then diverge into two distinct camps. Operational GFS
is the odd model out, as both the CMC and ECMWF are in line with
the GEFS mean. The energy that will become this low pressure
late next week is still over the northern Pacific. Expecting to
see variations in the details until this energy can be better
sampled, which probably will not happen until Monday at the
earliest.

Favored a consensus approach through Wednesday, then a non-GFS
solution toward the end of next week.

Details...

Sunday Night...

High pressure ridge moves offshore, allowing a warm front to
start its approach. Increasing clouds almost a certainty, but
cannot rule some showers late.

Monday-Tuesday...

A low pressure in the western Great Lakes lifts northeast into
Ontario, pulling a warm front north through New England Monday
or early Monday night. Questions remain regarding timing of the
warm front and associated wind shift. Some lingering showers
during the afternoon are possible, especially north of the Mass
Pike. But expect most of this to move off to the north.

Cold front sweeps through our region Monday night. A 50-60 kt
low level jet arriving late at night will provide some
organization to the modest instability and convergence along
this cold front. Expecting plenty of showers, with isolated
thunderstorms, despite the nighttime passage. Locally heavy
showers possible.

Becoming drier behind this front Tuesday, but it will be gusty.
Above normal temperatures with sunshine breaking out for the
afternoon.

Wednesday...

Surface low over the Maritimes and cloud shield into Northern New
England. Decent cold pool over Northern New England should be
just close enough to generate some diurnal clouds, especially
north of the Mass Pike. Lower max temperatures, but still above
normal.

Thursday-Friday...

Signal the past several days has been for a storm to impact our
region during this time. The details are much harder to come by
with confidence. Non-GFS model consensus on timing would bring
rain into our area Thursday, most likely mid to late afternoon.
The greatest chance for rainfall still looks to be Thursday
night and Friday.

&&

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

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

Short term...through Sunday.

Today...High confidence.
VFR with a risk for some showers this morning. CT/RI/SE MA site shave
the best chc for -TSRA between 09Z and 14Z from W-E. After these
move through expect SCT-BKN low end VFR clouds through the day.
Winds shift from SW to W in the morning with a few gusts around 20
to 25 kts during the afternoon.

Tonight...High confidence.
Westerly flow to start with VFR conditions.

Tomorrow...High confidence. Flow will turn east with VFR conditions.
Low prob of a passing showers during the later half of the day.

KBOS TAF...High confidence in TAF, low prob of -TSRA around 12z.

KBDL TAF...High confidence in TAF, low prob of -TSRA around 9z.

Outlook /Sunday Night through Wednesday/...Moderate confidence.

Sunday night to Tuesday...

Ceilings lower to MVFR/IFR Sunday night and the start of Monday
in low clouds and fog/drizzle. Brief improvement to VFR possible
Monday, then a cold front moves through Monday night and early
Tuesday with showers and scattered thunderstorms. Low level wind
shear likely towards the south coast, especially the Cape and
islands, ahead of this cold front with southwest winds of
50-60 kt at 2000 feet AGL. This cold front moves offshore
Tuesday morning, followed by clearing skies and southwest winds
gusting 25-30 kt.

Wednesday...VFR.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Sunday/...High confidence.

Small craft adv has been issued for the outer waters this afternoon
as passing frontal system combined with lingering swell will push
waters back to 5 feet. Also have issued a SCA for Boston Harbor and
Narragansett Bay for wind gusts near 25 kts. There is a chance that
this may be expanded for the other near shore waters, but confidence
was to low to issue it at this time.

High pressure from the north will slide across the region by Sunday.
This will allow for both wind gusts and seas to relax below SCA.

Outlook /Sunday Night through Wednesday/...Moderate confidence.

Monday...

Warm front moves north of the waters late Monday. East winds turn
from the southeast and eventually from the south but remain less
than 25 knots. Seas build Monday night on the exposed southern
waters as southwest winds increase ahead of a cold front. Very
strong winds at 2000 feet above the surface will increase to
50-60 knots, so potential for gusts to 30 knots Monday night.
Showers and possibly thunderstorms Monday night. A Small Craft
Advisory will probably be needed.

Tuesday...

Cold front moves across the waters early Tuesday. Winds will shift
west after this front moves through. Showers and thunderstorms
end after the wind shift. Southwest winds may gust 25-30 knots
Tuesday. A Small Craft Advisory will probably be needed.

Wednesday...

West winds will be 20 knots or less. Roughs seas linger on the
southern outer waters.

&&

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

The astronomical high tides remain elevated this weekend.

Will hold off on issuing a coastal flood statement for tonight`s
high tide, as the wind direction is not favorable and will limit
the risk for splashover. However, with the potential for
onshore flow during the Sunday night high tide, a Coastal Flood
Statement may be needed.

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

11.88 feet / Sunday 2:39 am
11.45 feet / Monday 3:35 am

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from noon today to 2 AM EDT Sunday for
     ANZ254>256.
     Small Craft Advisory from 1 PM this afternoon to 8 PM EDT this
     evening for ANZ230-236.

&&

$$
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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