Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 300011
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
811 PM EDT Sat Apr 29 2017

.SYNOPSIS...
After a cold frontal passage tonight, high pressure builds over
New England Sunday with mainly dry but much cooler air. A warm
front moves into the region on Monday, followed by a cold front
on Tuesday. Another storm moves toward southern New England
late Thursday or Friday, and could linger nearby into Saturday.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...

8 PM Update...
W-NW winds continue to gust up to 25-35 kt across E and central
Mass into RI at 00Z, but they are diminishing. Noting the peak
winds occurred between 7 and 730 PM and have lowered at the 00Z
OB time.

Wind gusts continue on Boston Harbor, up to 25 kt, so have
extended the small craft there until 10 PM.

Previous Discussion...
Secondary front clearing the region from N-S, with winds
shifting to NW and gusting up to 25-30 kt at 22Z. Several
reports of gusts over 30 kt, including 38 kt at KBOS, 37 kt at
KOWD, 34 kt at KBED and 29 kt at KTAN. Still noting gusts to
30-35 kt at 23Z across central and eastern areas.

Gusts up to around 30 kt also noted on the coastal waters ahead
of the front. Have extended the small crafts to Cape Cod Bay,
Nantucket Sound through 02Z, as well as the eastern outer
waters from Cape Ann to Plymouth through 06Z.

Cold front moving into western New Eng will push off the coast
this evening followed by a wind shift to NW then N as high pres
builds to the north. Cooler and much drier will advect into SNE
with dewpoints falling into the 30s overnight. Debris clouds
from decaying MCS upstream will move into the region this
evening, otherwise expect ptcldy and dry conditions tonight.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
Sunday...
High pres builds across Gulf of Maine to east of Cape Cod
bringing low level easterly winds. Much cooler airmass with
temps up to 20 degrees cooler than today and possibly up to 30
degrees cooler along the eastern MA coast. Highs ranging from
low/mid 50s eastern MA coast to mid 60s CT valley. Sunshine to
start the day will give way to increasing clouds from SW to NE
as mid level moisture spills over the ridge. There is a low
risk for a brief shower in the interior in the developing warm
advection pattern, but most of the day will be dry.

Sunday night...
As high pres moves offshore, warm front will approach SNE from
the south and west. Expect low clouds to develop overnight along
with patchy fog along the south coast as higher dewpoint air
moves in over colder SST. Models are generating some light QPF
which is likely some drizzle given the abundant low level
moisture and dry air aloft. Lows will be mainly in the mid/upper
40s.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Overview...

Overall medium range guidance remains in good agreement through
the middle of next week as long wave H5 high sets up off the SE
U.S. coast. However, changes see on the 12Z guidance for late
next week, as both the ECMWF and GFS have tended keep the H5
long wave cutoff low meandering across the SE U.S., while the
GGEM broadens it from the Carolinas northward to western Quebec.
This lends to even less confidence during the Fri-Sat
timeframe.

Went along with consensus forecast amongst the models, then
trended closer to blend without the GGEM for the latter portion
of this period, but with low confidence.

Details...

Monday-Tuesday...Moderate confidence.
Low pressure will push across the Great Lakes into Ontario and
western Quebec during this timeframe. Will see associated warm
front lift across the region, but low level moisture will get
trapped so will areas of drizzle and patchy fog forecast through
at least midday Monday across most of the region. This should
lift N as S-SW winds begin to pick up Mon afternoon. Will see
lingering showers through the afternoon mainly across N central
and western areas.

Low level SW jet, up to 50-60 kt along the S coast Mon night,
will combine with some decent instability (SLIs at zero to -1, K
indices in the lower 30s and CAPEs up to 200 j/kg) ahead of the
approaching cold front to kick off some convection. Have put in
a chance for thunderstorms as the front crosses the region
through the night. Also noting good PWAT moisture plume along
this front, up to 1.5 to 1.6 inches, so have also mentioned
possibility of heavy rainfall. Should see precip start to taper
off during the early morning hours across N CT into W Mass as
dry slot wraps in behind the passing front.

Even though a mainly SW winds continues, will see mild temps
and gusty winds in place. Diurnal clouds will linger across N
central and western areas with enough cold pooling aloft. Expect
highs across the coastal plain and lower CT valley reach the
lower 70s.

Wednesday...Moderate confidence.
Cyclonic flow continues across the region, so could see some
diurnal clouds develop across N central and western areas during
the day. A weak H5 short wave moves across but expect little if
any precip except possibly across the E slopes of the
Berkshires. Temps will run close to seasonal normals across the
coastal plain but down to 5 degrees below normal over the higher
inland terrain.

Thursday-Friday...Low to moderate confidence.
Continue to see another moisture plume working NE out of the SE
states toward the region for this timeframe. Kept likely POPs
going, with area of moderate to possibly heavy rainfall. Current
forecasted QPF suggests up to 1.5 inches possible, but will
monitor as noted wide solution spread amongst the suite over the
last several runs.

Saturday...Low confidence.
12Z GGEM appears to be the outlier this go-round, keeping
cutoff low pres spinning across the mid Atlantic states, while
GFS and ECMWF push high pres ridging SE out of the Great Lakes.
With the change on this package, have kept CHC POPs in for now,
but improving late Sat/Sat night.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
Forecaster Confidence Levels...

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

Short term...through Sunday.

Through 00z...High confidence.
VFR. Any lingering IFR VSBYS in fog near and over the islands
will quickly improve by around 02Z. W-NW wind gusts 25 to 35
kts through 01Z- 02Z with frontal passage, then diminishing.

Tonight...High confidence.
Any lingering IFR fog over the islands rapidly improving,
otherwise VFR. Diminishing winds becoming north.

Sunday...High confidence.
VFR cigs. Low risk for a brief shower in the interior. Easterly
winds 5-15 kt.

Sunday night...Moderate confidence.
Conditions deteriorating to MVFR/IFR after midnight as stratus
and patchy drizzle develops. Areas of fog along the south
coast.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Monday through Thursday/...

Monday...Moderate confidence.
MVFR-IFR CIGS through mid to late morning in areas of drizzle
and fog. Some improvement across central and portions of eastern
areas from late Mon morning through Mon evening, then will
lower to MVFR- IFR again Mon night with areas of fog and
scattered showers. MVFR- IFR CIGS linger along the S coast Mon,
then lower to mainly MVFR across most of the region Mon night.
Scattered TSTMS Mon night. SW LLWS up to 45-50 kt at 2000 ft AGL
along the S coast Mon night.

Tuesday...Moderate to high confidence.
MVFR-IFR conditions linger early Tue morning in leftover
showers, then improving to VFR through midday. LLWS with SW
winds 45-55 kt across S coastal areas, highest across the
islands through 18Z.

Wednesday...Moderate to high confidence. VFR.

Wednesday night-Thursday...Moderate confidence.
VFR early Wed night, then CIGS lowering to MVFR in areas of
-RA. Patchy fog with local IFR VSBYS after midnight Mon night
through around 12Z-14Z Thu. -RA and patchy fog lingers with
areas of MVFR CIGS/VSBYS into Thu night.

&&

.MARINE...
Forecaster Confidence Levels...

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

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

Through tonight...

Have extended Small Craft for Boston Harbor til 10 PM, along
with Cape Cod Bay, Nantucket Sound and the eastern outer waters
from Cape Ann to Plymouth to Small Craft. Gusts up to 25-30 kt
will diminish from 03Z (nearshore) to 06Z (outer waters).

Previous Discussion...
Winds shift to north overnight as high pres builds to the
north. Reduced vsbys in fog over south coastal waters through
early evening, then improving.

Sunday into Sunday night...
N/NE winds will veer to the E/SE
Sunday then eventually to SE/S Sunday night with speeds mostly
15 kt or less. Seas below SCA. Vsbys lowering in developing fog
after midnight Sunday night over south coastal waters.

Outlook /Monday through Thursday/...

Monday...Moderate confidence.
Warm front moves N of the waters late Mon night. SE winds along
the E coast shift to S-SW by Mon night, while remaining S-SW on
the southern waters. Gusts up to 30 kt develop on the outer
waters Mon night. Seas build up to 7-9 ft Mon night on the
southern waters and E of Cape Cod. Visibility restrictions in
areas of drizzle and patchy fog Mon through early afternoon,
then in showers through Mon night. Scattered thunderstorms Mon
night. Small crafts likely.

Tuesday...Moderate confidence.
SW winds gusting to 25-30 kt through Tue, then shift to W and
diminish Tue night. Seas remain up to 5-9 ft over the open
waters Tue, then slowly subside Tue night. Local brief
visibility restriction in patchy light rain and patchy fog Tue
through midday.

Wednesday...Moderate to high confidence.
W winds may briefly gust to 25 kt on the southern waters with
seas lingering at 5-6 ft during Wed. Winds diminish as they
shift to N Wed night and and seas should subside Wed night

Thursday...Moderate confidence.
Light N winds shift to SE and increase, gusting to 25-30 kt Thu
night. Seas will build after midnight to around 4-5 ft on the
southern waters.

&&

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

The astronomical high tides remain elevated this weekend.

Low risk and low impact for tonight/s high tide as winds will
be offshore during time of high tide with little or no surge.

The Sunday night tide is a bit lower but onshore flow may result
in minor splashover along the most vulnerable shoreline roads.

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 until 10 PM EDT this evening for
     ANZ230>232-251.
     Small Craft Advisory until 2 AM EDT Sunday for ANZ250-254>256.

&&

$$
SYNOPSIS...KJC/EVT
NEAR TERM...KJC/EVT
SHORT TERM...KJC
LONG TERM...EVT
AVIATION...KJC/EVT
MARINE...KJC/EVT
TIDES/COASTAL FLOODING...KJC


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