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Area forecast discussion
National Weather Service Taunton Massachusetts
1012 PM EDT Sat Apr 29 2017

Synopsis...
after a cold front 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/...
1010 PM update... west-northwest winds continue to gust up to 20-30 mph
across eastern Massachusetts but they were beginning to diminish in western
Massachusetts. The higher elevations of the Berkshires were still gusting
to near 30 mph. NAM shows 30-35 kt winds at 925 mb through 11 PM
(03z) then diminishing rapidly after 2 am (06z).

Previous discussion... winds will shift to northwest then north as high
pressure builds to the north. Cooler and much drier will advect
into southern New England with dewpoints falling into the 30s overnight. Expect
partly cloudy and dry conditions overnight.

&&

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 Massachusetts coast. Highs ranging from
low/mid 50s eastern Massachusetts 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 southern New England 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 quantitative precipitation forecast
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 500 mb high sets up off the southeast
U.S. Coast. However, changes see on the 12z guidance for late
next week, as both the European model (ecmwf) and GFS have tended keep the 500 mb
long wave cutoff low meandering across the southeast 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 north as S-SW winds begin to pick up Mon afternoon. Will see
lingering showers through the afternoon mainly across north 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 precipitable water 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 north CT into west 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 north
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 north central and western areas during
the day. A weak 500 mb short wave moves across but expect little if
any precip except possibly across the east 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 southeast
states toward the region for this timeframe. Kept likely pops
going, with area of moderate to possibly heavy rainfall. Current
forecasted quantitative precipitation forecast 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 European model (ecmwf) push high pres ridging southeast out of the Great Lakes.
With the change on this package, have kept chance pops in for now,
but improving late Sat/Sat night.

&&

Aviation /02z 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.

Overnight...high confidence. VFR. West-northwest wind gusts to 25 kts
through 06z in eastern Massachusetts and higher elevations of western MA,
then shifting to the north and diminishing overnight.

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 ceilings 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 ceilings linger along the S coast Mon,
then lower to mainly MVFR across most of the region Mon night.
Scattered thunderstorms Mon night. SW low level wind shear up to 45-50 kt at 2000 ft above ground level
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. Low level wind shear 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 ceilings lowering to MVFR in areas of
-ra. Patchy fog with local IFR visibilities after midnight Mon night
through around 12z-14z Thu. -Ra and patchy fog lingers with
areas of MVFR ceilings/visibilities 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.

Overnight...
small craft advisories remain posted for the eastern
outer waters until 2 am (06z). West winds will gust to
20-30 kts this evening, then shift to the north overnight
as high pres builds to the north.

Sunday into Sunday night... north/NE winds will veer to the east/southeast
Sunday then eventually to southeast/S Sunday night with speeds mostly
15 kt or less. Seas below Small Craft Advisory. Vsbys lowering in developing fog
after midnight Sunday night over south coastal waters.

Outlook /Monday through Thursday/...

Monday...moderate confidence.
Warm front moves north of the waters late Mon night. Southeast winds along
the East 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 east 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 west 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.
West 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 north Wed night and and seas should subside Wed night

Thursday...moderate confidence.
Light north winds shift to southeast 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 overnight 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.
Massachusetts...none.
Rhode Island...none.
Marine...Small Craft Advisory until 2 am EDT Sunday for
anz250-254>256.

&&

$$
Synopsis...kjc/evt
near term...gaf/kjc/evt

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