Area Forecast Discussion
Issued by NWS Boston, MA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS61 KBOX 241408

Area Forecast Discussion
National Weather Service Boston/Norton MA
1008 AM EDT Sat Mar 24 2018

A series of upper level disturbances will bring chilly
temperatures this weekend along with scattered snow
showers, mainly tonight into Sunday morning with the focus
across eastern Massachusetts. Canadian high pressure builds
across the region Monday through Wednesday bringing dry and
somewhat milder temperatures, particularly across the interior.
The chance for rain showers increase late next week as a cold
front slowly approaches.



Shortwave that moved over Southern New England last night is now
moving offshore into the Gulf of Maine. Lingering mid-level
clouds over Eastern Mass and RI late morning as well as a
thinner band over the CT River Valley. These clouds are showing
a dimimishing trend on satellite. Radar continues to show some
light echoes with the eastern cloud area, but little to indicate
anything more than virga.

Model data shows clouds moving south from NH/ME this afternoon
with showers late in the day over Eastern MA/RI. Not much
showing on satellite where the clouds are supposed to come. It
is possible that the sharp lapse rates...7-8C/Km...and solar
heating may regenerate clouds during the afternoon. We will show
a more optimistic midday/early afternoon before bringing higher
sky cover values later in the day. Expect a mainly dry
afternoon, but with a chance of showers late in the day in
Eastern Mass.

The other change concerns temperatures, which at 9 AM were
roughly 3F milder than the forecast values. So we have nudged
forecast temps up 2-3F, in line with the LAV data which was
closest to the 9 AM temp and dew point values. Max sfc temps
were also bumped up a couple of degrees, although remaining in
the 40s.


* Minor snow accumulations tonight/early Sun across eastern MA

Tonight and Sunday...

An impressive piece of shortwave energy will drop south out of
Quebec tonight. The result will be an inverted trough swinging
across the region...shifting the winds from north to northeast.
There is a band of impressive forcing with the inverted trough
along with a deep column of moisture. Low level lapse rates are
quite steep too...resulting in total totals well into the 50s.
This should result in scattered snow showers especially late
tonight into Sunday morning.

The scattered snow showers may begin as a brief period of rain
showers given the initially warm boundary layer. However...cold
temperatures aloft should quickly change an mixed precipitation
over to snow showers. A brief period of snow showers may impact
much of the region overnight/early Sunday as the inverted
trough swings across the region. However...the focus for the
snow showers will be across eastern MA. This is where moist low
level NNE flow will tap some instability from the ocean and
some enhancement via land/sea interface. The potential exists
for an inch or two of snow across eastern MA with the low risk
of 3 inch amounts. Climatology and pattern recognition would
favor the north shore and/or portions of Plymouth county
receiving the higher amounts. While the snow showers will be
banded in nature...given the instability, moisture and lift they
may be briefly heavy. So despite today/s mild temperatures snow
accumulations on roadways are possible along with potential
slippery travel overnight Sunday morning. Will go ahead and
issue a special weather statement to highlight these concerns.

The bulk of the snow showers will be later tonight into Sunday
morning...but a few snow showers may linger into the afternoon
across the eastern MA coast NNE flow and 850T below -10C.
Otherwise...a chilly day with gusty northeast winds along the
coast. High temperatures will be held into the middle to upper
30s across much of the region...but may see few locations in the
lower CT river valley break 40.



00Z model suite showing continued long, persistent NE wind
fetch into east coastal areas into early next week as high
pressure ridge at the surface and aloft slowly builds E. Winds
will slowly diminish as the ridge builds across the region early
next week. However, H5 cutoff low and its developing surface
storm center, as forecast by the Ocean Prediction Center, sets
up in the vicinity of about 37-38N/62-63W Mon through at least
Tue, which will pretty much keep the ridge nearly stationary in
the highly amplified mid level steering flow.

Some question as to whether the northern portion of the ridge
may try to break down toward the end of the long term, allowing
lower H5 heights to move across the region toward the latter
half of next week. This may allow the slow moving cold front to
push close enough to the region to bring some moisture across,
though uncertainty remains on the timing and track of the front
with the blocking pattern across the western Atlantic in place.


Sunday night and Monday...

Lingering snow showers across E Mass into portions of RI will
tend to weaken as they move offshore Sunday evening. As high
pressure ridge starts to gradually push S, with its 1044 hPa
center across N Maine into eastern Quebec. Tight pressure
gradient continues between the strong high to the N and a
developing storm center well SE of Nantucket, so will continue
to see NE winds gusting up to 25-35 mph across coastal areas
mainly S of Boston, highest across Cape Cod and the islands.
With the high to the north and low offshore nearly stationary,
the winds will continue through Monday.

Skies will become mainly clear across the CT valley and N
central Mass, but scattered clouds will linger across coastal
areas through through at least midday Monday.

Temps will remain well below seasonal normals as H85 temps will
range from -8C to -11C Sun night, then only recover to around
-6C to -7C Monday. Expect overnight lows ranging from 20-25
across the higher inland terrain to 25-30 along the coast.
Readings will recover especially across the CT valley and N
central Mass on Monday, where there will be more sunshine and
less effects from the cold onshore winds across coastal areas.
Highs will range from the upper 30s to around 40 across E Mass
into RI, up to the mid 40s across the mid and lower CT valley.

Monday night through Wednesday...

The high pressure will slowly sink south across New England
during this timeframe, so expect mostly clear skies through at
least Tuesday for most areas. Some clouds may linger across east
coastal areas with the continued onshore winds. There will
still be lingering cool temperatures along the coast with the
persistent NE wind, but readings will reach close to seasonal
levels inland. By Tuesday and Wednesday, highs will reach the
lower-mid 50s, but will hold in the lower-mid 40s along the
immediate E coastal areas.

As the high settles across the region by about Wednesday, a
cold front will start to slowly shift E out of the Great Lakes.
This front looks to remain well W of the region at mid week.
However, the coastal low may start to retrograde westward but
should remain well offshore. This interaction may keep N-NE
winds stirring especially near the coast.

Wednesday night through Friday...

Lower than average confidence during this timeframe, especially
with a high amplitude long wave steering pattern in place,
along with the mid level cutoff low and storm center spinning
well SE of Cape Cod. With the low offshore and the high to the
NW, timing the approach of the slow moving cold front is tough.
Depending upon how far the ridge builds across, winds may try
to shift to S-SW and will bring slowly moderating temperatures.

May see some light rain showers move in during Thursday
afternoon. If temps moderate, readings Thu night currently
forecast to remain at or above freezing so the precip should
remain all rain. Will be watching this aspect closely, though.
Current forecast suggests temps running close to or a bit above
seasonal levels. Again, not a whole lot of confidence for this


Forecaster Confidence Levels...

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

Short Term /through Sunday/...

This afternoon...High confidence. Mainly VFR despite a
scattered to broken deck of mid level clouds. A few scattered
rain/snow showers may develop later this afternoon especially
across eastern Mass but with vsbys expected better than 5 miles.

Tonight and Sunday...Moderate to high confidence. Conditions
should gradually deteriorate to MVFR /localized IFR conditions/
late tonight into Sunday morning in lower clouds and scattered
snow showers. The snow showers will be most numerous across
eastern MA where the best chance for IFR and perhaps even brief
LIFR conditions will be possible. Some improvement expected
Sunday afternoon across the interior...but MVFR conditions
likely persist across eastern MA along with a few snow showers.
NE wind gusts of 20 to 30 knots develop Sunday with the
strongest of those across southeast New England.

KBOS Terminal. High confidence in TAF.

KBDL Terminal...High confidence in TAF.

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

Sunday Night: Mainly VFR, with local MVFR possible. Windy with
local gusts to 30 kt. Slight chance SHSN.

Monday: VFR. Windy with local gusts to 30 kt.

Monday Night through Wednesday: VFR. Breezy.


Short Term /through Sunday/...

This afternoon...High confidence. North winds of 10 to 15 knots
but gusts/seas will remain below small craft advisory

Tonight and Sunday...High confidence. Strong high pressure
building eastward into Quebec and northern New England will
increase the pressure gradient. The result will be widespread
northeast wind gusts of 25 to 30 knots developing toward
daybreak and persisting Sunday. Brief marginal gale force gusts
can not be ruled out across our far southeast waters...but felt
strong small crafts were more representative. Seas will build to
between 8 and 11 feet across our eastern outer waters.

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

Sunday Night: Strong winds with local gusts up to 30 kt. Rough
seas up to 12 ft. Slight chance of snow showers.

Monday and Monday night: Moderate risk for Small Craft Advisory
winds with gusts up to 30 kt. Rough seas up to 12 ft. Seas may
be higher S and E of Nantucket.

Tuesday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 15 ft.

Tuesday Night: Low risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 17 ft.

Wednesday: Winds less than 25 kt. Rough seas up to 15 ft.


MARINE...Small Craft Advisory from 6 AM Sunday to 8 AM EDT Monday for
     Small Craft Advisory from 6 AM to 6 PM EDT Sunday for ANZ230-
     Small Craft Advisory from 3 AM Sunday to 8 AM EDT Monday for


MARINE...WTB/Frank/EVT is the U.S. government's official web portal to all federal, state and local government web resources and services.