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Area Forecast Discussion

Forecast Discussion for BOX NWS Office
000
FXUS61 KBOX 250549
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
149 AM EDT Sun Oct 25 2020

.SYNOPSIS...
A cold front will move across southern New England this
evening, followed by northwest winds and colder but seasonable
temperatures. Showers are expected for the start of the work
week, but not expecting a washout. High pressure will bring dry
weather Wednesday. Another system should bring rain showers
Thursday into Friday with a cool down by Friday.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
1030 PM Update:

Cold front has now crossed the southern waters south of
Nantucket as of late this evening. Fairly blustery northwest
winds (around 10-15 mph/gusts to 25 mph) are now ushering in a
much cooler and significantly drier air mass across much of
Southern New England. Dewpoints are now falling through the 30s
for areas north of the Mass Pike, with 40s to low 50s common
across CT/RI into SE MA and will continue to fall steadily
through the night. Temperatures, while falling, have been
slower to fall than prior indications and think this has to do
with the winds allowing for a better mixed air mass. Specific to
the winds, recent observations and short- term guidance do show
some decrease in speeds but keep at least modest northerly
winds for balance of the night, with fairly strong pressure
rises still back across Upstate NY. So some concern that that
forecast lows temps may prove to be a bit too cold, in spite of
progged dewpoints supporting a potential frost if we can radiate
down to those values. While the Frost Advisory remains in
effect, it`s fair to wonder if frost can materialize given a
potential lack of light/calm winds and enough mixing to keep
temps just "warm" enough to preclude frost development. It at
least makes it a more dicier prospect. Leftover clouds, with
some indication for some ocean effect stratocu toward daybreak,
may leave Cape Cod on the cloudier side as well.

For now, I`ve gone ahead and slowed down the strong hourly
temperature cooling a bit over the next few hrs across most of
the area given the winds and recent temperature trend. Still
much cooler than prior nights with lows upper 30s to mid 40s.

Previous Discussion...

A cold front was along the MA/New York border at
mid afternoon. This front will move across Srn New England, exiting
Cape Cod by early tonight. Winds will turn out of the northwest,
and eventually from the north. This will bring in clearing
skies, colder air, and lower dew points. How low? Dew points
will range from the upper 20s inland to the 30s in the coastal
plain. Thus expect min temps in the 30s, except 40s along the
immediate coast from Boston south, and on the Cape/Islands.

Frost Advisory continues for coastal Essex Co MA, and for
interior Plymouth County.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/...
Overview...

Broad upper trough centered over the Plains, leaving a west-
southwest upper flow over Srn New England. A shortwave moves
along this flow and up the coast from Florida, approaching the
Srn New England coast late Sunday night.

Sunday...

High pressure builds over New England with the center passing
across Quebec and the Maritimes. This means lots of subsidence
and sunny skies. The flow around the high will turn surface
winds out of the northeast and then east. Temps at 950 mb and
925 mb suggest max sfc temps in the upper 40s to mid 50s. Even
higher-level temperatures support this range. Ocean temperatures
are 57-59 along the east MA coast, and 60-63 along the south
coasts of MA and RI.

Expect increasing clouds in the afternoon, especially late
afternoon, as the upper southwest flow rides over the top of the
surface layer easterly flow.

Sunday night...

The upper trough moves through during the night, bringing an
increasing chance of showers. Amounts look limited with the
greatest amounts of precip remaining offshore. Certainly no
drought-buster! Clouds and east flow through the night. Look for
min sfc temps in the upper 30s to mid 40s.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Highlights...

* Scattered showers expected Monday and Tuesday

* Drier and milder Wednesday

* Rain chances return Thursday-Friday

Details...

Flow becomes more zonal as the subtropical ridge is suppressed
further to our south allowing for a more active weather pattern.
This as the northern stream becomes more influential and brings more
typical fall weather. Plenty of cloudcover is expected to start the
week, but a ridge of sfc high pressure extending from the maritimes
should keep showers from being too widespread over us. More wet
weather is expected to our northwest in closer proximity to a wave
of low pressure passing to our north. Additionally, mariners will
need to plan for wet weather as a weak low passes well offshore to
our southeast. Given the messy nature of the setup have leaned
heavily on ensemble data for Mon-Wed, which indicates the best
chance of appreciable rainfall in northwest MA and on the southeast
coast Monday, with only isolated to scattered showers in SNE on
Tuesday. The GFS continues to show another low bringing more rain on
Tuesday, but it remains the outlier, so keeping POPs lower on
Tuesday for now. By mid week high pressure will bring mostly dry
conditions for Wednesday.

The next shot at widespread rain comes Thursday into Friday as the
remnants from a system from the Gulf of Mexico pass somewhere in our
vicinity. It remains too early to lock in on specifics, but at the
moment guidance would take it south of us, placing the best rain
chances along the south coast.

Temperatures this week won`t stray too far from normal, but overall
look to be on the cool side, in the 50s. The warmest day will be
Thursday as a surge of warmer air brings highs in the upper 50s
before a cold front cools things down significantly for Friday into
Saturday.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
Forecaster Confidence Levels...

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

06z TAF Update:

Rest of the Overnight (thru 12z Sun): High confidence.

Mainly VFR for most airports. Some occasional MVFR bases at
times early this morning across the South Coast and the Cape Cod
airports but should trend SCT-BKN VFR by daybreak. NW winds
around 8-12 kt (strongest east/south), gusts around 20 kt early.
Gusts tending to subside by pre-dawn.

Today: High confidence.

VFR. Lowest ceilings at VFR-MVFR levels early across Cape Cod,
but VFR anticipated here by mid-AM. High clouds lower and
thicken as the day progresses at all airports but still in the
VFR range. Winds N to NE around 5-10 kt.

Tonight: High confidence thru about 06z, then trends moderate.

Ceilings continue to lower but should stay in the OVC VFR range
through about 06z. Thereafter, ceilings lower toward MVFR type
levels from south to north as stratiform light -RA overspreads
northward. Little if any restriction to visby, and may even be
drizzle at intervals. Confidence in onset of sub-VFR is still
in some question; however by the pre- dawn/AM push, anticipate
most TAFs to be in the MVFR range. East winds increase to 6-12
kt for most (strongest south/east), though around 15 kt with
low- 20s kt gusts at ACK.

Monday: Moderate confidence.

Mainly MVFR with periods of IFR mainly from stratus. Continued
light rain with intervals of -DZ/BR; rain lifts northward
around the afternoon toward more intermittent rain showers or
drizzle/mist, but not expecting much if any improvement to
ceilings by that point. East winds initially around 6-12 kt,
gusts to 20-25 kt Cape/Islands, trending E/ESE 4-8 kt late.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Monday Night through Thursday/...

Monday: Mainly VFR, with areas IFR possible. Breezy. Chance
SHRA.

Monday Night: Mainly VFR, with local IFR possible. Chance SHRA.

Tuesday: Mainly VFR, with areas MVFR possible. Breezy. SHRA
likely.

Tuesday Night: Mainly VFR, with local IFR possible. Chance
SHRA.

Wednesday: VFR. Slight chance SHRA.

&&

.MARINE...
Small Craft Advisories continue for all waters except Boston
Harbor and Narragansett Bay. Seas of 7-9 ft are due to
southeasterly swell from distant Hurricane Epsilon through
Sunday morning. These long period seas will bring rough surf and
a high risk of rip currents to southern/eastern exposed beaches
this weekend.

A cold front crosses the waters early tonight, turning winds
from the west and northwest with gusts of 25-30 kt. Winds then
turn out of the north overnight.

High pressure building over Northern New England Sunday will
further turn winds out of the northeast and east during the day.
Winds diminish to 15 kt and seas will diminish to 5-6 feet.

A weather system moves up the coast Sunday night and may bring
showers to the waters, mostly after midnight. Winds will be less
than 25 kt, but rough seas of 5 feet will linger along the outer
waters.

Outlook /Monday Night through Thursday/...

Tuesday: Winds less than 25 kt. Seas up to 5 ft. Rain showers
likely.

Tuesday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Rain showers likely.

Wednesday: Winds less than 25 kt. Seas up to 5 ft. Chance of
rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Frost Advisory until 8 AM EDT this morning for MAZ007-018.
RI...None.
MARINE...Small Craft Advisory until 11 AM EDT this morning for ANZ231-
     232.
     Small Craft Advisory until 8 AM EDT this morning for
     ANZ233>235-237.
     Small Craft Advisory until 5 PM EDT Monday for ANZ250-254>256.
     Small Craft Advisory until 8 PM EDT this evening for ANZ251.

&&

$$
SYNOPSIS...WTB/BW
NEAR TERM...WTB/Loconto/BW
SHORT TERM...WTB
LONG TERM...BW
AVIATION...Loconto
MARINE...WTB/Loconto/BW

NWS BOX Office Area Forecast Discussion

 



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