Small Craft Advisory 123, NWS Boston/Norton, MA

Area Forecast Discussion
National Weather Service Boston/Norton MA
318 AM EDT Sat Oct 13 2018

.SYNOPSIS...
Dry cool conditions will push across the region overnight as
the remnants of once Hurricane Michael tracks toward
Newfoundland. A low pressure trough pushing quickly east will
result in a period of chilly showers Saturday morning, with a
drying trend to follow in the afternoon. Dry pleasant weather
returns Sunday. A cold front will bring numerous showers Monday
afternoon and evening. Drier cooler air moves in behind the
front Tuesday. Another cold front moves through Wednesday, but
with scattered showers at most. The air trends colder through
Friday morning, then may moderate a little late Friday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
1020 PM Update...

More high clouds stream quickly E across the region as seen on
the latest GOES-East Air Mass RGB satellite composite. Even with
the high thin clouds, temps have been slowly but steadily
falling over the last few hours, with some readings down to the
lower-mid 40s at some of the normally cooler locations at 02Z.
Some lower clouds have worked into N central/NW Mass.

With the open, fast flow aloft, will see more clouds push across
the region as another quick moving H5 short wave shifts
eastward out of the Ohio Valley and Great Lakes.

Previous forecast pretty much on track, so only updated near
term to bring conditions current.

Previous Discussion...

Dry cool air continues to pour into the region via NW flow
aloft. SPC meso analysis already has the 0C isotherm at 850 mb
entering western MA. This will set the stage for a round of
chilly showers tomorrow morning. Progressive pattern already
bringing showers into the OH valley this evening. Latest Hi
Res guidance including the HRRR have these showers entering
western MA/CT 5 am to 6 am and then overspreading RI and eastern
MA by 8 am to 9 am. Again with cold air aloft advecting across
the area tonight will result in chilly showers tomorrow morning.
The good news is this system will remain progressive so a
drying trend develops during the afternoon along with some
breaks of sunshine. Previous forecast captures these details so
no major changes with this update.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
A period of instability showers is expected to continue through
the morning across much of southern New England, than
diminishing from W to E during the late morning into the
afternoon. Not expecting a washout. Compared the the rain
portions of our region saw earlier today, this rainfall will be
a comparative drop in the bucket, generally amounting to less
than one quarter inch, where it rains at all. Drier and even
colder weather arrives Saturday night.

Temperatures will be well below normal Saturday, with most
locations stuck in the 50s, with some 40s across the higher
terrain. Clearer skies with light winds Saturday night will set
the stage for potential frost. Frost Advisory headlines may be
needed for a portion of southern New England Saturday night,
mainly across the higher terrain of northern MA.

&&

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

Baffin Island upper low digs over North America and maintains a
broad trough for much of the coming week. Meanwhile ridges build
over the Pacific and Gulf of Mexico coasts. The result is a
progressively tilted trough over the Central USA with a strong jet
flow from the Southwest USA to New England.

The main weathermakers will be two shortwaves moving through the
progressive flow, each pushing cold fronts across the northern USA.
Timing will be on or about Monday and Wednesday. Contour heights are
above normal Monday, below normal midweek, and moderating Friday.

Mass fields continue to disagree on timing the Monday-Tuesday
shortwave, with the GFS 6-9 hours faster than the GGEM and
ECMWF. But forecast fields do agree that when the shortwave does
move through it will benefit from a supporting 170 kt jet that
will generate appreciable lift and a deep column of moisture.
The second shortwave and front are supported by a 150 kt jet,
but generate minimum lift and much more shallow moisture. This
means a chance of showers all areas Monday-Monday night, and
scattered showers Wednesday mainly in the hills and parts of
Western-Central Mass. The Wednesday cold front, though mainly
dry, is followed by the falling heights, suggesting another
period of below-normal temperatures the latter half of the week
with frosty early morning temps Thursday and Friday. Some
moderation toward normal follows later Friday.

Confidence is moderate to high through the period, with the lowest
confidence on Monday due to different model timings.

&&

.AVIATION /07Z SATURDAY THROUGH WEDNESDAY/...
Forecaster Confidence Levels...

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

0245Z update...

Short Term /through Sunday/...High confidence in trends.
Moderate confidence in timing.

Overnight...High confidence. VFR conditions continue through
around 04Z or so. Will see areas of MVFR-IFR CIGS/VSBYS move in
from W-E through the early morning hours. A weak trough will
bring scattered showers and patchy fog.

Saturday...VFR. Brief MVFR cigs/vsbys possible, mainly inland in
scattered SHRA.

Saturday Night...VFR.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

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

Sunday Night: VFR. Breezy.

Monday: Mainly MVFR. Windy with gusts to 35 kt. Chance SHRA.

Monday Night: Mainly VFR. Windy with gusts to 35 kt. Chance
SHRA.

Tuesday through Tuesday Night: VFR. Breezy.

Wednesday: VFR. Windy with gusts to 30 kt.

&&

.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.

03Z Update...

NW winds will continue to diminish across the coastal waters
overnight. Small Craft Advisories will continue through the
night across the open waters as well as RI/BI Sounds, mainly
for rough seas. Good visibility expected through midnight or
so.

Showers will approach the waters toward daybreak Saturday,
continuing through midday then will push offshore. May see
locally reduced visibility to about 3 NM for a brief time in
some heavier showers and patchy fog. W-NW winds 10-15 kt with
gusts up to 20 kt into Saturday afternoon.

W-NW wind gusts increase to around 25 kt again Saturday night.
Good visibility.

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

Sunday Night: Winds less than 25 kt.

Monday: Low risk for gale force winds with gusts up to 35 kt.
Areas of seas approaching 5 ft. Chance of rain showers.

Monday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Seas up to 5 ft. Chance of rain showers.

Tuesday: Low risk for Small Craft Advisory winds with gusts up
to 30 kt. Areas of seas approaching 5 ft.

Tuesday Night: Winds less than 25 kt.

Wednesday: Low risk for gale force winds with gusts up to
35 kt. Local rough seas.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 7 AM EDT this morning for ANZ235-
     237.
     Small Craft Advisory until 11 AM EDT this morning for ANZ250-
     254.
     Small Craft Advisory until 1 PM EDT this afternoon for ANZ255.
     Small Craft Advisory until 9 AM EDT this morning for ANZ256.

&&

SYNOPSIS...WTB/EVT
NEAR TERM...EVT
SHORT TERM...Belk
LONG TERM...WTB
AVIATION...WTB/Belk/EVT
MARINE...WTB/Belk/EVT

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