Small Craft Advisory 92, NWS Boston/Norton, MA

Area Forecast Discussion
National Weather Service Boston/Norton MA
205 PM EDT Sun Sep 24 2023

.SYNOPSIS...

Periods of rain will continue tonight into the first part of
Monday especially south of the Massachusetts Turnpike. Rain
tapers off late Monday, then dry, but cool and brisk weather
overspreads the region Monday night and Tuesday, as large
sprawling Quebec high pressure builds into New England. Dry
weather at mid week likely persist into next weekend, along with
moderating temperatures.

&&

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

2 PM Update...

* Showers along with areas of drizzle through the afternoon
* Cool Temps remaining in the upper 50s/lower 60s

The remnants of T.S. Ophelia across the mid-Atlantic combined
with high pressure across eastern Canada was generating a
cool/moist east to northeast flow of air across southern New
England this afternoon. Despite some mid level dry air across
our region...the remnants of Ophelia slowly lifting northward
coupled with moist easterly flow were enough to generate areas
of showers and drizzle. These conditions will continue for the
remainder of the afternoon which will hold temps in the upper
50s to the lower 60s for the remainder of the afternoon.
Northeast winds will gust up to 20 mph at times and up to 30 mph
across the Islands. So another rather cool afternoon in
progress.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...

Tonight...

Remnants of Ophelia slowly moves east off the mid Atlc coast and
tracks south of New Eng. Deep moisture plume moves into SNE,
especially south of the Mass Pike. PWATs 1.5-1.75" combined with
modest synoptic forcing will bring numerous showers and isolated t-
storms south of the Mass Pike tonight. Locally heavy rainfall is
possible, with HREF and ensemble probs targeting CT for heaviest
rainfall. We will still be fighting dry air to the north so showers
should be more scattered north of the Mass Pike. Lows will be in the
50s.

Monday...

Deep moisture plume will remain in place to start the day on Monday
which suggests showers of varying intensity will continue,
especially south of the Pike. Drier air from the north will
eventually push southward into SNE which will bring a drying trend
from north to south in the afternoon, but wet weather will likely
persist all day across CT, RI and SE MA. Additional rainfall of 0.50
to 1 inch is possible south of the Pike through Monday, with
localized amounts of 1-2 inches possible with any heavier showers,
especially in CT. Decreasing rainfall amounts north of the Pike.
Cool day on Monday with rainfall and gusty NE Winds holding temps in
the upper 50s to lower 60s. Increasing low level jet as pressure
gradient increases will result in 20-30 mph gusts, strongest near
the coast.

&&

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

Highlights:

* Dry, brisk conditions overspread the region Monday night

* Sunshine & dry weather Tue into at least early next weekend

* Mild days and cool nights with highs in the 60s and lows in the
  40s, then moderating into the low 70s Friday & Saturday

Monday Night...

Post frontal airmass overspreads SNE as the remnants of Tropical
Storm Ophelia exit out to sea. Any lingering rain along the south
coast Monday evening will quickly give way to dry weather, as 1035
mb high over Quebec and associated dry airmass advects southward
into SNE. It will be windy especially across southeast MA, Cape Cod
and the Islands, as NE low level jet up to 35 kt streams across
relatively warm SSTs (60s), will promote gusty NE winds given steep
low level lapse rates.  As you would expect, a cool airmass
associated with the 1035 mb anticyclone, as 925 mb temps cool down
to about +7C by 12z Tue. Low level NE jet will keep blyr well mixed
and some airmass modification given SSTs in the 60s, precluding even
cooler temps. Lows in the 40s, except 50-55 along the coast given
winds off the relatively mild ocean.

Tuesday...

Dry but cool airmass over the region with 925 mb temps only +7C
across eastern MA to +9C over western MA/CT. This will only support
highs from around 60 along the eastern MA coast, to mid 60s across
western MA/CT, about 5-10 degs cooler than normal. It will feel even
cooler given gusty NE winds, especially over southeast MA. This NE
flow likely yields more clouds than sun in the morning, then
increasing sunshine in the afternoon as ensembles indicate anomalous
dry air associated with 1035+ mb Quebec high advecting south into
SNE.

Wednesday thru Saturday...

Anomalous Ridge Wednesday over Hudson Bay into southern Quebec,
slowly traverses eastward during this time period. Meanwhile, a low
amplitude closed low over the upper MS/OH valley advects eastward
and tries to undercut the ridge. As it does so, it deamplifies and
likely gets shunted to the Mid Atlc region, leaving SNE with dry
weather. Cool/dry airmass over the region provides splendid fall
weather, with sunshine and mild days, cool nights. Highs in the 60s
and lows in the 40s, but moderating with probability of highs in the
low 70s increasing Fri and Sat.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...

Forecast Confidence Levels:

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

18Z TAF Update...

This afternoon into tonight...Moderate Confidence.

Low end MVFR to IFR conditions will persist this afternoon into
this evening in showers and areas of drizzle. We may see some
improvement after midnight north of the MA Turnpike as drier air
attempts to work into the region. Meanwhile...a band of steady
rain will impact areas south of the MA Turnpike and perhaps
heavy for a time in parts of our CT zones. NE winds 5 to 15
knots with gusts on the order of 20-25 knots for the Cape and
Islands.

Monday...Moderate Confidence.

Conditions should improve to MVFR-VFR levels near and north of
the MA Turnpike on Monday as drier air works in from the north.
South of the MA Turnpike....steady rain may impact areas
especially during the first part of the day. But enough mid
level dry air will probably allow these areas to improve to at
least MVFR conditions during the afternoon. NE winds 10 to 20
knots with gusts of 20-30 knots along the coasts.

Monday night...Moderate Confidence.

VFR conditions probably dominate during the evening with enough
dry air working down from the north. However...we will need to
watch for some MVFR ceilings re-developing after midnight with
northeast low level flow and cooling boundary layer temps
overnight. NE winds 10 to 15 knots with some 20-25 knot gusts
possible along the coast at times.

KBOS Terminal...Moderate Confidence in TAF. Biggest uncertainty
how quickly dry air works down from the north very late tonight
into Monday and allows cigs/vsbys to improve.

KBDL Terminal...Moderate Confidence in TAF.

Outlook /Tuesday through Thursday/...

Tuesday: Mainly VFR, with local MVFR possible. Windy with local
gusts up to 30 kt.

Tuesday Night through Thursday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels:

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

Winds will gradually diminish through today as low level jet
weakens, with 20-25 kt gusts by this afternoon. Winds ramp up
again late tonight and especially Monday as low level jet
increases. Gusts to 25-35 kt are expected Monday with the
strongest gusts over the south coastal waters. Gale warnings may
be needed if confidence increases for 35 kt gusts. Vsbys will be
reduced at times in occasional rain and fog through Monday.

Outlook /Monday Night through Thursday/...

Monday Night through Tuesday: Moderate risk for Small Craft
Advisory winds with gusts up to 30 kt. Rough seas up to 8 ft.

Tuesday Night through Wednesday: Low risk for Small Craft
Advisory winds with gusts up to 25 kt. Seas up to 5 ft.

Wednesday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft.

Thursday: Winds less than 25 kt. Seas up to 5 ft.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 AM EDT Monday for ANZ232>235-237-
     250-251-254>256.
     Small Craft Advisory until 2 PM EDT this afternoon for ANZ236.

&&

SYNOPSIS...KJC/Nocera
NEAR TERM...Frank
SHORT TERM...KJC
LONG TERM...Nocera
AVIATION...Frank/Nocera
MARINE...KJC/Nocera