NWS Technical Forecast Discussion

000
FXUS61 KBOX 242352
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
752 PM EDT Fri Sep 24 2021

.SYNOPSIS...

Mainly dry weather tonight into Saturday morning except for a
few showers towards the southeast New England coast. A second
low pressure system will bring a second chance for rain Saturday
afternoon and night, primarily across eastern Massachusetts and
Rhode Island. Cooler and less humid weather are on tap for the
second half of the weekend and much of next week; especially by
the latter half of the week. Much of next week will be dry,
except for a few showers possible later Monday into early
Tuesday. By late next week will have to watch an offshore low
pressure system; but it remains uncertain if it will track far
enough to bring a period a soaking rain.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...

750 PM Update...

The slow moving cold front was beginning to washout across
eastern MA/RI, so the drier air will struggle to make it much
further east tonight. Moist southerly flow just off the deck
will allow for a few spot showers at times across parts of
eastern MA overnight, but dry weather will dominate. However,
showers will be a bit more numerous across the Cape/Islands
where some surface instability remained along with a bit better
low level convergence.

We do expect plenty of clouds to persist across central/eastern
MA and RI given the weakening push of drier low level air along
with southerly flow off the deck. Meanwhile, areas near and
west of the CT River Valley should see just some scattered
clouds at times tonight. This coupled with the large moisture
gradient will allow for a big spread in overnight low temps.
Readings should bottom out in the upper 40s to lower 50s near
and west of the CT River; where some patchy dense ground fog may
develop late. Meanwhile, low temps across eastern MA/RI will
only bottom out in the upper 50s to the middle 60s with the
mildest of those readings found across the Cape and Islands.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...

Western MA and CT will wake up to mostly sunny conditions on
Saturday while Eastern MA and RI will continue to be socked in
with clouds for most of the day. While the day starts out mostly
dry, an approaching low pressure along the axis of the cold
front which passed across our area Friday/Friday night will
cause showers and embedded downpours to rotate back in across
eastern areas. It is expected that there will be a sharp
gradient in showers, such that areas west of Worcester will see
little to no precipitation, and areas east will see upwards of
an inch of rain through Saturday night. The tricky part of the
forecast lies in where this precipitation gradient sets up, with
some high resolution guidance and the GFS keeping the
precipitation shield much farther east than other guidance,
namely the ECMWF, which brings precipitation into Worcester
county and eastern Connecticut. Dry upper level air continues to
remain in place but will not work down to the surface until
sometime on Sunday. Temperatures will be seasonable on
Saturday, in the upper 60s and low 70s with primarily N/NE flow.
The warmest areas will be across the CT River Valley where
sunshine dominates the morning hours and Cape Cod where high
dewpoints set the area up for a unseasonably mild start.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...

Highlights...

* Cooler/less humid next week with early fall-like temperatures
  particularly by the second half of next week

* A few showers possible late Mon into early Tue & we will need to
  watch an offshore low pressure system by late in the week

Details...

A pattern change to more typical/seasonable early fall temperatures
is in the cards for next week. Upper level ridging that has
dominated most of the month so far will be replaced by a northeast
trough. We will break it down a bit more below.

Sunday...

Low risk for a left over shower or two early=mid morning Sunday near
the coast in association with the departing wave of low pressure.
Otherwise, plenty of sunshine on Sunday to close out the weekend
with high temps mainly in the lower to middle 70s. It will also be
turning less humid as drier low level air works in from the west.

Monday and Tuesday...

A few showers are possible sometime later Mon into early Tue in
association with a secondary cold front. Low level moisture though
will be limited; so any rainfall that occurs will be on the light
side. High temperatures probably reach the 70s in most locations
Mon, but probably the upper 60s to lower 70s on Tue behind the cold
front. Low temps will mainly be in the 40s and 50s.

Wednesday through Friday...

A 1035 MB high pressure system across eastern Canada will combined
with some sort of offshore low pressure system to generate northeast
low level flow for the second half of next week. High temperatures
will probably be held in the 60s to near 70 much of this period. The
bigger uncertainty revolves around whether this offshore low tracks
far enough north to bring a soaking rain with perhaps gusty NE winds
by very late next week. This remains quite uncertain given a large
spread in the ensembles, but it will need to be watched.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...

Forecaster Confidence Levels.

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

00Z Update...

Tonight...Moderate Confidence. Mainly VFR conditions will
continue tonight, but some patchy dense ground fog is possible
late across the typically prone locations of western MA.
Otherwise, lower ceilings will mainly be confined to the
southeast New England coast towards the Cape/Islands. This is
where MVFR conditions along with scattered showers are expected
at times. Light to Calm winds.

Saturday...Mainly VFR across the interior, with MVFR more likely
towards southeast MA, including the Cape and islands.
Scattered showers developing by afternoon as another low pressure
traverses a stalled front. Light W/NW flow across the interior, SE/E
flow across Cape and Islands.

Saturday Night...

Mainly VFR across western Terminals, possible MVFR across
eastern terminals as showers develop. Light westerly flow
develops except across Cape Cod and the Islands where southeast
flow prevails.

KBOS Terminal...Moderate confidence. VFR conditions push east across
our area this evening. Terminal expected to linger between VFR/MVFR
through the day Saturday. Winds shift to the west by 00Z this
evening.

KBDL Terminal...High confidence. VFR conditions persist through the
end of the TAF period. Winds shift westerly by 00Z.

Outlook /Sunday through Wednesday/...

Sunday through Monday: VFR. Breezy.

Monday Night through Tuesday: Mainly VFR, with areas MVFR possible.
Breezy. Slight chance SHRA.

Tuesday Night: VFR.

Wednesday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels.

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

Persistent southerly flow will maintain rough seas on the outer
coastal waters. Still looking like a period of gusts up to 25 kt
later today ahead of a cold front as it crawls east across
southern New England and the waters. This front is not likely
to pass completely east of the waters through Saturday. Winds
diminish some tonight, which will permit seas to subside
overnight. Tweaked the timing of Small Craft Advisories.

Outlook /Sunday through Wednesday/...

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

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

Monday: Winds less than 25 kt. Areas of rough seas.

Monday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers.

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

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...High Rip Current Risk until 8 PM EDT this evening for MAZ007-
     020-022>024.
RI...High Rip Current Risk until 8 PM EDT this evening for
     RIZ006>008.
MARINE...Small Craft Advisory until 2 AM EDT Saturday for ANZ250-255-
     256.
     Small Craft Advisory until 3 AM EDT Saturday for ANZ254.

&&

$$
SYNOPSIS...KS/Frank
NEAR TERM...Frank
SHORT TERM...KS
LONG TERM...Frank
AVIATION...KS/Frank
MARINE...KS/Frank

NWS BOX Office Area Forecast Discussion

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