River Flood Warning 62, NWS Boston/Norton, MA

Area Forecast Discussion
National Weather Service Boston/Norton MA
930 PM EST Mon Dec 18 2023

.SYNOPSIS...
Although conditions improve late this afternoon and early
tonight, it remains unsettled into Tuesday with clouds and
perhaps a spotty shower. A prolonged dry period sets up from
Wednesday through this weekend. Breezy conditions persist
through Friday. Temperatures will be near to below normal
through this weekend. Those hoping for a white Christmas will
need to wait for another chance in 2024, with little to no
precipitation expected after Tuesday.

&&

.NEAR TERM /THROUGH TUESDAY/...

10 PM Update...

Winds have finally calmed down across the region with gusts
dropping below 30mph. There is a chance for more showers over
Cape Cod and the Islands overnight as a weak surface trough is
able to tap into moisutre rich southerly flow at 850mb.
Accumulations overnight should generally remain less then a
1/10th of an inch.

Previous discussion.

A powerful low pressure finally moves into northern New England
this evening, then farther north overnight. This will bring an
end to the rainfall from south to north late this afternoon.
While remaining gusty, wind speeds also will diminish. Thinking
we may be able to drop the current land-based wind headlines, at
some point before 7 PM this evening, especially across interior
southern New England. Will be making that decision within the
next hour or so.

Well above normal low temperatures expected tonight. Many
locations should have low temperatures around what would be a
normal high temperature for mid December.

&&

.SHORT TERM /TUESDAY NIGHT/...
Deep mid level trough and its associated cold pocket of air
aloft establishes itself over our region Tuesday. Cold air aloft
will result in some diurnal cloudiness. Thinking mainly dry
conditions, but still cannot completely dismiss the idea of an
isolated shower, especially across the higher terrain. Slight
bump in in temperatures during the day, before falling off
during the afternoon and evening.

Turning even drier Tuesday night. West to northwest winds
diminish further. Near normal low temperatures.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Highlights

* Quiet and dry conditions

* Near to below normal temperatures

* Breezy through Friday esspically over the waters.

A strong 1035mb high begins to build north from the mid-Atlantic
states and merge with a 1045mb high dropping out of Ontario. This
will lead to a prolonged stretch of quiet and dry weather for
southern New England. As the surface highs move towards the region,
the pressure gradient will remain tight being sandwiched between the
remnants of Mondays low pressure system stalling offshore and even
intensifying a bit. What this will lead to is breezy conditions
lasting through Friday. Gusts inland wont be anywhere as strong as
we saw Monday topping out at 20-30mph on Thursday. Over the waters
and near the shores, Gale force gusts are possible with the latest
NBM showing 50-80% chance for gusts of 40mph mainly Thursday.
Starting Friday night, the center of the high pressure moves
overhead allowing the pressure gradient to relax and winds to calm
down. With little to no wind Friday night and beyond, overnight lows
likely begin to drop into the mid to low teens away from the coasts
with clear skies. Used a blend of the MOS guidance and NBM for
overnight lows Friday and beyond. As for highs, there will be a
downward trend through Friday and Saturday only topping out in the
mid to upper 30s. Next chance for precipitation could come Sunday
with the GFS showing a weak low exiting the Great Lakes, however,
the GFS appears to be an outlier at this time with ensembles showing
around a 10% chance for accumulating precip.

&&

.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
Forecast Confidence Levels:

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

Tonight: High confidence.

Lingering MVFR CIGS gradually give way to SCT/FEW CIGS during
the early overnight hours, allowing for VFR to prevail except
across the high terrain of interior MA/CT, which will take
longer to fully clear.

Winds continue to diminish out of the SW, with gusts generally
dropping to 20 kt or less.

Tuesday: High confidence.

Continued SCT-BKN VFR to MVFR bases, though may trend OVC in
the western higher terrain. Could see isolated -SHRA, or -SHSN
in the higher terrain of far W/NW MA, although drier weather
should prevail most of the time. W to WNW speeds 10-14 kt with
gusts 22-23 kt.

Tuesday Night: High Confidence.

VFR. Breezy.

KBOS TAF...High confidence in TAF.

VFR with decreasing winds overnight. Scattered to broken cloud
deck will form tomorrow around 2-3kt. Gusty west winds up to 20
knots

KBDL TAF...High confidence in TAF.

diminishing winds with VFR conditions tonight. Scattered to
broken cloud deck will form tomorrow around 2-3kt. Winds become
gusty out of the west up to 25 knots

Outlook /Wednesday through Saturday/...

Wednesday: VFR. Breezy.

Wednesday Night: VFR. Windy with gusts up to 35 kt.

Thursday: VFR. Strong winds with local gusts up to 40 kt.

Thursday Night: VFR. Windy with gusts up to 35 kt.

Friday: VFR. Windy with local gusts up to 30 kt.

&&

.MARINE...
Forecaster Confidence Levels:

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

Overall high confidence.

** Dangerous Marine Conditions Today **

Winds will continue to diminish this evening and overnight.
Storm Warnings will likely be converted to Gale Warnings later
this afternoon, and Small Craft Advisories overnight. Rough
seas will linger into Tuesday night, especially across the open
coastal waters.

Outlook /Wednesday through Saturday/...

Tuesday Night: Winds less than 25 kt. Rough seas up to 12 ft.

Wednesday: Winds less than 25 kt. Rough seas up to 10 ft.

Wednesday Night: Low risk for gale force winds with gusts up to
35 kt. Rough seas up to 11 ft.

Thursday: Moderate risk for gale force winds with gusts up to
40 kt. Rough seas up to 13 ft.

Thursday Night: Low risk for gale force winds with gusts up to
40 kt. Rough seas up to 13 ft.

Friday: Moderate risk for Small Craft Advisory winds with gusts
up to 30 kt. Rough seas up to 11 ft.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 1 PM EST Tuesday for ANZ230-236.
     Small Craft Advisory until 7 PM EST Tuesday for ANZ231>235-237-
     251.
     Small Craft Advisory until 7 AM EST Wednesday for ANZ250-
     254>256.

&&

SYNOPSIS...Belk/KP
NEAR TERM...Belk/KP
SHORT TERM...Belk
LONG TERM...KP
AVIATION...Belk/KP/Guest
MARINE...Belk/KP
TIDES/COASTAL FLOODING...