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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KBOX 222019
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
319 PM EST Sat Jan 22 2022

.SYNOPSIS...
-- Changed Discussion --
Ocean effect snow showers come to an end over the South Shore
this evening but may linger over The Cape this evening and
tonight. Increasing clouds Sunday precede a dry frontal passage
Sunday night. Cold and dry weather Monday precedes a Clipper
system for Monday night into Tuesday night. Light snow possible
into early Tuesday, with brief milder than normal temperatures
south of the Mass Pike supporting rain to light snow Tuesday
night. Arctic cold returns Wednesday and Thursday with very low
wind chills possible Wednesday night. Another weather system
passes off the coast by Saturday and could affect parts of the
region, mostly with snow.
-- End Changed Discussion --

&&

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

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Tonight

Mid-level ridge  and surface high pressure builds east of southern
New England this evening and tonight. This will bring an end to any
remaining ocean effect snow showers along the South Shore as we
transition to a prevailing southwesterly flow. May see some ocean
effect snow showers linger a bit longer over the outer Cape and
Islands as it will take a bit longer for the winds to shift. Even
after the transition to southwest winds over The Cape/Islands, there
will remain a chance for ocean effect snow showers from the
south/southwest over The Cape and Islands.

Drier air aloft works its way over the interior tonight which will
support clearing skies for most of the evening. Shortly before
sunrise we`ll begin to see increasing cloudiness from west to east
as a new plume of moisture approaches from the west. Southwesterly
flow increases temperatures aloft slightly with 925 hPa temps rising
to around -10C. This will support less frigid temperatures
Sunday morning ranging from the single digits in northwest MA to
the upper teens across southeastern MA. Areas along the
immediate coast may hang in the low 20s.
-- End Changed Discussion --

&&

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

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Sunday

Deep southwest flow allows temperatures in the low-levels to warm to
the -5 to -10 C range at 925 hPa. This will support a more mild
afternoon by mid-January standards with highs perhaps getting into
the mid-upper 30s. Plume of low-level moisture advances
eastward ahead of an approaching cold front. This will result in
increasing cloudiness throughout the day tomorrow. Generally
expecting dry conditions across the region tomorrow, but there
is a slight chance for some isolated upslope snow-flurries over
the Worcester Hills.

Sunday Night

We`ll return to a deep northwest flow pattern Sunday night as a dry-
cold front pushes through southern New England. Northwest flow over
Cape Cod Bay may produce another opportunity for ocean effect snow
showers over the outer Cape tomorrow night. Low-level CAA brings
temperatures at 925 hPa back down to the -10 to -15C range over
southern New England. This will support another frigid morning on
Monday with single digit temperatures north and west of I-90
and low-mid teens elsewhere.
-- End Changed Discussion --

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Big Picture...

Broad trough over the Northeast Monday, balanced by a ridge off the
Pacific coast. Individual shortwaves move through this pattern
through midweek. One shortwave diving down from Western Canada digs
over the Eastern USA late week, forming either a south-north flow or
a southwest-northeast flow.

Temperature fields aloft are forecast below normal Monday, near
normal Tuesday, then below normal again Wednesday-Thursday. Strong
differences develop late week and weekend, with the GFS and GGEM
above normal, and the ECMWF near normal.

Mass fields are in agreement through Wednesday, then diverge late
week. This along with the temperature field differences suggests
moderate-high confidence early week, trending to low confidence
by next Saturday.

Details...

Monday...

High pressure along the East Coast will bring subsidence and dry
weather. The airmass will be cold, with 925-mb temps minus 8 to
minus 12C, supporting surface max temps in the 20s and lower 30s.

Monday night-Tuesday...

Clipper low pressure approaches through the Great Lakes Monday night
and Tuesday, generating weak lift and scattered light snow showers
with the best chance along and north of the Mass Pike. Accumulations
may reach a coating, but low QPF suggest it won`t be more than that.
Min temps will range from the mid teens to mid 20s.

Light snow continues Tuesday morning before diminishing in the
afternoon. Temps at 925-mb climb from Monday, with a range of zero
to minus 5C, supporting 30s and low 40s.

Wednesday-Thursday...

High pressure builds over the region late Tuesday night and
Wednesday. Tight pressure gradient between the departing low and
approaching high. This will bring gusty winds Wednesday and
Wednesday night with lower wind chills.

Subsidence will bring clearing skies. Expect another surge of
cold air with max temperatures, as on Monday, in the 20s and low
30s. Similar max temps are expected Thursday.

Friday-Saturday...

High pressure moves offshore Friday. Clipper low pressure approaches
through the Great Lakes. Models then disagree on how the weather
evolves. The GFS forms low pressure over the Gulf of Mexico, sweeps
it up the east coast before sending it out to sea well south of the
40N/70W benchmark. The GFS brings some precipitation to the Cape and
Islands and possibly interior SE Mass but is mostly offshore.  The
ECMWF takes the clipper low and redevelops it off the
Carolinas...then takes it just outside the benchmark. Precip extends
a little more deeply into interior Southern New England, but with
limited amounts. Given the differences in the various mass fields at
the end of the week, and with the respective coverage of
precipitation, confidence is low for this system. It is a Day 6-7
system, with potential to affect Srn New England but showing signs
of staying offshore. Will show slight chance and low-end chance
Pops, highest over the Cape and Islands and lowest west of the CT
River.

&&

.AVIATION /20Z SATURDAY THROUGH THURSDAY/...
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.

18Z Update:

Through 00Z...High Confidence.

Any remaining ocean effect snow showers near BOS and north
shore should taper off in the next hour or so. OES showers
continue over The Cape terminals with MVFR ceilings and periods
of IFR visibilities to 2SM. VFR elsewhere.

Tonight...High Confidence. VFR with light SW winds.

Sunday...High Confidence. VFR with WSW winds of 5-15 knots.

KBOS Terminal...High Confidence in TAF. Only issue will be thru
15z, where some marginal MVFR ceilings and perhaps a few light
snow showers briefly impact the terminal.

KBDL Terminal...High Confidence in TAF.

Outlook /Monday through Thursday/...

Monday: VFR.

Monday Night: Mainly VFR, with local MVFR possible. Slight
chance SN.

Tuesday: Mainly VFR, with local IFR possible. Chance RA, chance
SN.

Tuesday Night: MVFR/IFR conditions possible. Windy with local
gusts up to 30 kt. Slight chance SN.

Wednesday: Mainly VFR, with local IFR possible. Windy with
gusts up to 30 kt.

Wednesday Night: VFR. Windy with gusts up to 30 kt. Slight
chance SN.

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

&&

.MARINE...
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Forecaster Confidence Levels.

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

Tonight

Surface high pressure moves offshore this evening bringing mostly
calm conditions over the coastal waters. Seas forecast to rise to 4-
6 feet on the outer waters after Midnight, thus have raised SCY
for outer waters through Monday morning. Marginal SCY wind
gusts possible for the near-shore waters with gusts up to 24
knots. Ocean effect snow-showers possible over the south coastal
waters tonight as well.

Sunday

Winds shift to the west/southwest tomorrow and pick up to 15-20
knots with 20-25 knot wind gusts. 4-6 foot seas over the outer
waters.

Sunday night

Gusty winds from Sunday afternoon diminish to 10 knots Sunday
night. Dry cold front moves over the coastal waters resulting in
a wind shift to the west/northwest. 4-6 foot seas linger on the
outer waters through Monday morning.


Outlook /Monday through Thursday/...

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

Monday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of snow.

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

Tuesday Night: Winds less than 25 kt. Seas up to 5 ft. Chance
of rain, chance of snow.

Wednesday: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of rough seas. Slight chance of snow.

Wednesday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Rough seas up to 9 ft. Freezing spray,
slight chance of snow.

Thursday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Rough seas up to 9 ft.
-- End Changed Discussion --

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 5 AM EST Monday for ANZ250-254-255.
     Small Craft Advisory from 3 AM Sunday to 5 AM EST Monday for
     ANZ256.
-- End Changed Discussion --

&&

$$
SYNOPSIS...WTB/RM
NEAR TERM...RM
SHORT TERM...RM
LONG TERM...WTB
AVIATION...WTB/RM
MARINE...WTB/RM