556
FXUS61 KBOX 160912
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
412 AM EST Thu Jan 16 2025

.SYNOPSIS...
A weak low pressure system will bring a period of light snow showers
tonight...mainly for areas near the south coast, Cape and Islands.
Temperatures then moderate Friday and especially by Saturday ahead
of an approaching cold front. This cold front will bring a period of
mainly rain showers later Saturday into Saturday evening. Dry
weather should prevail for the first part of Sunday...but a wave of
low pressure will likely bring a period of snow or rain changing to
snow late Sunday into early Monday. This will be followed by an
Arctic Outbreak later Monday into Wednesday with below zero Wind
Chills.

&&

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

* Another cooler day with high temperatures slightly below
  normal

* A few flurries across the outer-Cape

Quiet morning with chilly temperatures. Stations across the
higher spots in west and central MA have observed temperatures
in the single digits. Light ocean effect showers orient across
the Cape bringing flurries to light snow over the next couple of
hours.

It will be a quiet weather day today across southern New
England. The 850mb temperature anomalies show the below normal
airmass lingering over the region bringing another day of
slightly below normal highs. Highs range in the upper 20s to low
30s. A mid-level trough approaches from the west today keeping
winds light SW across the region. A few flurries across the
outer Cape are possible.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/...
335 pm update

Key Messages:

* Scattered flurries/light snow showers mainly along the south
  coast Thursday night.

Tonight:

A mid-level trough pushes eastward this evening. Synoptic
support will be limited, but will bring a period of weak ascent.
Moisture will be limited as well, but enough to support light
snow showers. HREF guidance shows showers developing in the
6-8pm timeframe this evening. Overall the higher probabilities
for getting snow showers will be across the Cape and islands.
Elsewhere will see lower chances (< 35%) for scattered showers
or flurries. Amounts will likely range from a trace to a half an
inch. The HREF LPMM highlights a band of higher amounts(1-2")
oriented across the islands, particularly Nantucket. Likely
picking up on ocean enhancement, so this is a possibility
depending on where the banded enhancement sets up. For most
areas, showers decrease by midnight. However, showers may stick
around longer across the Cape and islands. By sunrise, showers
should diminish.

Friday:

A mid-level ridge moves in Friday, pushing out the cooler
airmass. 850mb temperatures rise several degrees from Thursday
resulting in the start to the brief warm-up this weekend. Highs
will be more seasonable in the mid 30s to low 40s.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Key Messages...

* Turning Milder/Breezy Sat with highs well into the 40s/near 50
* A round of rain showers later Sat into Sat evening
* Period of snow or rain changing to snow late Sun into early Mon
* Arctic Outbreak later Mon into Wed with below zero wind chills

Details...

Saturday...

A ridge of high pressure off the mid-Atlantic coast will continue to
move further east and away from the region Sat. At the same time...a
cold front will be approaching from the west. This will result in
the development of gusty southerly winds. 925T moderate to above 0C
and with good mixing expect highs to reach well into the 40s to near
50 despite an abundance of clouds. The best chance of reaching 50
will be on the coastal plain. We think the shower threat will hold
off until mid-late afternoon.

As the shortwave and associated pre-frontal trough approaches from
the west the forcing for ascent will increase later Sat into Sat
evening. Thinking is that a period of rain showers is most likely in
the mid-late afternoon into the evening hours. Ptype will generally
be all liquid given the warm boundary layer temps. Perhaps a touch
of wet snow across the highest terrain along the east slopes of the
Berks...but little if an accumulation/impacts expected.

Sunday into Monday...

Although the cold front will have crossed the region by daybreak
Sun...it will take some time for the colder air to work into the
region. So we expect highs to reach the upper 30s to the middle 40s
on Sun with the mildest of those readings in the RI/SE MA region.
The first part of Sun will be dry with partial sunshine...but that
will likely change later Sun into early Mon which we will discuss
below.

The main forecast challenge will revolve around an anafrontal wave
of low pressure that will develop in the cold front. This will
likely bring a period of snow or rain changing to snow late Sun into
early Mon. There is still considerable spread on how close this wave
of low pressure tracks in the vicinity of southern New England. The
CMC model seems to be a west outlier...while the ECMWF is more of an
east outlier. That being said...most of the 00z guidance suite
indicates at least a period of snow or rain changing to snow over
this time period for a good portion of the region. While this does
not look like a major storm...accumulating snow is certainly
possible for some locations.

Later Monday into Wednesday...

The GEFS/EPS/CMC ensembles are in very good agreement in an Arctic
Outbreak later Mon into Wed. A -EPO will result in strong ridging
into northwest Canada and Alaska...allowing for the delivery of
arctic air across the central/eastern U.S. given cross polar flow.
850T drop to between -24C/-25C across the region. This will result
in overnight lows mainly in the single digits Mon night and Tue
night with some below zero readings possible too. Highs Tue and Wed
may not reach 20 in many locations. Wind Chills will certainly drop
below zero and we probably will eventually need to issue Cold
Weather Advisories.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
Forecast Confidence Levels:

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

06z TAF Update...

Today...High Confidence.

VFR. Light W winds becoming SW at 5-10 knots.

Tonight...High Confidence.

VFR conditions should prevail away from the south coast, but a
brief flurry/light snow shower can not be ruled out.
We do expect a period of MVFR conditions with some light snow
showers near the south coast, Cape and especially ACK. In
fact...we may even see some brief localized IFR conditions with
the best chance for that at ACK...where up to an inch or so of
snow accumulation will be possible. Light SW winds becoming NW.

Friday...High Confidence.

VFR. NW winds 5-10 knots.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Saturday through Monday/...

Saturday through Saturday Night: Mainly VFR, with local IFR
possible. Breezy. Chance SHRA.

Sunday: VFR. Breezy. Chance RA, chance SN.

Sunday Night: VFR. Breezy. Chance SN.

Martin Luther King Jr Day: VFR. Breezy. Slight chance SN.

&&

.MARINE...
Forecaster Confidence Levels:

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

High confidence.

Winds continue to diminish this morning. The current projection
that small craft advisories will be able to be discontinued (by
7am) look to be on track. Generally light winds (15kt and less)
are expected Thursday night through Friday.

Outlook /Saturday through Monday/...

Saturday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Areas of seas approaching 5 ft. Chance of
rain showers.

Saturday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of seas approaching 5 ft. Rain showers
likely.

Sunday: Winds less than 25 kt. Areas of rough seas. Chance of
rain.

Sunday Night: Winds less than 25 kt. Rough seas up to 9 ft.
Chance of snow, rain.

Martin Luther King Jr Day: Low risk for Small Craft Advisory
winds with gusts up to 25 kt. Rough seas up to 8 ft. Freezing
spray, slight chance of snow.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 6 AM EST early this morning for
     ANZ250-251-254>256.

&&

$$

SYNOPSIS...Frank/Mensch
NEAR TERM...Mensch
SHORT TERM...Mensch
LONG TERM...Frank
AVIATION...Frank/Mensch
MARINE...Frank/Mensch