392
FXUS61 KBOX 171917
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
217 PM EST Fri Jan 17 2025

.SYNOPSIS...
An approaching cold front will result in a southerly flow of
even milder air for Saturday with a period of rain showers
Saturday afternoon into early evening. Dry weather should
prevail for the first part of Sunday behind this cold front. A
low pressure will ride up and along this front and likely bring
an accumulating/plowable snowfall later Sunday, and especially
Sunday night. This will be followed by an arctic outbreak later
Monday into Wednesday with wind chills likely dropping to
between 10 and 15 below zero.

&&

.NEAR TERM /THROUGH TONIGHT/...
Key Messages:

* Near to above normal temperatures

High pressure moves off the Mid Atlantic coast tonight, shifting
winds to the S to SW across southern New England. Not especially
strong for this time of year. Increasing clouds expected, which
will temper the impact of radiational cooling. Anticipating low
temperatures to be near to above normal.

&&

.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
Key Messages:

* Above normal temperatures with breezy conditions Saturday.

* Rain showers developing in the afternoon, becoming more
  widespread during the evening.

A cold front is expected to cross southern New England Saturday
night. Showers becoming more widespread by evening, then
tapering off from west to east behind this front as it moves
offshore.


Saturday:

A weak shortwave trough and cold front approaches the region
Saturday. Moisture gradually increases into the afternoon with
precipitable water values around 150-200% of normal by early
evening. This wave will bring a broad area of ascent supporting
our next chance of precipitation. Showers begin to develop in
the afternoon from west to east, becoming more widespread mid-
afternoon to early evening.

Expecting mainly rainfall for this event given the increasing
warm air advection. There is a slight risk for some freezing
rain or light snow at the onset Saturday morning across the
higher terrain towards the Berkshires. At this point, thinking
up to an inch of snowfall is possible before rain mixes in or
all precipitation transitions to all rain.

Temperature-wise, thinking the significantly colder air starts
to arrive late Saturday night. This will not be enough time to
bring low temperatures even to near normal levels.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Key Messages...

* Plowable snowfall likely late Sun/Sun night ending by Mon AM
* Arctic Outbreak Mon/Tue/Wed with Wind Chills -10 to -15 below zero
* Actual Lows Mon night/Tue night single digits with some below zero
* Actual Highs Tue & Wed only in the middle teens to the lower 20s

Details...

Sunday and Sunday night...

The first part of Sunday should feature dry weather and probably
will see some partial sunshine in the morning. Given the airmass
behind the initial front is not that cold, high temps should
top off in the upper 30s to the middle 40s.

The main concern with this forecast revolves around the
increasing confidence in an accumulating/plowable snow event
later Sun and especially Sun night across the region. That being
said, there is still considerable spread amongst the guidance
and this forecast is not set in stone. The biggest question is
how far northwest an anafrontal wave tracks to the coast. The
00z NAM is the eastern outlier with a shutout across southern
New England as a weak wave of low pressure tracks well southeast
of the Benchmark. Meanwhile...the 00z RGEM continues to be the
western outlier with a significantly stronger low pressure
system that tracks much further northwest across southeast MA.
This solution is so far west that Ptype would mainly be rain
across the coastal plain with most of the snow across the
interior.

Given the considerable differences between the NAM/RGEM, there
remains plenty of uncertainty on the exact outcome. While no
solutions can be ruled out at this point...we are favoring the
GEFS/EPS Ensembles along with the UKMET that support a middle
ground with the wave of low pressure tracking near the
Benchmark. This solution would bring a period of
accumulating/plowable snowfall which may start as a brief period
of rain. A very preliminary snowfall forecast indicates that
2-6" of snow is possible across a good portion of the region,
which is supported by the latest NBM model. That is the most
likely solution based on the current data...but given that there
still is a large spread in the models this is not set in stone.
There still is a low risk for little if any snowfall if the
storm track trends east like the NAM or a far western solution
like the RGEM...which would support mainly rain on the coastal
plain. There also would be a low probability for a swath of over
6"+ of snow with a stronger low pressure system tracking just
inside the Benchmark. But right now odds favoring more on the
order of a 2-6" type of snow for most locations...but probably
less towards the Cape/Islands where Ptype issues are more
likely.

Monday through Wednesday...

The good news is that the steady snow will pretty much be over
by daybreak Mon. Otherwise, the main story will be an arctic
outbreak and likely the coldest weather since early February
2023! The arctic airmass begins to work into the region Mon on
blustery NW winds. Highs on Mon probably mainly in the lower to
middle 20s with the bitterly cold air works into the region late
Mon/Mon night and continuing into Wed. Overnight low temps will
be in the single digits Mon night and Tue night with some below
zero readings in the outlying locations...especially Tue night
when winds start to diminish. High temps Tue and Wed will only
be in the middle teens to the lower 20s. Blustery Northwest
winds will probably drop Wind Chills into the -10 to -15 below
zero. Cold Weather Advisories will likely be needed.

Thursday...

The core of the coldest air will begin to depart, but thinking
high temps will still be quite cold in the 20s to near 30.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:

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

Through Tonight...High Confidence.

VFR. Winds becoming light S or calm this evening.

Saturday...High Confidence in trends. Moderate Confidence in
timing.

VFR conditions through mid morning or so, gradually becoming
MVFR in the afternoon and early evening. Localized IFR conditions
possible by early evening. Rain showers will also overspread
the region during the afternoon hours from west to east. A few
scattered showers are possible after 15z.

Saturday Night...High Confidence in trends. Moderate Confidence in
timing.

MVFR trending to VFR. Areas of IFR could linger across RI and
southeast MA until after midnight, before improving late.

KBOS TAF...High Confidence in TAF.

KBDL TAF...High Confidence in TAF.

Outlook /Sunday through Wednesday/...

Sunday: Mainly VFR, with local MVFR possible. Breezy. Chance
SN.

Sunday Night: Mainly IFR, with local MVFR possible. Breezy. SN
likely.

Martin Luther King Jr Day through Tuesday: VFR. Breezy.

Tuesday Night: VFR. Breezy. Slight chance SHSN.

Wednesday: Breezy. Slight chance SHSN.

&&

.MARINE...
Forecaster Confidence Levels:

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

High confidence.

High pressure moves across the waters tonight, keeping light
winds and seas. S to SW winds increase Saturday ahead of an
approaching cold front. Building seas across the outer coastal
waters. Small Craft Advisories will be issued for the outer
coastal waters for a period from late Saturday morning into
Sunday morning. This advisory could be extended with later
forecasts.

Outlook /Sunday through Wednesday/...

Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Chance of rain.

Sunday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas up to 5 ft. Rain, chance of snow.
Visibility 1 to 3 nm.

Martin Luther King Jr Day through Monday Night: Moderate risk
for Small Craft Advisory winds with gusts up to 25 kt. Areas of
rough seas. Freezing spray, slight chance of snow showers.

Tuesday through Tuesday Night: Low risk for Small Craft
Advisory winds with gusts up to 25 kt. Areas of seas
approaching 5 ft. Freezing spray, slight chance of snow
showers.

Wednesday: Low risk for Small Craft Advisory winds with gusts
up to 25 kt. Areas of seas approaching 5 ft. Freezing spray,
chance of snow showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

$$

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