038
FXUS61 KBOX 220209
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
909 PM EST Sat Dec 21 2024

.SYNOPSIS...
Bitter cold temperatures tonight through tomorrow morning as
gusty winds contribute to feel like temperatures below zero,
with Cold Weather Advisories for the Berkshires through tomorrow
morning. Very cold weather continues Sunday night into
Monday...but with less wind. A weak clipper system may bring
very minor snow accumulations late Monday night into Christmas
Eve morning. Otherwise...dry weather dominates the rest of the
Holiday week with temperatures moderating back to seasonable
levels.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
9 PM update...

Forecast on track. Very cold air aloft over warmer SST will
result in significant instability which will support ocean
effect clouds and perhaps a few snow showers for the outer Cape.
However, Low level NW trajectory will keep bulk of snow showers
just offshore.

Previous discussion...

* Very cold tonight...lows mainly single digits-lower teens
* Wind chills Dropping Below Zero

Dry and gusty NW flow bring us the coldest night of the season
overnight. As high pressure builds into the eastern Great Lakes
it will funnel frigid air into SNE, as cold as near 0F in the
high elevations of the Berkshires and single digits/low teens
elsewhere. The unfortunate part is that the pressure gradient
between the exiting low and incoming high will remain tight
enough to keep modest wind speeds overnight, making it feel
even colder. Wind Chill values will dip into the negative low
teens in the highest elevations of the Berkshires and negative
single digits elsewhere. A Cold Weather Advisory is in effect
for Berkshire county where widespread wind chill values of at
least -15F are more certain.

Skies will trend to mostly clear overnight...except for ocean
effect clouds across parts of the Cape and Nantucket. Wind
trajectory is not ideal for ocean effect snow with too much of a
NW component and there also is a lot of dry air in the boundary
layer. However...a few light snow showers/flurries are possible
given temperature differential of 25C from the top of the
inversion to the SST.

&&

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

The very cold airmass settles over us on Sunday making for the
coldest day of the forecast period. Given the closer proximity of
the high pressure, winds will be less gusty than Saturday, but gusts
to 20-25 mph are possible, especially early on. This means
temperatures topping out in the teens and low 20s will feel more
like single digits on either side of 0. Dry weather expected, but
the one exception is a low probability of some ocean effect snow
showers reaching the outer Cape Sunday afternoon/night. This is
because as the high approaches winds shift from the NW to more NNW
which pushes the trajectory from over the ocean to clipping the
Cape. Looking into the overnight hours we yet again see our coldest
night of the season (beating Saturday night). Thanks to high
pressure, clear skies, and light winds, we`ll radiate very
efficiently so expect low temperatures to drop into the negative
single digits in the high elevation interior while elsewhere will be
"warmer" in the single digits above zero. It will actually feel
warmer than the night previous, though, owing to the lack of wind.

&&

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

* Mon dry & still cold...highs middle 20s to the lower 30s
* Light snow showers late Mon night/Tue AM...Dusting to 1" for most
* Temps moderate to near normal by mid to late in the Holiday Week
* Mainly dry Wed/Thu/Fri/Sat outside brief spotty very light precip

Details...

Monday...

A dry and frigid early Mon morning...except for perhaps a few
leftover ocean effect light snow showers/flurries across the
Cape/Nantucket which will be winding down. High temps will still be
cold/below normal on Monday...it will be several degrees milder than
Sunday with less wind too as large high pressure crosses the region.
Currently expecting highs Monday afternoon to generally be in the
middle 20s to the lower 30s.

Monday night and Tuesday...

Dry weather prevails Monday evening...but a weak clipper system and
its associated shortwave will cross the region late Monday night
into Tuesday morning. The better dynamics/forcing looks to pass
north of our region. That being said...there is enough forcing for a
brief period of light snow showers. This will be short-lived though
and there with limited moisture...thinking a dusting to 1" of snow
for most. It is possible a few locations in northern MA see up to 2"
of snow or so if we can muster enough forcing as suggested by the
RGEM. Either way...this will not be a big storm with mainly dry
weather by Tue afternoon. Highs should also recover well into the
30s across much of the region with perhaps even some lower to middle
40s across the Cape and Islands.

Wednesday through Saturday...

A mid level ridge axis will build into southern New England for the
second half of the Holiday Week. EPS/GEFS indicate well above normal
height fields...but a high pressure system in the vicinity of
northern New England and the Canadian Maritimes will offset this to
some degree. So while temps will moderate to seasonable
levels...they will not get too mild with that high to our
north/northeast. Highs probably in the 35 to 45 degree range for the
second half of the upcoming week. Generally dry weather is
anticipated for much of this time...but low level onshore flow may
result in spotty very light precipitation at times with the best
chance near the coast. Regardless...dry weather will dominate with
no significant storms for the second half of the Holiday Week.

&&

.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
Forecast Confidence Levels:

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

00z TAF Update...

Tonight and Sunday..High confidence.

VFR, but ocean effect clouds over the outer Cape, mainly along
and east of HYA. Most of the ocean effect clouds should be VFR
levels, but may flirt with MVFR thresholds at times. NW wind
gusts of 20 to 25 knots at times especially this evening and
again during the day Sunday.

Sunday night...High confidence.

VFR. NW winds 5-10 kts.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Monday through Thursday/...

Monday: VFR.

Monday Night through Tuesday: Mainly VFR, with local IFR
possible. Chance SHSN.

Tuesday Night: VFR. Breezy.

Christmas Day: VFR. Breezy. Slight chance SHSN.

&&

.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.

Key Messages:

* Small Craft Advisory in effect through Sunday night.

Tonight into Sunday...High confidence.

High pressure moving overhead. NW winds 15-20 kts gusting to 25
kts. Seas 5-7 ft. A few ocean effect snow showers are possible
Sunday across the eastern waters.

Sunday night...High confidence.

High pressure overhead. NW winds 10-15 kts. Seas 2-5 ft.

Outlook /Monday through Thursday/...

Monday: Winds less than 25 kt.

Monday Night: Winds less than 25 kt. Chance of rain showers,
chance of snow showers. Local visibility 1 to 3 nm.

Tuesday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain showers. Local visibility 1 to 3 nm.

Tuesday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of rain showers, slight chance of snow
showers. Local visibility 1 to 3 nm.

Christmas Day: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain showers, slight chance of snow
showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 10 PM EST this evening for ANZ230-
     233>237.
     Small Craft Advisory until 7 AM EST Sunday for ANZ231-232-251.
     Small Craft Advisory until 4 AM EST Monday for ANZ250-254>256.

&&

$$

SYNOPSIS...Frank/BW
NEAR TERM...KJC/Frank
SHORT TERM...BW
LONG TERM...Frank
AVIATION...Frank/BW
MARINE...Frank/BW