089
FXUS61 KBOX 211129
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
629 AM EST Sat Dec 21 2024

.SYNOPSIS...
Mainly dry but blustery and very cold this weekend into early
next week. A weak clipper system may bring light snow
accumulations Christmas Eve, then mainly dry for the rest of the
Christmas week with temperatures moderating into the 30s and
low 40s.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Updated: 4:25 AM

Key Messages:

* Light snow showers coming to an end by mid morning.

* Cloudy, cold, and breezy this afternoon. Cannot rule out a stray
  flurry or two, but otherwise dry.

An early morning look at regional radars show ongoing light snow due
to an approaching mid-level trough. High-res guidance indicates the
activity continues into mid morning, with a focus in Connecticut and
western Massachusetts. With CAA and drying aloft, there is little
QPF, perhaps a few hundredths of an inch. Any additional snow
accumulation is a few tenths of an inch.

This afternoon, cannot rule out festive flurries with the mid-level
trough overhead and shortwave energy rounding the base. With PWATs
falling between 0.1" and 0.2" this should lend more to periods of
clouds, strato-cu, with the occasional flurry. It will be quite cold
and breezy too. BUFKIT soundings have mixing of the boundary layer
up to 900mb and with forecast temperatures at 925mb -10C to -12C
will result in afternoon temperatures in the low 30s at the coast
and mid to upper 20s inland. Far northwest Massachusetts will be
colder in the teens. As mentioned, it will be breezy, northwest
gusts 20 to 30 mph. This will lead to apparent afternoon temps in
the upper single digits to mid teens.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
Updated: 4:25 AM

Key Messages:

* Very cold conditions tonight into Sunday. Minimum apparent
  temps near Cold Weather Advisory criteria across portions of
  SNE.

* Dry and sunny for Sunday, but there is potential for ocean effect
  snow showers reaching Cape Cod.

Tonight: 1035mb high builds across the Great Lakes, skies becoming
clear and gusts remain elevated. With CAA ongoing, overnight temps
fall into the single digits across most of the region and at the
coast temperatures are in the low to middle teens. With ongoing
gusts, the apparent minimum temperature overnight are below zero for
most locations, with exception of the islands.

Did hold off on the issuance of the Cold Weather Advisory. This is a
new product, replacing Wind Chill Advisory, now we are able to issue
related products for air temperature and/or wind chill when values
fall below to/below -10F in Connecticut, Rhode Island, and southeast
Massachusetts. For the remainder of Massachusetts the threshold is
-15F. Right now, the overnight minimum apparent temperature for
southern areas are -5F to -8F, while north it is -5F to -12F. In
Berkshire County, minimum apparent temperature lowers to/below the
threshold of -15F, WFO ALY has issued a Cold Weather Advisory for
the overnight hours. We will have to reassess today to see if we are
any closer to those thresholds. As previously mentioned, it is
borderline, but would not be surprised if the advisory is expanded
to the east slope of the Berkshire on the day shift.

Sunday: Very cold, 925mb temperatures settle between -16C and -20C
and with good mixing due to the CAA, should have highs in the teens
to low 20s at the coast, utilized the blend of the 25th and 50th
percentile of the NBM to achieve those temperatures. Gusts are not
as strong as they were on Saturday, generally up to 20 mph. The
apparent temperature mid afternoon is downright frigid, +5F to -5F!
While it is a mainly sunny day, PWATs plummet to less than 0.1" the
NNW wind direction over the relatively warmer eastern ocean waters,
could lead to ocean effect snow showers. High-res guidance shows
streamers moving towards the outermost Cape... added POPs here to
show the slight chance of snow.

&&

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

* Rather cold and dry Sunday night into Monday but with less wind

* Temps recovering to near seasonable normals for the rest of the
  Christmas week

* Weak clipper system may bring minor snow accum late Mon night
  and Tue, especially in the interior

* Mainly dry Christmas Day through Fri

Sunday night and Monday...

Strong high pres ~1040 mb builds into New Eng which will bring
diminishing wind and mainly clear skies, although the northerly flow
and cold air over warmer SST will keep ocean effect clouds over the
outer Cape into Mon morning and perhaps a few flurries. Sunshine
Monday will gradually give way to increasing high clouds in the
afternoon as next system approaches from the west. Coldest night of
the season will be Sunday night as radiational cooling allows for
low dropping into the single numbers, possibly near zero NW MA, but
teens SE coastal MA and Cape/Islands where slightly more wind and
cloud cover, especially outer Cape. Highs Monday will recover into
the mid-upper 20s with lower 30s near the south coast.

Monday night and Tuesday...

Next mid level shortwave approaches from the Gt Lakes Mon night
moving across New Eng Tue. This will be accompanied by a weak
clipper system. There is uncertainty with the track of the low but
this is expected to be a light QPF event with potential for some
light snow accumulations late Mon night into Tue.  Any changeover to
rain near the south coast will depend on whether low tracks to the
north with a wind shift to south. Latest ensemble guidance
indicating high probs for 1 inch, especially in the interior. The
75th percentile of the GEFS and EPS distribution indicating
potential 1-2 inch accums which is probably a reasonable expectation
for this event. After a cold night Mon night temps will recover into
the 30s Tue.

Christmas Day through Friday...

High pres will be building to the north on Christmas and persisting
into Friday. This will result in mainly dry conditions, but
persistent NE flow may lead to more cloud cover across eastern New
Eng with low risk for a few showers at times. Near seasonable temps
expected.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:

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

Today...Moderate confidence.

MVFR conditions across western southern New England this morning
due to -SN passing through, visibilities are 3-5SM and ceilings
are 025-040. These conditions continue through 12z/14z. This
afternoon mainly VFR cigs, but lower MVFR cigs possible early
Cape/Islands. NW wind 10-20 kt with some higher gusts.

Tonight and Sunday...High confidence.

VFR, but ocean effect clouds may lower cigs to MVFR at times
over the outer Cape, mainly along and east of HYA. NW wind 10-20
kt with higher gusts near the coast, diminishing Sunday
afternoon.

KBOS TAF...High confidence in improving trend to VFR by 12z.

KBDL TAF...Moderate confidence.

Areas of -SN leading to MVFR conditions, should improve to VFR
by 13z/14z.

Outlook /Sunday Night through Wednesday/...

Sunday Night through Monday: VFR.

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

Tuesday Night: VFR. Slight chance SN.

Christmas Day: VFR.

&&

.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.

Saturday...High confidence.

Low pressure system lifts northeast from southern New England, but
with high pressure building to the west, it will lead to northwest
flow with gusts continuing throughout the day. Have extended the
Small Craft Advisory as a result through the day. Seas remain rough
3 to 6 feet on the southern waters and 5 to 8 feet on the eastern
waters.

Saturday night 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.

Outlook /Sunday Night through Wednesday/...

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

Monday: Winds less than 25 kt.

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

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

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

Christmas Day: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 7 AM EST Sunday for ANZ231-232-251.
     Small Craft Advisory until 10 PM EST this evening for
     ANZ233>235-237.
     Small Craft Advisory until 7 PM EST Sunday for ANZ250-254>256.

&&

$$

SYNOPSIS...KJC/Dooley
NEAR TERM...Dooley
SHORT TERM...Dooley
LONG TERM...KJC
AVIATION...KJC/Dooley
MARINE...KJC/Dooley