719
FXUS61 KBOX 220006
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
706 PM EST Thu Nov 21 2024

.SYNOPSIS...
Periods of rain persist tonight and there may even be a change to
wet snow late across the highest terrain of the Berks...but no
impacts expected. A lull in most of the rain is expected Friday
morning into early afternoon...but another round of rain is expected
later Friday into Friday night, with the focus across eastern
and northern Massachusetts. Low pressure slowly pulls away from
New England this weekend, resulting in a drying trend but also
accompanied by blustery northwest winds. Considerable cloudiness
Saturday gives way to breaks of sunshine Sunday. Dry weather
Monday followed by a round of possible showers Monday night into
early Tuesday. Briefly mild Tuesday followed by a cooling trend
Wednesday, behind a departing cold front. Unsettled weather may
return to the region sometime Thanksgiving or Friday.

&&

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

7 PM Update...

Moist conveyor belt/firehose of Atlantic moisture with a very
large fetch from Georges Bank pivoting westward into SNE, is
providing a steady stream of light to moderate rain across the
area this evening. This will continue much of the night, with
steady rain tapering off toward morning, as the dry slot
overspreads the area. As the closed upper low over PA drifts
eastward overnight, associated cold pool aloft will begin to
cool the column over western MA/CT, resulting in rain mixing
with and changing over to snow at elevations AOA 1,500 ft.
Otherwise, a chilly/raw windswept rain continues tonight. Previous
forecast verifying nicely at 7 PM and captures the details
above. Therefore, no changes with this update. Earlier
discussion below.

-------------------------------------------------------------------------

* Periods of rain and fog tonight with gusty NE winds
* Any very minor wet snow accums confined to east slopes of Berks

Surface low pressure south of Long Island will gradually retrograde
northwest tonight in response the the deep closed upper level low
across PA. This will allow the easterly 850 mb LLJ to strengthen
between 45 and 55 knots tonight. In response...a band of good mid
level frontogenesis to lift northward across the region. The result
will be periods of rain and fog persisting tonight. It will also be
quite breezy with ENE wind gusts of 25 to 35 mph at times with the
strongest of those winds along the coast.

As the closed upper level low approaches from the west...some
cooling aloft will begin to work in from the southwest later
tonight. It may be just cold enough for rain to mix with or change
to wet snow in the highest terrain along the east slopes of the
Berks. Perhaps a coating to 1 inch of wet snow would be possible at
elevations near 1500 feet with a low risk of up to 2" late tonight
into Friday morning. Not much of an impact...but some very minor wet
snow accums are possible in the highest terrain late tonight into
Fri morning. Low temps should mainly be in the upper 30s to the
lower 40s...but a few degrees lower in the highest terrain.

&&

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

Key Points...

* Lull in most of the rain Friday morning into early afternoon
* Highs Fri mainly in the upper 40s to the middle 50s
* Next round of rain later Fri/Fri night eastern/northern MA
* Wet snow may mix in across highest terrain of Berks/N. Orh Hills

Details...

Friday and Friday night...

As the closed upper level low continues to lift northward to our
west...a dryslot should overspread much of the region Friday morning
into mid afternoon. So much of this time period will be dry except
for a few lingering showers mainly across western MA/western CT
closer to the upper level low. We may even see a peeks of sunshine
briefly with the best chance across eastern MA with the dryslot.
This should result in high temps recovering into the upper 40s to
the middle 50s on Fri.

The closed upper level low to our west will result in another piece
of shortwave energy approaching from the south. The track of this
piece of energy and how far west the main rain shield gets...but
appears eastern MA and northern MA stand the best chance for a
period of widespread rain later Fri into Fri night. Temps maybe
marginally cold enough for some wet snow in the highest terrain of
the Berks and northern Worcester Hills...but no real impacts
anticipated. Low temps should bottom out in the 30s to the lower 40s.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...

Highlights:

* Drying trend this weekend, but blustery and cool

* Dry, pleasant and seasonable Monday

* Some showers possible Monday night/early Tue, then dry and mild
  Tue PM followed by cool/dry weather Wed.  Good travel weather.

* Possible unsettled weather Thanksgiving and/or Friday

Details:

The Weekend:

Vertically stacked low near the 40N/70W benchmark 12z Sat, ejects
northeast towards the maritimes, courtesy of upstream jet energy
diving southeast through Ontario.  Although in its wake, blustery NW
winds 15 to 25 mph with gusts up to 40 mph possible at times. This
will make temps 45-50 in the afternoon feel much cooler. Mainly a
dry day Saturday, but can`t rule out a few light/nuisance scattered
rain showers, as comma-head precip pivots around the departing large
circulation.  More improvement Sunday, given height rises and flow
becoming less cyclonic. This should support some breaks of sunshine.
Seasonably cool with highs in the upper 40s to lower 50s, but a
blustery NW wind will make it feel chilly.

Monday:

Tranquil weather Monday with weak shortwave ridging advecting across
SNE. Not as cool with highs 50-55 and it will feel mild given plenty
of sunshine and light winds.

Monday Night/Tuesday/Wednesday:

Lead short wave approaches with ensembles having max PWAT plume
traversing SNE around 06z Tue. Thus, risk for some showers late
Monday into early Tuesday. Ensembles then have dry slot
overspreading the region in the afternoon. Modest warm sector over
SNE ahead of trailing s/wv and cold front later Tue/Tue night. Thus,
highs 55-60 look possible Tue afternoon. Then a dry frontal passage
later Tue/Tue night. Dry weather with CAA Wed. Looks like good
travel weather.

Thursday/Friday:

Pacific system marches across the CONUS and arrives here sometime
Thanksgiving and/or Friday. Short wave and attending cold front from
Tue night, provides a chilly airmass to overspread SNE Wed. Thus,
wintry precip is possible during this time. Ensemble situational
awareness tables (ESAT) from the NAEFS indicates a weak signal for
storminess here, while the ECENS ESAT is a bit more robust. Given
day 7 forecast, long way to go here.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
Forecast Confidence Levels:

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

00z TAF Update...no change from previous TAFs. See earlier
discussion below.

--------------------------------------------------------------

Tonight...High Confidence.

Low end MVFR-IFR conditions persist this afternoon and evening
along with periods of rain/drizzle and fog. ENE winds gusts of
20 to 30 knots with the strongest along the coast. In
addition...we may see a few gusts up to 35 knots tonight across
portions of the coast.

Friday and Friday night...Moderate Confidence.

We should see temporary improvement to MVFR and even VFR Fri
morning into part of the afternoon as dryslot overspreads the
region. This will be temporary though as we do expect conditions
to lower to MVFR with localized IFR conditions later Fri and
especially Fri night along with another batch of rain. Still
some uncertainty on how far west this next main band of rain
gets...but greatest risk for it to be most widespread appears to be
eastern MA & RI and possibly northern MA. Winds becoming SE at 5 to
15 knots Fri...shifting to the NE Fri evening and then to the NW by
daybreak Sat.

KBOS Terminal...High Confidence in TAF. Low end MVFR-IFR
conditions in periods of rain/drizzle and fog will persist
through the evening push. ENE wind gusts of 30+ knots at times
into tonight.

KBDL Terminal...High Confidence in TAF. MVFR-IFR conditions in
periods of rain/drizzle will persist through the evening push.

Outlook /Saturday through Tuesday/...

Saturday: MVFR/IFR conditions possible. Windy with local gusts
up to 30 kt. Chance RA.

Saturday Night: Mainly VFR, with local MVFR possible. Windy
with gusts up to 30 kt. Slight chance RA.

Sunday: VFR. Windy with gusts up to 30 kt.

Sunday Night: VFR. Windy with local gusts up to 30 kt.

Monday: VFR. Breezy.

Monday Night: Mainly VFR, with local MVFR possible. Chance
SHRA.

Tuesday: Mainly VFR, with local IFR possible. Breezy. Chance
SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Tonight through Friday night...

* Gale Warnings posted for tonight

Tonight...

Low pressure south of Long Island will gradually lift
northwest tonight. This will induce an easterly low level jet of 45
to 55 knots. Based on that...we opted to upgrade to Gale Warnings
tonight for most open waters with gusts to 35 knots expected. Seas
will build 7 to 11 feet across most open waters given the long
fetch. Areas of fog will also reduce visibility for mariners.

Friday and Friday night...

As the low pressure lifts northwest into eastern NY...the surface
winds will shift to the south by early Fri morning and turn more E
during the afternoon. Gusts will diminish...but seas will be on the
downturn but will still be above small craft levels.
Therefore...will need to replace the Gales with small craft
headlines.

Outlook /Saturday through Tuesday/...

Saturday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Areas of rough seas. Rain likely.

Saturday Night: Strong winds with gusts up to 35 kt. Rough seas
up to 10 ft. Chance of rain.

Sunday: Strong winds with gusts up to 35 kt. Rough seas up to
10 ft.

Sunday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Areas of rough seas.

Monday: Winds less than 25 kt. Areas of seas approaching 5 ft.

Monday Night: Winds less than 25 kt. Chance of rain showers.

Tuesday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of seas approaching 5 ft. Chance of rain
showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 4 AM EST Friday for ANZ230-236.
     Gale Warning until 4 AM EST Friday for ANZ231>235-237-250-251-
     254>256.

&&

$$

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