734
FXUS61 KBOX 230605
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
105 AM EST Sat Nov 23 2024

.SYNOPSIS...
Low pressure will rotate northeast into the Canadian Maritimes
through tonight. Cloudy conditions, with steadier rains mainly in
eastern New England will continue through the afternoon. Gusty
northwest winds are expected by this afternoon as cloudy and
rainy conditions improve. Winds remain gusty into tonight and
into early on Sunday before lightening up. Pleasant Monday with
light winds, full sun and seasonably mild temperatures. A
frontal system passing to our northwest on Tuesday brings
another round of rain to Southern New England. Blustery, cooler
and dry weather then returns for Wednesday. Monitoring another
storm system that could move near Southern New England on
Thanksgiving or Black Friday.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
350 PM Update...

* Rain develops this eve in eastern MA/RI & spreads west overnight
* Any wet snow & very minor accums confined to highest terrain

The vertically stacked low pressure system to our west will
gradually sink southeast and be located south of Long Island toward
daybreak. As this happens...secondary low pressure east of the
Benchmark will rapidly intensify and lift northward tonight. This
will allow another swath of widespread rain to overspread eastern MA
& RI tonight. While the focus for the rain will initially be across
eastern MA/RI...the rain should back into the interior during the
late night and overnight hours with good mid level frontogenesis.

The boundary layer will be warm enough to result in Ptype falling as
generally rain. Thermal profiles might become marginally cold enough
across the high terrain of the Berks/Worcester Hills to support
some wet snow during heavier precipitation rates. Any snow accums
will probably be just a dusting to 1 inch mainly on grassy surfaces.
Suppose there is a low risk of 2 inches if boundary layer ends up
colder than forecast. But like last night and earlier this
morning...not really expecting any impacts and any very minor accums
confined to the highest terrain. Overnight low temps should bottom
out in the middle 30s to the lower 40s.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SUNDAY/...
Key Messages...

* Rain Sat morning persists into the afternoon in eastern MA/RI
* Becoming Windy Sat afternoon/evening with NW gusts of 35-45+ mph
* Highs Sat will be in the 40s and the wind will make it feel colder

Details...

Saturday and Saturday night...

A secondary surface low pressure system east of our region will
rapidly intensify and lift northward on Sat. A cold rain will be
impacting much of the region Sat morning...but the back edge of this
precipitation will be pushing eastward as the low pulls away.
Again...any wet snow should be pretty much confined to the high
terrain and should not be impactful. Otherwise...the rain should
come to an end by afternoon across the interior but will linger into
at least part of the afternoon across parts of eastern MA and RI.

The other issue will be the strong winds that will develop on
Sat...especially during the afternoon and into the evening. As this
ocean storm intensifies and lifts northward the pressure gradient
will increase. A northwest low level jet of 45 to 55 knots will
develop at 850 mb. Bufkit soundings indicate northwest wind gusts of
35-45+ mph will mix down Sat afternoon and evening. The strongest
winds will likely be in the interior and it is not out of the
question that a few brief gusts of 50 mph occur. Later shifts may
need to consider a Wind Advisory...but given it is in the latter
half of the 3rd and into the 4th period figured we would let the
next shift take a look. High temps on Sat will be held in the 40s
and with the windy conditions will make it feel colder...especially
with the rain!

Any lingering rain should pretty much be over by late
afternoon/early evening along the coast...but the windy conditions
will persist with 35-45+ mph wind gusts continuing during the
evening. Winds may drop off a tad overnight...but it still will
remain windy. Low temps Sat night should only drop in the middle 30s
to the lower 40s given the atmosphere will not decouple.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Highlights:

* Sunny, dry with easing winds for Mon with slightly above
  normal temps.

* Frontal system passing to our north and west on Tue brings another
  round of beneficial wetting rains.

* Cooler and blustery but dry weather for the Wednesday travel day.

* Monitoring a potential storm that could brush Southern New England
  on Thanksgiving and/or Black Friday, but low confidence due to
  large uncertainty. Stay tuned!

Details:

Sunday Night and Monday:

Decreasing WNW winds Sun night with skies trending clear as ridge of
high pressure moves in from the west. Lows in the upprer 20s to the
mid 30s. This high pressure ridge then crests over Southern New
England on Monday, leading to a mostly sunny, dry and seasonably
mild day (highs mid to upper 50s). Though we start off mostly clear
for Mon evening, expect increasing cloudiness in response to an
approaching frontal system, bringing lows in the mid to upper 30s,
however dry weather is still expected.

Tuesday:

Ensembles coming into better agreement on lead 500 mb shortwave
disturbance and ~994 mb sfc cyclone moving through the Gt Lakes and
St. Lawrence Valley on Tue. With a rather mild warm sector (850 mb
temps around +6 to +8C) rain showers should break out in earnest
starting Tue morning, progressing through Southern New England
through the daytime hours, before moving offshore for the evening.
Likely due to the progressive nature of the system, most models
suggest rain amounts in the third to half inch range common for
most, with low (< 20%) probs for rain amounts at or over 1". Will
turn blustery behind the cold front with moderately strong cold
advection. With cloud cover for most of the day, reduced highs into
the upper 40s to mid 50s even though thermal profiles would support
warmer. With WNW winds around 10-15 mph behind the front, kept lows
on the milder side in the upper 20s/mid 30s.

Wednesday:

Still under a broad WSW cylonic flow with a rather chilly low-level
airmass (925 mb temps 0 to -3C). Still looks to be a dry day with
blustery WNW winds, speeds 10-15 mph with gusts 20-25 mph. Mostly
sunny conditions should help take the edge off the colder airmass,
with highs in the 40s, with upper 30s in the higher terrain. All in
all, conditions still seem favorable for holiday travel. Decreasing
winds Wed night should lead to a pretty chilly night, with lows in
the 20s for most, though the Greater Boston area and the
Cape/Islands should stay around freezing.

Thursday / Friday:

Still a low-confidence forecast for the Thanksgiving holiday to
Black Friday period. Considerable disparity exists in potential
outcomes across the models and their ensembles, associated with
Pacific energy coming out of the Rockies and its potential
interaction with an injection of northern-stream energy digging out
of the Canadian Prairies. Compared to its prior run which was
flatter/weaker and a cold and dry out-to-sea passage, the 00z GFS
and its GEFS now show a more robust low pressure passing from the
southern Appalachians to near the 40N/70W benchmark early Fri. The
ECMWF shows more interaction with the northern stream, with the EPS
mean favoring a track through the OH Valley and into the Northeast,
suggesting the potential for a storm that has the potential for some
of it to be wintry in the interior. However EPS member low tracks
still show quite a range with not much clustering, ranging from the
eastern Gt Lakes to the Carolinas. The 12z Canadian GEM favors a
track through the mid-Atlantic coast into coastal Southern New
England, with an interior snow and a snow-to-mainly-rain outcome for
the coastal plain.

While the background pattern is one which lends itself to
storminess, given the range in possible outcomes and ensembles not
exactly breaking the tie on what is still a Day 6 forecast, there is
still too much uncertainty to favor any solution at this point. All
outcomes, including a cold and dry pass out-to-sea or a significant
storm are still on the table. Will continue to monitor trends in the
models, take a probabilistic approach and make finer adjustments
once the global models/ensembles show more congruence. For now, kept
PoPs in the higher end of Chance range for both days. The other
aspect to keep in mind is that, provided we see a storm track
favoring prolonged onshore flow, sea surface temperatures are still
in the 50s and that maritime air could also significantly dictate
durations of rain vs snow. Something we`ll be continuing to monitor,
so keep abreast with the latest forecasts/changes as we move through
the next few days.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:

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

06z TAF Update:

Through 12z Saturday: Moderate confidence.

Mix of OVC MVFR to VFR ceilings for most of SNE, with 4-6 SM
rain from FIT to EWB south and east. Rain will gradually pivot
southward and start to fill into the interior as the early
morning progresses, with ceilings trending toward MVFR, though
could get near IFR levels for the eastern coast. Light E/NE
winds become N/NW and increase in speed to around 5-10 kt thru
daybreak.

Today: Moderate confidence.

MVFR ceilings/perhaps IFR at times near the coast, with periods
of rain thru the morning hrs. Rain and lower ceilings could
linger into the aftn for eastern airports before trending all
VFR later in the day. By late morning to the afternoon, expect
a rapid increase in NW winds and gusts, peaking later in the day
around 25-35 kt in gusts. Gusts could get near 40 kt near the
interior high terrain.

Tonight: High confidence.

SCT-OVC VFR ceilings. Gusty NW winds around 25-35 kt.

Sunday: High confidence.

VFR. Gusty NW winds 25-35 kt continue into the morning hours,
although NW gusts should ease to around 20-25 kt thru the aftn.

KBOS Terminal...Moderate confidence in TAF. MVFR ceilings with
4-6 SM rain will continue into the early aftn; ceilings could
get near IFR this morning but MVFR should predominate. Rain
gradually pulls away into the rest of the aftn with gradual
improvement toward VFR. Gusty NW winds develop around 16-18z,
with gusts around 35 kt which continue into the evening.

KBDL Terminal...Moderate confidence in TAF. BKN/OVC VFR and dry
initially, but MVFR ceilings and rain develops around the pre-
dawn hrs with increasing N/NW winds. Rain pulls away by late
morning, but NW winds then increase and become gusty, around
25-35 kt, which continue into the evening.

Outlook /Sunday Night through Wednesday/...

Sunday Night through Monday: VFR. Breezy.

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

Tuesday: MVFR/IFR conditions possible. Breezy. RA likely.

Tuesday Night through Wednesday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels:

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

Tonight through Saturday night...High Confidence.

* Gale Warnings Sat afternoon and night

Low pressure east of the Benchmark will rapidly intensify as it
lifts northward tonight into Sat. In response...ESE winds at 5 to 15
knots early this evening will shift to the NE later tonight and NW
by daybreak Sat. These winds will also begin to increase and with
the strong pressure gradient developing expecting NW wind gusts of
30-40 knots Saturday afternoon and night. Gale Warnings have been
hoisted for all our waters over this time.

Outlook /Sunday Night through Wednesday/...

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

Monday: Winds less than 25 kt. Local rough seas.

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

Tuesday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas locally approaching 5 ft. Rain likely.

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

Wednesday: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Rough seas up to 9 ft.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Gale Warning from 11 AM this morning to 4 AM EST Sunday for
     ANZ230-236.
     Gale Warning from 11 AM this morning to 7 AM EST Sunday for
     ANZ231>235-237-250-251-254>256.

&&

$$

SYNOPSIS...Loconto/RM
NEAR TERM...Frank
SHORT TERM...Frank
LONG TERM...Loconto
AVIATION...Loconto/RM
MARINE...Loconto/RM