779
FXUS61 KBOX 242347
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
647 PM EST Sun Nov 24 2024

.SYNOPSIS...
High pressure builds into the region Monday with dry and seasonable
conditions along with diminishing winds. A frontal system passing to
our northwest on Tuesday brings another round of rain, then
blustery, cooler and dry weather returns Tuesday night and
Wednesday. Monitoring another storm system that could impact
southern New England Thanksgiving into Friday with rain, but some
accumulating snow possible over higher elevations. Turning blustery
and colder next weekend.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
645 PM update...

Mid level shortwave is moving south across SNE this evening.
Sct-bkn strato-cu will erode later this evening leading to
mainly clear skies. Gusty NW winds will continue along the
coast but will gradually diminish elsewhere overnight.

Previous discussion...

The region remains under NW flow aloft overnight with dry and cooler
air in place. The LLJ responsible for the past windy conditions the
past day or two stays positioned over the region. Without the
stronger CAA keeping lapse rates steeper, areas will be more likely
to decouple tonight resulting in lighter winds. This will be likely
for areas in the CT and Merrimack River Valleys. Winds in the higher
elevation spots may stay more elevated with gusts around 20 mph. For
the Cape/Islands, the water will act to keep lapse rates steep
enough for gusts 20-30 mph overnight. For coastal areas and east MA,
there is some question in if the boundary layer decouples or not,
but there shouldn`t be much impact either way. With lighter winds
overall compared to last night and a cooler airmass, temperatures
cool into the low to mid 30s with upper 20s in some spots.

&&

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

* Winds/gusts continue to decrease Monday afternoon

* Clear skies with seasonable temperatures Monday


Monday:

A weak mid-level ridge builds into the region Monday bringing a dry
day across southern New England. The pressure gradient continues to
weaken, resulting in a continued downward trend in wind magnitudes
across the region into tomorrow afternoon. High temperatures range
in the upper 40s to low 50s.

Monday Night:

A shortwave trough approaches the region Monday night into early
Tuesday. This will bring our next chance at a quick rainfall.
Moisture gradually increases as plume of above normal moisture
pushes in from west to east (150-200% of normal). Clouds increase in
the evening with increasing moisture/synoptic ascent into the
region. Showers increase and move across from west to east in
the 2 am to 7 am timeframe. Given the quick nature of the
system, it is more of a quick period of rainfall compared to the
event this past Thurs-Sat. More details in the long term
discussion below.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Highlights:

* Another round of beneficial rains Tue

* Cooler and blustery but dry weather for the Wed

* A storm system will likely bring rain Thanksgiving into early Fri,
  but potential for some accumulating snow over higher elevations.
  Confidence in specific details remains low.

* Drying out for the weekend, but blustery with below normal
  temperatures

Tuesday into Wednesday:

Fairly robust negative tilt shortwave will move north of the region
on Tue with a triple point low developing on a frontal boundary as
it moves into SNE. Modest low level jet will advect 1"+ PWATs
northward into SNE ahead of the boundary. Decent large scale forcing
acting on this moisture plume will deliver a period of widespread
showers to SNE, likely beginning across western MA/CT late Mon
night, then overspreading rest of SNE during Tue morning. This is a
quick moving system with a pronounced dry slot pushing into the
region from W to E after 18z, with cold front moving off the coast
21-00z. Expect a wet Tue morning, then rain should end from W to E
during the afternoon, moving off the coast by late afternoon.
Rainfall amounts of 0.2" to 0.5" are expected.

Expect a wide range of temps Tue from north to south. Warm front
expected to advance north into SNE with northward progress halted by
developing surface wave on the front. Highs will reach into the
upper 50s near the south coast which will be south of the boundary.
However, it will be much cooler to the north of the front, with
highs in the 40s north of the MA Pike and probably not getting out
of the lower 40s across interior northern MA.

Clearing and turning colder and blustery Tue night into Wed in cold
advection pattern. Wed will start out with lots of sunshine, but
high clouds will begin to overspread the region during the
afternoon. Lows will range from the upper 20s to mid 30s, with highs
Wed mostly in the 40s, ranging from near 40 northern MA high terrain
to upper 40s near the coast.

Thanksgiving Day into Friday:

There is still a large degree of uncertainty with the track of low
pres from shortwave which lifts NE from the mid MS Valley region.
GFS is weakest and most suppressed while ECMWF is stronger and
further north with track along the south coast. However, with lack
of cold high pres to the north and onshore flow ptype likely to be
mostly rain in the coastal plain, with any snow confined to the
distant interior and particularly over the higher elevations given
very marginal thermal profile.

GEFS ensembles follow the deterministic run with bulk of members
showing a storm track remaining well to the south near or south of
the benchmark which is an outcome with less QPF with rain near the
coast and light snow accum higher terrain. GEFS indicating low
probs(20-30%) of 3 inches higher terrain. ECMWF ensemble members
show storm track clustered near the SNE coast which results in a
heavier QPF event with potential for more appreciable snowfall over
higher elevations. ECMWF ensembles indicate moderate probs (40-70%)
of 3+ inches over interior MA high terrain with low probs (20-40%)
of 6 inches confined to the Berkshires. But this is the worst case
scenario outcome. Still plenty of uncertainty with potential QPF and
snow amounts in the interior, but confidence is high the coastal
plain will see mainly rain.

Timing wise, it is looking like bulk of storm will be Thu and Thu
night, with gradually improving conditions on Fri as the storm pulls
away.

Saturday and Sunday:

The storm will be in the Maritimes next weekend with much drier NW
flow leading to mainly dry conditions. It will be blustery and
colder with temps well normal as ensemble mean 850 mb temps average
-8 to -10C.

&&

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

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

00Z TAF Update:

Tonight: High confidence. Moderate for wind speeds overnight.

VFR conditions. WNW gusts to 25 kt near the immediate coast and
Cape and Islands, otherwise gradually diminishing wind.

Monday: High confidence.

VFR. WNW winds 8-12 kts with a few gusts up to 20 kts. Winds
decrease in the afternoon.

KBOS Terminal...High confidence in TAF. VFR. Gusty WNW winds
this afternoon 25-30 kts then gust speeds steadily decrease this
evening. WNW winds around 10-14 kt with a few gusts to 20 kts
overnight. Winds decrease further tomorrow (Monday) afternoon.

KBDL Terminal...High confidence in TAF. VFR, WNW gusts 25-30 kts
this afternoon, decreasing steadily later this afternoon into
the early evening. WNW winds around 10 kt early tonight
decrease to 5 kt by early Mon AM.

Outlook /Tuesday through Friday/...

Tuesday: Mainly MVFR, with local IFR possible. Breezy. RA.

Tuesday Night through Wednesday: VFR. Breezy.

Wednesday Night: VFR.

Thanksgiving Day: Mainly VFR, with local MVFR possible. Breezy.
Chance RA.

Thursday Night: Mainly VFR, with local MVFR possible. Breezy.
Chance RA, chance SHRA.

Friday: VFR. Breezy. Slight chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Sunday Night through Monday:

Winds/gusts gradually decrease late this afternoon into the
evening. Winds/seas stay in Small Craft Advisory criteria
overnight into Monday morning with winds 25-30 kts and wave
heights 5 to 8 feet. Conditions improve more on Monday with
high pressure building in from the west supporting diminishing
west/northwest winds. By Monday evening, winds/seas weaken
enough to get out of Small Craft criteria.


Outlook /Tuesday through Friday/...

Tuesday: Winds less than 25 kt. Seas locally approaching 5 ft.
Rain likely.

Tuesday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas up to 5 ft.

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

Wednesday Night: Winds less than 25 kt.

Thanksgiving Day: Winds less than 25 kt. Seas locally
approaching 5 ft. Rain likely.

Thursday Night: Winds less than 25 kt. Seas up to 5 ft. Rain
likely, chance of rain showers.

Friday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain
showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 7 AM EST Monday for ANZ230-236.
     Small Craft Advisory until 4 PM EST Monday for ANZ231>235-237-
     250-251-254>256.

&&

$$

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