858
FXUS61 KBOX 150533
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
133 AM EDT Sun Sep 15 2024

.SYNOPSIS...
Dry weather with above normal temperatures will continue for
the weekend and into next week. Chances for rain comes mid to
late next week, but uncertainty remains high.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Update: 10:30PM

In general our forecast remains on track, did modify the sky
cover as the marine stratus that moved on shore earlier this
evening did dissipate in many locations, leaving behind a few
to scattered group of lower clouds. Heading into the overnight
hours this will remain our biggest challenge, which will have
the more significant impacts for aviation; cloud base forecast.

Temperature continue to slowly fall, following the trend from
earlier this evening, at this time did not deviate from original
forecast. Will be interesting as cloud cover isn`t as expansive
although if you look at the nighttime microphysics can see some
stratus trying to develop along the Sea Coast of NH which has
started to move south into NE MA.

745 PM Update...

Ocean stratus already working its way inland across eastern MA.
Have significantly increased sky cover in latest update as
latest NAMNest handling current situation quite well. Should see
the stratus/fog overspread much of central/eastern MA and RI.
Only unsure in how widespread the fog will be as haven`t yet
seen visibilities falling as of this update. Temps looked to be
on track, but may need to increase them in future updates
especially where stratus is quite widespread.

Previous discussion...

High pres remains in control tonight as it builds south from
northern New Eng. This will provide dry weather, but will have to
monitor potential stratus and fog moving westward from the ocean.
There are mixed signals in the guidance regarding the extent of
stratus and fog so confidence is not high. Soundings do show very
shallow moisture near the ground below the inversion so we are
continuing increased cloud cover for areas of stratus overnight.
Lows will range through the 50s with light winds.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/...
Sunday...

Any stratus and fog should burn off by mid morning as shallow
moisture mixes out, leading to another day with lots of sunshine and
warm temps as deep later ridge builds across New Eng. However, low
level temps are a bit cooler across eastern New Eng as the surface
high pres builds to the east with persistent E flow. Highs will
range through the 70s (coolest eastern MA coast) with lower 80s in
the CT valley. It will also be a bit drier with dewpoints in the
50s.

Sunday night...

High pres will bring mostly clear skies and light to calm winds
leading to good radiational cooling. Lows will bottom out in the
lower 50s for much of the region, with some upper 40s in the colder
spots in eastern MA.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Highlights

* Dry and quiet weather to start the week with a few more mild
  days along with cool nights. AM fog possible.

* Turning unsettled mid to perhaps late in the week.
  Considerable uncertainty to the exact track of a system off
  the coast of the Carolinas. This brings the next shot for
  showers and more seasonable temperatures.

Monday through Tuesday...

A highly amplified ridge axis will initially (Mon AM) be in
place from the Great Lakes region through New England into the
central Atlantic, while there is a disturbance just off the
Carolinas coastline. The ridge gradually builds offshore
beginning late on Mon, but especially on Tue. The disturbance
off the Carolinas coast will rotate inland into the Mid
Atlantic/OH Valley into Tue. High pressure builds overhead on
Mon before shifting offshore Mon night into Tue, but still
nudges into the region.

Dry and quiet weather anticipated through this timeframe with
high pressure continuing to dominate the weather. Big question
for both AMs will be the stratus/fog development. Given the
E to SE/S increase in moisture this should really amplify the
risk, especially on Tue. Think on Mon would most likely be
radiation fog. High temps both days ranging from the 70s to mid
80s.

Wednesday through Friday...

Ridge axis continues to shift further offshore, with a broad
trough/upper low overhead from the disturbance previously
mentioned. Overall not certain how things will evolve with this
feature with how north it traverses and if/when it dives further
south. At this point have fairly heavily leaned toward the
latest NBM guidance given the uncertainty.

This is likely the next opportunity for more widespread rain
showers. The big question is how far north/northeast does the
upper low lift and the moisture plume associated with it. There
are considerable differences amongst deterministic guidance at
this point with the GFS/GEM bringing the 1.5 to 2+ inch PWATs
overhead Wed into Thu, whereas the ECWMF keeps this moisture
locked more to the south of our region. Warm cloud layer depths
would be between 3-4.5 km, which would bring more warm rain
processes, though there appears to be little instability to work
with at this point. Both the NAEFS/EPS guidance showing a tight
PWAT gradient as well per the Situational Awareness Table, but
the elevated 1.5-2 STD anomalies generally remain to our south.
Can also see differences between ensemble systems where the GEFS
generally keeps any heavier precip to the south as opposed to
the GEPS/EPS. There are nil probs of 24 hr QPF AOA 1" for the
GEFS guidance through this timeframe for southern New England,
whereas the GEPS/EPS have low (10-30 percent) probs. Something
to keep an eye on in the coming days.

Given the prolonged easterly flow during this timeframe will see
our temps generally near to cooler than seasonable.

&&

.AVIATION /05Z SUNDAY THROUGH THURSDAY/...
Forecast Confidence Levels:

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

06z TAF Update:

Through 12z...Moderate confidence in trends and timing.

VFR, with periods of IFR/LIFR between 06z-12z as low stratus and
pockets of fog develop across the eastern half southern New
England. Guidance has been more hit-or-miss with the ceilings
for the first part of the overnight, and do think TAF sites
will bounce between flight categories, IFR to VFR, with no in-
between through 12z. Light to calm winds.

Today...High confidence.

VFR. East winds 5 to 10 knots, becoming southeast later in the
day.

Tonight...High confidence in trends, moderate in timing.

Mainly VFR, but patchy late night IFR fog/stratus may develop
in the CT valley. Light to calm winds.

Monday... High confidence.

VFR. South winds 5 to 10 knots.

KBOS TAF...Moderate confidence through 12z, high confidence
there after.

VFR with LIFR cigs nearby at KOWD. Do think the lower ceilings
and vsby remain away from the terminal, although not our of the
question. Given the intermittent of lower flight categories did
opt for a TEMPO 08z-11z for IFR conditions. Rapidly becoming
VFR after 12 with NE to E winds this morning to early afternoon,
and then winds become SE late afternoon.

KBDL TAF...High confidence.

VFR. Calm winds through 12z to 14z and then becoming light from
the E, it is possible to have some low ground fog develop but
should not lead to any vsby restrictions. Better chance for fog
tonight into Monday morning.

Outlook /Monday Night through Thursday/...

Monday through Tuesday: VFR.

Tuesday Night: VFR. Slight chance SHRA.

Wednesday through Wednesday Night: Mainly VFR, with local IFR
possible. Chance SHRA.

Thursday: MVFR/IFR conditions possible. Slight chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Through Sunday night: High Confidence.

Tranquil boating conditions with winds, mostly E-SE, and seas below
SCA levels. Vsbys may be reduced in developing fog overnight.

Outlook /Monday Night through Thursday/...

Monday through Tuesday: Winds less than 25 kt.

Tuesday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain showers.

Wednesday: Winds less than 25 kt. Seas locally approaching
5 ft. Chance of rain showers.

Wednesday Night through Thursday: Winds less than 25 kt. Areas
of seas approaching 5 ft. Chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

$$

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