506
FXUS61 KBOX 170007
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
807 PM EDT Fri Aug 16 2024

.SYNOPSIS...
Dry weather continues for the region Saturday. A slow moving
front will lead to unsettled weather with showers and isolated
thunderstorms Sunday evening through Monday night.  Sunday
through Tuesday. A drying trend with seasonable temperatures are
expected for the middle of next week. Meanwhile, Hurricane
Ernesto will track well southeast of New England, but it will
bring rough surf and strong rip currents to south-facing ocean
beaches this weekend.

&&

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

8PM Update...

Haze from wildfire smoke has resulted in near total obscuration
of the sky this evening even after lingering stratus dissipated.
While smoke will become less visible after sunset, visibility
will fall as fog develops. HRRR smoke suggests near identical
conditions are expected tomorrow so took the opportunity to add
haze to the weather grids for tomorrow. Estimating that
widespread vsbys of 5-6SM will be observed.

300 pm update...

Other than a few light showers across the Berkshires, dry
weather prevails. Still areas of stratus/low clouds across the
east that should clear out just in time for sunset. Given the
light flow regime we are in, the airmass isn`t any different
than last night, so we should see another round of stratus/fog
develop across most of the area before midnight. Could be some
areas with visibility dropping below 3/4 mile. Overnight lows
should be in the 60s.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
300 pm update...

Forecast uncertainty for tomorrow will be how quickly the
stratus and fog dissipates. Given another day with light winds,
it could very well be until noon/early afternoon before it all
dissipates. This in turn could have impacts for how warm it
gets. Went with the guidance blend for highs, so most of the
region should be into the lower 80s. With light winds, sea
breezes will prevail along the coast, keeping temperatures in
the 70s.

As we go into Saturday night, a slow moving frontal system to
our west will start to spread clouds and increasing moisture
into our region. We could see a few showers move into far
western areas late at night. Not looking for any significant
rainfall however.

The prime concern will be the arrival of long-period S to SE
swells from distant Hurricane Ernesto. We have raised a headline
for High Risk for Rip Currents for south facing beaches along coastal
RI, Cape and Islands. This is for the entire weekend. We may
need to expand that to cover the coast of Cape Ann as well. In
addition to the expected stronger rip currents, surf heights
will be elevated. Those heading to the beaches this weekend
need to heed the advice of local lifeguards and beach patrols.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
300 pm update...

Highlights
* Late afternoon and evening showers develop Sunday, with a chance
  for an isolated thunderstorm

* Best chance for widespread precipitation comes Monday with a cold
  front swinging across southern New England

* Dry, tranquil, and seasonable conditions develop mid next week


Sunday and Monday...

Mid level ridging gradually moves east of southern New England
during the wee hours of Sunday, though it`s slow movement towards
the Atlantic should yield mainly dry conditions for at least the
first half of the day. Warm front lifting ahead of approaching
trough, pushing into the northeast from the Great Lakes, will
likely result in some prefrontal scattered afternoon showers by late
Sunday afternoon. Shower chances will be greatest across the
terrain/interior of SNE, and a rumble of thunder or two can`t be
ruled out either. Will note, however, that the actual warm front
will fall short of our region before sunset, with the greatest
instability remaining to our southwest across southern NY/NJ/PA,
which should mitigate the chance for severe weather. CSU Machine
Learning probabilities have actually removed the threat for any
damaging wind from our region through 12Z Monday that was present in
yesterday`s forecast, though does show both low tornado and wind
probabilities to our south and west across PA/NY/NJ. Something that
we will need to keep an eye on should the timing of the front change
by a few hours.

Showers become more numerous overnight Sunday into Monday as
trough/cold front are finally able to push into the region.
Preceding warm front lifts north into northern New England which
will allow PWATs to climb to ~1.50"; while moist, nothing to write
home about for mid-August. Anticipate the greatest amount of rain
will fall across interior MA and CT where the GEFS/ECMWF/GEM
probabilities highlight a 30-40% chance of 1" of rain to fall during
the 24 hour period ending Monday night. QPF probabilities fall off
considerably the further east you are in our CWA, with the chance
for 24 hour QPF to exceed a half inch hovering around 20-40% across
eastern MA. Overall, not looking like this will be a significant
rain event, and continue to suspect, as the previous forecaster
stated, the chance for severe thunderstorms remains low with a lack
of shear and significant instability.

Tuesday and Beyond...

Cold front should be east of the region by late Tuesday, which will
result in an early fall airmass filtering into the region; dewpoints
are expected to fall back into the 50s by late Tuesday evening.
Strong ridging develops across the central CONUS by mid week but the
northeast looks to remain on the eastern edge of the ridge, with
resulting prolonged NW flow. Thus, expecting a very pleasant,
tranquil mid to late week with highs right around average (70s/low
80s), with low rain chances and comfortable humidity.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:

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

00z TAF Updates

Overall moderate confidence.

The area is stuck in a very weak flow regime, and with no
airmass changes expected, the forecast relies on persistence.
That is, what happened last night should happen again tonight.
Thus the forecast has widespread IFR ceilings developing in the
02-06z timeframe. Guidance also indicates that MVFR visibilities
should be fairly widespread. Could drop to IFR in some
locations (ORH, the Cape & Islands). Guidance was not showing
much fog in northern CT, so went along with that, but it`s
possible that forecast does not work out. The low clouds and fog
should slowly dissipate tomorrow morning, and in general VFR
conditions should be developing after 14z. However, like today,
that may end up being later than currently expected.

For Saturday night, we may see some additional stratus/fog
developing in the east to produce some MVFR conditions. May also
have some showers late at night across the far western areas.

KBOS TAF...Moderate confidence. Expecting IFR conditions to
develop overnight, probably similar in timing to last night.

KBDL TAF...Moderate confidence. Should have MVFR ceilings
develop late tonight, perhaps IFR. Uncertainty as to the
development of any fog, though if there is, believe 3-5SM would
be the result.

Outlook /Sunday through Wednesday/...

Sunday: Mainly VFR, with local MVFR possible. Slight chance
SHRA, isolated TSRA.

Sunday Night: Mainly VFR, with local IFR possible. Chance SHRA,
isolated TSRA.

Monday: Mainly MVFR, with local IFR possible. SHRA likely,
isolated TSRA.

Monday Night: Mainly VFR, with areas MVFR possible. Chance
SHRA, isolated TSRA.

Tuesday: Mainly VFR, with local MVFR possible. Chance SHRA.

Tuesday Night: VFR. Chance SHRA.

Wednesday: VFR.

&&

.MARINE...
Forecaster Confidence Levels:

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

300 pm update...

Overall high confidence in the forecast.

Although winds will be 15kt or less over the weekend, Small
Craft Advisories are in effect for the elevated wave heights due
to the powerful swells coming in from the SE due to Hurricane
Ernesto. The swells will also be of very long period (13 to 16
seconds), so this will also result in strong rip currents and
high surf developing along south-facing coast lines. This may
also result in rough conditions at the entrances to inlets and
harbors.

Outlook /Sunday through Wednesday/...

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

Sunday Night: Winds less than 25 kt. Areas of rough seas.
Slight chance of rain showers, isolated thunderstorms.

Monday: Winds less than 25 kt. Areas of rough seas. Chance of
rain showers, isolated thunderstorms.

Monday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of
rain showers, isolated thunderstorms.

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

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

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Air Quality Alert until midnight EDT tonight for MAZ002>004-
     008>012.
     High Risk for Rip Currents through Sunday evening for MAZ022>024.
RI...High Risk for Rip Currents through Sunday evening for RIZ006>008.
MARINE...Small Craft Advisory from 1 PM Saturday to 8 PM EDT Sunday for
     ANZ235-237.
     Small Craft Advisory from 7 AM Saturday to 8 PM EDT Sunday for
     ANZ254-255.
     Small Craft Advisory from 4 AM Saturday to 8 PM EDT Sunday for
     ANZ256.

&&

$$

SYNOPSIS...KS/Nash
NEAR TERM...KS/Nash
SHORT TERM...Nash
LONG TERM...KS
AVIATION...KS/Nash
MARINE...KS/Nash