748
FXUS61 KBOX 151105
AFDBOX

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

.SYNOPSIS...
Strong area of high pressure over the northeast will continue
the dry and quiet weather through Tuesday. A subtropical low
pressure system develops off the coast of the Carolinas which
could bring our next chance of precipitation sometime Wednesday
into Thursday, although there remains uncertainty with the
overall track of the system.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
640 AM Update:

Stratus and fog has started to expand across a wider cross
section of Southern New England. Visbys in fog thus far have
been highly variable and a few spots have seen visby dip into
the quarter-mile range. Fog should become less extensive over
the next hour, although stratus could linger until the mid
morning as this moisture is trapped underneath a strong subsidence
inversion. It looks as though we should see improvement by 13z
or so per BUFKIT forecast profiles. Because of the anticipated
short duration of fog and that visbys have been flip-flopping,
opted to not hoist dense fog advisories. Did opt to add partly
to mostly cloudy sky cover in the forecast until around 10 AM.

After fog and stratus disperses, we then return to sunny and dry
weather.

Previous discussion:

Good morning. While a quiet start, the challenge with the forecast
will be around fog and low stratus. Thinking that this issue has a
shelf life through 7am to 9am. Not seeing much in the way of dense
fog, areas less than 1/4 mi, but doesn`t necessarily mean it can`t
develop. Would think areas along Rt. 2 from Fitchburg towards the
metro west of Boston and areas south along I-95 to Providence, and
the interior Bristol and Plymouth Counties. Confidence does remain
low, though if trends in lowering visibilities were to increase, a
short-fused Dense Fog Advisory could be issued to raise the
situational awareness.

Heading into this afternoon, no weather concerns, as it has been the
past several days. Sunshine is accompanied by mild temperatures in
the upper 70s and low 80s, though cooler in eastern coastal towns of
Massachusetts. Easterly flow keeps towns from Cape Ann to Cape Cod
in the lower to mid-70s. In addition, dewpoints this afternoon are
between 5 and 8 degrees cooler, so less in the way of humidity as
well.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
Update: 2:50AM

Highlights:

* Patchy areas of dense fog possible overnight and followed by
  another dry and mild afternoon for Monday.

Tonight...

With high pressure, clear skies, and light winds if not calm, do
expect a rinse and repeat forecast tonight. The forecast challenge
will continue to be how widespread any fog becomes. One of the main
difference between the last two nights and upcoming night are lower
dewpoint temperatures. With that said, feel most confident if any
fog were to develop it would do so in prone locations; ie locations
that typically radiate under clear skies and river basins. Looking
at the forecast soundings in BUFKIT, NAM and NAM3km highlights this
well. Lows tonight drop into the upper 40s to low 50s. Boston will
retain some of the daytime heat, urban heat island, with a low in
the upper 50s.

Monday...

Any morning fog disperses shortly after sunrise. With high pressure
still in place, looking at another mostly sunny day. HRRR shows the
potential for smoke aloft, which could lead to a milky color in the
sky. HREF does show high clouds moving in from north to south late
in the day as well, this is likely tied to the developing system
off the coast of the Carolinas.

Winds become south, this on shore wind along the south coast
will limit how warm we get across coastal Rhode Island and southeast
Massachusetts. Expect highs there to be in the mid 70s. Away from
the coast, temperatures reach the upper 70s to low 80s.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Update: 2:50AM

Highlights:

* Continuation of dry weather, mild days and cooler nights Mon night
  into Tue.

* Unsettled Tue night into Thurs as low pressure near the mid-
  Atlantic region could bring our next chance for showers, along
  with enhanced onshore breezes. Details are still uncertain at this
  time.

* Generally dry late this week into the weekend, although coastal
  areas may see more clouds than sun and onshore breezes. Temps
  seasonable in the interior but could be cooler than normal near
  the coasts.

Details:

Monday Night and Tuesday:

High and dry in this portion of the forecast, with an expansive
ridge of high pressure still in place. Later on Tue, the ridge axis
is progged to either shift northward and/or weaken, with a modest
increase in easterly onshore flow. All in all though, expect a
continuation of sensible wx conditions that have been something of a
broken record over the last several days: mild daytime highs with
cool nighttime lows, along with patchy radiation fog in the
typically favored spots. Lows Mon night in the 50s, with upper
50s/near 60 for the urban areas and coastlines. Highs should reach
into the upper 70s to lower to mid 80s.

Tuesday Night through Thursday:

More unsettled weather then looks to take hold in this portion of
the forecast, but there is still pretty substantial uncertainty in
the details.

An area of disturbed weather off the Carolina coast is forecast to
move NW into the Carolinas and/or the mid-Atlantic region at some
point early next week (as soon as Mon but potentially into Tue/Tue
night). NHC is monitoring this area of disturbed weather for
possible subtropical development; refer to the latest NHC forecasts
regarding this area of disturbed weather. As its circulation moves
NW through the mid Atlantic states, a portion of its moisture on its
eastern periphery advances northward into the entrenched surface
ridge that has been in place over the Northeast around the middle of
the upcoming workweek. However the global model ensembles continue
to show pretty strong diversity in outcomes both in timing and on
potential rain amounts. Looking at the individual members comprising
each ensemble system, the non-GFS based models are generally soonest
to bring this rain northward (either Tue night and/or Wed); while
the GEFS-based solutions are slower (Wed night and/or Thurs), and a
few of the GEFS members are shutouts with QPF shunted to the waters.
01z/15th NBM PoPs were generally maintained in this period, but
reduced them into the slight to low chance range Tue night, and kept
them around the 30-40% range on Wed and into Thurs, with a decrease
thereafter. Challenging forecast and still too low confidence to go
much higher or lower than those ranges.

Overall this is the next best chance at widespread rains, although
the exact details are far from set in stone. The other potential
impact will be over the waters and beaches, with an enhanced
easterly fetch bringing some enhancement to onshore flow, and wave
heights could become elevated enough to pose a risk for rip currents
on southeast-facing beach exposures into the midweek period.

Temps were left more or less unchanged from NBM guidance, but these
too will need adjustments, potentially toward a narrower diurnal
range (e.g. cooler highs and milder lows) than the forecast
currently shows.

Friday into Next Weekend:

Strong reinforcing ridge of high pressure over northeast Canada
reasserts itself over the Northeast states in this period; with low
pressure from the midweek period shifting well ESE of Georges Bank.
This could bring a period of enhanced east to northeast flow along
with cooler temps on that east to northeast flow. Thinking the
interior portions of Southern New England should be high and dry
with seasonable temps, whereas eastern/coastal areas may see cooler
than normal temps, an enhanced onshore breeze and more in the way of
cloud cover and perhaps some light showers at times.

&&

.AVIATION /12Z SUNDAY THROUGH THURSDAY/...
Forecast Confidence Levels:

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

12z TAF Update:

Today: Overall high confidence, though moderate on timing
dispersion of early-morning stratus and fog.

Stratus and fog are around with ceilings in the IFR-VLIFR range
and visbys pretty variable. Expect improvement by 13-14z for all
airports with VFR thereafter. 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...High confidence.

Should be VFR directly at the airport, but opted for a tempo
thru 14z for lower conditions nearby, especially given observed
fog and 200 ft cigs at OWD could lead to loss of side-by-side
ops. Otherwise, VFR prevails. 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. Better chance for fog tonight into Monday morning.

Outlook /Monday Night through Thursday/...

Monday Night through Tuesday: VFR.

Tuesday Night: VFR. Slight chance RA.

Wednesday through Wednesday Night: VFR. Chance RA.

Thursday: VFR. Slight chance RA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Today through Monday...High confidence.

Surface high pressure continues tranquil conditions for the
waters surrounding southern New England. Visibilities may be
reduced overnight in areas of coastal fog. Seas and winds remain
well below advisory criteria.

Outlook /Monday Night through Thursday/...

Monday Night through Tuesday: Winds less than 25 kt.

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

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

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

&&

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

&&

$$

SYNOPSIS...Loconto/Dooley
NEAR TERM...Loconto/Dooley
SHORT TERM...Dooley
LONG TERM...Loconto
AVIATION...Loconto/Dooley
MARINE...Loconto/Dooley