059
FXUS61 KBOX 121412
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1012 AM EDT Thu Sep 12 2024

.SYNOPSIS...
High pressure will continue to dominate our weather through at
least the middle of next week. Although there is a low chance
at a shower or thundershower in northeast Massachusetts on
Friday, largely dry weather and above average temperatures will
prevail across Southern New England for the foreseeable future.

&&

.NEAR TERM /THROUGH TONIGHT/...

10 AM Update:

Quiet weather this morning with the forecast remaining on track
for today. No major updates needed to the previous forecast.
Made some minor adjustments to temperatures and dewpoints due to
a cooler start in the valleys with fog around this morning.
Forecast is still on track for a warm, sunny Sept. day.

7AM Update:

The forecast continues on track and no modifications were made
to the near term. As of 7AM patchy fog continues to erode
across the Connecticut River Valley and parts of Cape Cod and
the adjacent islands. Should see any lingering fog disperse
over the next one to two hours.

Previous forecast discussion below.

230 AM Update:

High pressure remains established in the waters just east of
Provincetown early this morning bringing another night of
strong overnight radiational cooling. Currently MVY is the
coldest spot in the mid 40s, as is typical on strong radiational
cooling nights. Temps were generally coolest (upper 40s to low
50s) in southeast New England, with lower to mid 50s more common
elsewhere. Although fog has again developed in the CT River
Valley, there`s been some fog at times at Nantucket and at New
Bedford but it`s been more intermittent at these latter
locations. We could see additional development thru sunrise but
should be pretty temporary.

So for today, high pressure over the waters will lurch
southeastward but still be nearby Southern New England and will
maintain dry weather again today. There could be a little more
cloud cover than the past couple days, (and by "a little more",
more of a partly to mostly sunny look vs the bluebird skies the
last few days) especially to the north as a low-amplitude mid-
level shortwave trough seen on water vapor satellite imagery
near southwest Quebec moves across northern New England. A
surface trough developing in association with this mid-level
wave looks to develop in the lee of the White Mtns, and that
should support a hybrid synoptic onshore flow/seabreeze over
eastern and northeast MA today. While it should be pretty mild
today in many areas, ended up incorporating some of the
Canadian-GEM Regional guidance to show the relatively cooler
onshore flow over the North Shore/Essex County area.

Highs today should reach well into the 70s to the lower 80s for
most, with cooler mid 70s along the south coast and the North
Shore area from the seabreeze/onshore flow.

&&

.SHORT TERM /FRIDAY/...
230 AM Update:

Tonight:

Another night of strong radiational cooling again anticipated
for tonight, with surface ridge of high pressure still in
control. Dewpoint temps are about 3 to 5 degrees higher than
last night, and radiation fog across a wider portion of CT-RI-
Southeast MA seems more likely tonight than the last few nights.
NAM-based guidance hits this potential the hardest but most
available visby guidance sources show visbys in the half to 5 SM
range south of the Mass Pike. Ended up showing fog developing
after midnight for these areas, but as this moisture is really
shallow and becomes trapped under a strengthening temperature
inversion, it is less certain if fog develops when it might
dissipate. Lows mainly in the 50s, given milder daytime highs
and milder 925-850 mb temps.

Friday:

Although the general theme of warming temps and generally dry
weather for most of Southern New England will continue into
Friday, there are a couple things that we`ll need to monitor
with subsequent guidance.

The first is when any nighttime fog/stratus over the southern
roughly half of the forecast area dissipates. As mentioned
above, fog becomes trapped underneath warming temps aloft;
although I opted for dissipating fog by sunrise with how dry it
has been, BUFKIT profiles indicate if fog develops it may not
fully dissipate until mid to late morning. Thereafter, full sun
should bring highs to above normal levels, in the upper 70s to
the mid 80s, with mid 70s for the Cape and Islands.

The other aspect of the forecast that will need to be monitored
is if we can pop a shower or thunderstorm or two over the
Merrimack Valley/North Shore area (or, move off the White Mtns
in NH and move SE to these areas) after 3 PM til sundown. Most
guidance shows a digging shortwave trough over northeast Quebec
into the Gulf of Maine, rotating around an anomalously strong
(590 dm) upper level ridge over the U.P of MI. Associated with
this feature is a plume of pretty steep lapse rates between
850-500 mb which are around 7-7.5 C/km, but also is pretty
capped, midlevels are dry and there isn`t much of a lifting
source other the mesoscale wind effects such as seabreezes.
Despite this, high res guidance sources (NSSL WRF, Canadian GEM
Regional, WRF FV3, NAM-3km) as well as the global GFS show some
pop-up convection in northeast MA. Thinking drier weather
prevails, but opted for a 15% PoP for thunderstorms in northeast
MA Friday afternoon; its possible if anything develops it could
make it near the Boston area and possibly bring the first
measurable (non-trace) rain since August 20th.

&&

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

* Moderate confidence in areas of low stratus forming late Friday
  night into Saturday morning across coastal areas, which may lead
  to patchy drizzle.

* Otherwise, very quiet weather continues this weekend into next
  week with no appreciable rainfall during the forecast period.

* Temperatures are comfortable with slightly above normal highs and
  seasonably cool overnight lows.

Very quiet weather continues across the northeast for this weekend
through potentially Wednesday or Thursday of next week. Why? The
northeast is under the influence of a mid-level ridge and surface
high-pressure. While no rain is in the forecast, low-level moisture
may become trapped below the subsidence inversion overnight Friday
into Saturday morning and possibly lead to low stratus and drizzle
for areas along the coast in eastern Massachusetts and Rhode Island.
Will say, have moderate confidence in this occurring, the tough part
are the exact areas where this may develop. Perhaps there will be
greater confidence as the near term/high resolution begin to reach
this portion of the forecast. If the low stratus develops, it may
take as late as noon time to fully lift due to the declining sun
angle. Otherwise, dry weather prevails, with the best chance for any
rain late Wednesday to Thursday. That said, 00z guidance does hint
the surface high to the north builds back south and suppresses any
tropical moisture to the south - which is supported by the global
ensembles. Probs of 0.01" in 24 hours are less than 10% right
through Thursday. Only time will tell.

Nevertheless, quiet stretch of weather continues with mild afternoon
temperatures and cooler at night. As mentioned before, the NBM does
not do well in regards to minimum temperatures on nights when there
is effective radiational cooling and blended in cooler guidance to
lower these temperatures. Normal afternoon highs for mid-September
are middle to upper 70s, as for normal night time lows, those are
mid-50s to 60F. Expect highs in the low to mid-80s and overnight
lows in the upper 40s to mid-50s.

Tropics continue to `heat up` which comes as no surprise since this
is climatologically the peak for tropical systems in the Atlantic
basin. Tropical Depression Seven located west of Cape Verde is
forecast to a Tropical Storm some point today. Closer to home, NHC
monitors an area of development off of the southeast coast of the
United States and has a 30% chance of development over the next 7
days. Fortunately for our region, strong high pressure and the mid-
level steering should keep any tropical impacts away from southern
New England.

&&

.AVIATION /14Z THURSDAY THROUGH MONDAY/...
Forecast Confidence Levels:

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

12z TAF Update:

Today: High confidence.

VFR. S winds around 3-7 kt, although becoming SE for eastern MA
around 6-10 kt by 15-16z, becoming S/SW around 22-00z.

Tonight: High confidence overall, but moderate on fog
development and coverage.

Mainly VFR along and north of the Mass Pike, although should be
a better chance for radiational BR/FG across CT-RI-southeast
MA. If fog does develop as forecast indicates it will, it may
linger until well after sunrise, but the end timing is still a
bit uncertain. Light SSW winds, calm at times.

Friday: Moderate to high confidence.

Overnight fog could linger around CT-RI-Southeast MA until 15z,
then become VFR all airports. A low (<15%) chance at a SHRA/TS
near BED or perhaps near BOS after 20z Fri until sundown, but
thinking dry weather prevails.

Tonight: High confidence overall, though is moderate on fog
development.

Mainly VFR; higher moisture levels would favor a better chance
for patchy radiation fog across portions of southeast MA and RI
and into portions of eastern CT after 06z. May need to
introduce mention of BR/FG for the Cape airports and perhaps
into PVD too with later TAFs issuances. Light SE to S winds,
calm at times. S/SW winds 5-10 kt.

KBOS TAF...High confidence in TAF. SE to SSE wind 6-10 kt
develops around 15-16z (directions closer to 140-150 than 110),
becoming S around 22z.

KBDL TAF...High confidence in TAF. VFR, although fog is more
likely after 05z Fri. If fog develops, it may linger until after
the Fri AM push period.

Outlook /Friday Night through Monday/...

Friday Night through Saturday: VFR. Patchy FG.

Saturday Night through Monday: VFR.

&&

.MARINE...
Forecaster Confidence Levels:

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

Through Friday: High confidence.

High pressure will continue remains over the waters for the
next several days. Light winds with daily sea breezes are
expected, and seas 2 ft or less expected.

Fog may develop tonight over the southern waters and near Cape
Cod Bay, which could reduce visbys to under 1 mile. There is
also a low (<15%) chance at a thunderstorm over the northeast
waters late Friday afternoon, although dry weather should
prevail.

Outlook /Friday Night through Monday/...

Friday Night: Winds less than 25 kt.

Saturday: Winds less than 25 kt. Local visibility 1 to 3 nm.

Saturday Night through Monday: Winds less than 25 kt.

&&

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

&&

$$

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