214
FXUS61 KBOX 120545
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
145 AM EDT Fri Jul 12 2024

.SYNOPSIS...
Mainly dry and sunny Friday outside a few isolated showers and
thunderstorms possible during the afternoon. A frontal boundary
dropping south will bring showers and embedded thunderstorms to the
region sometime Friday night into Saturday with localized torrential
rainfall possible. Hot and humid weather returns for Sunday
into at least the middle of next week leading to high heat
indices. Heat-related headlines are likely to be needed for
portions of this period of time. While Sunday is dry, the risk
for daily thunderstorms increases Monday through Wednesday.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
950 PM Update...

* Dry overnight other than a few showers near the Cape/Islands
* Overnight low temps in the upper 60s to the lower 70s

Subtle upper level ridging building into the region will result
in generally quiet weather overnight. Southwest flow aloft and
a left over low level jet/lingering moisture may result in a
few showers impacting the Cape/Islands overnight...but dry
weather should prevail elsewhere. Overnight low temps should be
in the upper 60s to the lower 70s...still quite mild but an
improvement over the last few nights with slightly lower
dewpoints.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/...
Tomorrow

The stalled front retrogrades back inland tomorrow as a weak
shortwave traveling through the SW flow approaches the region from
the south. This could set off a couple of isolated showers and
thunderstorms in the late morning to early afternoon with MUCAPE
values AOA 1000 J/kg. There is little to no sfc-6km shear with weak
mid level lapse rates which will keep severe weather from occurring
with any thunderstorms that form. There could be some heavy rain
with any showers or thunderstorm with PWATS around 1.8-2.0 inches
and warm cloud depths around 11kft. With little to no shear,
updrafts will not be able to sustain themselves for long or cause
training, therefore, not expecting a flash flood threat. High temps
tomorrow remain in the mid to upper 80s with dewpoints increasing
back into the low 70s.

Tomorrow Night

The weak shortwave in the SW flow moves through overnight along with
increasing moisture. Widespread rain with embedded thunderstorms are
possible overnight, however, guidance remains mixed on exact timing
and placement, with some hi-res guidance showing rain holding off
until late Saturday morning. With PWATS increasing AOA 2.0 inches
and better forcing to bring possibly multiple rounds of heavy
showers and thunderstorms, flash flooding could become possible
esspically in urban and poor drainage areas. Overnight lows continue
the above normal trend stay in the low 70s region wide.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Highlights:

* Showers and embedded t-storms continue into Sat; heavy downpours
  with potential for localized flash flooding is possible, but still
  uncertain which area(s) may see the heaviest rains. Humid but not
  as warm (highs mid 80s).

* Hot and Humid weather returns Sunday through Wed, with high heat
  indices looking likely. Heat headlines seem likely to be needed
  for portions of this timeframe.

* Dry weather most of the time, but a risk for daily t-storms
  Mon thru Wed, lingering into southeast New England Thurs.

Details:

Saturday:

Carrying over from Fri evening, Sat looks generally active as a
deamplifying shortwave disturbance over the Gt Lakes region
interacts with disorganized subtropical energy from the northern
Bahamas. Substantial moisture advection (PWAT values 2 to 2.25" per
model ensemble consensus, which is about 2 to 3 standard deviations
above normal) will be associated with this interaction and favor
periods of rain, some locally heavy at times. Rather deep warm cloud
depths favoring efficient warm-rainfall processes as well as the
passage of a 300 mb jetstreak of 60 kt, with Southern New England
placed in the equatorward entrance region of that jet leading to
some enhancement to upward vertical motions, are factors which could
favor heavy rain in some areas. From a synoptic perspective, it
seems to be a pattern favorable for heavy rainfall somewhere in the
region; this is seen by some pretty notable QPF bullseyes in the
deterministic solutions. However there still is a bit of uncertainty
on where the heaviest rains would be more favored; GEFS/EPS ensemble
QPF percentiles and probabilities seem to favor the western MA/CT
area in particular, but there are still some members which bring
local maxima in rainfall to central and southeastern portions of
Southern New England. PoPs were increased into the Likely range for
Sat with a gradual shift south and east through the daytime hrs,
while generally drying out/shifting into the coastal waters by
evening. It looks to be a pretty soggy start to the weekend, and
while temps are in the mid 80s, dewpoints in the mid 70s will make
it continue to feel quite muggy.

Sunday through Thursday:

Very warm to hot and humid weather again resumes for this period.
Steady warming trend to temperatures are expected, with the peak of
the heat being on Tue. It is looking like high temps are in the
lower to mid 90s (low to mid 80s South Coast, Cape and Islands) with
dewpoints in the mid 60s to lower 70s, leading to the risk for high
heat indices. At the moment it is looking like heat indices could
reach levels which would support heat headlines being needed, with
little nighttime relief. While Sunday looks generally dry, there is
potential for t-storms Mon thru Wed. It isn`t clear if severe
weather is favored in that timeframe, although the trained machine
learning datasets from Colorado State show lower probs for severe
weather in the Days 5-7 period. This added cloud cover could add a
level of uncertainty as to how high heat indices get; regardless,
hot and humid weather resumes with heat indices also on the rise for
late in the weekend into at least the middle portion of next
week.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
Forecast Confidence Levels:

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

06Z TAF Update:


Through 12Z...High Confidence

Continued VFR across the interior with IFR/MVFR over The
Cape/Island terminals. A stray shower possible near the south
coast, Cape, and Islands. Steady southwest winds around 10 knots.

Friday...Moderate Confidence

VFR with the exception for the Cape and Islands once again could
still be stuck in MVFR/IFR. Low chance for isolated showers and
thunderstorms in the afternoon. Steady southwest winds around 10
knots.

Friday Night...Moderate Confidence

MVFR with localized IFR possible. Widespread rain and
thunderstorm chances increase between 06Z and 12Z from west to
east.

Saturday...Moderate Confidence

MVFR/IFR ceilings through about 18Z for the interior with
periods of heavy rainfall and embedded thunder. Imporvements to
MVFR after 18Z. MVFR/IFR ceilings linger over The Cape/Islands
for most of the day.


KBOS TAF...Moderate confidence in TAF.

VFR today with generally SCT cloud decks around 040-060 feet.
Low chance for a stray shower or thunderstorm. Conditions
deterirorate to MVFR after 06Z as areas of heavy rainfall begin
to overspread southern New England. Expect conditions to improve
after 18Z Saturday.

KBDL TAF...Moderate confidence in TAF.

VFR today with a low chance for a stray shower or thunderstorm.
Conditions deteriorate over night as areas of heavy rainfall
move over the region. Expect improvements by late morning/early
afternoon Saturday.

Outlook /Saturday Night through Tuesday/...

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

Saturday: MVFR/IFR conditions possible. Chance SHRA, slight
chance TSRA.

Saturday Night: VFR. Slight chance SHRA.

Sunday through Sunday Night: VFR.

Monday: VFR. Breezy. Slight chance SHRA, isolated TSRA.

Monday Night through Tuesday: VFR. Breezy. Slight chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Marine

Tonight though Tomorrow Night

Winds remain gusty out of the SSW tonight up to 25 knots through
tomorrow afternoon. Waves begin decreasing through tomorrow night
back to 4-5 feet for the outer waters, and 2-3 feet for the
near coastal waters. With decreasing waves, will allow the high
surf advisory to expire tonight and will not reissue for
tomorrow.

Outlook /Saturday Night through Tuesday/...

Friday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of rain showers.

Saturday: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain showers.

Saturday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Slight chance of rain showers.

Sunday through Sunday Night: Winds less than 25 kt. Seas
locally approaching 5 ft.

Monday: Winds less than 25 kt.

Monday Night: Winds less than 25 kt. Seas locally approaching
5 ft.

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 11 AM EDT this morning for
     ANZ232>235-237.
     Small Craft Advisory until 8 AM EDT this morning for ANZ250.
     Small Craft Advisory until 9 PM EDT this evening for
     ANZ254>256.

&&

$$

SYNOPSIS...Loconto/KP
NEAR TERM...Frank
SHORT TERM...KP
LONG TERM...Loconto
AVIATION...Loconto/RM
MARINE...Loconto/KP