007
FXUS61 KBOX 121104
AFDBOX

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

.SYNOPSIS...
A few isolated showers/thunderstorms today will be followed by
more widespread showers and thunderstorms tonight into Saturday. Hot
and humid weather returns for Sunday into the middle of next
week. Afternoon Heat Indices in the 95-100+ degree range are
likely...which will eventually require Heat Headlines. While
Sunday is dry, the risk for scattered showers and thunderstorms
will exist in the Monday through Wednesday time frame...but
plenty of dry weather expected over this time period too.
Appears the heat and humidity finally will break by Thursday and
Friday.&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

345AM Update

Today

Offshore stalled frontal boundary moves back onshore this
morning/afternoon with a plume of 2+ inch PWATs. A modest low-level
jet may trigger a few isolated showers/thunderstorms this afternoon,
but with little no shear in the atmosphere any thunderstorms would
be short-lived and sub-severe. Otherwise most areas should
experience another hot/humid day with a mix of sun and clouds. Once
again cloud cover will be more persistent over the south coast,
Cape, and Islands. High temps generally in the upper 80s across the
region. With dewpoints rising back into the mid 70s this will
translate to heat indices in the low 90s. Steady southwest winds
around 10 mph.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
Tonight and Tomorrow

Short-wave energy approaching from The Great Lakes region will
introduce a heavy rainfall threat to southern New England tonight
into tomorrow. The atmosphere will be ripe for heavy rainfall with
PWATs up to 2.2 inches which is nearly 3 standard deviations above
normal. Warm cloud layer depths will be greater than 10000 feet
which is usually a good indicator for more efficient rainfall
processes. Even during the overnight hours with a lack of heating,
there will be a sufficient amount of instability to work with with
MLCAPE values exceeding 200 to 300 J/kg during the overnight hours,
so rumbles of thunder will be likely as well.

As far as timing for heavy rainfall goes, the latest suite of hi-res
model guidance suggests heavy downpours may begin to trickle into
western MA and CT a few hours before sunrise Saturday morning.
Expect showers and thunderstorms to continue east into eastern MA
and RI during the mid to late morning hours. Signals for excessive
rainfall are rather robust from the 00Z HREF with some 10 to 20
percent probabilities of 6 hour rainfall exceeding 100 year average
return intervals (ARIs). Furthermore, the HREF localized probability
matched mean QPF product is highlighting the potential for as much
as 5 inches of rain over localized areas. There is considerable
uncertainty with respect to which locations will experience the
heaviest rainfall, but generally all of southern New England will be
at risk, especially the urban areas. Given the strong signals for
heavy rainfall, we`ve raised a flood watch for all of southern New
England minus The Cape/Islands from 2AM Saturday to 8PM Saturday.
Activity should begin to wane by mid-afternoon on Saturday and
eventually clear our by Saturday evening. The atmosphere will remain
warm and muggy during this time, but with extensive cloud cover for
much of the day on Saturday, high temperatures should be confined to
the low to mid 80s.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Key Points...

* Hot & Humid Sun through Wed with Heat Indices 95-100+
* A round or two of scattered showers/t-storms sometime Mon/Tue/Wed
* Relief from the heat & humidity likely Thu & Fri

Details...

Upper level ridging in the Atlantic will continue to result in above
normal height fields across southern New England for the first half
of next week. In addition...shortwave energy dropping into south
central Canada will generate modest westerly flow aloft. The result
will be above normal high temperatures in the upper 80s to the
middle 90s in the Sun through Wed time frame...at least away from
any localized marine influences near portions of the immediate
coast. This coupled with humidity should result in afternoon Heat
Indices of 95-100+ degrees...so Heat Advisories will be needed for
much of this time.

Surface ridging should generally result in mainly dry weather on
Sunday. However...there will be the potential for a round or two of
scattered showers and thunderstorms in the Mon through Wed time
frame. Fast zonal flow makes this tough to time...but appears the
greatest risks for more widespread convection will be Mon
afternoon/evening and Wed afternoon/evening but timing certainly
subject to change. This will be typical summertime activity...where
much of this period features dry weather...but the risk for some
showers and t-storms especially during the afternoon and evening
hours will be possible. Appears that we may also have some sort of
remnant EML around too...so there will be a threat for severe
weather depending on timing and if winds are strong enough aloft.
The CSU Machine Learning probs do indicate some modest severe
weather probs as well for this time range. So certainly something
will have to monitor in the coming days.

Guidance is in fairly good agreement that amplifying shortwave
energy in eastern Canada will result in lowering height fields along
with relief from the heat and humidity by Thu and Fri.

&&

.AVIATION /11Z FRIDAY THROUGH TUESDAY/...
Forecast Confidence Levels:

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

12Z TAF Update:

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. Improvements 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
deteriorate 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/...

Saturday Night: VFR. Slight chance SHRA.

Sunday through Sunday Night: VFR.

Monday: Mainly VFR, with areas MVFR possible. Breezy. Chance
SHRA, chance TSRA.

Monday Night: Mainly VFR, with local MVFR possible. Breezy.
Slight chance SHRA, slight chance TSRA.

Tuesday: Mainly VFR, with areas MVFR possible. Breezy. Chance
SHRA, chance TSRA.

&&

.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/...

Saturday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Slight chance of rain showers. Local
visibility 1 to 3 nm.

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

Monday: Winds less than 25 kt. Seas locally approaching 5 ft.
Slight chance of rain showers, slight chance of thunderstorms.

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

Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Slight chance of rain showers, slight chance of thunderstorms.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Flood Watch from late tonight through Saturday evening for
     CTZ002>004.
MA...Flood Watch from late tonight through Saturday evening for
     MAZ002>021-026.
RI...Flood Watch from late tonight through Saturday evening for
     RIZ001>007.
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-
     255.
     Small Craft Advisory until 8 AM EDT Saturday for ANZ256.

&&

$$

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