373
FXUS61 KBOX 130543
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
143 AM EDT Sat Jul 13 2024

.SYNOPSIS...
Isolated showers and possibly a rumble of thunder this evening.
Heavy showers and thunderstorms likely early Saturday morning
ending Saturday afternoon. 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 /THROUGH TODAY/...
8 PM Update...

Guidance is really struggling with diagnosing the areas of
continued scattered downpours across southeast MA this evening.
Blended the NAMDNG into the PoP forecast to account for shower
activity through ~03Z this evening.

Forecast overnight looks generally dry, with shower activity
renewing sometime between 09-13Z according to CAMs, though some
light shower activity currently across the Hudson River Valley
may stream across NW MA/CT around 03Z. Did opt to trend towards
a drier forecast across the far interior of MA and
central/northern CT given guidance trending the main precip
shield a bit farther southeast over the last several model
updates. In general, think the best chance for thunderstorms and
downpours tomorrow morning will be south and east of the MA
Turnpike. Elected to keep the flood watch in place to allow the
next shift to evaluate the complete 00Z suite of guidance,
though given the lack of forcing and fast moving nature of
downpours, feel the flood threat will be more localized urban
and poor drainage flooding, especially if heavier rain/storms
set up over the PVD metro.

Tonight and Tomorrow

Weak shortwave trough approaching from the Great Lakes will send
shortwave energy and increased moisture content to the region
overnight into tomorrow morning. With PWATS climbing to 2.0 inches
and warm cloud depths approaching 13kft, there is a good chance that
any rain that falls will be very heavy with rain rates AOA
2in/hr which could cause poor drainage and urban flooding. With
MUCAPE values around 500 J/kg per the 12z HREF, there could be
embedded thunderstorms tomorrow morning as well. Rain will move
from SW to NE early tomorrow morning with the heaviest rainfall
expected between 6am to noon. Latest guidance has trended the
heaviest rainfall further south along the south coast and
Islands. There could still be localized areas that see up to 3-5
inches of rain as seen in the 12z HREF 24 hour LPMM. Opted to
leave the flood watch up for all of SNE until better run to run
consistency can be established, but may need to be trimmed back
the north end with future updates. WPC has also downgraded much
of the region from a slight risk to a marginal risk for
excessive rain which makes sense given the southward shift.

Temperatures tonight remain quite warm in the
low 70s. Trended temperatures Saturday afternoon cooler into
the low to mid 80s with the expectation that thick cloud cover
and rain will be around all morning, lingering into the
afternoon. Could see some clearing by Saturday evening
esspically across the western interior MA.

There could be a second round of isolated convection in the
late afternoon across the western interior. Not expecting
anything severe with SBCAPE values around 1000 J/kg, sfc-6km
shear around 30 knots, and bad mid level lapse rates around 5
C/km.

&&

.SHORT TERM /TONIGHT THROUGH 6 PM SUNDAY/...
Tomorrow night:

Drying out with clearing skies due to rising heights overnight.
This will allow temperatures to at least cool into the upper
60s outside urban areas. Dewpoints will remain in the upper 60s
overnight making it feel quite muggy still. With the high
dewpoints and good radiational cooling, there could be areas of
fog that form overnight.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Key Points...

* Hot & Humid through Wed with Heat Indices 95-100+

* A few rounds of scattered showers/t-storms possible during
  the first half of the week.

* A less humid airmass finally arrives by the latter half of the
  week.

Details...

While the broader western Atlantic ridge remains in place directing
anomalously hot and humid air into the region, a transient ridge in
the zonal flow Sunday will provide a break from the wet weather and
clouds leading to a warm but dry day. This zonal flow then continues
through Tuesday with the first in a series of disturbances around
late Monday into Tuesday. This will bring the chance for unsettled
weather including thunderstorms; while instability will be there,
bulk shear is limited as are lapse rates so severe storms, if any,
should be isolated. The more robust looking severe potential looks
to be around Wednesday when deeper shortwave approaches from the
Great Lakes with a good deal of instability which may align with
favorable shear values depending on timing. Something to watch at
the very least.

Temperature-wise Sunday we`ll see temps creeping back up into the
low 90s in the first of several days of steadily increasing
temperatures. At this point, given dewpoints "only" in the mid to
upper 60s and low 70s conditions are marginal for a Heat Advisory
that, if necessary, would likely be limited to more southern areas
where the dewpoints are higher. The more concerning period for
dangerous heat and humidity will be Monday and Tuesday, perhaps even
Wednesday as the airmass warms (850 mb temps rise to the 20-22C
range) and w/SW flow pushes dewpoints back into the mid to upper
70s. Thus, we`ll also see little relief overnight with low temps
limited to the low to mid 70s. Finally, though, some relief from the
humidity is on the horizon as guidance indicates a cold front around
Thursday that has the potential to drop dewpoints significantly for
the first time in over a week.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:

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

Through 12Z...Moderate Confidence

MVFR/IFR conditions persist through 12Z. Showers with embedded
thunder begin to overspread southern New England from southwest
to northeast during the hours leading up to 12Z.

Today...Moderate Confidence

Showers with heavy downpours and embedded thunder for most of
southern New England through about 18Z. Confidence in TSRA
is highest at PVD and Cape/Islands terminals. Moderate
confidence that BED/BOS will be impacted by storms near or over
the terminal between about 12-16Z. Lowest confidence in TSRA is
at BED and BDL. Conditions should begin to improve after 18Z
with VFR conditions settling in, but there is a risk for some
redevelopment of showers and storms mainly across the interior
between about 18 and 21Z. Confidence not high enough to include
mentions of thunder during this time period, but did leave VCSH
in the TAF update through 00Z.

Tonight...Moderate to High Confidence

Any remaining showers or storms should diminish shortly after
00Z. VFR across the interior with MVFR/IFR ceilings over The
Cape/Islands terminals. Winds remain steady out of the
southwest through 06Z and shift to light out of the northwest
thereafter.

Tomorrow...High Confidence

VFR. Light northwest winds becoming more westerly during the
afternoon. Winds may be weak enough to support sea-breezes along
the coast.


KBOS TAF...Low to Moderate confidence in TAF.

Conditions deteriorate to MVFR through 12Z. Showers with heavy
downpours and embedded thunder are expected to be in the
vicinity of the terminal this morning, but there is a chance the
greatest activity could stay to the south. Improvements to IFR
likely after 18Z.

KBDL TAF...Moderate confidence in TAF.

MVFR/IFR ceilings this morning. There is a risk for showers with
heavy downpours and embedded thunder to be in the vicinity of
the terminal, but latest model guidance has been trending toward
shower/thunderstorm activity staying to the south and east of
BDL. Nonetheless, a risk still remains so we included a PROB30
group for TSRA between 10-14Z. Improvements to VFR likely after
16Z.

Outlook /Sunday Night through Wednesday/...

Sunday through Sunday Night: VFR.

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

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

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

Wednesday: VFR. Breezy. Chance SHRA, isolated TSRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Marine

Tonight through Saturday night

Gusty SSW winds up to 30 knots prompted the issuance of small
crafts for the near coastal waters from Cape Cod Bay to Block
Island through 09z. Small crafts in the open waters remain into
Saturday for seas of 4-5 feet. Winds remain gusty from the SSW
tomorrow at 20-25 knots, before finally decreasing to 5-10 knots
Saturday night.


Outlook /Sunday Night through Wednesday/...

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

Sunday Night through Monday: Winds less than 25 kt.

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

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

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

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Flood Watch from 5 AM EDT early this morning through this
     evening for CTZ002>004.
MA...Flood Watch from 5 AM EDT early this morning through this
     evening for MAZ002>021-026.
RI...Flood Watch from 5 AM EDT early this morning through this
     evening for RIZ001>007.
MARINE...Small Craft Advisory until 5 AM EDT early this morning for
     ANZ231>237.
     Small Craft Advisory until 9 AM EDT this morning for ANZ254-
     255.
     Small Craft Advisory until 9 PM EDT this evening for ANZ256.

&&

$$

SYNOPSIS...BW/KP
NEAR TERM...KP/KS
SHORT TERM...KP
LONG TERM...BW
AVIATION...BW/RM
MARINE...BW/KP