399
FXUS61 KBOX 050750
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
350 AM EDT Fri Jul 5 2024

.SYNOPSIS...
Warm and very humid weather expected over the next few days.
Early morning showers this morning give way to brief dry
weather, although scattered thunderstorms are expected to
develop in the interior this afternoon. Some could produce
heavy downpours. Another risk for showers and storms for
Saturday. Mainly dry Sunday afternoon through early Tuesday, but
more unsettled weather is on the horizon for middle of next
week.

&&

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

Key Points:

* Variable cloudiness, highest south and east, but quite humid!

* Scattered t-storms in CT and western/central MA as soon as
  noon, but more likely 2-10 PM. Torrential downpours are the
  main risk, but isolated strong wind gusts are possible.

Bottom line up front: the forecast for today is marred with
quite a bit of uncertainty on timing details, especially on
potential for re- developing showers/storms this afternoon. In a
weak pressure pattern with nebulous forcing mechanisms and a
very humid air mass, it won`t take much heating to generate at
least pop-up showers, and as they typically do in this weakly-
forced setting, near-term and high-res guidance are really
struggling with run-to-run consistency. Potential exists for
changes today, but our best estimate on anticipated conditions
is below.

For today...ongoing showers in CT and western/central MA will
continue to work their way through Southern New England in
isolated to scattered coverage. Could be some downpours in these
as they move offshore, but lightning isn`t expected. The still-
expanding stratus/low clouds from overnight should start to
scatter out in most locations by mid to late morning north and
west of RI and southeast MA today; but it could take quite a
while to scatter out for RI and southeast MA and that leads to
somewhat lower temperatures (70s-low 80s) for that portion of
Southern New England, as well as low instability. Better
heating north and west and especially in the interior seems to
favor a second round of scattered showers and thunderstorms
moving in from eastern NY or developing over the
Berkshires/Litchfield Hills this afternoon. Decent signal across
the high-res guidance on this potential, but timing varies. So
for PoPs, offered generally dry weather for the mid to late
morning in all areas, but a steady increase in PoP to around 30-
50% from Fitchburg to Worcester to Willimantic west. It`s a
VERY humid airmass and even modest heating in that corridor
looks sufficient for CAPE values around 1000-1500 J/kg, falling
off sharply further east into eastern MA and SE MA and RI due to
the low clouds and slower destabilization. Though we do have
pretty good SW flow in mid to upper levels, 0-6 km shear is
still on the weaker side. Under assumption storms develop in
that airmass, any storm is capable of producing torrential
downpours (warm cloud depths are around 13-14,000 ft and PWATs
are over 2 inches). I don`t think this is a severe weather
setup, but we could have isolated stronger gusts through water-
loading effects. Eastern extent of this activity in some
question but weakening on approach to the BOS-PVD corridor is
more likely (if they get that far), and opted to leave these
areas dry for the afternoon. Sided highs today in the mid to
upper 80s away from the South Coast where there`s a better
chance at sunny breaks.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
345 AM Update:

Tonight and Saturday:

Any storms from the daytime hrs should shift NE and/or
dissipate early tonight. Thinking tonight should be dry for the
vast majority of the time, but with the very humid airmass, I
couldn`t rule out a shower at any time. Kept PoPs around the
20-30% range for tonight. There are some signals in the GFS/FV3
solutions for another round of showers/storms toward daybreak
into the western counties, but guidance is again pretty mixed in
general on that outcome. Thus couldn`t justify going any higher
with PoP. We should see expanding fog and stratus again
tonight, potentially across a wider portion of Southern New
England. Kept lows in the low to mid 70s with expected overcast
and the very humid air.

For Saturday there`s again quite a diversity in outcomes when
it comes to timing of showers and storms, associated with a weak
impulse in the SW flow aloft. The GFS shows two potential
rounds, one in the morning and the other late in the day, while
the NAM solutions favor a more early to midafternoon timing.
It`s not likely to be raining the whole day, but western areas
again have a little better chance at showers and thunderstorms
than east. Kept a rather broad brushed 30-60% PoP, lowest east
and higher west. Will need to wait to see how today`s convection
unfolds before there`s really any confidence in timing. Early
overcast should give way to partial clouds by late morning with
similar highs to today.

&&

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

* Weak front brings showers and storms, mainly to northwestern areas
  Saturday night and diminishing by Sunday morning. Sunday morning
  could feature areas of coastal stratus and fog.

* Drier Sunday and Monday, although a slight chance Sunday afternoon
  for a spot shower or thunderstorm remains. Still rather warm and
  muggy both days.

* Summer heat and humidity continues into next week with additional
  rain chances starting later on Tuesday.

Saturday Night:

A front/cool(ish) front associated with mid-level shortwave energy
moves across northern New England with showers and thunderstorms. As
we`ve been mentioning, PWATs are anomolous for southern New England,
forecasts continue to indicate values between 2.0 to 2.3 inches.
05/00z NAM 3km shows a robust line, but signs it will decay after
exiting Vermont and New York. Greatest forcing to the north, plus
the forecast lapse rates diminish to next to nothing 00z-03z Sunday.
The better chance for any severe weather would be far northwestern
Massachusetts, but severity should quickly diminish as these storms
move into a stable airmass.

Unfortunately this is not a strong front, will not bring much if any
relief from the high dew points. The front/boundary could stall over
the coast waters and be a region for a few spot showers into early
Sunday morning.

In addition, high dewpoints and air temperatures in the upper 60s
(north) to the mid 70s (south) could spell areas of coastal stratus
and fog to start Sunday morning.

Sunday and Monday:

Southern New England is on the outer periphery of a mid-level ridge
which is anchored over Bermuda. Do think most of this time we are
dry, but with bouts of shortwave energy riding the outer periphery
of the ridge, cannot rule out a spot shower/thunderstorm. Have kept
a mention of `slight chance` POPs Sunday afternoon, mainly across
the interior as we would expect the terrain to influence the
development. As for Monday, likely dry with even less forcing from
weak shortwave energy.

With more in the way of sun, should see temperatures rebound back
into the upper 80s and lower 90, while the coast sits in the lower
to middle 80s. Dew points are still elevated, but a far cry from the
middle 70s, look for dews in the upper 60s and lower 70 both days. A
heat index could push the mid 90s for places in locations such as
the Connecticut River Valley and I-495 corridor. No heat headlines
expecting at this time due to the criteria, heat index of 95F to 99F
for two consecutive days. Never the less, it will be plenty warm!

As for the overnights, its warm with lows in the upper 60s and the
lower 70s around the populated urban centers.

Tuesday through late next week:

Another warm and muggy day for Tuesday, expecting highs in the upper
80s to lower 90s, away from the coast. Dew points are elevated and
returning to the low 70s! The heat index to return to the lower and
middle 90s. But feel this heat falls just short of needing any heat
related headlines. Still a few days out, it is possible things could
change. With rain and clouds mid to late week temperatures fall back
a few degrees to the low and middle 80s on Wednesday and Thursday.
Still, there is no relief from the summer humidity with dew points
remaining elevated, upper 60s to middle 70s.

Becoming unsettled late Tuesday with mid-level heights falling and
bursts of shortwave energy ahead of a more robust shortwave that
will be over the eastern Great Lakes. This feature does moves east
with a broad mid-level trough overnight. Return of showers and
storms as early as Tuesday afternoon and continues into the
overnight hours. Mid-levels over the northeast are quasi-zonal and
will allow for additional bursts of shortwave energy to pass through
and produce showers into Thursday. As we`ve mentioned before, do not
expect wall-to-wall rain, rather both periods of rain and periods of
dry weather. As for the overnights, its warm with lows in the upper
60s and near 70F around the populated urban centers.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
Forecast Confidence Levels:

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

06Z TAF Update:

Though 12z Fri: Moderate confidence overall, but low on timing.

Initially, mostly VFR but with pockets of MVFR-IFR
ceilings/visbys around. Deterioration ancipiated to a general
MVFR to IFR-LIFR from stratus and areas of fog, with lowest
categories for PVD and southeast MA with reasonably high
confidence. Categories along and north of the Mass Pike on the
other hand are less certain and could stay in the VFR-MVFR
range. Ongoing -SHRA/SHRA over CT to move eastward into RI-SE
MA through the overnight/pre-dawn hrs and could briefly reduce
visby to MVFR levels. Light S winds for most, though around 5-8
kts for BOS and the south coast.

Today: Moderate confidence overall, but low on timing.

Main aviation concerns this period revolve around timing
improvement, if any, of stratus and then SCT SHRA/TSRA for
central and western airports. MVFR-LIFR stratus is likely to
begin this morning for most, and while we should start to see
SCT-BKN VFR bases for most by 13-15z, sites such as PVD and the
Cape airports could struggle to see much improvement. There
looks to be a period of TSRA today in western New England as
skies start to scatter, indicated PROB30 groups for TSRA after
18z for BAF, BDL and ORH, but confidence in the timing is lower
than normal. Heavy donwpours likely in TSRA. SW winds today
around 5-10 kt; it is possible that BOS could seabreeze for at
least a brief period of time ~15-18z before returning to SWly by
mid to late aftn.

Tonight: Moderate confidence overall, but low on timing.

Any TSRA for central/western airports to weaken thru 02z; dry
weather should prevail for several hours, but we could see
another round of SHRA/TS for these same areas later
tonight/overnight. Deterioration toward a widespread IFR- LIFR
tonight into overnight but timing uncertain. Light S winds.

Saturday: Moderate confidence overall, but low on timing.

IFR-LIFR generally improves to SCT-BKN VFR, but seems to be a
better chance at TSRA on Sat especially ORH-PVD north and west.
Timing of TSRA uncertain and subject to adjustment. SW winds
4-8 kt.

KBOS TAF...Moderate confidence. VFR should deteriorate to MVFR
cigs by pre-dawn hrs today but should see improvement quickly.
Can`t rule out a shower early this morning but more likely dry.
Possible seabreeze period ~15-18z but this isn`t certain.
Aftn/evening SHRA/TS chances today too unlikely to mention in
TAF, better chances further west. Categories deteriorate to IFR
levels tonight. SW winds around 5-10 kt outside of a potential
brief seabreeze.

KBDL TAF...Moderate confidence. VFR should deteriorate to
MVFR/IFR briefly 08-12z, before returning to SCT-BKN VFR bases
by 13z. Early SHRA dissipates by 08z, with dry weather until
aftn. PROB30 for TSRA after 18z and some could be strong with
heavy downpours and localized wind gusts if storms develop. Risk
should end by 02z but categories then deteriorate to IFR-LIFR
with stratus. S winds 4-8 kt.

Outlook /Saturday Night through Tuesday/...

Saturday Night: Mainly IFR, with local MVFR possible. Breezy.
Chance SHRA, chance TSRA, patchy BR.

Sunday: Mainly VFR, with local IFR possible. Slight chance
SHRA, slight chance TSRA.

Sunday Night through Monday Night: VFR.

Tuesday: VFR. Slight chance SHRA, slight chance TSRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Today through Saturday: High Confidence.

Persistent SW flow with winds around 10-15 kt through the
period, and seas could get near 5-ft thresholds given the long
SWly fetch. Still think it is borderline for SCAs. Morning
showers dissipate by late-morning, with fog and stratus tonight
over the waters. Better chance for showers and storms over the
southern waters on Saturday, but widespread storms not expected.

Outlook /Saturday Night through Tuesday/...

Saturday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Chance of rain showers, chance of
thunderstorms, patchy fog. Visibility 1 to 3 nm.

Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Chance of rain showers, slight chance of thunderstorms, patchy
fog. Local visibility 1 to 3 nm.

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

Monday through Tuesday: Winds less than 25 kt.

&&

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

&&

$$

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