415
FXUS61 KBOX 080003
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
803 PM EDT Sun Jul 7 2024

.SYNOPSIS...

Oppressive heat and humidity to start the week, which may linger
into Wed. Remains humid throughout the rest of the week, but
temperatures return to more seasonable levels. These cooler
temperatures bring increased shower and thunderstorm chances
with locally heavy downpours possible.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...

8 PM Update...

Forecast generally on track. Did increase our temps overnight,
especially along/southeast of I-95 as a stratus deck will
largely be in place. This should keep our temps up, so bumped up
to the 75th percentile of guidance. Elsewhere just minor tweaks
to bring things in line with observations.

Previous discussion...

Mid level cap still evident with the radar largely quiet.
Scattered cumulus on the visible satellite imagery, but not much
else. Stratus persisted across portions of the Cape and islands
this afternoon, and will only expand after sunset in the very humid
air. Thinking this stratus will stay generally south and east of
a line from Marshfield to Smithfield to Willimantic. Areas of
fog also should expand, and will issue an Special Weather
Statement to account for some patchy dense fog.

Not much change in low temperatures from past nights given the
high humidity continuing.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...

Yet another day of heat and humidity for Monday. Mid level dry
air gets event deeper, meaning even less risk for showers. based
on the 2-day threshold of heat indices 95 or greater, will go
forward with a Heat Advisory start Monday where confidence is
highest. To keep things simpler, will continue the headline
through Monday night even though heat index values are expected
to fall back into the 70s. It is likely this Heat Advisory will
be expanded with later forecasts.

Above normal temperatures and humidity continue.

Stratus around the Cape and islands could linger through Monday
night, although do expect some improvement during the day.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Highlights

* Hot and humid Tue and Wed. Heat Advisory may need to be extended
  in Wed. Remains humid through the rest of the week, but temps
  return to more seasonable levels.

* Unsettled with a stalled front nearby/overhead through much of the
  week. The result is daily opportunities for showers/storms. More
  widespread rain possible late in the week associated with the
  remnants of Beryl.

Tuesday and Wednesday...

Stuck under cyclonic flow through this timeframe. A shortwave trough
will slide through portions of northern New England on Tue. Should
see ridging setting up for Wed across the Mid Atlantic/eastern Great
Lakes, but a shortwave rides on top of the ridge. A quasi-stationary
front will be positioned over portions of the interior on Tue. It
may become more oriented east to west just to our north or over us
for Wed.

Main story for this timeframe will be the heat and humidity. Have
already hoisted a Heat Adv that extends into Tue as we meet the 2
day criteria. Though this will likely need to be extended into Wed
and perhaps expanded a bit more in future updates. Have held off for
now due to uncertainty on heating given increased cloud cover. Both
days featuring 925 hPa temps roughly of 22-26 degrees Celsius with
prolonged SWly flow. The result are highs in the upper 80s to low
90s. The only exception being along the immediate south coast where
readings generally will be in the 80s. Expect dew points in the low
to mid 70s. The result will be heat indices of roughly 90-100
degrees across much of the region, other than the immediate south
coast where it will be cooler.

The other risk for this timeframe is showers and thunderstorms given
we will have a stalled out frontal boundary overhead/nearby. Risk on
Tue appears to be highest across western/central MA and CT. This is
where have chance PoPs. A bit trickier on Wed as the stalled out
front may reorient itself to more of an east-west configuration over
our area or just to the north. For now have gone with consensus of
guidance, which focuses activity more over NH/VT/MA border. Both days
will have the risk of heavy downpours, though a bit higher on Wed vs
Tue. Should see PWATs around 2 inches on Tue, which is 1.5-2 STD
above model climo per the NAEFS. This climbs firmly to 2-2.5 inches
on Wed with NAEFS showing us 2-2.5 STD above model climo. Warm cloud
layer depths range from 3.5-5 km on both days. Instability somewhat
similar with a few hundred to roughly 2000 J/kg of MLCAPE. The big
difference between the two days is the upper forcing is a bit more
removed further to the NW on Tue as opposed to Wed it is closer by.
Should note that deep layer shear in 0-6 km layer is 30-40 kts. Mid
level lapse rates are pretty meh as well as low level lapse rates.
The risk is higher for flash flooding given this environment per the
marginal ERO from WPC on both days. Will note that ML guidance per
CSU does highlight a severe risk on Wed across our region, so will
be something we need to monitor. Not highlighted yet at this point
per SPC Outlook and will need a better handle on where the frontal
boundary set up.

Thursday through Saturday...

Still unsettled through this timeframe with cyclonic flow in place.
The remnants of Beryl and moisture associated with it remain either
nearby or over our area for a portion of this timeframe. The result
is chances for more widespread showers/storms. Though at this point
will need to really hone in on where frontal boundaries are setup as
these will be key for where there will be an increased risk for
flash flooding.

Generally have stuck with the NBM at this point in time as it looks
reasonable given the uncertainties in the forecast. Temperatures
returning to more seasonable levels, but the humidity remains given
the prolonged southerly flow. Still quite moisture laden with PWATS
of 1.5 to 2.5 STD above model climo per the NAEFS and warm cloud
layer depths of roughly 4-5 km. Think anywhere where we`ve got a
frontal boundary will be the focus for heavier rainfall and perhaps
flash flooding. This is highlighted per Day 5 ERO per WPC and CSU ML
Excessive Rain probs guidance. Will be something to monitor as the
week progresses.

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...

Forecast Confidence Levels:

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

Tonight through Monday...High confidence in trends, moderate in
exact timing.

IFR to LIFR fog/stratus across the Cape/Islands. Think this does
slip into PVD and perhaps OWD, but think will remain SE of
BOS/ORH as well as BDL. If it does move into BOS it would
probably be heading into the AM push. Should see the stratus/fog
lift fairly quickly for PVD/FMH roughly 13-17Z. May take awhile
for HYA, while ACK may still have IFR/LIFR ceilings linger with
improved vsby Mon afternoon. Light winds tonight and Monday,
with seabreezes at BOS and PVD.

Monday Night...Moderate confidence.

VFR conditions across interior MA and BOS. Roughly to the S/SE
of I-90 will have IFR to LIFR stratus and fog lifting in. Risk
greatest along the immediate south coast. S/SSW winds 5-10 kts.

KBOS TAF...High confidence in TAF.

VFR with seabreezes likely to develop around 14-16Z. IFR/LIFR
stratus possible after 04Z into the AM push, but confidence
higher to the SE. Have held off from including in TAF for now.

KBDL TAF...High confidence in TAF.

VFR through the forecast. MVFR to IFR stratus possible Mon Night
into early Tue.

Outlook /Tuesday through Friday/...

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

Tuesday Night: VFR. Breezy. Slight chance SHRA, isolated TSRA.

Wednesday: VFR. Chance SHRA, isolated TSRA.

Wednesday Night: Mainly VFR, with local MVFR possible. Chance
SHRA, isolated TSRA.

Thursday: Mainly VFR, with areas MVFR possible. Breezy. Chance
SHRA, isolated TSRA.

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

&&

.MARINE...

Forecaster Confidence Levels:

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

Through Monday Night...High confidence.

Relatively light winds and seas across the waters through Monday
night. The main concern will be poor visibility in fog tonight.
Visibility should improve Monday, then not get quite as low
Monday Night.

Outlook /Tuesday through Friday/...

Tuesday: Winds less than 25 kt.

Tuesday Night through Wednesday: Winds less than 25 kt. Slight
chance of rain showers, isolated thunderstorms.

Wednesday Night: Winds less than 25 kt. Slight chance of rain
showers.

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

Thursday Night: Winds less than 25 kt. Seas up to 5 ft. Slight
chance of rain showers.

Friday: Winds less than 25 kt. Seas up to 5 ft. Slight chance
of rain showers, isolated thunderstorms.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory from noon Monday to 8 PM EDT Tuesday for
     CTZ002>004.
MA...Heat Advisory from noon Monday to 8 PM EDT Tuesday for MAZ005-
     012-013-017-018.
RI...Heat Advisory from noon Monday to 8 PM EDT Tuesday for RIZ001-
     002.
MARINE...None.

&&

$$

SYNOPSIS...Belk/BL
NEAR TERM...Belk/BL
SHORT TERM...Belk
LONG TERM...BL
AVIATION...Belk/BL
MARINE...Belk/BL