132
FXUS61 KBOX 291144
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
744 AM EDT Sat Jun 29 2024

.SYNOPSIS...

Mainly dry weather continues today, outside a few brief spot
showers across the distant interior. A slow-moving frontal
system brings two potential rounds of scattered showers and
thunderstorms, mainly Saturday night into early Sunday morning,
and then perhaps again later Sunday into Sunday night. Drier
weather with seasonable temperatures and comfortable humidity
levels returns early next week as high pressure builds in from
the west. This high pressure will slide east of the region late
next week, allowing very warm and humid weather to return for
the start of the long holiday weekend.

&&

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

730 AM Update...

Have made a few minor adjustments in the latest update. Mainly
was to increase wind speeds/gusts as NBM running a bit too low
now and with the 20-40 kt LLJ at 925 hPa pushing in this
afternoon, wanted to reflect the higher winds. Have also
increased sky cover and decreased high temps a bit in the latest
update.

Previous discussion...

Relatively quiet this morning. An approaching warm front this
afternoon will bring in increasing clouds as well as some
showers arriving from the west late today, mainly across the
western half of southern New England. Increasing south winds
should result in near normal high temperatures despite the
clouds.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...

Steadiest period of rainfall is tonight, especially after
midnight. Could be a few thunderstorms as well, but mid level
lapse rates should be mediocre at best. Not a lot of buoyancy
expected tonight, but high shear is expected. It`s more likely
that this shear could sustain already developed thunderstorms
that move into New England, rather than having thunderstorms
develop locally.

Guidance continued to exhibit significant detail differences
in the mesoscale. That will take more time to come into better
focus. There is rather good agreement on the synoptic scale, so
based this forecast on the overall consensus, realizing that
further adjustments will be required with later issuances.

For Sunday, thinking we will see the last of the overnight
showers moving off the south coast during the morning hours.
While perhaps not being completely dry, there should be at least
a lull in the action across the interior. How much of a lull
will be key. Very high shear values are expected. Should the
clouds break enough for appreciable insolation, buoyancy could
become elevated to better balance the shear, raising the stakes
for more widespread severe weather. At present, thinking CAPE
values between 1,000-2,000 J/kg, which is more than enough to
support a few strong to severe thunderstorms. Main threats are
strong gusty winds and some hail.

Becoming increasingly humid and warm, if not hot, Sunday.
Precipitable water values still projected to be near 2 inches,
indicating a risk for localized downpours and possible
flooding.

&&

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

Highlights

* Any lingering showers/storms Sun Night tapering off from NW to
  SE. Moisture laden airmass, so heavy downpours still
  possible.

* Isolated showers/storms on Mon. Perhaps some small hail in any
  more vigorous storms.

* Dry and quiet weather Tue/Wed with near seasonable temps.

* Turning more unsettled late in the week with increasing
  humidity.

Sunday Night through Monday...

Caught in cyclonic flow through much of this timeframe. A trough
will be situated over the central/eastern Great Lakes Sun Night.
The trough will dig into the eastern Great Lakes/Mid Atlantic
by early Mon. The trough begins to lift and cutoff over southern
New England Mon afternoon/evening before lifting offshore. A
slow moving cold front will still be working its way through
southern New England Sun Night into early Mon, but should mostly
be offshore by Mon AM. High pressure will begin nudging in from
the Great Lakes on Mon.

Fairly good agreement amongst guidance with showers/storms
tapering off from NW to SE as the cold front slides through
Sun Night into early Mon. Do wonder if synoptic guidance is a
bit too slow to push this activity through as several CAMs in
the latest HREF showing activity is almost completely through
our region. For now have leaned on the synoptic guidance
agreement vs the tail end of the CAMs, but may need to be
adjusted in future forecast updates. Still think some of these
storms could perhaps be strong/severe though our instability
will start to wane. At this point will still have a few hundred
to roughly 1500 J/kg of MUCAPE in place. Should still have
plenty of deep layer shear at 40-60 kts Sun Night into early
Mon. Low/mid level lapse rates not looking too great, but think
there still could be some stronger activity maintaining for a
bit as front slides through. Also concerned with locally heavy
downpours given NAEFS SATA table still 1.5 to 2.5 STD above
model climo with the 1.5- 2+ inch PWAT plume sliding offshore
and warm cloud layer depths of 3.5-4.5 km. Heaviest rains during
this period would be before midnight. Low temps heading into
Mon will be in the 60s.

Overall for most should be fairly quiet on Mon. Though will have
a fair amount of CU developing given the trough cutting off over
us. Expect a fairly cold airmass at 500 hPa with temps of -15 to
-20 degrees Celsius. The big question will be if there will be
enough moisture given the dry N/NNW flow through the day and
PWATs falling to 0.75 to 1 inch. Think this is enough moisture
for isolated activity, so bumped up our precip chances to
reflect this. Wonder if there is also the potential for an
isolated strong storm or two. Will see low level lapse rates of
6-8 degrees and given the cold pool moving in overhead will have
mid level lapse rates of 6-7 to perhaps 8 degrees Celsius. Deep
layer shear of 20-50 kts will slide southeastward. Though there
could be a brief period, especially earlier in the afternoon
where there is some overlap, which could help maintain some
organized convection...provided there is enough moisture in
place. Given the setup think that hail would be primary risk,
but this is not supported by latest CSU ML guidance. Something
to stay tuned on for future updates. Highs will be near
seasonable levels.

Tuesday through Wednesday...

A ridge axis builds from the eastern Great Lakes early on Tue
into New England by late in the day. That ridge gets pushed
offshore by early Wed, while a weak shortwave lifts in. Another
ridge builds in from the eastern Great Lakes on Wed. High
pressure builds overhead on Tue and slides offshore to the
southeast Tue Night through Wed.

Dry and quiet weather expected through this timeframe with high
pressure in control. Temperatures will be near to slightly
warmer than normal. Humidity levels will generally be pretty
comfortable, but we may start to creep up a bit on Wed as flow
becomes more southerly. High temps will generally be in the 80s.

Thursday through Friday...

Flow becomes quasi-zonal during this timeframe. Appears that
there may be one or two shortwaves lifting into/through the
region. Though at this point these are quite hard to time and
there is a lot of spread amongst guidance. Appears a front
pushes into our region on Thu and stalls out heading into Fri.

Given the spread amongst guidance have generally stuck with the
NBM at this point in time. Unfortunately at this point cannot
completely rule out that some showers/storms could be around.
Will have increasing humidity levels as another moisture laden
airmass advects in. The NAEFS guidance showing PWATs of 1.5 to
2 STD above model climo with values ranging roughly from 1.5 to
2.5 inches. Warm cloud layer depths will be roughly 3.5 to 4.5
km, which given the environment could be conducive to heavy
downpours. High temperatures generally in the 80s, but we could
see some low 90s across the Merrimack and CT River Valley on
Thu.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...

Forecast Confidence Levels:

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

Today...High Confidence.

VFR, despite a fair amount of mid-high level cloudiness. S
winds increasing to between 10 and 15 knots with some gusts
around 25 knots. Could have some spotty showers across the
interior this morning/early afternoon, but think for most will
be dry.

Tonight... Moderate confidence in timing, higher confidence in
trends.

MVFR, to eventually mainly IFR, conditions overspread the
region from west to east. A round of scattered showers and
perhaps a few thunderstorms possible. S winds 10 to 15 knots
with gusts up to 25 knots.

Sunday...Moderate confidence.

Areas IFR to start should improve to mainly VFR. More showers
and thunderstorms expected during the afternoon and evening,
with brief MVFR conditions.

KBOS TAF...Moderate confidence in TAF. Mainly due to timing of
showers this evening and overnight. Likely dry through the
evening push. Could have some embedded thunder, but think the
risk is quite low.

KBDL TAF...Moderate confidence in TAF.  Mainly due to timing of
showers this evening and overnight. Evening push could be
impacted by showers and thunderstorms.

Outlook /Sunday Night through Wednesday/...

Sunday: Mainly VFR, with local IFR possible. Breezy. Chance
SHRA, slight chance TSRA, patchy BR.

Sunday Night: Mainly VFR, with local MVFR possible. Breezy.
Chance RA, slight chance TSRA.

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

Monday Night through Tuesday Night: VFR.

Wednesday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels:

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

Through Sunday...High confidence.

Tranquil boating conditions this morning. Increasing southerly
winds by this afternoon. Small Craft Advisories continue into
Sunday. Areas of rain, and even some thunderstorms, arrive late
tonight into Sunday morning.

Outlook /Sunday Night through Wednesday/...

Sunday: Moderate risk for Small Craft Advisory winds with gusts
up to 25 kt. Seas up to 5 ft. Rain showers likely, isolated
thunderstorms, patchy fog.

Sunday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain, chance of thunderstorms.

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

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

Tuesday through Wednesday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from midnight tonight to 7 PM EDT Sunday
     for ANZ230-236.
     Small Craft Advisory from 8 PM this evening to 7 PM EDT Sunday
     for ANZ231>235-237-254>256.
     Small Craft Advisory from noon today to 7 PM EDT Sunday for
     ANZ250-251.

&&

$$

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