044
FXUS61 KBOX 011336
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
936 AM EDT Mon Jul 1 2024

.SYNOPSIS...
An upper level disturbance will bring hit or miss showers today
and possibly an isolated thunderstorm, otherwise dry weather
with slightly cooler than seasonable temperatures. High pressure
brings dry weather and seasonable temperatures with comfortable
humidity for Tuesday and Wednesday. Turning more humid and
unsettled for Independence Day into this weekend with a couple
of disturbances offering chances for showers and thunderstorms.

&&

.NEAR TERM /THROUGH TONIGHT/...
930 AM update...

Rather robust mid level trough and cold pool will be moving
across SNE this afternoon. Diurnal CU already developing and
will expand across the region as low and mid level lapse rates
steepen. A few showers will develop by late morning, probably
first across portions of eastern CT/RI and central MA where CU
is most developed per day cloud phase, then focus should shift
to eastern MA this afternoon where best moisture is located.
Also can`t rule out an isolated t-storm as there will be
marginal instability with CAPES up to 500 J/kg. Small hail will
be possible given cold temps aloft.

Previous Discussion...

Highlights:

* Hit or miss showers and perhaps a few isolated thunderstorms
  today. Activity generally east of the CT River Valley. In any
  thunderstorms there is the potential for some small hail.

A sharp trough and cold pool over the eastern Great Lakes this
morning will dig into southern New England by this afternoon.
The trough lifts offshore by this evening, while a ridge builds
into the central/eastern Great Lakes. A surface trough will
slide through our region today, while high pressure builds into
the central/eastern Great Lakes.

Main concern in the forecast is hit or miss showers along with
isolated thunderstorms. This will largely be a result of diurnal
heating in combination with the -15 to -20 degree cold pool
sliding in overhead with the trough. Should see a fair amount of
CU developing in this setup, but given the position of the
trough think that risk of activity will be highest east of the
CT River Valley. At this point have slight chances for PoPs for
a good portion of the region with chances for eastern areas.
Should see up to 500 J/kg of CAPE with 6-8 degree low level
lapse rates and 6-7 degree mid level lapse rates. Actually could
have a brief window where 0-6 km deep layer shear is 40-60 kts,
late AM to early afternoon. Wonder if this could perhaps be
enough for a strong storm to develop. Though should note the
limiting factors at this point are we don`t have a whole lot of
instability or moisture (only 0.75 to 1 inch PWATs and mid 50 to
low 60 degree dew points) to work with. Just something we will
need to monitor today. Think any thunderstorms will bring the
risk for small hail given the cold pool aloft. If a stronger
storm were to develop think risk could be some larger hail.

Given the limited moisture have held off from including the
small hail mention in the grids. This is also supported by the
latest ML guidance per CSU, HRRR Neural Network and Nadocast
guidance. Should note the 00Z HREF thunder probs are nil at
this point, but did include thunder given the environmental
setup. Temperatures anticipated to be a bit cooler than normal
in the post-frontal airmass and won`t be as humid. Highs will
mostly be in the 70s.

&&

.SHORT TERM /TUESDAY/...
Highlights

* Any diurnal clouds erode quickly with clear skies expected
  tonight. Slightly cooler than seasonable for lows.

* Dry with comfortable humidity and seasonable temperatures on
  Tue.

A ridge axis will be in place across the central/eastern Great
Lakes tonight. The ridge builds into the eastern Great Lakes and
Mid Atlantic by late Tue. High pressure builds into the eastern
Great Lakes and Upstate NY tonight. By Tue the high will be
overhead.

Dry and quiet weather expected through this timeframe. Only
question in the forecast really is how quickly does the pressure
gradient slacken tonight. This will impact how well we are able
to radiate given the clear skies. For now have gone with the
25th percentile of guidance for lows heading into Tue. The
result is it will be somewhat cool with lows in the 50s.

Abundant sunshine expected on Tue with high pressure overhead.
Could start to see some high clouds pushing into western areas
late as a shortwave lifts into the eastern Great Lakes. High
temps will be around seasonable levels with comfortable
humidity.

&&

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

* Dry and warm with tolerable humidity levels for Wed.

* Turning more humid and active for Independence Day, and
  potentially into Fri/Sat too, with clouds, showers and storms
  possible. Exact timing remains uncertain.

01/00Z guidance suite was in rather good agreement with the overall
synoptic pattern, but still exhibited some detail differences with
the smaller scale features. These become important during the summer
months when convection is more prevalent. Rather subtle changes can
have a big impact on on the outcome. Have high confidence in the
forecast through Wednesday, then only average confidence in the
details from Independence Day into next weekend.

High pressure at the surface moves offshore Wednesday, leading to
another warm day with slightly higher humidity. No rainfall expected.

More unsettled conditions start to develop Wednesday night into
Thursday. A passing mid level shortwave along with a warm front
passage may trigger some showers, mainly across northern MA. But this
will be influenced by how far offshore the high pressure can get. If
it is just a little closer, then the expected showers would be
shunted farther north, or at least great diminished due to some
lingering subsidence.

This in turn feeds into the Thursday forecast. High pressure still
parked over the North Atlantic, with a cold front approaching from
the west. This front is expected to move into our region some time
late on Independence Day into Thursday night, then stall heading
into Friday. This frontal boundary should move back north as a warm
front into Friday night, only to be followed by a cold front
Saturday night into Sunday. While not raining the entire time from
Wednesday night into Sunday, not seeing much opportunity for a
clearly dry period either. Have at least a slight chance for
rainfall during this time, with measurable rainfall more likely
heading into this weekend due to the increased humidity.

Temperatures generally above normal for this portion of the forecast.

&&

.AVIATION /13Z MONDAY THROUGH FRIDAY/...
Forecast Confidence Levels:

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

Today...High confidence.

VFR with 4-6 kft CU deck developing late morning through the
afternoon. The only exception is across the Cape/Islands where
ceilings may be borderline MVFR, especially during the morning.
This will generate scattered showers along with isolated
thunderstorms. Cannot completely rule out some small hail in
any thunderstorms. Due to uncertainty on the thunder coverage at
the terminals, have kept VCSH for now. Risk for storms highest
across the Merrimack Valley. Winds out of the N/NNE at 10-15 kts
with gusts up to 20 kts.

Tonight...High confidence.

VFR with skies quickly becoming clear during the evening and
diminishing winds.

Tuesday...High confidence.

VFR with light winds and increasing high clouds across western
areas late. Localized sea breezes developing roughly 15-18Z.

KBOS TAF...High confidence.

VFR through the forecast. NW winds shifting to the by daybreak.
Turning NNE by late morning into the afternoon. Risk for hit or
miss showers and isolated thunderstorms. If a thunderstorm moves
over the terminal there is a risk for small hail. Due to
uncertainty on the coverage have kept thunder out of the current
forecast.

KBDL TAF...High confidence.

VFR through the forecast. Winds shifting from the NW to the N by
daybreak. Will be gusty throughout the day at 15-20 kts. Cannot
completely rule out an isolated shower during the afternoon.

Outlook /Tuesday Night through Friday/...

Tuesday Night: VFR.

Wednesday: VFR. Breezy.

Wednesday Night: VFR. Breezy. Slight chance SHRA.

Independence Day: Mainly VFR, with local MVFR possible. Breezy.
Slight chance SHRA.

Thursday Night: VFR. Breezy. Slight chance SHRA.

Friday: Chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Today...High confidence.

Winds shifting to the NW as a cold front crosses the waters.
Should see winds turning northerly toward daybreak. Wind speeds
of 10-15 kts with some 15-20 kt gusts. Seas diminish to 2-4 ft.

Tonight...High confidence.

Winds out of the N to NW at 5-10 kts. Dry weather with seas 1-3
ft.

Tuesday...High confidence.

Winds out of the N to start, but will quickly diminish and shift
to the E/SE as high pressure moves overhead. Seas 1-3 ft with
dry weather.

Outlook /Tuesday Night through Friday/...

Tuesday Night through Wednesday: Winds less than 25 kt.

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

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

Friday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain showers.

&&

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

&&

$$

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