560
FXUS61 KBOX 010318
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1118 PM EDT Sun Jun 30 2024

.SYNOPSIS...

A strong cold front will move off the coast tonight pushing
showers and thunderstorms offshore. An upper level disturbance
will bring hit or miss showers Monday and possibly an isolated
thunderstorm, otherwise dry weather with below normal
temperatures. High pressure brings dry weather, seasonably warm
temperatures and low levels of humidity for Tuesday and
Wednesday. Turning more humid and unsettled for the Fourth of
July thru the early part of the weekend with a couple of
disturbances offering chances for showers and thunderstorms.

&&

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

11 PM Update...

Highlights

* Dry for most other than portions of the south coast where
  showers/storms will be exiting offshore as the night
  progresses.

* Humidity levels and cloud cover decreasing elsewhere. Lows
  around seasonable levels.

The main shortwave that triggered earlier convection is offshore
at this point. A trough will dig into the eastern Great Lakes
late tonight. The cold front is in the process of working its
way through southern New England. Will completely slide through
by late tonight. A surface trough will extend from a low riding
along the front into southern New England.

Main change in the latest update from the previous forecast was
to focus the shower/storm risk more to portions of the south
coast. This is where there is still a few hundred to 1000 J/kg
of MUCAPE in place. Really will mostly be focused for Nantucket
and Marthas Vineyard, but could see some activity leak into the
Cape. Not anticipating any strong to severe activity in this
area given the marine layer is place and any storms would have
quite the inversion layer to overcome per latest RAP guidance.

Rest of the forecast generally on track with cloud cover
decreasing and humidity levels dropping as flow turns more NW to
N as the night progresses. Think that despite some areas
receiving rain will be tough for fog formation as the boundary
layer should be pretty well mixed as colder air is filtering in.
Anticipate it remains breezy overnight with 10-15 mph winds and
gusts up to 20 mph at times. Low temps around seasonable levels
in the 60s.

&&

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

Monday...

Sharp mid level trough with cold pool will be moving across the
region with 500 mb temps dropping to -16 to -18C. This cold pool
combined with daytime heating will result in BKN CU developing along
with widely scattered showers, mainly east of the CT valley and
especially across eastern MA. Marginal instability develops with
CAPES up to 500 J/kg so can`t rule out an isolated t-storm with
small hail given cold temps aloft. Temps will be a bit below normal
in post-frontal airmass with highs in the 70s and dewpoints in the
50s, to lower 60s near the coast.

Monday night...

Mid level trough moves offshore with rising heights as high pres
builds in from the west. Any diurnal clouds will melt away in the
evening leading to a mostly clear and somewhat cool night with light
north winds. Lows will range through the 50s, except lower 60s outer
Cape/Islands and Boston metro.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...

Highlights:

* Dry and warm with tolerable humidity levels for Tue and 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.

30/00Z guidance suite was in rather good agreement with the overall
synoptic pattern. Broad mid level ridging to start out this portion
of the forecast is expected to transition to broad troughing towards
next weekend. At the surface, a large high pressure should be over
southern New England Tuesday into Wednesday. This high pressure
should be far enough offshore to permit a cold front to approach
from the west on Independence Day, but it is a little complicated.
The offshore high pressure may not permit this front to make it all
the way into, or through, our region before being driven back north.

Dry weather with near to slightly above normal temperatures Tuesday
and Wednesday. Increasing risk for some showers and isolated
thunderstorms Wednesday night into Thursday. Also expecting
increased humidity with above normal temperatures Thursday into
Saturday. The timing and coverage of these showers and thunderstorms
remains the most uncertain aspect of this forecast. With many
outdoor plans for the holiday, it would be best to monitor the
forecast over the coming days.

This uncertainty lingers late this week. As such, stayed close the
NationalBlend solution for now, as it is ensemble-based. This meant
a broad chance for showers and thunderstorms Friday into Saturday,
but am not expecting it to be raining this entire time.

&&

.AVIATION /03Z MONDAY THROUGH FRIDAY/...

Forecast Confidence Levels:

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

Tonight...Moderate confidence.

Showers and t-storms especially south of the MA Pike will end
from N to S through midnight. VFR interior with partial clearing
overnight. IFR-LIFR south coast and Cape/Islands improving to
VFR after midnight but lower cigs lingering at ACK. Wind shift
to NW 00-06z from W to E.

Monday...High confidence.

VFR cigs 4-6k ft developing with scattered showers developing
late morning through the afternoon, especially eastern MA. Can`t
rule out an isolated t-storm with small hail. N wind gusts to
20 kt.

Monday night...High confidence.

VFR with diminishing wind.

KBOS TAF...Moderate confidence in TAF.

Expect a few t-storms developing 20-00z with brief lower
conditions and potential for strong wind gusts. Included a
TEMPO group to highlight this potential. Otherwise VFR. SW
winds shift to W this evening then NW overnight.

KBDL TAF...Moderate confidence in TAF.

One cluster of t-storms moving to the E but expect additional
showers and storms into early evening. VFR but brief lower
conditions and strong wind gusts in any storms. Wind shift to
NW around 00z.

Outlook /Tuesday through Friday/...

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 through Saturday: Chance SHRA.

&&

.MARINE...

Forecaster Confidence Levels:

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

Tonight through Monday night...High confidence.

Gusty S-SW winds to 25 kt will be diminishing this evening as
modest low level jet moves offshore. Winds shift to NW overnight
then N during Monday with gusts to 20 kt. Diminishing N winds
Mon night. Showers and t-storms through this evening, moving
offshore from the south coastal waters late tonight.

Outlook /Tuesday through Friday/...

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

Saturday: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 6 AM EDT Monday for ANZ254>256.

&&

$$

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