059
FXUS61 KBOX 061431
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1031 AM EDT Thu Jun 6 2024

.SYNOPSIS...
Showers move across the region this morning with brief heavy
rainfall and perhaps isolated thunderstorms, especially near the
south coast. A second round of scattered showers and
thunderstorms cross the region late afternoon and evening.
Unsettled conditions continue with scattered showers and
thunderstorms Friday through Monday but it will not be a
washout.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Did make some tweaks this morning. Updated rainfall chances and
timing based on the latest runs of the HRRR and NationalBlend,
which matched up with regional radar data the best. This kept
the majority of the showers off the south coast of New England,
with the risk for thunderstorms even farther offshore.

Latest SPC mesoanalysis kept the greatest surface-based CAPE
across western MA. This is where we`ll need to watch for
additional thunderstorm development later today. Will need to
get more insolation before we would have to worry about stronger
thunderstorms becoming more widespread. Right now, still looking
few and far between. Also have concerns about timing, which
should be late this afternoon into the evening. The window may
be short before sunset, also limiting the risk.

Just minor tweaks to temperatures to reflect observed trends.

630 AM Update

KBOX radar revealing a cluster of moderate to heavy rain showers
and embedded thunder over the south coastal waters at this hour.
Expect these showers to continue on an ENE trajectory eventually
bringing periods of moderate to heavy rainfall to the south
coast, Cape, Islands, and southeast MA. Beginning to think
northward extent of the greatest shower activity will be roughly
I-90. North of that mark, showers may be more hit or miss this
morning. Adjusted near-term PoPs to reflect higher confidence
for areas to the south and east. No other changes are needed at
this time. See previous discussion for more details.

Key Points...

* Numerous showers and isolated t-storms with brief heavy rain
  this morning, with highest confidence across CT/RI & SE MA

* A second round of scattered showers & t-storms late this
  afternoon and evening

A robust mid level shortwave from the mid Atlc region will be
lifting across SNE this morning and act on anomalous PWAT plume
of 1.5 to 2 inches. Result will be numerous showers and perhaps
a few t- storms moving across SNE this morning as there is some
elevated instability. It appears heaviest rain will be focused
near a weak boundary/warm front across CT/RI and SE MA. While
00z HREF has backed off somewhat on heavy rain potential it is
still indicating 30-50 percent probs of 3 hr rainfall exceeding
1" which may lead to some nuisance street flooding if these
amounts are realized. Will have to monitor convective trends
over the ocean as this could cut back on potential rainfall
amounts. The system is progressive and showers will be exiting
from west to east later this morning, but early afternoon over
Cape/Islands.

We expect a period of dry conditions this afternoon after this
initial round of showers moves through. Then will have to watch
for a second round of scattered showers/t-storms moving in from
the west late this afternoon ahead of next shortwave. It is
possible there may be a few breaks of sunshine in western New
Eng which will help to generate modest instability with CAPES up
to 1000 J/kg in western MA/CT. Low and mid level lapse rates
are not favorable which will limit severe potential. However,
CSU and HRRR Neural network machine learning probs still
indicating a low prob of severe storms in western New Eng. The
better chance however will be to the west where updraft helicity
swaths are more robust, likely due to greater forcing and
instability to the west along with stronger wind fields closer
to the shortwave energy. Regardless of severe potential, any
storms will have the potential to produce heavy rainfall.

Mainly cloudy skies will keep highs in the low-mid 70s, but could
get close to 80 in the CT valley. Rather humid airmass with
dewpoints 65 to 70.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
Tonight...

Ongoing scattered convection expected in the interior to start the
evening, and this activity should weaken as it moves into the
coastal plain with a low risk for an isolated t-storm in eastern MA
and RI. Mid level shortwave will be lifting NE from the Gt Lakes
tonight and passing well to the north with mid level drying moving
in overnight. So, mainly dry conditions expected after evening
convection dissipates. Stratus and patchy fog should gradually lift
overnight from west to east. Low temps are forecast to be mostly
between 60 and 65.

Friday...

Mid level low moves slowly east from the Gt Lakes with another
shortwave approaching from the west. The accompanying cold front
will be moving into western New Eng late in the day. Expect partly
sunny skies with scattered showers developing in the afternoon in
the interior as the shortwave approaches. However, soundings show a
strong mid level cap so thunder risk is low. It will be a warm day
as 925 mb temps increase to 18-20C ahead of the front. This
supports highs in the low-mid 80s, but cooler near the coast
where sea breezes expected. it will be somewhat humid with
dewpoints in the 60s but drier air will be moving into the
interior in the afternoon with dewpoints dropping through the
50s.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Highlights

* Mainly dry on Saturday with some showers and storms possible west
  of Worcester

* Scattered showers and possibly some embedded thunder on Sunday

* Unsettled weather continues into early next week with a possible
  break in the pattern by Wednesday

Saturday

The forecast for Saturday has improved since our last update, as
most model guidance is calling for a mainly dry day across
southern New England. Despite a persistent upper-low and
relatively steep lapse rates, limited moisture and atmospheric
forcing will make it difficult for anything more than a few
isolated showers to develop.

Steady westerly flow and deep diurnal mixing should support a
warm afternoon despite the anomalously cool air aloft. Expect
most locations to reach the upper 70s to low 80s with
downsloping from westerly winds supporting the warmest temps
over eastern MA. Thinking that even the east facing shorelines
should be warm as well as steady westerly winds should be able
to fend off the cool sea breeze. Any shower/thunderstorm
activity should be focused to the north and west where the
steepest lapse rates and greatest forcing will reside. Areas to
the south and east can likely expect a dry/sunny day with a low
risk for an isolated diurnal shower.

Sunday

A short-wave embedded in the broader upper-level low aloft will
rotate through southern New England on Sunday. Low-level wind
field takes on a more southwesterly wind component and allows
PWATs to recover to around 1.2 to 1.3 inches. This coupled with
forcing provided by the short-wave aloft should support a period
of scattered showers on Sunday. Not too concerned about any
embedded thunder given unimpressive dewpoints in the low to mid
50s and cooler temps in the low to mid 70s, but if the upper-
level 500 hPa cold pool drops far enough south to enhance mid-
level lapse rates and elevated instability, thunder could become
a possibility.

Next Week

Model guidance continues to suggest that the upper-level low
responsible for this prolonged period of unsettled weather will
still be lingering into early next week. Furthermore, there is
likely to be embedded short-waves aloft that will introduce daily
shower/thunderstorm chances on both Monday and Tuesday. Details
are vague at this time frame, so have leaned on the NBM for
guidance which places chance PoPs over the region for Monday and
Tuesday afternoon. There is some agreement among global
ensembles that the pattern may break by Wednesday as a mid-level
ridge builds over the eastern US. More details to follow as we
ahead into the weekend.

&&

.AVIATION /14Z THURSDAY THROUGH MONDAY/...
Forecast Confidence Levels:

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

Today...Moderate confidence.

Widespread IFR-LIFR conditions. Numerous showers lingering near
the south coast through this morning, and perhaps into early
afternoon. Thunderstorms should stay well south of our region
this morning. A second round of scattered showers and t-storms
with locally heavy rainfall will impact interior MA into CT late
this afternoon. SE-S wind 5-15 kt.

Tonight...Moderate confidence.

Scattered showers & t-storms will weaken as they move into the
coastal plain this evening, then drying out overnight. IFR-LIFR
conditions in the evening may improve to VFR from W to E
06-12z, but stratus and patchy fog persisting across eastern MA.
Light to calm wind.

Friday...Moderate confidence.

Any lingering stratus will burn off in the morning, otherwise
VFR. Scattered showers developing in the afternoon. SW wind
5-15 kt, with sea-breezes developing along the coast.

KBOS TAF...Moderate confidence. Deteriorating cigs to IFR with
LIFR possible.

KBDL TAF...Moderate confidence. Improving to MVFR this afternoon
with additional showers/t-storms possible late this afternoon.

Outlook /Friday Night through Monday/...

Friday Night: VFR. Slight chance SHRA.

Saturday: VFR. Breezy. Slight chance SHRA.

Saturday Night: VFR. Slight chance SHRA.

Sunday: VFR. Breezy. Chance SHRA.

Sunday Night through Monday: VFR. Slight chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Moderate confidence through Friday.

Today...SE winds across the northern waters with S-SW winds
increasing over southern waters where some 20+ kt gusts
expected. Seas will build to 5 ft over southern waters where
SCA will continue. Numerous showers and a few t-storms move
through this morning into early afternoon. Vsbys reduced in fog
and showers.

Tonight...SW wind 10-20 kt over southern waters, with SE winds
shifting to NW over NE MA waters overnight. Seas around 5 ft
over southern waters. Vsbys reduced in fog.

Friday...SW wind 10-15 kt over southern waters and shifting back
to E-SE across NE MA waters. Persistent 5 ft seas over southern
waters.

Outlook /Friday Night through Monday/...

Friday Night through Saturday: Winds less than 25 kt. Areas of
seas approaching 5 ft.

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

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

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

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 2 PM this afternoon to 8 PM EDT
     Friday for ANZ254>256.

&&

$$

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