905
FXUS61 KBOX 061024
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
624 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 & 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/...

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 /10Z THURSDAY THROUGH MONDAY/...
Forecast Confidence Levels:

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

06z TAF Update...

Through 12z...

IFR-LIFR cigs expanding northward across SNE. Showers and
isolated thunder overspreading portions of SW MA, N CT and RI
09-12z.

Today...Moderate confidence.

Widespread IFR-LIFR conditions. Numerous showers will be
overspreading the region this morning and exiting Cape Cod early
this afternoon. Isolated thunder and locally heavy rain
possible near the south coast. A second round of scattered
showers & 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. Showers develop this morning, but thunder
chances have diminished as best chance will be closer to the
south coast.

KBDL TAF...Moderate confidence. Deteriorating cigs to IFR as
showers develop 11-15z with low risk for a t-storm, but better
chance near the south coast. 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...KJC
SHORT TERM...KJC
LONG TERM...RM
AVIATION...KJC/RM
MARINE...KJC/RM