-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KBOX 200515
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
115 AM EDT Sun Jun 20 2021

.SYNOPSIS...
A round of showers and thunderstorms is possible late this afternoon
and evening ahead of a cold front, especially across CT, RI and
south of the Massachusetts Turnpike. Dry, very warm but less humid
conditions (away from the south coast) follow Sunday. Hot and
very humid conditions arrive Monday which will be followed by
more showers and thunderstorms Monday night into Tuesday. The
heat and humidity break late Tuesday into Wed, with much more
seasonable and less humid weather. Warmer and more humid return
Fri into next weekend.

&&

.NEAR TERM /UNTIL 9 AM THIS MORNING/...
1245 AM update...

Short-wave aloft still slowly moving over southern New England.
KBOX radar still displaying light showers scattered across
southern New England. Light showers will continue over the next
couple of hours as the short-wave begins to make its way east of
southern New England. Adjusted PoPs to reflect latest radar
trends, but otherwise the forecast for the rest of the night is
on track.

&&

.SHORT TERM /9 AM THIS MORNING THROUGH 6 PM MONDAY/...
400 PM Update:

Sunday:

Zonal flow aloft but with rising 500 mb heights for most of Father`s
Day. Southerly flow should bring in warmer low-level temps (850 mb
temps rise to around +15 to +17C) with mostly full sun. Dewpoints in
the mid 60s should make it feel fairly muggy out but not looking at
oppressive humidity levels. Surface-based CAPEs given the strong
insolation and the higher dewpoints are progged around 800-1500
J/kg, highest west towards the Berkshires. That said, given
background weak subsidence and lack of lifting/triggering sources
most of the area should be dry. Some guidance offer some weak
upslope flow that could pop off a shower or thunderstorm in the
Berkshires but kept PoPs at 15-20% as most should be dry. Given the
more humid air mass, do also have to watch for some lower
stratus/fog near the South Coast and the Islands. Highs should reach
well into the 80s with lower 90s in the interior.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
226 PM update...

Highlights...

* Hot and very humid Monday
* Scattered T-storms & heavy downpours late Mon/Tuesday
* More seasonable & less humid Mid Week
* Warmer & more humid Fri into next weekend

Sunday night/Monday...short wave ridging ahead of remnants of TS
Claudette should provide mainly dry weather, other than an isolated
shower/T-storm western MA/CT late Monday. SSW flow provides hot and
very humid conditions, with 850 mb temps warming to +18C to +19C
(+22C to +24C inland at 925 mb!) by late Mon along with dew pts
rising into the low 70s! Thus, low 90s likely away from the south
coast along with heat indices (apparent temp) 95-100!

Mon night/Tuesday...12z guidance has trended remnants of Claudette
farther offshore. Subsidence on NW side of system may yield mainly
dry weather here Monday night. However, by Tue remnants of Claudette
exiting off to the northeast and with mid level trough and surface
front approaching from the west, Tue likely the greatest risk of
showers and storms. It`s far out there in time, but some favorable
parameters for severe weather Tue including robust CAPE/Shear
profiles. Although timing of front will be critical.

Tue night/Wed/Thu...FROPA late Tue/Tue night ushering in drier/less
humid air across the region. 1030 mb high (impressive by late June
standards) will provide mild to warm days Wed and Thu with
comfortable humidity, along with cool nights.

Friday/Saturday...return flow, in response to mid level trough
digging into the High Plains and Great Lakes, yields a warming trend
here Fri/Sat along with increasing humidity. Increasing chance of
scattered storms by Sat.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --
Forecaster Confidence Levels.

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

Through 12Z...High Confidence

VCSH taper off by about 09Z for the eastern terminals.

Today...High Confidence

VFR with light westerly winds. Cape Terminals could see gustier
westerly winds greater than 15 knots by mid-afternoon.

Tonight...High Confidence

VFR conditions continue at all terminals minus ACK. May see
some fog develop after midnight at ACK resulting in IFR
visibilities.


=====================================================================

Tonight: Moderate confidence.

Generally VFR, though brief periods MVFR-LIFR visbys mainly
south of the Mass Pike 01-07z west to east as rains and embedded
thunder move eastward from southern NY/PA. Clearing from west to
east around 05-10z with VFR. WSW to W winds 3-6 kt.

Sunday: High confidence.

VFR. Can`t rule out an isolated TSRA near the Berkshires by
afternoon but stays away from the TAFs. Do have to watch for
lower clouds/possible FG towards Cape Cod/Islands late in the
day as moisture levels start to rise. SW winds 5-10 kt,
strongest Cape Cod/Islands.

Sunday Night: Moderate/high confidence.

Generally VFR; somewhat better chance for stratus/fog and
associated IFR/lower categories for South Coast/Cape and
Islands.

KBOS TAF...High Confidence in TAF.

KBDL TAF...High Confidence in TAF. Possible TSRA 18-22z but
lower probability.

Outlook /Monday Night through Thursday/...

Monday: VFR. Breezy. Slight chance SHRA.

Monday Night: MVFR/IFR conditions possible. Breezy. Chance
SHRA, chance TSRA, patchy FG.

Tuesday: Mainly MVFR, with local IFR possible. Breezy. Chance
SHRA, chance TSRA, patchy FG.

Tuesday Night: Mainly VFR, with areas MVFR possible. Chance
SHRA.

Wednesday through Thursday: VFR.
-- End Changed Discussion --

&&

.MARINE...
Forecaster Confidence Levels.

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

Short Term /through Monday/...High Confidence.

* Small Craft Advisory remains in effect for the outer waters
  through Sunday morning; expiring for the near-shore waters at
  6 PM.

Gusty SW winds across most waters (20-25 kt) should subside
early tonight, then shift to W and ease to 10-20 kt. Seas to
remain in the 4-6 ft range especially outer waters. Potential
for thunder and lightning particularly for the southern waters
later this evening and into the overnight.

For Sunday/Sunday night: Winds become SW again but at sub-SCA
levels. Seas begin to subside on all waters to 2-4 ft. Patchy
fog and stratus could lead to lower visibilities, particularly
Sunday night.

Outlook /Monday Night through Thursday/...

Monday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Patchy fog.

Monday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers,
chance of thunderstorms, patchy fog. Areas of visibility 1 to
3 nm.

Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Chance of rain showers, chance of thunderstorms, patchy fog.

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

Wednesday: Winds less than 25 kt. Areas of seas approaching
5 ft.

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

Thursday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 AM EDT this morning for
     ANZ254>256.

&&

$$
SYNOPSIS...Nocera/Loconto
NEAR TERM...RM
SHORT TERM...Loconto
LONG TERM...Nocera
AVIATION...RM
MARINE...Nocera/Loconto/RM