-- Discussion containing changed information from previous version are highlighted. --
914
FXUS61 KBOX 282332
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
732 PM EDT Tue May 28 2024

.SYNOPSIS...
Summer warmth and humidity Tuesday will be replaced by more
seasonable, cooler weather along with lower humidity Wednesday
through Friday. Dry weather through Wednesday morning, then
scattered showers and thunderstorms Wednesday afternoon into
Thursday. Drier weather with plentiful sunshine for Friday.
After a few days of temperatures at or slightly cooler than
normal, the weekend into Monday offers a warming trend toward
above normal temperatures and still tolerable humidity levels.
Drier weather should generally prevail this weekend into Monday,
though there is a chance for showers or thunderstorms on
Sunday.

&&

.NEAR TERM /UNTIL 7 AM WEDNESDAY MORNING/...
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725 PM Update:

Pleasant early evening underway with westerly breezes and
dewpoints falling into the 50s, with current temps in the upper
60s to mid/upper 70s for most, with cooler mid 60s over the
Cape. The leading edge of upper level trough aloft is being
marked by a line of weakening showers now moving into Berkshire
County MA, and while a few of these showers could skirt over the
Berkshires and perhaps into western Hartford County through mid
evening, weakening trends are anticipated. Even then, these rain
showers are not especially significant.

Overall should be a pretty tranquil evening, although especially
in eastern MA and RI, temps could be a little slower to cool off
as W winds should stay up for a good part of the night. That
also may preclude patchy fog from developing, and the
approaching dry advection may also limit the areal coverage of
any fog which could develop. Lows in the mid to upper 50s.

Previous discussion:

Thru this evening...

Beautiful spring weather across the region late this afternoon,
with temps in the upper 70s and lower 80s, under partly to
mostly sunny conditions. Good boundary layer mixing is
supporting dew pts falling into the 50s from west to east late
this afternoon. Dry weather expected, with just a 10-20% chance
of an isolated shower/Tstm across western MA/CT, as cold pool
aloft advects into the region from the west.

Overnight...

Short wave moves across the region, ushering in drier, less
humid and cooler weather across the region. Although, min temps
in the mid to upper 50s tonight, will average 5-8 degs above
normal. Any leftover evening clouds will dissipate overnight.
Low prob of some patchy ground fog as radiational cooling
develops.
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&&

.SHORT TERM /7 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
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330 PM update...

* Dry weather into Wed AM, then scattered PM thunderstorms

Wednesday...

Dry weather Wed AM along with sunshine. However, cyclonic flow
aloft combined with 500 mb temps lowering to -18C yields
steepening mid level lapse rates on the order of 6.5 to 7.0C/KM.
This combined with 0-6 km deep layer shear of 25-35 kt should be
sufficient for scattered thunderstorms. Given the cold air aloft
and upper jet streak offshore, these parameters overlap across
RI and southeast MA. This is where there will likely be
sufficient instability and shear to support a few storms with
small hail. Given the steep lapse rates, a few storms could
overachieve and possibly approach severe across RI and southeast
MA. Nonetheless, most if not all storms will be sub-severe. Not
a washout, but definitely will have to dodge a few storms Wed
afternoon into early evening.

Not as warm or humid as today, with highs 75-80 Wed and more
comfortable dew pts in the 50s. Coolest temps along the coast
with PM seabreezes.

Wed night...

Early evening diurnal convection/thunderstorms dissipate with
sunset, given loss of daytime heating and upper jet stream
exiting, decreasing deep layer shear. Thus, drying trends thru
the evening. However, another round of showers is possible late
Wed night and toward Thu morning, as a trailing short wave
approaches the region. Highest probs for this second round of
showers will be along the south coast. Seasonable temps with
lows 50-55 and light onshore winds in the evening becoming north
overnight.
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&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
330 PM update...

Highlights:

* Periods of showers with embedded thundershowers on Thurs, though
  diminishing by evening. No severe weather or soaking rains are
  anticipated. Temps slightly cooler than normal.

* Drier weather on Fri with seabreezes near the coasts.

* Gradual warming trend into the weekend into early next week. While
  drier weather prevails, there is a small window of opportunity for
  hit or miss showers or storms on Sunday.

Details:

Thursday and Friday:

12z ensembles continue to indicate that upper-level longwave
troughing and an associated colder pool of air aloft will govern the
weather over SNE through this forecast period.

Shortwave disturbance rounding the base of the longwave trough from
Wed night will continue to promote the potential for showers or
embedded thundershowers on Thurs, with somewhat better chances over
the southern third of SNE. With limited deep moisture (PWAT values
0.8-1 inch), don`t see this being a substantial precip maker, with
NBM 4.2-based QPF probs indicating moderate probs (30-50%) of 24-hr
rain over a quarter inch, and lower to moderate (25-30%) for 24 hr
rain over a half inch. With the shortwave moving offshore during the
evening, highest PoPs during the daytime hrs and then diminishing in
coverage late afternoon to early evening. With a good amt of cloud
cover around and periodic showers to dodge, showed cooler highs in
the 60s to lower 70s.

For Fri...though we are still under troughing aloft, sprawling
surface high pressure over the Gt Lakes and the northern
Appalachians will begin to ridge into the area, supporting abundant
sunshine. Local seabreezes near the coasts should also develop and
keep temps along the shore a little cooler, but Fri looks to be
shaping up to be a really nice day with highs in the lower to mid
70s with mid 60s along the coasts.

The Weekend into Monday:

Consistent with prior forecasts, 12z ensembles continue to show
pattern change that takes place in mid/upper levels early this
weekend, as the mid/upper trough shifts offshore and to be replaced
by 500 mb height rises. With that will bring a warming trend toward
more summerlike temperatures; Sat looks to be the coolest day with
highs in the mid to upper 70s, but by Sun and Mon we should see
highs reach into the lower to mid 80s for most away from the coasts.
Humidity levels will be creeping up too, especially Sun and Mon, but
should still be tolerable.

It`s also a generally dry forecast period with a good amount of
sunshine each day. Did include a slight-chance mention of showers/t-
storms later on Sun as the ECMWF shows what could be a convectively-
augmented vort max from the upper Midwest nearing the Northeast
states; as of now it doesn`t have much support from the other global
models, but it`s shown this signal over the last couple of its model
runs and it can`t be completely discounted as an outcome as yet. But
all in all, outlook favors drier weather.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
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Forecast Confidence Levels:

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

18z TAF Update:

Tonight: High confidence.

Predominantly VFR; low chance at patchy fog development in
southeast New England, if it were to develop wouldn`t be until
around the pre-dawn to early Wed AM hrs. West winds around 10-12
kt with gusts to 20-25 kt early, decreasing to around 5-10 kt
while shifting to WNW overnight.

Wednesday...High confidence on trends, lower on details
including areal coverage and severity of TSRA Wed PM.

VFR to begin the day. Then in the afternoon scattered -TSRA
develops with MVFR conditions, perhaps focused across RI and
southeast MA. A few of the stronger storms may contain small
hail from 18z-00z. Winds, light west winds will become locally
onshore along the coast.

Wednesday night...high confidence on trends, but lower
confidence on timing and details.

VFR/MVFR in early evening scattered -TSRA, then a possible lull
in the activity with a 2nd round of -SHRA & -TSRA second half of
the night. Light onshore winds become north overnight.

KBOS TAF...High confidence thru Wed AM, then some uncertainty
Wed PM with exact areal coverage and severity of storms.
Activity may be focused across RI and southeast MA, with a few
stronger storms there containing small hail. Activity could be
less widespread & less intense northward from KBOS to the NH
border. Given this, inserted a prob30 into the TAF but VCTS
farther south given higher probs. Also, afternoon seabreeze Wed.

KBDL TAF...High confidence in the TAF. Some uncertainty on areal
coverage of -TSRA Wed PM. Left out of the TAF for now with
higher prob eastward into RI and southeast MA. We may need to
include prob30 for -TSRA 18z-23z Wed in later TAF.

Outlook /Thursday through Sunday/...

Thursday: VFR. Chance SHRA.

Thursday Night: VFR. Slight chance SHRA.

Friday through Saturday Night: VFR.

Sunday: VFR. Slight chance SHRA.
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&&

.MARINE...
Forecaster Confidence Levels:

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

Tonight...

SW winds 15-20 kt with seas up to 5 ft offshore this evening,
will slacken and become westerly overnight. This shorter fetch
from SW to W will slowly subside seas. Low clouds and fog east
of Cape Cod at 330 pm will continue moving farther offshore
tonight.

Wednesday...light west winds become locally onshore in the
afternoon. Scattered showers and thunderstorms in the afternoon,
most numerous near shore. A few storms may contain small hail.

Wednesday night...light onshore winds in the evening become
light north overnight. Early evening scattered
showers/thunderstorms dissipate late evening. However, a new
area of showers may develop late Wed night or toward Thu morning
across the southern waters.

Outlook /Thursday through Sunday/...

Thursday: Winds less than 25 kt. Chance of rain showers.

Thursday Night through Sunday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 5 AM EDT Wednesday for ANZ250-
     254>256.

&&

$$

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