-- Discussion containing changed information from previous version are highlighted. --
847
FXUS61 KBOX 050506
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
106 AM EDT Sun May 5 2024

.SYNOPSIS...
Cloudy and cool weather is on tap through Sunday with a period of
widespread showers arriving from the west...mainly later Sunday into
Sunday night. Mild and dry to start the work week before cooler and
unsettled conditions Wednesday through next weekend

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
730 PM Update...

Widely variable conditions across southern New England at this
hour with temps in the mid 40s along the eastern MA coastline,
thanks to onshore flow, and in the mid 60s in parts of CT that
saw sunshine for the better part of the day. Cloud cover is
variable as well, with several layers of clouds ranging from IFR
to VFR, with the lowest clouds colocated with the coolest
temperatures.

Low clouds will continue to spread inland this evening with some
possible fog development along the south coast, Cape, and high
terrain of central and western MA.

330 PM Update...

* Clouds continue to overspread the region off the ocean tonight
* Overnight low temps mainly in the 40s

The upper level ridge axis will be shifting east of the region. This
coupled with high pressure in the vicinity of the Canadian Maritimes
will result onshore flow. As the boundary layer cools...expect low
clouds to continue to develop and expand westward tonight. Dry
weather will prevail tonight...but we may see a few spot showers
develop near daybreak west of the CT River Valley. Overnight low
temps will bottom out mainly in the 40s.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/...
Key Points...

* Cloudy/cool Sun with showers arriving across the interior
* A period of widespread showers Sun night across the entire region

Details...

Sunday and Sunday night...

High pressure will shift east of the Canadian Maritimes as shortwave
energy approaches from the west on Sunday. Onshore flow low level
flow will result in cloudy skies persisting and cool temperatures
too. Highs will only be in the 50s even across the distant interior.

While a few warm advection spot showers are possible across the
interior during the morning...the stronger forcing/deeper moisture
does not arrive until the afternoon. So thinking the main threat for
showers will be be Sunday afternoon across interior MA & CT...but
should wait until late Sunday afternoon/evening across the coastal
plain. Enough forcing exists for a period of widespread showers
Sunday night. Modest forcing and Pwats 1-2 standard deviations above
normal could result in a brief downpour or two. While we can not
rule out a rumble or two of thunder with some marginal elevated
instability...thinking it was not worth inserting into the forecast
at this point. Low temperatures Sunday night will mainly be in the
middle to upper 40s.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
* Generally dry with above normal temperatures Monday and Tuesday

* Persistent period of cool temps and heightened rain chances
  Wednesday through early next week.

Tale of two patterns for the upcoming work week with strong
upper level ridging in place through Tuesday before a trough
develops for the second half of the week.

Some residual showers may linger into Monday morning, primarily
across far southeastern MA and the Cape. Weak frontal passage may
initiate some shower activity come Monday evening but with drying
flow aloft, questions remain on the geographic spread of this second
round of showers. All in all, Monday looks to shape up as a
primarily dry day, with above normal temperatures as boundary layer
temperatures warm to around 15C. As noted by the previous
forecaster, ensemble probabilities of 70F+ temps remain high,
between 80-100%, across the interior. Tuesday continues to look like
the pick of the week as temperatures soar well into the 70s.
Downsloping northwest flow that develops after the lunch hour and
abundant sunshine should allow for a few localities in the CT River
Valley to make a run at 80F. While ensemble probabilities remain low
regarding temps hitting the 80F mark, conditions appear to be a
recipe for an overachieving type day. For both Monday and Tuesday,
weak pressure gradient will allow for seabreeze development, so
while it may sound like a broken record, temps along the coastline
will be significantly cooler.

Ridge breaks down as trough develops over the eastern CONUS Wednesday-
Friday. CMC, GEFS, and ECMWF remain at odds regarding how potent the
trough will be, but a series of shortwaves and persistent low
pressure located over the Great Lakes and a stalled frontal boundary
will bring rounds of showers to southern New England Wednesday
through the weekend. Ensemble probs aren`t particularly remarkable
when it comes to QPF, with just 20-50% probs of 0.5" QPF over any 24
hour period, but onshore flow will make for a prolonged period of
stratus and shower chances with temperatures locked in the upper 50s
and low 60s.

&&

.AVIATION /05Z SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --
Forecast Confidence Levels:

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

06z TAF Update...

Through 12Z...High Confidence in trends, but more uncertainty
in regards to specific timing.

Borderline IFR/MVFR ceilings between 008-012 feet with light
easterly winds.

Sunday...High Confidence.

IFR/MVFR ceilings will trend to mainly MVFR thresholds with
some diurnal heating despite the cloudy skies. Some showers will
work into mainly interior MA & CT during the afternoon hours, but
will not reach the coastal plain until late Sunday
afternoon/evening. SE winds 5 to 10 knots.

Sunday night...Moderate Confidence.

IFR/LIFR ceilings develop with light showers spreading west to
east across southern New England overnight. SE winds shift to
more of a S direction at 5 to 10 knots.

Monday...

IFR ceilings lifting to VFR levels by late morning/early
afternoon. Though lower IFR ceilings may persist longer over
The Cape Islands. Light southwest winds becoming more westerly.
Winds may be weak enough to support a sea-breeze circulation
along the coastline.

KBOS TAF...High confidence

KBDL TAF...High confidence

Outlook /Monday Night through Thursday/...

Monday: Mainly VFR, with local IFR possible. Chance SHRA.

Monday Night through Tuesday: VFR. Slight chance SHRA.

Tuesday Night: VFR. Chance SHRA.

Wednesday: Mainly VFR, with areas MVFR possible. Chance SHRA,
isolated TSRA.

Wednesday Night: MVFR/IFR conditions possible. Chance SHRA.

Thursday: Mainly VFR, with local IFR possible. Chance SHRA.
-- End Changed Discussion --

&&

.MARINE...
-- Changed Discussion --
Forecaster Confidence Levels:

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

Tonight through Sunday night...High Confidence.

High pressure in the vicinity of the Canadian Maritimes tonight will
shift east of there on Sunday. This as a shortwave energy approaches
from the west late Sunday and Sunday night. That being said...the
pressure gradient remains rather weak so winds/seas will remain
below small craft advisory thresholds through Sunday night. E winds
5 to 15 knots tonight shift to the SE Sunday and then more to the S
on Sunday night.

Outlook /Monday Night through Thursday/...

Monday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain showers. Local visibility 1 nm or less.

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

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

Tuesday Night through Thursday: Winds less than 25 kt. Chance
of rain showers.
-- End Changed Discussion --

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

$$

SYNOPSIS...Frank/KS
NEAR TERM...Frank/KS
SHORT TERM...Frank
LONG TERM...KS
AVIATION...Frank/RM
MARINE...Frank/KS