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535
FXUS61 KBOX 052329
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
729 PM EDT Sun May 5 2024

.SYNOPSIS...
A period of widespread showers impacts the region tonight with the
focus for them this evening. Partial sunshine develops on Monday
with much warmer temperatures. A brief band of scattered showers is
expected Monday afternoon/evening...but the majority of the time
will feature dry weather. Tuesday will be the pick of the week with
abundant sunshine and above normal temperatures. Unsettled
pattern develops for Wednesday and beyond with below normal
temperatures. Some uncertainty revolves around the weekend
forecast.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...

-- Changed Discussion --
730 PM Update...

Light rain continues to fall across the CWA but some breaks in
the precipitation shield have started to develop across central
MA and will continue to push eastward this evening. Away from
the Cape and Islands, where showers will linger through early
tomorrow morning, should see rain come to an end between 03-06Z
this evening. As noted in the previous update, southwest flow
and residual moisture should lead to patchy fog formation
overnight, especially across interior MA/CT and along the south
coast. S/SW flow is not generally conducive to fog in the Boston
area, so do expect it to stay south of the metro this evening.

Previous Update...

335 PM Update...

* Period of widespread showers tonight with the focus this evening
* Low temps between 45 and 50 with areas of fog developing

Approaching shortwave/mid level warm front was inducing a modest
southwest low level jet this afternoon. This has allowed a band of
widespread showers to overspread areas northwest of I-95. This band
of showers will gradually sink southeast and impact the Boston to
Providence corridor by late afternoon/early evening. Once the steady
showers arrive they should generally last between 3 and 6 hours. The
bulk of the showers will come to an end northwest of I-95 near or
shortly after midnight...but linger towards the Cape and Islands.

Overnight low temps should only drop a few degrees from their
current readings...mainly in the 45 to 50 degree range. We do expect
some fog to develop overnight given increasing low level moisture
with light southerly flow.
-- End Changed Discussion --

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
Key Points...

* Partial sunshine developing away from south coast Monday
* Turning much warmer with highs well into the 70s for most on Monday
* Scattered brief showers Mon PM, but most of the time it will be dry

Details...

Monday and Monday night...

Any lingering showers towards the Cape/Islands should come to an end
Monday morning as the shortwave departs. Subsidence and enough
westerly flow aloft should allow for partial sunshine to develop.
Temperatures will quickly respond give 850T near +10C. It will be
much warmer than today with highs well up into the 70s. May even
feel a tad humid given dewpoints in the upper 50s to near 60...so
quite the change. It will be cooler near the south coast, Cape and
Islands where low clouds and fog patches may linger.

The vast majority of Monday will feature dry weather. However...a
cold front dropping south will probably result in a band of brief
scattered showers dropping south Monday afternoon and evening. There
probably will be a few hundred J/KG of Cape developing...but mid
level dry air advecting in from the west will limit potential. So
while a rumble or two of thunder is possible...opted to keep out of
the forecast for now. Later shifts may have to take another look.
Low temps Monday night will mainly be in the upper 40s to the middle
50s. There may be some patchy fog development too.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
* Dry and Mild on Tuesday

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

Tuesday continues to be the pick of the week, and while heights
begin to fall as more zonal flow develops aloft, west/northwest
downsloping boundary layer flow will support well above normal temps
with 850mb temps between 7 and 9C and 925mb temps around 13C. Weak
pressure gradient will lead to a seabreeze along the immediate
coastline, so while temperatures soar into the mid and upper 70s
across the interior, coastal localities will likely see peak temps
in the late morning before temps drop back into the upper 50s/low
60s by late afternoon.

Synoptic shift towards a more zonal pattern on Wednesday and
Thursday with a few shortwaves enhancing shower chances across
southern New England. Robust trough develops over the eastern CONUS
by Friday, allowing very unsettled pattern to persist through much
of the weekend as low pressure remains nearly stationary over
southern Ontario. Fortunately, the weak shortwaves wont bring
tremendous rain chances to the region, with 7 Day QPF ensemble
probabilities of 1" ranging between 40, SE MA, and 80, NW MA,
percent through next Monday. While still a week out, the persistence
of the pattern into late next weekend is a bit uncertain, with some
global guidance, like the CMC and GFS, shifting the trough offshore
late Saturday/early Sunday, which could yield improving conditions
for the second half of the weekend.

Aside from scattered rain chances later this week, temperatures will
be stuck below to well below normal thanks to aforementioned stalled
front and very persistent onshore flow. Temps will be stuck in the
50s most days across the eastern half of the CWA. Frontal boundary
placement will make temperature forecasting a bit tricky for CT and
western MA, where there are few opportunities late week for temps to
climb into the 60s in that region.

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
-- Changed Discussion --
Forecast Confidence Levels:

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

00z TAF Update...

Tonight...

Very low end MVFR to IFR conditions will trend more towards
IFR cigs/vsbys tonight with even localized LIFR conditions with
the cooling boundary layer. Showers will continue through 03-06Z
away from the south coast and through 12Z across the Cape and
Islands. Light S/SW winds overnight with a brief period of
minor LLWS will also impact areas to near the south coast toward
daybreak with a modest SW low level jet.

Monday and Monday night...High Confidence.

MVFR-IFR conditions Monday morning will tend to improve to
mainly VFR thresholds by mid afternoon and persist Mon night
outside localized patchy ground fog. However...MVFR-IFR
conditions in low clouds and fog may persist near the south
coast well into Monday night with moist light SW low level flow
ahead of a slow moving cold front. Bulk of the showers will exit
the Cape/Islands Monday morning. Dry weather should then
dominate later Monday into Monday night...but a round of
scattered brief showers will work southward along a slow moving
cold front Monday afternoon and evening but they will not last
long in a give location. Light SW winds Monday will shift to a
light NW wind Monday night behind a weak cold front.

KBOS TAF...High Confidence in TAF.

KBDL TAF...High Confidence in TAF.

Outlook /Tuesday through Friday/...

Tuesday: VFR. Slight chance SHRA.

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

Wednesday: Mainly MVFR, with areas IFR possible. Breezy. SHRA
likely, isolated TSRA.

Wednesday Night: Mainly VFR, with local IFR possible. Breezy.
Chance SHRA.

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

Thursday Night: MVFR/IFR conditions possible. Breezy. SHRA
likely, isolated TSRA.

Friday: MVFR/IFR conditions possible. Breezy. Chance SHRA.
-- End Changed Discussion --

&&

.MARINE...
Forecaster Confidence Levels:

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

Tonight through Monday night...High Confidence.

A mid level warm front will cross the region tonight this will be
followed by the passage of a weak cold front Monday night.
However...the pressure gradient will remain relatively
weak...keeping winds/seas below small craft advisory thresholds. We
may have enough of a LLJ for some southerly wind gusts of around 20+
knots to develop very late tonight into Monday morning. Winds
gradually shift to more of a W direction Monday afternoon and then
NW Monday night...but well below small craft advisory thresholds.
The main issue for mariners will be areas of fog developing
overnight and persisting at times through Monday evening...until the
cold frontal passage brings drier air and scours out the remaining
fog.

Outlook /Tuesday through Friday/...

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

Tuesday Night: Winds less than 25 kt. Chance of rain showers.

Wednesday: Winds less than 25 kt. Chance of rain showers,
isolated thunderstorms.

Wednesday Night: Winds less than 25 kt. Seas locally
approaching 5 ft. Chance of rain showers.

Thursday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain showers, isolated thunderstorms.

Thursday Night: Winds less than 25 kt. Seas up to 5 ft. Chance
of rain showers, isolated thunderstorms.

Friday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain
showers.

&&

.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/KS
MARINE...Frank/KS