555
FXUS61 KBOX 151118
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
718 AM EDT Wed May 15 2024

.SYNOPSIS...
Isolated to scattered showers today before more widespread
showers develop as low pressure moves south of SNE tonight.
Drying trend on Thursday. Weather pattern for late in the week
into the weekend is a cloudy and unsettled one with onshore
breezes forcing cooler temperatures near the coastlines. While
we can`t rule out a few showers from time to time, drier weather
generally prevails late this week into the weekend. Trending
drier with a potential warm-up into early to mid next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
705 AM Update:

Updated PoPs/Wx to match current radar/observations and expected
near-term trends with this update. While these rains are not
expected to be significant or notable, forecast confidence in
the timing of an anticipated second round of rain is pretty low.

At least variable amounts of mid-level cloud cover early this
morning across all of Southern New England, but cloud bases
lower and thicken with westward extent associated with a band of
light rains across the Berkshires and into western/southwestern
CT.

Latest guidance indicates two general periods of rain today. The
first is the ongoing area of light rains over interior western
New England, which could expand a bit further east into central
MA and eastern CT but expecting much of if not all of eastern MA
and RI to be dry through much of today. This lead area of rains
seems to be being driven by moisture advection in light SE
flow, is not amounting to much in terms of QPF and is not
expected to yield much. This lifts northwestward during the
morning to early afternoon period, with a potential brief break
for the afternoon. The bigger uncertainty then comes with an
anticipated second round of rains associated with low pressure
near the Chesapeake Bay area. Most solutions show this rain
reaching our southern coastline but varies as far as when, with
some guidance including past few HRRR cycles indicating an
arrival by late afternoon (4-6 pm timeframe) while better
consensus in rain arriving later tonight. That will need to be
better pinned down but I show another round of PoPs increasing
during the later afternoon period along the south coast. Though
I couldn`t rule out a rumble of thunder given meager
instability, rain showers to predominate. All in all, a better
day further east one goes, but still will be a generally cloudy
day.

Previous discussion:

Light returns on radar have been very slow to translate into
observed precipitation overnight as shower activity advances
northward from Long Island/NYC into the Hudson River Valley/Central
CT given dry air from the sfc to ~800mb. Scattered showers are
expected to fill in across Connecticut and southwestern MA this
morning, but lingering dry air associated with weak persistent
ridging (that brought highs into the 80s for some yesterday!) should
be enough to stave off significant shower activity for the eastern
half of the CWA. CAMs, and model soundings, do introduce a bit of
uncertainty, particularly prior to 18Z this afternoon, regarding how
far east shower activity can advance but all in all not expecting a
washout of a day for any particular location. Will note that there
is just a tiny bit of instability, about 150J/kg CAPE, that could
translate into an isolated rumble or thunder or two. Should see a
dry period develop later this afternoon ahead of increasing precip
chances tonight.

Temperatures aloft remain mild but do cool through the day, with
850mb temps falling from ~10C to ~7C this afternoon. Given
significant cloud cover, its unlikely we mix much above 925mb, where
temps hover around 12C, so highs will top out in the mid 60s to low
70s, warmest across eastern MA where showers are delayed the
longest.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
Low pressure moves northward from the mid-Atlantic coast to just
south of southern New England overnight which will pivot a more
robust precipitation shield towards the region after 03/04Z tonight.
As mentioned by the previous forecaster, the lack of baroclinicity
this time of year introduces significant uncertainty regarding how
far northward more stratiform precipitation can extend with low
pressure centered south of the benchmark, but overnight guidance has
trended, just slightly, towards a more northern and "wetter"
solution, wetter in quotations as less than a half inch of rain is
expected for far southern New England through the period.

Widespread shower activity will linger through at least the first
half of Thursday before low pressure pulls seaward, which will allow
PoPs to diminish through the afternoon. Concurrent with lessening
shower chances, may see a few breaks of sunshine develop across the
far interior by sunset.

With surface flow shifting to the E/ENE, onshore flow will impact
highs, with mid to perhaps upper 60s expected across the interior
and low 60s along the immediate eastern coastline. It will be a
breezy day, with a 925mb jet of 35kt draped south of I-90,
translating to gusts between 20-25kt along the south shore.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Highlights:

* Unsettled late-week into the weekend, with onshore flow favoring
  generally dry weather but with considerable cloudiness on most
  days. Better, although limited, chance for rain is around late
  Sunday but no significant rains or washouts are expected.

* Possible pattern change toward even milder weather around midweek?

Details:

00z suite of global ensembles still depict a generally unsettled
weather pattern in this period, with two closed-off upper level lows
moving through the mid-Atlc states, thus progged to be suppressed to
our south. One of these features sags ESE Thursday night into Friday
south of our waters, with another anticipated to pass to our south
around Sunday night or into Monday. Related moisture tied to these
disturbances will keep a generous amt of cloud cover around on most
days; while we can`t rule out a spot shower or two, the
southward/suppressed tendency of these disturbances depicted in most
of the ensembles should favor drier weather more often than not.
Onshore flow being produced by a surface ridge of high pressure
nosing in from Nova Scotia would tend to favor cooler temps near the
coast and several degrees warmer inland for late in the week through
the weekend. There is more uncertainty in the pattern as we move
into early to mid next week, with some solutions offering a warmup
and less cloud cover, while the Canadian GEM indicating a
continuation of unsettled conditions.

Thursday Night through Friday:

Coastal low pressure which is expected to bring showers to areas
largely south of the Mass Pike on Thurs will continue to shift
southward Thurs night into early Fri, with surface ridge of high
pressure over Nova Scotia gradually taking hold. We should see
decreasing rain chances into the evening and overnight hrs, with Fri
trending drier but still with partly to mostly cloudy conditions and
onshore breezes, with greater cloud cover south and east. Rain amts
on Thurs night are light though. For temperatures, highs could
struggle to reach the lower 60s near the coasts on Fri with the
cooler onshore flow, but seem likely to reach into the lower to mid
70s further inland. Above-normal lows in the low to mid 50s for
Thurs and Fri nights.

The Weekend into Monday:

Saturday is still looking cloudy but generally dry under continued
surface ridge of high pressure, with cooler onshore breezes and
similar high temps to those from Fri.

Next upper level low pressure tries to move in around later Sunday
or into Mon. The Canadian GEM is the most bullish in bringing steady
rains in, while the GFS keeps any rains to far southwestern areas,
and the ECMWF is the driest and would favor dry weather for all of
SNE. So still uncertainty in the specifics to work through; I opted
to keep a slight to low chance mention of showers in the forecast
for now. PoPs will need adjusting once there is better cross-model
agreement. Kept highs in the 60s in all areas both days, again
coolest near the coast.

As of now, Saturday looks to be the pick of the weekend but it still
will feature a good amt of cloud cover.

Tuesday and Wednesday:

While the Canadian solution in this period maintains continued
cloudy conditions with periodic showers, indications in the ECMWF
and GFS solutions depict a potential warmup toward early-summerlike
temps and less cloud cover. For now maintained NBM for this portion
of the forecast given the disparity in outcomes, though with a
little lean toward the GFS/ECMWF drier/warmer idea.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
Forecast Confidence Levels:

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

12z TAF Update:

Today: High confidence in TAF/trends but moderate on rain
timing.

Mainly VFR for most, with VFR/MVFR mix over the CT Valley
airports with embedded light -SHRA thru 17z. VFR should
generally continue elsewhere, although confidence in timing the
next round of rain coming up from the southern waters is low.
Ceilings should then trend sub-VFR as this second round of rain
develops, but could happen as soon as mid-afternoon for the Cape
airports and PVD but more likely after 00z Thu. South winds
under 10 kt today; sea breeze ESE winds along the eastern MA
coast by mid/late morning should trend back to south later in
the day.

Wednesday night...Moderate Confidence.

Light S-SE winds become east overnight. VFR/MVFR conditions become
MVFR overnight, as more organized rain shield comes onshore to the
south coast of CT/RI/MA generally after 04Z. Localized IFR/LIFR
possible. Forecast uncertainty in how far north this rain shield
tracks overnight.

Thursday... Moderate Confidence

Uncertainty surrounds precipitation shield on Thursday but expecting
widespread shower activity through at least 12Z.
Showers possible all day but chances diminish through the afternoon.
Generally MVFR with pockets of IFR, improving to VFR late Thursday.
Breezy winds from the ENE/E gusting to 25kt along the south coast.

KBOS TAF...Moderate confidence in TAF. OVC VFR with mainly dry
weather through early afternoon. S winds trend SE/ESE early this
afternoon, before flipping back to S again later today. More
widespread showers after 03Z Thursday as ENE flow develops.

KBDL TAF...Moderate confidence in TAF. VFR to MVFR today with
light SHRA this morning, lifting N while briefly trending dry
for mid to late afternoon. More widespread rain moves into the
terminal after 03z tonight.

Outlook /Thursday Night through Sunday/...

Thursday Night: VFR. Breezy. Slight chance SHRA.

Friday: VFR. Breezy.

Friday Night: VFR.

Saturday: VFR. Slight chance SHRA.

Saturday Night: Mainly VFR, with areas IFR possible. Slight
chance SHRA.

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

&&

.MARINE...
Forecaster Confidence Levels:

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

3 AM Update...

Wednesday...

Weak high pressure offshore results in light S-SE winds. Mainly dry
weather and any morning fog burns off by midday with good vsby
thereafter. Scattered showers across the southern waters.

Wednesday night...

Low pressure south of New England drifts north, with increasing east
winds 15-20 kt toward Thu morning. Vsby lowers to 1-3 miles in areas
of fog and rain, especially southern MA and RI waters.

Thursday...

E/ENE winds increase as low pressure tracks closer to SNE, gusts to
30kt possible. Areas of rough seas with increased rain chances.

Outlook /Thursday Night

Thursday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of rough seas. Chance of rain showers.

Friday through Saturday: Winds less than 25 kt. Seas up to
5 ft.

Saturday Night through Sunday: Winds less than 25 kt. Seas up
to 5 ft. Slight chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 8 AM to 8 PM EDT Thursday for ANZ232.
     Small Craft Advisory from 2 AM to 11 PM EDT Thursday for
     ANZ235-237-254.
     Small Craft Advisory from 11 PM this evening to 11 PM EDT
     Thursday for ANZ255-256.

&&

$$

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