-- Discussion containing changed information from previous version are highlighted. --
330
FXUS61 KBOX 170154
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
954 PM EDT Thu May 16 2024

.SYNOPSIS...
Rainfall tapering off for most late this afternoon, but may not
be until this evening for parts of the south coast. Patchy fog
spreading into the eastern half of southern New England. Could
perhaps be dense at times in a few spots. Temperatures rebound
nicely on Friday after the AM fog burns off. The weekend
features generally dry weather and onshore breezes, but still a
good amount of cloud cover. A warming trend then develops Monday
through Wednesday, and we could see a couple days of high
temperatures in the low 80s over interior sections of Southern
New England. After today, our next chance for rain develops late
next week.

&&

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

-- Changed Discussion --
10 PM Update...

A last gasp of light showers has been impacting the islands over
the last few hours, the greatest impact of which is persistent
low stratus and a few hundredths of QPF, as low pressure
continues to draw south of souther New England. Many localities
away from the immediate south coast were able to break out into
sunshine before sunset this evening, allowing for pretty quick
radiation where winds calmed quickly. As mentioned by the
previous forecaster, fog and stratus redevelopment overnight
will be fueled by residual moisture and onshore flow. The
question remains on if NNE/ENE will be strong enough to advect
low clouds into the Boston metro area, which will be something
we watch closely overnight.

Otherwise, very seasonable night expected. Many towns have
already fallen back into the mid-50s. Should start to see fog
form over the next few hours, with Tds in the low to mid 50s, as
dewpoint depressions drop below 3F across the interior. Winds,
still gusting as high as 25mph along the south coast/in RI, will
delay fog formation in these locations.

Previous Update...


* Marine stratus/fog possibly dense at times spreading into
  central MA/RI eastward tonight.

A cutoff low will meander from south of southern New England
late tonight to the southeast of our region by early Fri. Behind
the cutoff a ridge slides from the Mid Atlantic/eastern Great
Lakes into western New England by early Fri. Low pressure south
of Long Island late today will rotate southeastward tonight,
while high pressure nudges in from Upstate NY.

Main change to the forecast was slightly slow down precipitation
tapering off from the low meandering offshore. Think for the
MA-Pike northward things should end by this evening, but may not
be until 10 PM to midnight for precip to cease for the MA-Pike
southward. This will take the longest for MVY/ACK. Fortunately
the heaviest precipitation is over with as the mesoscale band
that set up is falling apart. This axis of precip will slide
southeastward. Leaned pretty heavily on the previous ARW and
current NSSL WRF as it is handling this band quite well based on
observations.

The other main concern to the forecast for tonight is given the
onshore flow am anticipating marine stratus/fog along with some
drizzle to spread into southern New England. This has been
hinted at by the past two cycles of the HREF and several GLAMP
runs. Have trended the forecast in this direction tonight for
central MA/RI eastward. Not out of the question there could be
some spots where the fog is dense, but not completely certain on
this risk at this junction as guidance is all over the place.
Something we will need to monitor given the prolonged ENE to NE
flow as it could linger into the Fri AM commute.

Cloud cover will be slow to clear for most other than portions
of western MA/CT as this is closer to the high nudging its way
in. Not expecting much radiational cooling and think the 50th
percentile of guidance looks reasonable at this point. Lows in
the low/mid 50s.
-- End Changed Discussion --

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
Highlights

* Any stratus/fog anticipated to erode Fri AM. Mix of sun and
  clouds through Fri.

* Increasing clouds Fri Night into early Sat. Could see the
  stratus/fog returning to portions of eastern MA.

Ridge axis over western New England early on Fri builds over
southern New England and into the Gulf of ME by late in the day.
The ridge essentially remains in place as we head into Fri
Night, but may flatten out a bit as a shortwave lifts across the
eastern Great Lakes into northern New England. A weak high
nudges into New England on Fri and Fri Night.

Dry and quiet weather anticipated on Fri with high pressure in
control. Should see any of the lingering stratus/fog burning off
by mid to perhaps late AM. Will still have prolonged ENE to NE
winds, but think given the breaks of May sun we should warm up
quite nicely. Should see 925 hPa temps of 11-15 Celsius. The
result should be widespread highs in the 60s with some mid 70s
across the CT River Valley. Still may struggle to hit 60 degrees
for portions of the east coast given the onshore winds, but will
still have roughly 15-30 kt ENE to NE LLJ at 925. Should result
in a fairly well mixed boundary layer, which should keep our
temps up. It will be a bit breezy into the afternoon.

Still anticipating dry and quiet weather to persist as we head
into Fri Night/Sat AM. Though we will see increasing cloudiness
as the ridge axis gets shunted to the south due to the shortwave
lifting in. Not a whole lot of moisture to work with in the mid
levels, but there is increasing low level moisture per 1000-850
hPa RH fields. Should have PWATs of 0.75 to roughly 1 inch. At
this point leaning on a dry forecast, but the ECMWF does eek out
some spotty showers across the interior. Think there is a better
shot given prolonged ENE to NE winds that we see another round
of marine stratus/fog/drizzle across eastern areas heading into
Sat AM.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Key messages...

* Outside of a spot shower, mainly dry weather is expected through
  at least the middle of next week.

* After a slightly cooler than average weekend a big warm-up arrives
  for early next week with 80s possible by Tuesday.

Details...

Saturday and Sunday...

Overall a welcome trend in the forecast for the weekend over the
last 24-48 hours for anyone with outdoor activities as, even though
the clouds will stick around, things should be dry on the whole.
This is thanks to a ridge of high pressure which will extend SW from
Nova Scotia further into SNE each day. The positioning of that high
will continue to direct cool, moist NE flow into the region. Thus,
Saturday should be mostly cloudy, and Sunday, while drier air does
start to work in from the upper levels down for lessening clouds,
will still be at least partly cloudy. Besides keeping the clouds
around this wind direction also keeps temperatures below normal;
highs will be coolest in eastern MA (upper 50s/low 60s) and warmest
in the CT Valley (low 70s).

Next week...

A pleasant week is setting up through at least Wednesday as high
pressure continues to center overhead pushing one low pressure
further to our east and suppressing one to the south over the
Carolina coast. Surface flow eventually veers to the SW while at the
same time we`ll be seeing more insolation (thanks to less clouds)
and a warming mid level airmass. 850 mb warm from +8C on Sunday to
+15C on Tuesday which looks to be the hottest day of the week;
expecting temps well into the upper 70s for many locations and even
low 80s for places like the CT and Merrimack Valleys. EPS and GEFS
ensemble guidance currently outline a 40-50% chance of temps AOA 80F
on Tuesday afternoon for those locations. It`s not until around
Thursday that we could see this dry pattern breaking down with the
arrival of our next shortwave, but confidence is low at this
distance in time.

&&

.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --
Forecast Confidence Levels:

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

Tonight...Moderate confidence.

Western interior terminals may briefly improve to VFR this
evening before lowering to MVFR/IFR as stratus spreads in.
Leaned more pessimistic for central MA/RI eastward due to
prolonged ENE to NE winds (onshore flow). Anticipating that the
marine stratus/fog layer spreads in lowering us to IFR and LIFR
conditions. Could even see some dense fog in spots, especially
across portions of Cape/Islands. For now kept things no worse
than 1/2 SM, but may need to be adjusted in future updates.
Winds out of the ENE to NE at 5-15 kts. Still could see 20-30
kt gusts across MVY/ACK.

Friday...High confidence in trends, moderate in timing.

Widespread VFR after any stratus/fog burns off by roughly mid to
late AM. Though may not be until the afternoon for ACK. Winds
out of the ENE to NE at 5-15 kts with gusts of 20-25 kts across
the Cape/Islands.

Friday Night...Moderate confidence.

VFR for most with increasing mid/high clouds. The only exception
is across eastern MA, but especially SE MA where MVFR/IFR
stratus/fog spreads in late. NE winds at 5-15 kts.

KBOS TAF...moderate afterward.

Prolonged onshore flow will advect IFR to LIFR stratus into
southeast MA areas south of the terminal overnight. While there
is a chance that these conditions make it far enough north/west
to impact the terminal, odds are low that this happens.

KBDL TAF...High confidence in TAF.

VFR, but borderline MVFR/VFR ceilings may spread in late.
Should see this lift to VFR early on Fri as the boundary layer
grows.

Outlook /Saturday through Tuesday/...

Sunday through Tuesday Night: VFR.

Wednesday: Slight 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...High confidence.

Rain tapering off across the southern waters north to south for
most before midnight, though the far outer southern waters may
not be until daybreak. Winds ENE to NE at 10-20 kts with gusts
20-30 kts gradually easing heading into Fri AM. Patchy to areas
of stratus/fog with visibility`s of 1/2 to 4 SM. Could even see
some spot where fog is dense at times.

Friday... High Confidence.

Any pockets of fog burning off by mid to late Fri AM. E/ENE
winds 15-20 kt with 20-25 kt gusts. Seas remain elevated across
the outer waters, so the SCA remains.

Friday Night...High confidence.

Winds remain out of the NE at 10-20 kts. Could see a return of
stratus/fog across the waters late. Visibilities of 1-4 SM with
the lowest across the eastern waters. Seas remain elevated so
have extended the SCA through the period.

Outlook /Saturday through Tuesday/...

Sunday through Monday: Winds less than 25 kt. Seas up to 5 ft.

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

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

Wednesday: Winds less than 25 kt.
-- End Changed Discussion --

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 11 PM EDT this evening for ANZ232-
     236.
     Small Craft Advisory until 2 AM EDT Friday for ANZ235-237.
     Small Craft Advisory until 8 AM EDT Saturday for ANZ250-
     254>256.
-- End Changed Discussion --

&&

$$

SYNOPSIS...BW/BL
NEAR TERM...BW/BL/KS
SHORT TERM...BL
LONG TERM...BW
AVIATION...BW/BL
MARINE...BW/BL