586
FXUS61 KBOX 241123
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
723 AM EDT Fri May 24 2024

.SYNOPSIS...

Warm and less humid conditions today into Saturday as high
pressure builds into the region. Mild with hit-or-miss showers
and storms possible on Sunday. Unsettled with widespread rains
Monday into Tuesday and more seasonable temperatures. Rainfall
could be heavy at times. Still unsettled mid to late in the
week, but with considerable uncertainty in the forecast.
Temperatures turning cooler as we head late into next week.

&&

.NEAR TERM /THROUGH TONIGHT/...

715 AM Update...

Main change in the latest update was to bump up our temps a bit
more. Expect the boundary layer to be well mixed per forecast
soundings and with a 15-20 kt W to WNW 925 hPa jet sliding in.
Given this setup think the default NBM will be a bit underdone,
so bumped our temps up to the 75th percentile of guidance. This
looks a bit more reasonable. Will have widespread 80 degree
readings, but the immediate south coast will struggle to get out
of the 70s due to onshore flow.

Previous discussion..

A front was stalled across southern new England early this
morning, generally from just south of Boston, to near Norwood,
to just north of Hartford. This was most evidenced by dew points
in the 40s to the north, with much more humid air pooled just
along the front, where dew points were in the lower 60s.

Thinking this front makes very slow progress towards the coast
today. It should still linger near the Cape and islands towards
daybreak. Thus, it will take a while for the humidity to ease
across eastern MA and RI.

Much ore quiet day today weatherwise, with just a secondary cold
front arriving late this afternoon and evening. Abundant
sunshine today and less humid. Above normal temperatures
continue. It should eventually become breezy enough from the
SW to W to prevent the development sea breezes today.

&&

.SHORT TERM /SATURDAY/...

Secondary cold front should finally pass across southern New
England tonight, with a high pressure to follow for Saturday.
Generally cooler for Saturday, but not by much. While still
sunny and dry, the weakening pressure gradient will make it
easier for sea breezes to develop along both coasts, leading to
even cooler conditions along the immediate coasts.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...

Highlights

* Mild Sun with a hit-or-miss showers/storms possible,
  especially during the afternoon/eve.

* Unsettled with widespread rain possible Mon into Tue. Rain may
  be heavy at times along with embedded thunder. Temps returning
  to more seasonable levels.

* Still unsettled mid to late in the week. Considerable
  uncertainty with how things evolve during this timeframe.

Saturday Night through Sunday...

Caught between a broad cutoff/trough south of New England late
Sat into Sun, while a ridge axis builds into the eastern Great
Lakes. Appears that a weak frontal boundary/low will be located
over southern New England during this period. Though a weak high
will also nudge into our area as well.

As mentioned 24 hours ago am generally anticipating dry and
quiet weather through much of this timeframe. Really are lacking
forcing with rising 500 hPa heights through the timeframe.
Though despite this there is a nearly stationary front/broad low
nearby/overhead. This in combination with the WSW/SW flow will
advect a 1-1.25 inch PWAT plume overhead, which isn`t all that
atypical for this time of year per the NAEFS/EPS situational
awareness tables. Given the weak forcing confidence overall not
the highest through this period, so think that slight chance to
chances of precip suffice. Best opportunity for the hit-or-miss
showers and storms is across the interior. This is depicted well
per 24 hr probs of measurable QPF from the EPS/GEFS/GEPS
guidance. Even have some mod probs (40-60 percent) of 24 hr QPF
AOA 0.1 inches per the GEFS. The EPS/GEPS not as high with only
low probs (10-30 percent) of 24 hr QPF AOA 0.1 inches.

Should see another mild day across southern New England with
925 hPa temps ranging from 15-21 degrees Celsius. There may be
enough cloudiness, which would keep us cooler than Sat. Highs on
Sun range from the 60s across the immediate south coast to
generally the 70s. Though will likely see some low 80 degree
readings across the CT River Valley.

Memorial Day through Tuesday...

Next opportunity for more widespread rains and potentially
impactful weather. Will have a complex cutoff low situated over
Manitoba/Ontario and the Great Lakes region early on Mon.
Several troughs/shortwaves rotate into the eastern Great Lakes
and New England region during this period. In response a frontal
system lifts into and perhaps through southern New England.

Given the complex setup confidence lower than typical,
especially on the Tue timeframe. As mentioned previously a dry
slot still looking like it punches in, which would quickly erode
our precip heading into Tue. Though with this said there are
signals that we could have strong winds and heavy downpours,
which could potentially lead to flooding concerns.

Strong wind risk...

Will have an anomalously strong low level jet impinging on our
region. The latest NAEFS and EPS guidance indicate winds of
1.5-2.5 STD above model climatology. These anomalies are highest
at the 850 hPa level. At this point looks like a 30-40+ kt S to
SW/W low level jet slides through. The timing appears most
likely late Mon into early Tue. The V component of the wind is
actually 2-3.5 STD above model climo signaling a fairly
anomalous event. The question will be how much of this can
actually mix down, as GFS soundings at this point show we remain
inverted. Something to keep an eye on, but this anomalous
north/south component of the wind will also act to pump in
higher moisture values.

Heavy rain/thunder risk...

As mentioned the S/SW low level jet impinging on the region
will pump in anomalously high moisture values. At this point
PWATs appearing to increase to roughly 1-2 inches. The NAEFS/EPS
are more muted at 1.25-1.5 inches, which is still 1.5-2 STD
above model climo. Could have a few hundred J/kg of MUCAPE in
place along with warm cloud layer depths of 3.5-4 km. So,
rainfall processes could be efficient. Given this setup and
these values think that the WPC Marginal Excessive Rainfall
Outlook suffices for now. The GEFS continues to not be as amped
up with the heavy rain risk with low to nil probs of 24 hr QPF
AOA 1 inch into early Tue. The EPS/GEPS indicating low to mod
probs (10-40 percent) of 24 hr QPF AOA 1 inch and highlight the
greatest risk along the immediate south coast. The EPS even
shows some low probs for 24 hr QPF AOA 2 inches. Given the
discrepancy have just stuck with WPC for QPF for now.

Will also note that there is roughly 30-50 kts of 0-6 km bulk
layer shear in place. The low/mid level lapse rates are quite
poor. Given the GFS inverted profiles am thinking will be tough
for any stronger storms, but CSU MLP do indicate some low probs
for strong/severe storms. More concerned with the heavy rain
risk at this point, but something to keep an eye on.

Wednesday through Thursday...

Caught under cyclonic flow through this timeframe with a cutoff
nearby or a trough overhead. Still unsettled through this
period, but with considerable uncertainty on how things evolve
given it will depend on how things pan out in prior periods.

Due to the high uncertainty in this period have just stuck with
the NBM. This keeps slight chances to chances of precip. This
should suffice for now. Temperatures still around seasonable
levels on Wed, but we may turn cooler as we head later into the
week.

&&

.AVIATION /11Z FRIDAY THROUGH TUESDAY/...

Forecast Confidence Levels:

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

Today...High confidence. Moderate at ACK.

VFR conditions anticipated everywhere today with gusty (20-25
kts) W winds. The only exception is for ACK where LIFR stratus
will linger nearby for much of the day. Think the sun should
burn most of this off for a bit this morning, but as winds turn
more SWly this afternoon could see it redevelop as we head into
the evening. Have only lowered to MVFR levels to hint at it, but
will need to be lowered in future updates if it appears more
likely.

Tonight...High confidence.

VFR at all locations with winds shifting from the W/WNW to the
NW as a cold front slides through. Should see any lingering LIFR
stratus/fog at ACK clear as winds turn NW roughly 04-07Z.

Saturday...High confidence.

VFR with sea breezes expected to develop by mid to late morning.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Saturday Night through Tuesday/...

Saturday Night: VFR. Slight chance SHRA.

Sunday: VFR. Slight chance SHRA, isolated TSRA.

Sunday Night: VFR.

Memorial Day: Mainly VFR, with local MVFR possible. Breezy.
Chance RA.

Monday Night: MVFR/IFR conditions possible. Breezy. RA,
isolated TSRA.

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

&&

.MARINE...

Forecaster Confidence Levels:

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

Through Saturday...High Confidence.

A cold front should move across the waters today, followed by a
secondary cold front tonight. Gusty SW to W winds today diminish
this evening and turn NW to N. More light and variable winds for
Saturday. Local sea breezes near shore Saturday. Rather light
seas expected through Saturday.

Outlook /Saturday Night through Tuesday/...

Saturday Night: Winds less than 25 kt.

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

Sunday Night: Winds less than 25 kt.

Memorial Day: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain.

Monday Night: Winds less than 25 kt. Seas up to 5 ft. Rain
likely, isolated thunderstorms.

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

&&

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

&&

$$

SYNOPSIS...Belk/BL
NEAR TERM...Belk
SHORT TERM...Belk/BL
LONG TERM...BL
AVIATION...Belk/BL
MARINE...Belk/BL