945
FXUS61 KBOX 070228
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1028 PM EDT Mon May 6 2024

.SYNOPSIS...
Dry and partly sunny conditions persist this afternoon except for a
slight chance of a band of isolated showers and an embedded
thunderstorm this afternoon and evening. Tuesday will be the pick of
the week with abundant sunshine and above normal temperatures.
Unsettled pattern mid to late in the week with cooler temperatures.
A few rumbles of thunder are possible, especially across the
interior on Wednesday. Milder this weekend with drier weather,
especially on Saturday.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
1020 PM update...

Low level drier air will gradually advect south across the
region overnight behind the weak front. But it will take until
the morning for the Cape/Islands where stratus and patchy fog
will linger tonight. Otherwise, high clouds will clear out late
tonight. With light winds, lows will settle into the 50s.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
Tuesday is the pick of the week as high pressure and a dry air mass
will bring a sunny day with even warmer temperatures than we saw
today. 925 mb temps increase from 15C today to 16-17C on Tuesday
which will support high temperatures in the mid 70s (inland) and mid
to upper 60s (coast). Winds will be light, becoming westerly in the
afternoon. By afternoon high clouds are on the increase ahead of a
warm front which approaches SNE overnight extending from an
approaching surface low over the Great Lakes. Clouds will thicken
and lower through the overnight hours ahead of widespread rain
showers moving in from the west. There remains some uncertainty as
to how quickly the showers move in, more likely holding off until
near or just after 8am.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Highlights

* Unsettled and cooler Wed through Fri.

* Trending drier on Sat with temps starting to rebound.

* Lots of uncertainty for Sun at this point, but the upward
  temperature trend may continue.

Wednesday...

Stuck under cyclonic flow through this period. A shortwave trough
lifts from the central Great Lakes early on Wed into Upstate
NY/northern New England by late in the day. A frontal boundary lifts
toward and perhaps through portions of our region. Lot of
uncertainty at this point which areas will be within the warm sector.

Still a fair amount of spread amongst guidance with how things
exactly evolve through this period. Latest suite of guidance has
trended a bit faster with bringing in the precip. Though there is
spread in where the heaviest rains will fall at this point in time
as there is spread in guidance with how convection evolves. At this
point appears that the greatest risk for thunderstorms is across the
interior, but especially across the Berkshires. This is where
ensembles GEFS/GEPS/EPS indicate anywhere from low to mod (10-70
percent) probs of CAPE AOA 500 J/kg. The risk is highest across the
Berkshires as even convective ensembles such NCAR C-ShiELD and MPAS
guidance also highlighting this area as well. This does coincide
with the GEPS/EPS guidance of total precip AOA 0.5" with low to mod
probs (10-60 percent) whereas the GEFS is essentially nil for our
area. Seems that the latest deterministic echoing the ensembles with
the ECWMF/GEM showing more precip for our area than the GFS. Hard to
say which is correct as we are a bit more removed from the
shortwave, but there is roughly 1-1.5 inch PWATs in place. For now
have stuck with NERFC QPF.

Still think that the latest SPC Day 3 Outlooks is reasonable given
the setup. The deep layer shear will not be an issue with bulk shear
of 40-70+ kts in the 0-6 km layer. The instability is more of a
question as mentioned previously and where we warm sector. The low
level lapse rates look quite pitiful at this point for our region.
However, mid level lapse rates are around 6-8 degrees Celsius during
the day. Forecast soundings show much of our area being quite
inverted or stable. This would limit activity to being more elevated
in nature. Think that there could be some hail risk with this. This
matches well with the CSU-MLP for Day 3. It does highlight a risk of
winds out in far western MA/CT where there is potential for being
more within the warm sector. Stay tuned for future updates.

Thursday and Friday...

Still unsettled through this timeframe as we remain under cyclonic
flow. Another shortwave ejects into and perhaps through our region
on Thu. The deeper trough over the Great Lakes is anticipated to
start moving late Thu through Fri. The trough digs from the Great
Lakes into the Mid Atlantic/southern New England on Fri. A frontal
boundary will still be nearby or over the region during this
timeframe. A few waves may ride along the front bringing us showers.

Guidance in a bit better agreement through this timeframe with a low
sliding along the front that is nearby/south of our region. This
will keep us unsettled with rain showers. Given the location of the
front and low we will remain on the cool side with persistent
onshore flow. Did nudge down our temps a bit from the NBM on Thu as
it is much too warm with persistent onshore low. For now have stuck
with the 50th percentile of guidance, but suspect we will need to
lower further in future updates. Actually appears that the NBM is
more dialed in on Fri with temps as again we`ve got persistent
onshore flow. Highs on Thu range from the 50s to mid 60s whereas Fri
we are generally in the 50s.

At this point it appears that showers will be around for a good
portion of this timeframe. The heaviest activity appears to be later
on Thu into early Fri as low pressure is deepening south of our
area. Removed thunder chances at this point given the cool onshore
flow and little if any instability. Ensembles indicating that 24 hr
probs of QPF AOA 0.5 inches is low to mod (10-60 percent) generally
southern New England region wide. Will also have a bit of an uptick
in wind speeds/gusts out of the E/ENE during this period. Though the
LLJ strength is a bit spread out amongst guidance from 10-20 kts to
up to 30-40 kts. This coupled with the high astro tides will likely
result in some issues across the eastern MA coast. See the coastal
flooding section for more details.

Saturday and Sunday...

Still under cyclonic flow through this period. Though does appear
that a shortwave ridge builds into the eastern Great Lakes/New
England for Sat. The next wave/trough slides into the Great
Lakes/Mid Atlantic for Sun. Drier on Sat as high pressure nudges in.
Another frontal system could slide in on Sun bringing us more
showers.

Not a whole lot of focus on this period given the active weather for
mid to late in the week. Have stuck with the NBM, which seems
reasonable at this point. Temperatures will be on an upward trend
through the weekend. High temps range from the mid 50s to the low
60s on Sat as we will still be under northerly flow. Winds shift to
a southerly direction on Sun, which will result in temps continuing
to trend upward. Highs generally in the 60s.

As mentioned there could be some showers spreading in on Sun, but
there is a significant amount of timing, intensity and placement
differences with the forcing. Think the NBM is fine at this point
with chances of precip.

&&

.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
Forecast Confidence Levels:

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

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

VFR for much of the interior with relatively light winds.
Elsewhere conditions deteriorate to MVFR/IFR along with LIFR,
especially along the immediate coastline. This is a result of
marine stratus/fog spreading in. Most confident for FMH/HYA and
ACK in LIFR conditions developing now through 02Z. Could see
some improvement visibility wise by 10-13Z as winds turn
northerly, but ceilings will be much slower to respond. Moderate
confidence for BOS/PVD and BED. Think BOS will briefly go down
to IFR before winds turn northwesterly and scatter things out.
PVD/BED should generally stay VFR, but a some IFR level bases
could leak in. Light SW winds turn to the N/NW late.

Tuesday...High confidence away from the Cape/Islands. Moderate
confidence for the Cape/Islands.


VFR for most of the region. The exception is Cape Cod, Nantucket
and Marthas Vineyard. Will start off across the Cape/Islands
with MVFR to LIFR stratus/fog. This will gradually erode and
improve to VFR, but timing wise probably not until 15-18Z.
Though ceilings may not improve at ACK as has been my experience
in these type of patterns in the past. Light northerly winds
shifting to the NW across the interior. Sea breezes along the
coastline due to light winds.

Tuesday Night...High confidence in trends, moderate in timing.

Starting off VFR for most. The only exception is at ACK where
lingering MVFR/IFR conditions possible. Will see an emergence of
MVFR to IFR stratus along the south coast. Could see some rain
showers spreading into the interior late, but think MVFR
ceilings won`t spread in until toward daybreak. Winds will be
relatively light out of the south.


KBOS TAF...High confidence in TAF through 06Z. Moderate
overnight into the AM push Tue.

Starting off VFR, but will see IFR/LIFR stratus/fog spread in
toward 06-10Z. Should see these lower ceilings scatter out
to VFR during the AM push, but some uncertainty here given the
weak winds. Will sea breeze on Tue 14-16Z with VFR conditions
for rest of TAF.

KBDL TAF...High Confidence in TAF.

Outlook /Wednesday through Saturday/...

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

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

Thursday: Mainly VFR, with local IFR possible. Breezy. SHRA
likely.

Thursday Night through Friday Night: Mainly VFR, with areas IFR
possible. Breezy. SHRA likely.

Saturday: Mainly VFR, with local MVFR possible. Breezy. Slight
chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Tonight through Tuesday night...High Confidence

Modest winds and seas continue tonight and tomorrow. Expect
areas of dense fog over the coastal waters tonight as moisture
increases from southerly winds. Fog should dissipate early on
Tuesday as a weak front ushers drier air over the coastal waters.

Outlook /Wednesday through Saturday/...

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

Thursday: Winds less than 25 kt. Chance of rain showers.

Thursday Night through Friday: Winds less than 25 kt. Seas up
to 5 ft. Rain showers likely.

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

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

&&

.TIDES/COASTAL FLOODING...
.Coastal Flooding...

High astro tides this week and concern becomes late Thu into Fri
with potential frontal wave tracking south of New England,
generating onshore flow into eastern MA. Magnitude of potential
inundation and erosion will depend on strength and timing of surface
low. Too early for specifics with any certainty, but given astro
tides are already over 11 ft at Boston, it will only take a 1 ft
storm surge and modest wave action to yield minor inundation and
erosion. Stay tuned throughout the week for updated information.

&&

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

&&

$$

SYNOPSIS...BW/BL
NEAR TERM...KJC/BW
SHORT TERM...BW
LONG TERM...BL
AVIATION...BW/BL
MARINE...BW/BL
TIDES/COASTAL FLOODING...BL