590
FXUS61 KBOX 251436
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1036 AM EDT Tue Jun 25 2024

.SYNOPSIS...
Very warm, if not hot, conditions with comfortable humidity
today. Increasing humidity levels Wednesday with the risk for
showers and thunderstorms, and some could become strong. Drier
and less humid to end the workweek, although summerlike warmth
and humidity return by late this weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
1020 AM Update:

Forecast in general seems on track with a very warm day ahead
but one with tolerable levels of humidity. Surface ridge to our
west over the Catskills in NY is expected to shift eastward thru
midafternoon. That will result in a period of easing WNW winds
toward a WSW/SW windshift by later in the day. In the
intervening period of time around later-morning to early
afternoon, the gradient slackens enough to open the door for a
possible seabreeze near the coast, indications reflected in
recent NAM-3km and HRRR surface wind guidance. It`s not really
set ins tone but if we do seabreeze on the eastern MA and
Narragansett Bay coastlines, it ultimately may be short-lived
with prevailing synoptic SW gradient developing. Tried to better
show this potential by incorporating some of the HRRR wind
guidance into the wind grids for the early aftn. But all in all,
pretty pleasant mid-summmer conditions for Tuesday.

Previous discussion:

Highlights

* Quiet and mild conditions across southern New England today.
  Could be a bit breezy at times this afternoon. Increasing
  mid to high clouds late.

Currently caught between a a trough over the Gulf of ME and a
ridge building into the eastern Great Lakes. The ridge axis
will build into New England today, while a decaying MCs rides in
its wake into the eastern Great Lakes late today. High pressure
builds over our region today.

Dry and quiet weather anticipated across southern New England
today. As that decaying MCs slides into the eastern Great Lakes
we will see some increasing mid to high clouds, especially late
this afternoon. Otherwise weather is quite nice today with
plenty of sunshine. Could be a bit breezy as the boundary layer
should be able to mix to roughly 700-800 hPa per Bufkit
soundings. Given the NW to W flow for much of the day should see
us mixing out the dew points a bit, so blended down from the
default NBM due to downsloping. Have also bumped temps up to
the 75th percentile of guidance to account for downsloping.
Highs in the 80s for most, but will see some lower 90s across
the Merrimack and CT River Valley. Should be fairly nice with
dew points comfortably in the 50s.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
Highlights

* Still fairly quiet tonight into early Wed. Though there could
  be a few decaying spot showers across the interior tonight.

* Hot and muggy on Wed. Will have late day thunderstorms.
  Isolated severe risk possible with the main threats of
  damaging wind gusts and heavy downpours, which could lead to
  localized flooding.

Pattern becomes quasi-zonal during this timeframe. The
MCs/shortwave over the eastern Great Lakes will lift through New
England tonight. A more substantial trough (and our next weather
maker) will dig from the Northern Plains tonight into the
western/central Great Lakes by mid Wed. The trough lifts into
the eastern Great Lakes by late Wed. A warm front lifts into and
through much of southern New England tonight. The trailing cold
front slides in later on Wed.

Next shot for potentially impactful weather comes later on Wed
where we could have some isolated strong to severe storms. This
is the main focus of the short term. Though will note that did
put in slight chances of a few spotty showers tonight across the
interior as the warm front is moving through. For most should
be dry tonight, but with mid/high clouds overhead.

Since previous update it appears that guidance continues the
trend of bringing the cold front in slower. This generally
keeps our weather dry for much of the day, but there is an
increasing risk for showers/storms during the afternoon/evening.
Will see instability values increasing to roughly a few hundred
to 1500 J/kg across. Appears at this point that would be
maximized across CT and portions of the interior. Will see deep
shear in the 0-6 km layer increase to 30-40+ kts, which is more
than sufficient for organized thunderstorm development. Some
uncertainty on timing a potential EML as some pieces of guidance
showing 6-8 degree mid level lapse rates overhead during the
afternoon, while low level lapse rates are roughly 7-9 degrees.
The big questions at this point are we are somewhat removed from
the stronger upper forcing, mid level moisture may be lacking a
bit and there could be a bit of a cap to break per Bufkit
soundings. Though some pieces of guidance do bring in 1.5+ inch
PWATs into the afternoon/early evening, but most showing more
impacts for our area Wed Night. With this all said and taking
into the account the ML guidance. There are signals for strong
to perhaps damaging wind gusts along with heavy downpours, which
if they fall over the wrong spots could produce localized
flooding. Think at this point the latest SPC Marginal Risk for
Severe Weather in Day 2 and WPC Marginal Risk for Excessive Rain
is fine. The HREF does show some low probs with 3-hourly PMM of
3 hr QPF greater than 3 inches late on Wed across portions of
western MA/CT. This is also the area where ML guidance (CSU ML
and NCAR HRRR Neural Network) indicating greatest risk for
stronger storms in our area. Stay tuned for future updates on
this risk.

Given the increasing S to SWly flow ahead of the cold front
will see oppressive dew points spreading in as we get well into
the 60s for much of the region. Will also be quite warm with
temps ranging from the mid 80s to the mid 90s. Should see those
warmest readings across the CT/Merrimack Valley. Though it will
be muggy, we fall well short of Heat Advisory criteria at this
time. Still will be a good idea to take typical summertime
precautions of staying hydrated and cool.

&&

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

* Couple rounds of showers and thunderstorms during this portion
  of the forecast.

* Expecting temperatures to fluctuate between near normal and
  above normal.

* Becoming less humid late this week into Saturday, before
  briefly becoming very humid Sunday. Trending less humid
  early next week.

Looking like our region will be contending with leftover
convection Wednesday night into Thursday. Latest guidance
communicated a mixed message. While there are some ingredients
to support stronger thunderstorms, they may not all be in place
at the proper time. For example, the peak mid level lapse rates
and shear may not quite line up with the peak instability. Will
need to monitor the details and adjust over the next day or so.
Current thinking is the most likely outcome will be
diminishing/weakening convection across most of southern New
England as it moves east Wednesday night. The steeper than moist-
adiabatic mid level lapse rates may sustain a few stronger
thunderstorms past sunset.

The cold front helping to trigger these showers and thunderstorms
should still be somewhere across southern New England Thursday
morning, thus still a lingering risk for some showers. These would
be most likely across RI and eastern MA. Once this front finally
moves offshore, we should be looking at less humid conditions
arriving for Friday.

Drier conditions should last until another cold front approaches
from the west sometime Sunday. Still too early to pin down the
details. In general terms though, thinking our region gets into a
brief period of very warm and humid conditions, but not like the
heat we had last week. It should certainly not last nearly as long.
Expecting cooler and less humid air to arrive early next week.

&&

.AVIATION /15Z TUESDAY THROUGH SATURDAY/...
Forecast Confidence Levels:

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

15z TAF Update:

Today: High confidence, though closer to moderate on seabreeze
potential.

VFR, with increasing covg of mid/high clouds later in the day
into tonight. NW winds around 10 kt to start are projected to
slacken a bit late this morning into the early aftn, which could
open the door for a possible seabreeze on both coasts around
~16-18z; still is somewhat uncertain if it develops but if it
does, it would be be pretty short-lived with prevailing WSW/SW
winds by late-aftn.

Tonight...High confidence.

VFR with mid to high clouds continuing to increase. Winds out of
the SW at 5-15 kts. Could see some 15-25 kt gusts after 06Z with
the highest speeds along the immediate south coast.

Wednesday...High confidence in AM. Lowers to moderate for PM.

VFR conditions are anticipated for much of the day. Confidence
lowers to moderate during the afternoon/evening as a cold front
triggers showers and thunderstorms. Not certain at this point on
coverage and exact timing, but risk seems highest across CT into
interior MA. If individual storm moves over terminal could see
brief MVFR to IFR conditions. Not out of the question there are
strong to damaging wind gusts if a stronger storm or two can
develop. Winds out of the WSW/SW at 10-15 kts with gusts of
20-30 kts.

KBOS TAF...High confidence in TAF, though moderate on sea-breeze
development. VFR for much of the TAF period. WNW winds arounhd
10 kt to start, though may slacken enough in the 16-18z window
to allow a potential seabreeze to develop in that period of
time, but this isn`t set in stone and if it develops, would be
short- lived. By late-aftn, winds shift to SW/WSW around 10 kt.
Possible TS after 21z Wed but timing is still uncertain.

KBDL TAF...High confidence in TAF. VFR for most of the TAF
period. Winds to become SW around 10 kt this aftn/tonight with
increasing covg of mid/high clouds. Possible TS after 18z Wed
though timing is still uncertain.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: Mainly MVFR, with areas VFR possible. Breezy.
SHRA likely, slight chance TSRA.

Thursday: VFR. Chance SHRA.

Thursday Night through Friday Night: VFR.

Saturday: VFR. Breezy. Slight chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Have extended the Small Craft Advisory for the outer waters
through Wed evening. Though seas/winds will fall below SCA
conditions late today into this evening, they will redevelop
tonight into Wed with a strong SWly low level jet sliding in.

Hoisted Small Craft Advisory for the rest of the southern waters
and Cape Cod Bay due to the strong SWly low level jet previously
mentioned moving in late tonight into Wed.

Today...High confidence.

Winds shifting from the NW to the W/WSW as the day progresses.
Winds will be increasing this afternoon into the evening to
10-15 kts with some 20-25 kt gusts. Seas diminishing to 2-4 ft.

Tonight...High confidence.

Increasing SW to SSW winds with gusts of 20-30 kts. Seas
building 3-6 ft across the southern and eastern outer waters.


Wednesday...High confidence.

Winds remain out of the SW/SSW at 15-25 kts with gusts of 20-30
kts. Seas 4-6 ft across the southern waters and eastern outer
waters. Scattered thunderstorms could spread into the waters
late in the afternoon/evening.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Local rough seas. Rain showers likely,
isolated thunderstorms.

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

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

Friday through Saturday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 2 AM to 8 PM EDT Wednesday for
     ANZ231>237.
     Small Craft Advisory until 8 PM EDT Wednesday for ANZ254>256.

&&

$$

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