467
FXUS61 KBOX 251751
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
151 PM EDT Tue Jun 25 2024

.SYNOPSIS...
Although we will see an increase in cloud cover tonight, dry
weather and southwest breezes are expected. Increasing humidity
levels for Wednesday, with a risk for showers and thunderstorms
later in the afternoon into the evening. Some storms could turn
strong Wednesday afternoon and evening. Drier weather for late
in the week along with decreasing humidity levels. However we
enter a warming trend into the weekend, which will also increase
our chances for showers and thunderstorms this weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
150 PM Update:

Pleasant afternoon across Southern New England this afternoon
under influence of surface ridge of high pressure. Temperatures
at this hour are in the 80s for most, with mid to upper 80s
being common over the interior. Northerly breezes and tolerable
levels of humidity (e.g. dewpoints in the mid 50s to around 60)
are accompanying this summer warmth, so all in all, hard to
find much fault in the weather today. Well to the west over the
eastern Gt Lakes/far western NY, day cloud phase satellite
imagery shows quite a plume of mid to high level cloud cover
within a seasonably strong belt of westerly flow aloft. This is
associated with a re-organizing cluster of strong thunderstorms
over OH and Lower MI; while this active area of thunderstorms
will remain over OH and PA well to our west with high confidence,
its associated shield of mid and high cloud cover will be
overspreading our area for the evening and overnight.

So for tonight...expect winds to gradually shift from a WNW
direction to a WSW/SWly one around 10 mph. With that windshift
will bring the aforementioned shield of mid and high level cloud
cover that is over the eastern Gt Lakes region. Despite high res
guidance insisting otherwise, this guidance is too bullish in
showing any rain with this shield of cloud cover as it is (1)
too high in the sky to generate any precipitation and (2) quite
dry in the lowest few thousand feet AGL to support precip. So
really just expecting an increase in midlevel cloud cover but
looking for dry weather for the balance of the evening and
overnight. It will however start to bring humidity levels back
up some with dewpoints in the lower 60s by daybreak Wed, but
still fairly tolerable overall. Sided lows toward the milder end
of guidance since SW winds should stay up all night and the
advancing canopy of midlevel cloud cover should mitigate much
radiational cooling. Opted for lows in the mid 60s, with upper
60s/around 70 possible in the urban areas.

&&

.SHORT TERM /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 /17Z TUESDAY THROUGH SATURDAY/...
Forecast Confidence Levels:

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

18z TAF Update:

Through 00z Wednesday: High confidence.

VFR. WNW winds around 10 kt to begin a gradual turn/backing
to WSW/SW through late-aftn. Still a window for a seabreeze on
the eastern MA coast between 18-20z but indicated TEMPO for this
potential.

Tonight: High confidence.

VFR, although with an increasing canopy of mid to high clouds
(at/above 11kft) tonight. SW winds around 7-10 kt.

Wednesday and Wednesday Night: High confidence in the morning,
then becomes moderate for the afternoon/evening.

VFR with SW winds around 10-12 kt (gusts 23-27 kt) during the
morning to at least the early aftn. Scattered t-storms are
still anticipated, better shot along/south of I-90, but the
timing is uncertain. Storms could begin in the 18-21z timeframe
but seem more likely after 21z and into the evening hours. Some
storms could be strong, especially if they develop on the
earlier end of that timing window. SW winds ease to around 5-10
kt for the evening while shifting a bit to W late.

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 18-20z window
for a possible seabreeze. 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 8 PM this evening to 8 PM EDT
     Wednesday for ANZ231>234.
     Small Craft Advisory from 8 PM this evening to 8 AM EDT
     Thursday for ANZ235-237.
     Small Craft Advisory from 2 AM to 8 PM EDT Wednesday for
     ANZ236.
     Small Craft Advisory until 8 AM EDT Thursday for ANZ254>256.

&&

$$

SYNOPSIS...KJC/Loconto/BW
NEAR TERM...Loconto
SHORT TERM...BW
LONG TERM...KJC
AVIATION...KJC/Loconto/BW
MARINE...KJC/BW