470
FXUS61 KBOX 251900
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
300 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 with increasing humidity into the
weekend, which will also increase our chances for showers and
thunderstorms this weekend.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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 /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
The most active period of the forecast continues to be centered on a
shortwave and associated cold front that will move from the Midwest
to the Great Lakes and into the Northeast on Wednesday. At the mid
levels we`ll see zonal flow become more meridional through the day
on Wednesday as the neutrally tilted trough axis digs into NY/PA.
The progression of the trough and cold front has been slowing down
over the last few days and with it the severe threat decreasing for
our area thanks to misalignment of the best forcing and axis of max
instability/shear. CSU machine learning probs of severe winds are in
line with this trend, continuing to back west where we expect the
better chance of severe weather. The warm, moist air that is
advected into SNE during the day on Wednesday behind a warm front
will lead to much more humid conditions and destabilization,
especially for areas south of a Hartford-Worcester-Boston line. This
is because hi-res guidance is indicating a weak shortwave and cold
front ahead of the main front which may keep dewpoints lower in
northwest/north central MA as it stalls overhead. Convergence
associated with this boundary may be the focus for a few isolated
thunderstorms Wednesday evening ahead of the main line, but the bulk
of the action should be overnight, between 8pm and 4am as the cold
front crosses the region. Confidence in the placement of this
boundary is low to moderate, however. Strengthening mid level flow
in the 500-700 mb layer will increase the 0-6 km bulk shear to 30-40
kts in the afternoon/evening so if there is enough lift to kick off
a storm in the 1500 J/kg CAPE environment there is potential a storm
could be organized enough to become severe. However, odds are low,
and by the time the best lift arrives overnight the instability will
have waned substantially making severe weather unlikely.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Highlights:

* Showers and a few t-storm lingering SE New Eng Thu AM, otherwise
  improving conditions

* Dry and seasonable Fri with low humidity

* Another round of scattered showers/t-storms Sat afternoon into
  Sun. Becoming rather humid Sun

* Dry and less humid Mon & Tue

Thursday and Friday...

Expect improving conditions from west to east on Thu as deep
moisture axis will be moving offshore. Still some timing differences
with how quickly the moisture moves to the east but consensus of the
deterministic and ensemble guidance suggests showers and a few t-
storms lingering Thu morning across SE New Eng near the cold front,
then should see at least partial sunshine developing from west to
east as good mid level drying moves in. Mid level shortwave will be
passing to the north Thu afternoon so can`t rule out a spot shower
but better chance will be across northern New Eng closer to the cold
pool aloft. Highs should reach into the 80s with decreasing humidity
in the interior, but it will remain humid in the coastal plain as
weak front hangs up near the coast.

The mid level trough moves to the east Thu night with high pres
building into New Eng through Fri. This will result in clear skies
Thu night and abundant sunshine Friday. Highs Fri will be in the
upper 70s to near 80, with coastal sea-breezes developing. Humidity
levels will be rather low as dewpoints drop into the 40s and lower
50s.

Saturday into Sunday...

Next mid level trough will be moving east across the Gt Lakes and
approaching New Eng Sun evening.  Deeper moisture axis with high
PWATs exceeding 2 inches will be moving into SNE, especially during
the afternoon and Sat night. Risk for showers and a few t-storms
will be increasing in the west Sat afternoon, but better chance will
be Sat night into Sunday across entire region as forcing for ascent
and instability increases ahead of the mid level trough along with
the cold front moving into SNE Sun afternoon. Given rather high PWAT
airmass, heavy rainfall will be the primary threat, but as surface
instability increases on Sunday will have to watch the potential for
a few strong storms.  A lot will depend on timing of drier air
moving in from the west which is uncertain at this time range. Temps
will be close to seasonable norms but humidity levels will begin to
increase late Sat-Sat night, peaking on Sunday with oppressive
humidity possible as dewpoints potentially reach the low to mid 70s.

Monday and Tuesday...

Cold front moves offshore Sun night followed by high pres and much
drier airmass Mon into Tue. Will set the stage for sunshine,
seasonable temps and low humidity early next week.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
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 around
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 /Thursday through Sunday/...

Thursday: VFR. Breezy. Slight chance SHRA.

Thursday Night through Friday Night: VFR.

Saturday: VFR. Breezy. Chance SHRA.

Saturday Night: MVFR/IFR conditions possible. Breezy. SHRA
likely, chance TSRA.

Sunday: Mainly MVFR, with local IFR possible. Breezy. SHRA
likely, chance TSRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Small Craft Advisories have been extended for the most of the
southern waters through Wed night. Though seas/winds will fall
below SCA conditions this evening, they will redevelop tonight
into Wed with a strong SWly low level jet sliding in.

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.

Wednesday night...High confidence.

Winds SW 15-25 kts with gusts of 20-30 kts. Seas 5-7 ft.
Scattered showers and thunderstorms continue into the morning.

Outlook /Thursday through Sunday/...

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

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

Friday through Friday Night: Winds less than 25 kt.

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

Saturday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers,
slight chance of thunderstorms.

Sunday: Low risk for Small Craft Advisory winds with gusts up
to 20 kt. Seas up to 5 ft. Rain showers likely, chance of
thunderstorms.

&&

.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