154
FXUS61 KBOX 251823
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
223 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 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 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 /19Z 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 /Thursday through Saturday/...

Wednesday Night: MVFR/IFR conditions possible. Breezy. Chance
SHRA, isolated TSRA, patchy BR.

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.

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 Saturday/...

Wednesday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Local rough seas. Chance of rain showers,
isolated thunderstorms, patchy fog. Visibility 1 to 3 nm.

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