076
FXUS61 KBOX 181740
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
140 PM EDT Wed Jun 18 2025

.SYNOPSIS...
Overcast and humid today with a period of morning showers, and
another round of showers mainly south of the Mass Pike early
tonight. Hot and humid weather for Thursday with heat indices
95 to near 100, with a risk for strong to severe thunderstorms
Thursday afternoon as a cold front moves through. Drier and
seasonably warm Friday and Saturday. A multi- day stretch of
significant heat is possible starting early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
350 AM Update:

Key Messages:

* Overcast conditions most of today, with foggy conditions early
  this morning dissipating by mid to late morning.

* Morning showers give way to brief dry weather this afternoon, then
  another round of showers and a rumble of thunder late this
  afternoon mainly south of the Mass Pike.

* Foggy conditions return again tonight.

* Humid with highs in the 70s, and muggy nighttime lows in the mid
  to upper 60s.

Details:

Not much has changed on the large scale compared to 24 hours
ago; the only real notable change being that its turned
increasingly more humid with dewpoints in the low to mid 60s.
We`re still stuck in a broad SW flow aloft in a regime of lower-
level moist SE/S flow. The increased moisture has led to a
blanket of stratus and areas of mist/fog but coverage of truly
dense fog is too sparse for dense fog headlines. A weak
disturbance embedded in the SW flow aloft is moving through
eastern PA, and this will spread an area of what should be
passing light to moderate showers ENE through the morning, which
will also impact morning commuters. Fortunately stronger
convection associated with this wave is well south of even the
Philadelphia, PA area so we`re not expecting any thunder with
this morning activity. We should then see a relative break in
shower activity by the afternoon.

There are two main question marks for today. The first is the
extent to which morning cloud cover lingers and tempers daytime
heating. RAP-based BUFKIT profiles are pretty saturated this
morning - makes sense, there`s stratus out there - but tends to
decrease in depth somewhat as we move into the early to
midafternoon. Probably still ends up cloudier on the whole even
if low cloud bases lift, due to an abundance of mid/high clouds,
and so high temps were reduced to the mid to upper 70s, but
these could still be a few degrees too warm. The next is the
location of another round of scattered showers arriving toward
late in the day and into the early evening, perhaps with a
rumble of thunder or two as showalter indices dip negative. This
is associated with another weak disturbance in the SW flow
aloft; seems to be greater agreement on this feature and its
associated showers passing over the southern third of SNE (south
of the Mass Pike including CT, RI and southeast MA), which also
will include the offshore waters. After a decrease in PoPs for
early to midafternoon, they again ramp up into the 30-50% range
south of the Mass Pike, and around 15-20% north of the Mass
Pike.

After this wave passes offshore, we`ll likely be dealing with
another period of fog and stratus with an even more muggy
airmass. Lows tonight only fall into the mid to upper 60s, which
will also be close to dewpoints.

&&

.SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
350 AM Update:

Key Messages:

* Hazy, hot and humid! Feeling like 95 to as much as 105 degrees by
  afternoon. Heat Advisory headlines could be needed.

* Scattered strong to severe thunderstorms as soon as 3 PM, but more
  likely between 5 to 9 PM as a line of storms moving through
  interior Southern New England, potentially to the coast. Damaging
  straight line winds are the main hazard, along with torrential
  downpours and frequent lightning.

* Much less humid Thursday night and drying out.

Thursday:

Likely will be dealing with a considerable amt of stratus and
fog, carrying over from the overnight. That being said, Thursday
still looks to be quite active, as this cloud cover should
erode early, leading to a hazy, hot and humid late morning to
midafternoon. A strong cold front associated with a pretty
strong frontal system for late-June will also lead to the
potential for strong to severe thunderstorms Thurs aftn. Let`s
talk about both below.

1/ Heat and Humidity

Without question, Thurs stands to be one of the hottest days
experienced to this point in the summer, but it will also be met
with high humidity levels. 850 mb temps warm on increasing SWly
low level flow to around +17 to +20C. High temps should soar
into the mid 80s Cape and Islands to the low to mid 90s. Given
dewpoint temps in the low to mid 70s, it may feel like it is
100-105 degrees outside in portions of the CT and Merrimack
Valleys, and could feel like 95-100 degrees across a wider
portion of Southern New England (excluding the south coast/Cape
Cod where it may feel closer to 90 degrees). Seabreezes are not
expected as SW surface winds pick up to around 10-15 mph. We
considered heat advisories, but consensus among surrounding
offices was to wait to re-evaluate if dewpoints could mix lower.
We encourage those to take appropriate heat-related precautions
such as taking frequent breaks in shaded and air conditioned
areas, and checking in on those sensitive to heat such as the
elderly and pets.

The high heat and humidity is not expected to break until the
cold front moves across the area later in the day on Thurs.

2/ Strong to Severe Thunderstorms Late in the Day

The hot and humid weather will also be accompanied by rather
steep lapse rates in the 850-500 mb layer at around 6.5 to 7
C/km, which will create an environment expected to be moderately
to strongly unstable. Afternoon CAPEs using a 100-mb mixed
parcel range around 1500-2500 J/kg with the highest values in
interior Southern New England. Quite high. Most models show
capping which should act to suppress convection until the cold
frontal forcing arrives; that`s the biggest question mark is
that there`s still some disagreement as to when the front
arrives. We anticipate the main threat for severe weather to
begin after 3 PM in western New England, and particularly in the
5-9 PM timeframe as a line of storms.

If any isolated storm were to develop on the prefrontal trough in
the mid to late afternoon, it would likely become strong to severe
quickly. But the main threat is from a line of strong to severe
storms moving in from eastern NY after 5 PM with the cold
front, as indicated by most convection allowing models. Of some
concern is that flow fields have trended a little stronger (850
winds now near 50 kt in some models), and bring deep shear
values to around 40 kt. While the greater threat for severe
weather is mainly west of I-95/I-495, some threat is possible
toward sundown in the Boston to Providence corridor, especially
if convection can get going sooner.

Damaging wind gusts are the primary hazard, but with a linear
storm mode and the increased low level windfields, a brief
tornado embedded in the line could exist too. Street flooding
could be possible in isolated instances, but the storms should
be moving along at a good clip. Hail`s secondary risk too, but
the linear storm mode and the hot airmass probably limits this
potential. Included gusty winds, small hail and heavy downpour
hazards in enhanced wording, and messaged as scattered
thunderstorms to bring greater awareness.

Those with plans outside during the afternoon, especially from
the Berkshires/Litchfield Hills eastward to Metrowest, will want
to keep close tabs on the forecast for the afternoon.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
Key Messages:

* Seasonably warm but less humid Fri into Sat.

* Growing confidence in a multi-day stretch of heat and
  humidity, starting as soon as Sunday but peaking Mon thru Wed.
  Air temps could reach the mid to upper 90s with humidity
  making it feel even hotter. Heat headlines could be needed.

* Mainly dry, but will need to monitor for possible T-storms. Timing
  is still uncertain.

Details:

Quasi-zonal midlevel pattern begins on Fri per ensemble means, but
is expected to amplify rather significantly for late in the weekend.
This occurs as a strong upper trough moves into the Pacific
Northwest states, causes a building heat ridge over the center of
the country to amplify downstream to anomalously strong levels, with
the center of this heat ridge moving eastward into the mid-Atlantic
states.

As for temperatures, Friday and Saturday are generally seasonably
warm and less humid. As the upper ridge amplifies and settles over
the mid-Atlantic region, there is growing confidence in a multi-day
stretch of high heat and humidity. We may begin to see temperatures
return into the 90s on Sunday, but the heat peaks in the Mon thru
Wed timeframe. Latest ensembles continue to point to heat and
humidity levels at least as high as Thurs, if not higher, and also
over a stretch of a few days. Heat headlines could be needed at some
point if confidence continues to increase.

We will have to monitor for embedded shortwave trough "ridge
rollers" along an active storm track over the northern tier of
states, rotating around the heat ridge. Some models indicate Sat
night into Sun as one possible period to watch, but confidence is
lower on those details. Thunderstorms could be possible if we lie in
the track of these disturbances but it is too difficult to pinpoint
at this point in time.

&&

.AVIATION /18Z WEDNESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels...

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

18Z TAF Update:

Rest of Today: Moderate confidence.

Still some lingering IFR CIGS out there, otherwise MVFR for the
remainder of the afternoon and evening. Cape and Islands remain
IFR/LIFR the rest of the day. Light south winds at 5-10 knots

Tonight: High confidence.

IFR/LIFR stratus and fog sets in between 02z-06z with periods
of light rain and drizzle esspically over the Cape and Islands.
Light SW winds.

Thursday: Moderate confidence.

IFR/LIFR Fog and stratus should be quicker to burn off
tomorrow, generally dissipating between 13-15z except over the
Cape and Islands where IFR conditions will persist. Then VFR
with gusty SW winds at 20-30 knots. Thunderstorms form in
Western MA around 21-23z and move east through about 02-04z.
Greatest area of uncertainty is between ORH and BOS where
Thunderstorms may not quite make it to the eastern sea board.

Thursday Night: Moderate Confidence.

Winds turn west with the passage of a cold front, allowing CIGS
to remain VFR with the exception of the Cape and Islands. Cold
front may not clear there until Friday morning finally allowing
CIGS to improve to VFR.

KBOS Terminal...Moderate confidence in TAF.

MVFR this afternoon and evening. IFR stratus and fog should move
in around midnight, with LIFR CIGS between 08z-12z. CIGS should
improve to VFR quickly after 15z tomorrow with gusty SW winds
around 20-25 knots. Thunderstorms may reach the terminal around
00z friday, but more likely to occur out west.

KBDL Terminal...Moderate confidence in TAF.

MVFR the remainder of the afternoon and evening. IFR/LIFR status
and fog move in after midnight tonight. Should see clearing to
VFR by 15z tomorrow, then chance for thunderstorms late tomorrow
afternoon/early evening

Outlook /Friday through Sunday/...

Friday: VFR. Breezy.

Friday Night through Saturday: VFR.

Saturday Night: VFR. Slight chance SHRA.

Sunday: VFR. Breezy. Slight chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Winds and seas through Wednesday night should remain below small
craft advisory thresholds. S winds around 10-15 kt with seas
around 4 ft or less. Could need small craft advisories on Thurs
at least from building seas to near 5 ft, although SW winds will
become around 20-25 kt.

Foggy conditions this morning should begin to disperse by this
afternoon, but fog is likely to return again tonight. Potential
for strong to severe thunderstorms in the nearshore waters late
Thursday.

Outlook /Friday through Sunday/...

Friday: Winds less than 25 kt. Local rough seas.

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

Saturday through Sunday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory from 11 AM to 8 PM EDT Thursday for CTZ002>004.
MA...Heat Advisory from 11 AM to 8 PM EDT Thursday for MAZ003>007-
     010>019-026.
RI...Heat Advisory from 11 AM to 8 PM EDT Thursday for RIZ001-002.
MARINE...None.

&&

$$

SYNOPSIS...Loconto
NEAR TERM...Loconto
SHORT TERM...Loconto
LONG TERM...Loconto
AVIATION...KP
MARINE...Loconto