538
FXUS61 KBOX 191154
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
754 AM EDT Thu Jun 19 2025

.SYNOPSIS...
Hot and humid weather is expected today, with afternoon to early
evening strong to severe thunderstorms. The best chance of
severe weather today is in interior Southern New England.
Turning drier and much less humid on Friday, but also quite
windy by late June standards. Seasonably warm temperatures are
expected this weekend. Monitoring for thunderstorm potential
this weekend but the overall risk is low. A multi-day stretch
of significant heat is looking more likely for Monday through
Wednesday, with the potential for heat to reach dangerous
levels.

&&

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

Key Messages:

* Hot and humid weather with potentially dangerous heat indices away
  from the South Coast, Cape and Islands. Heat Advisories
  remain posted.

* Scattered to numerous thunderstorms in western New England
  between 2-7 PM, which move eastward toward eastern MA and
  northern RI toward sundown. Some storms are expected to become
  severe with damaging straight line winds, torrential
  downpours and frequent lightning.

Details:

Similar to the last few nights, we are again dealing with low
clouds and fog given the humid conditions. This cloud cover and
fog should gradually erode shortly after sunrise, although it
does look to linger well into today over the South Coast, Cape
and Islands.

All that said, we are expecting an active period of weather for
today. Today should easily be the hottest and humid day
experienced to this point in summer 2025, which will bring
elevated heat indices between 95-104 degrees. Meanwhile, we also
expect scattered to numerous thunderstorms to break out as soon
as 2 PM in far western New England, which will then move
eastward toward the eastern coastline late in the day. Some of
these storms are expected to become severe given the hot and
humid airmass in place. These storms are in response to a
seasonably-potent, 1000 mb low pressure area now over central
MI, a feature which is expected to deepen to around 994 mb as it
moves ENE into the St. Lawrence Valley later today.

1/ Heat and Humidity

The Heat Advisory issued yesterday remains valid for today and
there have been no changes to its status. With several hours of
full sun after early- day fog and stratus disperses, we expect
temperatures to warm into the lower to mid 90s, and with
dewpoint temperatures in the low to mid 70s, it may feel closer
to the low 100s.

Though there is potential for storms to arrive earlier in the
afternoon than previously anticipated (more on that to follow),
which could perhaps cut into heat indices in the western end of
the Advisory area, it should nonetheless be quite hot and humid.

While still quite muggy over the south coast, Cape and Islands,
these areas are likely to remain in low clouds most of the day
which will keep high temps into the 70s to low 80s.

2/ Strong to Severe Thunderstorms This Afternoon

The hot and humid conditions will help generate pretty sizable
instability today, with surface based CAPEs reaching as high as
2000-3000 J/kg, although decreases pretty sharply as one moves
toward southeast New England. It`s pretty uncommon to have this
strong a low pressure interact with this degree of instability,
but when it happens it usually results in scattered to numerous
thunderstorms. It looks like convective inhibition becomes
minimized by early to midafternoon in western New England, and
by then we`ll be waiting for either a pre-frontal surface trough
or a remnant outflow left behind by overnight storms which
impacted northeast OH and western NY to help spark storms in
eastern NY. The degree of instability along with deep layer
windshear values nearing 40 kt should lead to a few severe
storms.

While the HRRR is slower and less bullish, most of the 00z
convective-permitting model suite has increased its
thunderstorm coverage into western and central MA and into
northern CT between 2-7 PM, which then moves eastward closer to
the eastern coast toward sundown. While the greatest risk for
severe weather today is mainly west and north of I-95, the
somewhat earlier start to storms supports a growing potential
for thunderstorms making the trip into eastern MA and northern
RI.

Damaging straight line winds is the primary severe weather risk,
along with torrential downpours which could lead to instances of
street flooding. While the risk of occurrence is low, with most
of the strongest flow confined to within the lowest 3-km,
leading to some fcst-hodograph curvature, wouldn`t rule out a
tornado in interior Southern New England. Hail is a remote
possibility given how warm it is out, although somewhat steep
700-500 mb lapse rates could support a risk.

&&

.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
Key Messages:

* Turning drier and becoming breezy tonight, with humidity
  levels dropping after midnight.

* Sunny, seasonably warm and tolerable humidity levels for
  Friday, but pretty windy with gusts 25-35 mph.

Tonight:

The cold front doesn`t actually arrive until late this evening,
but the risk for additional showers or thunderstorms after
sundown will be dwindling. It still ends up being partly to
mostly cloudy and still pretty humid until the front shifts
winds toward the west. It does turn somewhat breezy with speeds
10-15 mph and gusts 20-25 mph overnight, with falling dewpoints
toward more tolerable levels.

Friday and Friday Night:

The sub-1000 mb low pressure area passes offshore during the day
on Friday. Humidity levels are tolerable, and under full
sunshine we should see highs turn more seasonable in the lower
to mid 80s. The main story for Friday is that it should be
pretty windy for a typical summer day. A deepening PBL with full
sun with a 35-40 kt low level jet favors westerly gusts in the
25-35 mph range. But all in all, not a bad way to close the
workweek with dry weather. Wind speeds should decrease more
steadily into Friday evening, with lows in the mid 50s to around
60.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Key Messages:

* Warmer temperatures by the weekend. Possible risk for
  t-storms, but confidence in when and where is still uncertain.

* Multi-day risk of dangerous levels of heat for early to mid
  next week. Air temperatures themselves could reach as high as
  100 degrees away from the coast by Tuesday, with humidity
  making it feel even hotter.

Not much change in the anticipated pattern in midlevels in this
period per ensembles. A pronounced trough off the Pac NW coast
is expected to amplify a building midlevel ridge downstream in
the center of the nation this weekend, a feature will will
settle somehwere in vicinity of the mid-Atlantic states early
next week. Underneath this amplifying ridge is very hot and
conditionally unstable air, with an enhanced westerly jetstream
near/north of the ridge across the northern tier of states. In
fact 850 mb temps over the mid-Atlantic and Southern New England
could reach into the +22-24C range!

Saturday and Sunday:

Warmer weather then begins to return for the weekend as we get
into the northern periphery of the building ridge over the Ohio
Valley. High temps in the mid/upper 80s both days and turning
more humid as we move into Sunday.

The one thing that is less certain is the potential for
thunderstorms. Most of the ensembles and their deterministic
GFS/ECMWF/Canadian models show shortwave energy coming out of
northern Plains/Gt Lakes/Ontario area and then digging
southeastward on the periphery of extremely steep mid-level
lapse rates progged as high as 8.5 C/km. We could be having to
watch for thunderstorms, some of which could turn severe, but
too much uncertainty in the placement and timing of the
shortwaves aloft at this time. That could also help delay the
arrival of the really hot and humid air into early next week.

Early to Mid Next Week:

Confidence continues to grow regarding a spell of well above
normal temperatures and potentially dangerous heat Mon thru Wed.
ECMWF Extreme Forecast Index output continues to suggest
potential for highly anomalous heat. While both Mon thru Wed
look to feature highs in the 90s, air temps on Tue could
approach 100 degrees with high dewpoints making it feel even
hotter. Little nighttime relief is also anticipated.  HeatRisk
values rise into the Moderate to High levels, which translate to
a significant potential for heat- related illnesses. Heat
headlines will need to be considered for this potential stretch
of heat and humidity.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
Forecaster Confidence Levels...

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

12Z TAF Update:

Today: High confidence in trends, though moderate on timing.

IFR-LIFR stratus and fog dissipate for most airports between
13-15z; although at least IFR is likely to continue over the
Cape and Islands much of the day. VFR with hazy conditions once
stratus dissipates.

Growing consensus in scattered to numerous t-storms between
18-23z for BAF-BDL-HFD-ORH corridor, some which may turn severe.
Elected for prevailing VCTS with TEMPO 2 SM +TSRA in the
aforementioned timeframe. It`s still a question if BOS, PVD and
BED sees t-storms but the potential seems to be on the increase,
best chance between 22-00z. Maintained PROB30s for these TAFs,
and later TAF issuances could increase the t-storm potential
here. Damaging wind gusts and torrential downpours are the
primary severe-storm hazards. SW winds increase to around 10 kt
by late this morning, with developing gusts to 20-25 kt during
the afternoon.

Tonight: High confidence.

A low chance for lingering TSRA thru 02z but improvement is
expected at all airports. IFR stratus and fog out over the Cape
and Islands may still linger until we see a gusty westerly
windshift overnight. SW to W winds increase to around 10-15 kt
with gusts low-20s kt range and LLWS for the Cape and Islands
from a 40kt westerly low level jet.

Friday: High confidence.

VFR. W/WNW winds become gusty by late morning, with speeds
13-18 kt and gusts 25-35 kt.

KBOS Terminal...Moderate confidence in TAF.

IFR ceilings scatter to VFR after 14z, with possible HZ due to
very humid air. Monitoring for possible TSRA 22-00z; while
confidence is still lower on occurrence, the potential continues
to increase. Maintained PROB30 -TSRA for now. SW winds becoming
10-13 kt today with gusts 20-23 kt, with a windshift to W
overnight at similar speeds.

KBDL Terminal...Moderate confidence in TAF.

IFR ceilings scatter to VFR 14-15z, with possible HZ due to
very humid air. Greater potential for TSRA/+TSRA between 18-23z
and indicated VCTS starting 18z with TEMPO 2SM +TSRA 19-23z due
to growing confidence. Damaging winds, frequent lightning and
heavy downpours all threats in +TSRA. S winds around 10-12 kt
with gusts to 20 kt today, then with a windshift to W around
midnight at similar speeds.

Outlook /Saturday through Monday/...

Saturday: VFR.

Saturday Night: VFR. Chance SHRA, isolated TSRA.

Sunday: VFR. Breezy. Slight chance SHRA.

Sunday Night through Monday: VFR.

&&

.MARINE...
Forecaster Confidence Levels...

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

Small craft advisories have been expanded to all waters starting
this afternoon and were also extended into Friday. SW gusts
today should reach into the 25 kt range, although we expect
stronger gusts on Friday on all waters to around 30 kt. Gusts
could approach near gale force at times on Friday. Seas will
also be building today to around 3-5 ft, and then increase to
around 4-7 ft on Friday.

Because of the building seas and SW to W winds expected for
today and tonight, we`ve also hoisted a rip current statement
for today and Friday on south-facing beaches. It is somewhat
borderline today, but the threat for dangerous rip currents
should increase tonight and into Friday.

Outlook /Saturday through Monday/...

Saturday: Winds less than 25 kt.

Saturday Night through Sunday: Winds less than 25 kt. Slight
chance of rain showers.

Sunday Night through Monday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory from 11 AM this morning to 8 PM EDT this evening
     for CTZ002>004.
MA...Heat Advisory from 11 AM this morning to 8 PM EDT this evening
     for MAZ003>007-010>019-026.
     High Risk for Rip Currents from 2 PM EDT this afternoon through
     Friday evening for MAZ023-024.
RI...Heat Advisory from 11 AM this morning to 8 PM EDT this evening
     for RIZ001-002.
     High Risk for Rip Currents from 2 PM EDT this afternoon through
     Friday evening for RIZ008.
MARINE...Small Craft Advisory from 4 PM this afternoon to 8 PM EDT
     Friday for ANZ230>237-250-251-254>256.

&&

$$

SYNOPSIS...Loconto
NEAR TERM...Loconto
SHORT TERM...Loconto
LONG TERM...Loconto
AVIATION...Loconto/McMinn
MARINE...Loconto