623
FXUS61 KBOX 051111
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
711 AM EDT Thu Jun 5 2025

.SYNOPSIS...
Hot and somewhat humid conditions are on tap for today with the risk
of afternoon and evening isolated showers and thunderstorms...but
most locations will remain dry. A much better chance of showers and
thunderstorms exists Friday especially north of the Connecticut and
Rhode Island border...where localized torrential rainfall and an
isolated threat for severe weather will exist. A few showers and
thunderstorms will remain possible Saturday but with temperatures
cooling to seasonable levels. Mainly dry and seasonable weather is
expected Sunday and Monday before the next chance of showers arrives
by next Tuesday and/or Wednesday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Key Messages...

* Hot & somewhat humid today with isolated showers/thunderstorms
  possible this afternoon and evening...but most locations remain dry

* High temps in the 90-95 degree range away from the immediate coast

Details...

Upper level ridging will be in control of our weather today. The
above normal height fields will result in 925T reaching around +25C
this afternoon. Plenty of sunshine is expected today and while the
HRRR/RAP indicate some smoke/haze in the sky today...the values are
not as high as yesterday so do not expect a big impact on
temperatures. Given the above...expect a hot and somewhat humid day.
High temps to reach between 90 and 95 today in many locales away
from the very immediate coast. Dewpoints will be in the lower to
middle 60s...so heat index values will reach the lower to middle 90s
in many locations. We do not meet the criteria for any heat
headlines...but our experimental HeatRisk page is indicating
moderate impacts to individuals who are sensitive to heat.
Temperatures will be a few degrees cooler in the high terrain as
well as the immediate coast with some localized sea breezes.

The other issue is the risk for isolated showers/thunderstorms this
afternoon and evening with modest instability developing. Upper
level ridging overhead will limit forcing/upper level support...so
any activity that develops should be isolated with most locations
remaining dry. Some of the high resolution guidance indicates a bit
better chance for isolated activity near and south of I-90...
especially on any weak sea breeze front that develops or near
terrain changes as a result of elevated heating.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
Key Messages...

* Dry/mild tonight after any isolated evening activity dissipates

* Areas of showers/t-storms Fri with localized torrential rain with
  the focus for more widespread activity north of CT/RI/MA border

* Isolated severe weather potential Fri

Details...

Tonight...

Any isolated activity that is able to develop this afternoon will
dissipate this evening with the loss of daytime heating and limited
upper level support. Otherwise...mainly dry and unseasonably mild
temperatures tonight. A ridge of high pressure off the mid-Atlantic
coast will result in a most low level southwest flow tonight. This
will hold low temps mainly in the middle to upper 60s...except a bit
cooler from the modified marine airmass near the south coast. We may
have some low clouds and fog patches try to develop near the south
coast...but do not think any of that will make it much further north
than that.

Friday...

A warm and humid airmass is on tap for Friday. While it will not be
as hot as today...highs will still be into the 80s with dewpoints in
the 60s. This will create a modest amount of instability with the
HREF indicated 1500-2000 J/KG of Cape. This combined with a
shortwave and a weak low level convergence boundary to ignite
showers and thunderstorms. While this activity may occur just about
anywhere...it looks like the primary area of concern will be north
of the boundary where there is deeper moisture/forcing. So thinking
that areas north of the CT/RI/MA border and especially across
northern MA will see a fair amount of showers and thunderstorms
developing by Friday afternoon. Pwats in excess of 1.5 inches and
weak wind fields may result in torrential rainfall with any of the
stronger t-storms along with very localized street flooding.
Effective shear is on the lower side of what we like to see for
severe weather...generally 20-30 knots but that is enough for some
organized convection and perhaps an isolated severe weather risk
too. The HREF is indicating fairly impressive probs of 2-5 KM UH
swaths north of the CT/MA/RI border and especially in northern MA.
The CSU Machine learning probs along with the HRRR Neural Network
indicate an isolated severe weather risk...especially across
western/central and northern MA. The main threat will be localized
strong to damaging wind gusts.

Given the above...we expect a fair amount of showers and
thunderstorms to develop Friday. While the activity is possible
anywhere...the focus or the majority of them north of the CT/RI/MA
border. Main concern is pockets of torrential rainfall with the
stronger slow moving storms and very localized street flooding.
While shear is limited...20-30 knots north of the CT/RI border
combined with the UH swaths might be enough to support an isolated
severe weather threat. The main severe threat would be localized
strong to damaging wind gusts the main concern.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Key Messages:

* Chance that showers and thunderstorms linger into Saturday

* Briefly dry Sunday into Monday before rain chances return Tuesday

* Highs mostly in the upper 70s and low 80s through this period,
  aside from Saturday

Details...

Another round of showers likely throughout Saturday as a cold front
moves into southern New England. While thunder can`t be ruled out as
the NAM`s SBCAPE values look to be around 1000-1200 J/kg, severe
storms are not likely.

Guidance is hinting at a mostly dry Sunday heading into Monday as a
broad high pressure starts to build over central Ontario. Rain
chances and elevated surface moisture make a return Tuesday through
Wednesday as a cold front sweeps through the Mid-Atlantic.

Regarding temperatures... highs across southern New England are
expected to remain in the upper 70s and low to mid 80s through the
period. Saturday could be the exception as there is a chance some
areas could remain in the lower 70s. Lows generally expected to
remain in the high 50s to low 60s through the period.

&&

.AVIATION /11Z THURSDAY THROUGH MONDAY/...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

12z TAF Update...

Today...High confidence.

VFR. SW winds 5-10 knots except for sea breeze development on
portions of the immediate coast and 15-20 knots gusts over the
Islands. There also will be an isolated shower/t-storm threat
this afternoon into this evening...but most locations will
remain dry.

Tonight...High confidence.

VFR outside some patchy of fog and low clouds which may develop near
the south coast, Cape and Islands. Winds becoming light-calm.

Friday...Moderate confidence.

Varying conditions expected with VFR conditions and then times of
MVFR-IFR cigs/vsbys in scattered showers and t-storms...a few of
which might be strong and contain torrential rainfall resulting in
brief LIFR conditions. Areal coverage will be greatest north of the
CT/RI/MA border. Light and variable winds.

Outlook /Friday Night through Monday/...

Friday Night: Mainly VFR, with local MVFR possible. Chance
SHRA, isolated TSRA.

Saturday: Mainly MVFR, with areas VFR possible. Chance SHRA,
isolated TSRA.

Saturday Night: Mainly VFR, with local MVFR possible. Chance
SHRA.

Sunday: VFR. Slight chance SHRA.

Sunday Night: Mainly VFR, with local MVFR possible. Slight
chance SHRA.

Monday: Mainly VFR, with local IFR possible. Slight chance
SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Today through Friday...High Confidence.

Pressure gradient will remain weak enough to keep winds/seas below
small craft advisory thresholds through Fri. The main concern will
be the risk for an isolated t-storm this afternoon/evening near
shore with a better chance Fri especially across the waters adjacent
to northeast MA. Lastly...areas of fog will be possible late tonight
into Friday morning across the southern waters.

Outlook /Friday Night through Monday/...

Friday Night: Winds less than 25 kt. Slight chance of rain
showers.

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

Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Slight chance of rain showers.

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

Monday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Slight chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Air Quality Alert until 11 PM EDT this evening for CTZ002>004.
MA...Air Quality Alert until 11 PM EDT this evening for MAZ006-007-
     013-015-016.
RI...None.
MARINE...None.

&&

$$

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