741
FXUS61 KBOX 171801
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
201 PM EDT Wed Jul 17 2024

.SYNOPSIS...
Dangerous heat and humidity will continue today. Scattered
showers and thunderstorms will move into the region this evening
before weakening. A cold front will bring much more comfortable
temperatures and dewpoints to the region starting Thursday
afternoon with dry conditions expected through the weekend.

&&

.NEAR TERM /THROUGH THURSDAY/...
2 PM update...

* Severe Thunderstorm Watch for CT and interior MA north and
  west of I-95

Lots of sunshine has developed as area of clouds moves off the
coast. Instability is lacking with MLCAPES around 500 J/kg with
the presence of a cap, but heating will result in
destabilization with MLCAPES increasing to 1000-1500 J/kg and
an eroding cap. Line of convection developing across eastern NY
into S VT and expect storms to intensify as they move into
western New Eng during next few hours as instability increases.
Effective shear 30-40 kt which is more than sufficient for
storms to organize into line segments and clusters. Damaging
wind remains the primary threat, but latest CSU machine learning
guidance is indicating there is a low prob for a tornado. Main
focus for severe weather will be in the interior north and west
of I-95

Previous discussion...

Not much change from previous forecast thinking. Expecting
another round of showers and t-storms with potential for severe
weather late afternoon and evening. Storms will likely fire
along a developing pre-frontal trough, with updraft helicity
fields and machine learning guidance highlighting areas north
and west of I-95 corridor for best chance of severe weather.
Moderate instability and shear with CAPES 1000-1500 J/kg and
effective shear 30-35 kt support organized storms and CAMs
indicating storm clusters and line segments with damaging wind
the primary threat, although there is a localized flash flood
threat as well given high PWATs. Timing wise, looking like
storms move into western MA/CT 4-6 pm then move eastward this
evening, but activity should weaken as they approach RI and SE
MA given more stable marine layer.

No change to heat headlines. Expect highs 90-95, hottest
across CT valley and portions of eastern MA, with mid-upper 80s
along the immediate south coast. High dewpoints 70-75 will
bring peak heat indices to 95-100.

&&

.SHORT TERM /THURSDAY NIGHT/...
Key Point

* Still warm and muggy overnight

Showers and possibly a rumble or two of thunder could linger near
the coastal waters through about 2am, otherwise drying conditions
overnight. Even with the passage of the cold front, the cooler temps
and lower dewpoints lag far behind the front not arriving until
Thursday afternoon. Overnight temperatures stay in the upper 60s to
low 70s with dewpoints remaining near 70F. Low status and fog will
fill in for the southcoast, Cape, and Islands one last time before
drier air will kick it out Thursday afternoon.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
Key Point

* Dry and seasonal weather Thursday through this weekend

After an extended period of hot, muggy, and unsettled weather, a
major pattern change is store for SNE starting Thursday. Drier air
and cooler temps arrive Thursday afternoon with PWATS falling below
1.0 inches and dewpoints falling into the low 60s to even upper 50s,
and staying there through the weekend. Temperatures will be much
more comfortable Thursday and Friday with highs in the low to mid
80s, warming into the upper 80s for the weekend. Overnight lows will
also stay more comfortable in the low to mid 60s, even some upper
50s, through the weekend.

As for precipitation, high pressure and rather dry airmass will drop
down from Canada helping suppress rain and thunderstorm chances
through the weekend. Next chance for precip looks to be Tuesday or
Wednesday next week as a shortwave drops into the southern plains
before lifting north into the Northeast.

&&

.AVIATION /18Z WEDNESDAY THROUGH SUNDAY/...
Forecast Confidence Levels:

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

Through tonight...Moderate confidence.

Scattered to numerous showers/t-storms will move west to east
across interior MA and CT 20-00z with a few severe storms
possible with strong wind. Storms should weaken as they approach
the south coast after 00z, but may see a regeneration of
showers and a few t-storms late tonight along the south coast.
IFR stratus and patchy fog will develop over Cape/Islands late
afternoon and evening likely expanding across southern RI and
SE MA. But rest of area should remain VFR outside of any
convection.

Thursday...High confidence.

Areas of MVFR-IFR cigs likely impacting portions of RI and
eastern MA in the morning, but improving to VFR 14-16z except a
bit later over the Cape/Islands. VFR interior. A few showers or
a t-storm possible over Cape/Islands in the morning. NW wind
around 10 kt interior, with winds turning SW along the south
coast.

Thursday night...High confidence.

VFR. Light winds.

KBOS TAF...Moderate confidence in TAF.

A few t-storms may impact the terminal sometime between 00-02z.
A period of MVFR cigs possible late tonight and Thu morning,
otherwise VFR.

KBDL TAF...High confidence in TAF.

Line of t-storms likely impacting the terminal sometime between
23z-02z.

Outlook /Friday through Sunday/...

VFR.

&&

.MARINE...
Forecaster Confidence Levels:

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

Today through tomorrow: Moderate confidence.

Gusty SSW winds continue today into tonight up to 25 knots. Seas
climb to 4-6 feet tonight into Thursday. Winds turn west
Thursday as the surface cold front moves through. The cold front
will also help to kick out the low status and fog that has been
stuck over the southern waters for the past few days.
Thunderstorms will weaken as they approach the waters tomorrow
evening, but could still bring brief gusty winds above 30 knots
with occasional lightning.


Tides and Rip Currents.

A rip current statement is in effect today due to the moderate
to high risk for rip currents. Strong southerly winds of
20-30mph and waves between 4-6 feet will likely cause strong rip
currents to occur for south facing beaches. Another rip current
statement will likely be needed tomorrow with waves increasing
to 5-7 feet.


Outlook /Friday through Sunday/...

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

Friday Night through Sunday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory until 8 PM EDT this evening for CTZ002>004.
MA...Heat Advisory until 8 PM EDT this evening for MAZ003>007-
     010>021-026.
     High Risk for Rip Currents until 8 PM EDT this evening for
     MAZ020>024.
RI...Heat Advisory until 8 PM EDT this evening for RIZ001>007.
     High Risk for Rip Currents until 8 PM EDT this evening for
     RIZ006>008.
MARINE...Small Craft Advisory until 8 AM EDT Thursday for ANZ232.
     Small Craft Advisory until 8 PM EDT Thursday for ANZ235-237.
     Small Craft Advisory until 8 PM EDT Thursday for ANZ254>256.

&&

$$

SYNOPSIS...KP
NEAR TERM...KJC/KP
SHORT TERM...KP
LONG TERM...KP
AVIATION...KJC/BW/KP
MARINE...KP