358
FXUS61 KBOX 170457
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1257 AM EDT Wed Jul 17 2024

.SYNOPSIS...
Dangerous heat and humidity will continue through Wednesday
with little nighttime relief expected. Scattered showers and
thunderstorms will move into the region this evening before
weakening, with another round of showers and thunderstorms
Wednesday afternoon and evening. A cold frontal passage
Wednesday night into Thursday will give way to a much more
comfortable airmass to end the work week. Rain-free weather
expected into early next week.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Thunderstorm threat has ended with clearing conditions tonight
outside the south coast, Cape, and Islands where low status and
fog are present. Overnight lows stay quite warm in the low to
mid 70s tonight.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM THURSDAY/...
Wednesday will be the last day of excessive heat and humidity.
Slight cooling at 925/850 mb will result in a slightly cooler
temps, but still 90-95 across a large portion of SNE, with mid-
upper 80s along the south coast. Oppressive humidity with
dewpoints low-mid 70s will lead to heat indices of 97-102F and
heat advisories will continue.

The main concern in the afternoon and evening will be another
round of showers and t-storms moving into the region. Fairly
robust mid level trough amplifies across Gt Lakes with
convection likely firing along a pre-frontal trough which
develops across interior SNE in the afternoon. Environment is
more favorable for severe weather with CAPES 1000-2000 J/kg and
0-6km shear approaching 35 kt, with hi-res CAMs indicating a
storm mode of multicellular clusters and line segments. HREF
2-5km updraft helicities favor areas north and west of I-95 for
best chance of severe weather, with nadocast and CSU machine
learning probs suggesting damaging wind will be the primary
threat. Given the high PWATs exceeding 2 inches, localized heavy
rainfall and flash flooding will also be possible. Rainfall
rates up to 2"/hour will be possible.

It appears convection will weaken as it approaches the south
coast late afternoon and evening due to stabilizing effect of
marine layer but can`t rule out an isolated strong storm making
it to the coast. The main cold front will be dropping south
across SNE overnight so there will be a continued risk of
showers and isolated storms through the night, especially near
the coast. Another warm and humid night with lows 70-75 in the
coastal plain with 60s further inland across interior MA.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Key Points...

* Dry and seasonal weather Thursday through this weekend

Still seeing signs for a significant pattern change across
southern New England during this portion of the forecast. Most
notable will be the decrease in humidity, which is something
because dew points in the 60s are usually considered muggy
around these parts. Away from the immediate coast, dew points
should be around 60F, which will be much more comfortable
compared to what we have just experienced this past week.

Daytime temperatures also expected to lower 5-10 degrees from
where we have been Thursday into early next week. This is still
near to slightly above normal for late July. Low temperatures
may not lower quite that much towards the immediate coasts, but
should do so across interior southern New England.

As for precipitation, high pressure and a relatively drier
airmass will drop down from Canada, helping suppress rain and
thunderstorm chances through this weekend. Next chance for rainfall
looks to be early to mid next week as a weak shortwave exits
the Great Lakes.

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
Forecast Confidence Levels:

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

Today...Moderate to high confidence.

VRF inland. For the Cape and Islands, IFR becoming MVFR/VFR mid
morning, before dropping back to IFR in the afternoon. Moderate
to high confidence that thunderstorms will move into western MA
and CT around 22-00z, and move east through 02-04z. As storms
approach the east coast, they will likely fizzle into light rain
showers. SW winds at 10-15 knots gusting 20-25 knots.

Tonight...Moderate confidence

Showers could linger through midnight. VFR for western terminals
overnight. VFR/high end MVFR for northern terminals. low end
MVFR/IFR for southern terminals including the Cape and Islands.
SW winds turning west at 5-10 knots, gusting 20-25 knots near
the waters.

Tomorrow...High confidence.

Gradual clearing becoming VFR for all terminals in the
afternoon. West winds at 10 to 15 knots.

KBOS TAF...Moderate confidence in TAF.

VFR today with SW winds at 10-15 knots. Line of thunderstorms
should weaken into light rain showers as they approach the
terminals between 01-04z.

KBDL TAF...High confidence in TAF.

VFR with SW winds at 10-15 knots. Line of thunderstorms likely
reaching the terminal sometime between 23z-02z.

Outlook /Thursday Night through Sunday/...

Thursday: VFR. Slight chance SHRA.

Thursday Night through Sunday: VFR.

&&

.MARINE...
Forecaster Confidence Levels:

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

Tonight through Wednesday night: High confidence.

A period of 25 kt wind gusts likely through this evening along
the south coastal waters as low level jet develops. Winds
diminish a bit overnight with another pulse of near 25 kt gusts
developing Wed afternoon/evening along south coastal waters.
Seas building to 4-6 ft over southern waters. Areas of fog will
develop and reduce vsbys over southern waters tonight and Wed
morning, with more fog likely Wed night. Chance of showers and
t-storms Wed night.

Outlook /Thursday Night through Sunday/...

Thursday: Winds less than 25 kt. Local rough seas. Chance of
rain showers.

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

Friday: Winds less than 25 kt. Areas of seas approaching 5 ft.

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 until 8 PM EDT this evening for CTZ002>004.
MA...Heat Advisory until 8 PM EDT this evening for MAZ003>007-
     010>021-026.
RI...Heat Advisory until 8 PM EDT this evening for RIZ001>007.
MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ232.
     Small Craft Advisory until 8 AM EDT Thursday for ANZ254>256.

&&

$$

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