459
FXUS61 KBOX 141027
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
627 AM EDT Sun Jul 14 2024

.SYNOPSIS...
Hot weather is on tap for today, but it will be slightly less humid
than yesterday with sunny skies. Dangerous Heat and Humidity is on
tap for the region Monday through Wednesday, with the chance for
mainly afternoon and evening thunderstorms each day and especially
later Wednesday into Wednesday night. A cold frontal passage late
Wednesday/Thursday will give way to a much more comfortable airmass
to end the work week.

&&

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

625 AM Update...

* Patchy fog burns off by mid morning, otherwise sunny & hot
  with highs mainly in the lower 90s away from immediate coast

Patchy dense fog is fairly shallow early this morning...so
expect it to burn off rather quickly by mid morning in most
locations. Previous forecast covers this quite well below.

A subtle mid-level ridge builds over southern New England today with
weak high pressure at the surface. This will support a sunny/hot
afternoon. Not expecting humidity to be as oppressive as with
previous days as light west/northwest flow will allow dewpoints to
drop into the low to mid 60s across much of interior southern New
England. Humidity may linger over the southeastern areas with
dewpoints still in the low 70s. Expect highs in the upper 80s to low
90s with some mid 90s possible in the CT River Valley. Coastal areas
may be slightly cooler as the gradient wind may be weak enough to
support sea-breezes along the coast.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...

Tonight

Quiet evening across southern New England. Light winds and clear
skies should support efficient cooling overnight. Low temps will
likely be bounded by dewpoints in the low to mid 60s across the
interior northwest and mid to upper 60s elsewhere. Urban areas
likely stay in the low 70s. Some patchy fog development is likely as
well. Winds becoming light out of the southwest.

Monday

Southwest flow returns on Monday allowing dewpoints to climb back
into the low to mid 70s across southern New England. Southwest flow
will also advect warmer air over The Northeast with 925 hPa temps
rising at or above 25 Celsius. With sunny skies for much of the day
we should observe surface temps in the low to mid 90 across much of
the region with heat indices in the mid to upper 90s. A heat
advisory is currently in effect for most of southern New England
minus those at elevation and The Cape/Islands.

By mid to late afternoon, short-wave energy approaching from the
west may introduce the potential for a few scattered showers and
thunderstorms. Instability will be on the moderate to high side with
1500+ J/kg of CAPE. There looks to be sufficient moisture available
as well with PWATs rising above 1.5 inches. Mid-level lapse rates
also look favorable with some guidance suggesting 6.5 C/km lapse
rates possible in the 700-500 hPa layer. The limiting factor will be
wind shear as current model guidance is supporting rather modest
wind fields with only 20 to 25 knots of 0-6km shear. 00Z HREF from
this evening is supporting thunder chances between 30 and 40 percent
for areas west of Worcester after 5PM Monday. Thus, we`ll be
monitoring this portion of the forecast closely as a strong storm
capable of producing large hail or gusty winds could certainly be a
possibility. Check back for more details with tomorrow afternoon`s
update.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...

Key Points...

* Dangerous Heat & Humidity Tue & Wed...Heat Indices 98 to 105+

* Scattered showers & t-storms Tue and especially Wed/wed night with
  the potential for some severe weather/localized flooding

* Relief from the heat & humidity Thu/Fri/Sat with seasonable temps
  and dry weather other than some lingering showers possible Thu

Details...

Tuesday and Wednesday...

Shortwave trough dropping across the Great Lakes coupled with an
upper level ridge off the Atlantic coast will result in dangerous
Heat & Humidity in our region Tue and Wed. Westerly flow aloft
coupled with 850T of +20C to +22C will result in high temps well
into the 90s with the only slight bit of relief near the Cape and
Islands. So we are looking at Heat Indices on the order of 98 to
105+. Dewpoints are tricky to forecast this far out...but as the
previous forecaster pointed out some spots may have Heat indices
reach into the 105 to 107 degree range. Greatest risk for this is
Tuesday...where we will continue the Excessive Heat Watch that was
already issued. We may need to extend the Excessive Heat Watch into
Wednesday and will certainly need Heat Advisories at the the very
least. Opted to let later shifts examine this a bit more...but
regardless the main story is Dangerous Heat and Humidity is in store
for the region on Tue and Wed.

The other concern will be for a couple rounds of scattered showers
and thunderstorms on Tue PM and especially later Wed/Wed night when
a strong cold front pushes into the region. Given the anomalous
airmass in place...do expect instability to be on the high side for
southern New England standards. There also appears to be a remnant
EML in place at least for a portion of this time. The effective
shear looks to be on the low side...but if we end up with even 25 to
30 knots of shear that will be enough for some organization given
the amount of instability that we are expecting. In fact...the CSU
Machine learning probs have been showing some probs for severe
weather with the main risk being straight line damaging wind gusts.
In addition...Pwats near 2 inches will support localized torrential
rainfall with any thunderstorms and the risk of localized flooding.

Thu/Fri/Sat...

Depending on the timing of the front...we have may or may not have
some showers lingering into Thu. Otherwise...the main story will be
significant relief from the heat and humidity with generally dry
weather as high pressure builds in from the west. Expect seasonable
high temps in the 80s with lower humidity too.

&&

.AVIATION /10Z SUNDAY THROUGH THURSDAY/...

Forecast Confidence Levels:

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

12z TAF Update..

Today...High Confidence

Patchy IFR-LIFR in fog early this morning should burn off in
most locations by mid morning. Otherwise...VFR with light west
winds except sea breezes developing along the immediate coast in
the 14z to 16z time frame.

Tonight...High Confidence

Mainly VFR with calm/light southwest winds. The exception will
be mainly near the south coast and especially the Cape/Islands
where areas of IFR-LIFR cigs/vsbys will likely develop tonight
especially across Nantucket.

Tomorrow...High Confidence

VFR. Steady southwest winds 10 to 15 knots with some afternoon
20+ knot gusts possible in the afternoon. This should fend off
any sea breeze. Some later afternoon/evening thunderstorms are
possible especially across the interior.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Monday Night through Thursday/...

Monday Night: VFR. Slight chance SHRA, isolated TSRA.

Tuesday through Tuesday Night: VFR. Breezy. Slight chance SHRA.

Wednesday: VFR. Breezy. Chance SHRA, isolated TSRA.

Wednesday Night: Mainly VFR, with areas MVFR possible. Breezy.
SHRA likely, isolated TSRA.

Thursday: VFR. Chance SHRA, isolated TSRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Today through Tomorrow

Weak high pressure builds over the region today. This will support
relatively calm conditions over the coastal waters onshore winds/sea-
breeze near the coast and light west/southwest winds over the outer
marine zones. Seas will be sub-SCY over all the marine zones. Winds
become more steady out of the southwest tomorrow from 15 to 20
knots, but conditions remain relatively calm with seas ranging from
1 to 4 feet.

Outlook /Monday Night through Thursday/...

Monday: Winds less than 25 kt.

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

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

Tuesday Night: Winds less than 25 kt. Seas up to 5 ft.

Wednesday: Low risk for Small Craft Advisory winds with gusts
up to 20 kt. Seas up to 5 ft. Slight chance of rain showers,
isolated thunderstorms.

Wednesday Night: Winds less than 25 kt. Local rough seas. Rain
showers likely, isolated thunderstorms.

Thursday: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain showers, isolated thunderstorms.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory from 8 AM to 8 PM EDT Monday for CTZ002>004.
     Excessive Heat Watch from Tuesday morning through Tuesday
     evening for CTZ002>004.
MA...Heat Advisory from 8 AM to 8 PM EDT Monday for MAZ003-005>007-
     010>019-026.
     Excessive Heat Watch from Tuesday morning through Tuesday
     evening for MAZ002>021-026.
RI...Heat Advisory from 8 AM to 8 PM EDT Monday for RIZ001>004.
     Excessive Heat Watch from Tuesday morning through Tuesday
     evening for RIZ001>004-006-007.
MARINE...None.

&&

$$

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