-- Discussion containing changed information from previous version are highlighted. --
472
FXUS61 KBOX 162017
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
417 PM EDT Sun Jun 16 2024

.SYNOPSIS...

-- Changed Discussion --
High pressure will bring dry weather and warming temperatures
to start the week. Dangerous heat and humidity arrives on
Tuesday and peaks in the Wednesday through Friday time frame.
Near to record breaking high temperatures are possible with
afternoon Heat Indices between 95 and 105 degrees. Not much
relief at night with near record breaking warmest low
temperatures and heat indices still in the 70s.
-- End Changed Discussion --

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...

High level cirrus clouds continue to stream overhead as a weak
shortwave rounds the ridge. Meanwhile the radar is clear except for
one feature of note: the leading edge of the seabreeze moving north
into RI and southeast MA. More of the same quiet weather is expected
tonight under high pressure with mostly clear skies. This will allow
for some radiational cooling once again, though slightly warmer
dewpoints thanks to southerly flow will limit it a bit. Lows dip
into the low to mid 50s.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...

Mid level ridging continues to build over the region which, along
with surface high pressure shifting east, will start to further warm
the airmass overhead. 850 mb temps increase from 9C this afternoon
to 16C by Monday afternoon. This translates to high temperatures in
the low to mid 80s for many. The exception will be for much of Rhode
Island and southeast MA where increasing southerly flow off the
water will hold temps in the 70s. It will feel more humid on Monday
as dewpoints increase from the 40s today to the upper 50s/low 60s.
Monday night southwest flow continues to increase dewpoints a few
degrees keeping lows quite mild, in the low to mid 60s.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...

-- Changed Discussion --
Highlights

* Dangerous Heat and humidity Tue through Fri. Heat Indices range
  from 90-105.

* Near to record breaking high temperatures along with warmest
  low temperatures during this stretch. Not much relief from the
  heat anticipated at night. Heat peaks on Wed-Thu.

* Could see some spotty t-storms from Wed-Fri. Better
  opportunity for more widespread activity over the
  weekend/early next week.

Tuesday through Friday...

Dangerous Heat and Humidity expected with generally dry and
quiet weather. As previous shift mentioned and is still the
case, ensembles are in excellent agreement. The anomalous 500
hPa height fields will approach 600 dm. This is rarely seen in
our area and a strong signal for the potential of record heat.
Both the NAEFS and EPS situational awareness tables show several
parameters outside model climatology. Generally looks like the
peak is in the Wed/Thu timeframe. This is a strong indication of
a rare/highly anomalous weather event. The ridge axis planted
over us begins to get shunted later on Wed/Thu, but especially
Fri as shortwaves slide across its northern periphery.

The dangerous heat/humidity begins to arrive on Tue. Confidence
quite high for the risk across the interior, but should be more
limited for locations along the immediate coastline due to localized
sea breezes. Think that given the S/SWly flow should see more relief
along the immediate south coast, but especially the Cape/Islands.
The heat and humidity peaks in the Wed-Fri timeframe. Current
Excessive Heat Watches look fine, though may need to expand in
future updates as though we may fall just shy of the 105 heat
index in spots think that there is a significant risk for heat
impacts given we don`t get much relief at night. At this point
away from coastal/sea breeze areas will have heat indices in the
afternoons of roughly 95-105 degrees. At night will have heat
indices still remaining in the 70s as well.

Does appear that there will be spotty thunderstorm risk in the Wed-
Fri timeframe as the ridge begins to be shunted a bit to the
south/southeast. Though there is some uncertainty in this as did
have to bump up to slight chances on Wed/Thu from the NBM. Did
this as there is fair amount of instability and in combination
with the heat there could be some spotty t-storms triggered.

Will have the risk for challenging the all time June high
temperature records in spots, daily high temperature records for the
18-21 and warmest low temperature records as well. See the climate
section below for more of these details.

Next weekend...

Ridge axis gets shunted to the south, which will return us to a
quasi-zonal flow pattern. Could see a shortwave or a more
substantial shortwave swinging in, which would bring us shots
for more widespread showers and thunderstorms. Still looks like
we could perhaps see another mild day on Sat before we cool down
to more seasonable values by Sun into early next week.

For now have stuck with the NBM guidance through this period as it
seems quite reasonable given the pattern. Main focus of the extended
was on the dangerous heat/humidity during the week.
-- End Changed Discussion --

&&

.AVIATION /20Z SUNDAY THROUGH FRIDAY/...

Forecast Confidence Levels:

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

18z TAF Update...

This afternoon: High Confidence.

VFR. Light S winds. Localized sea breezes near the coasts.

Tonight: High Confidence

VFR, calm/light southerly winds. Low chance for patchy fog to
develop.

Monday:

VFR. Increasing southerly winds at 10-15 knots, gusting 20-25
knots.

Monday night: Diminishing SW winds 5-10 kts.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Tuesday through Friday/...

Tuesday through Wednesday Night: VFR. Breezy.

Thursday through Thursday Night: VFR. Breezy. Slight chance
SHRA, isolated TSRA.

Friday: VFR. Slight chance SHRA, isolated TSRA.

&&

.MARINE...

Forecaster Confidence Levels:

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

Tonight:

Clear conditions and light southerly winds. Seas around 2-4
feet.

Monday:

Continued clear conditions with increasing southerly winds at
10-15 knots, gusting 20-25 knots.

Monday night: Clear conditions with slowly decreasing southwest
winds 10-15 kts. Seas 2-4 ft.

Outlook /Tuesday through Friday/...

Tuesday: Winds less than 25 kt.

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

Juneteenth: Winds less than 25 kt.

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

Thursday: Winds less than 25 kt. Slight chance of rain showers,
isolated thunderstorms.

Thursday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain showers, isolated thunderstorms.

Friday: Winds less than 25 kt. Slight chance of rain showers,
isolated thunderstorms.

&&

.CLIMATE...

All Time June High Temperature Record (Daily)

BOS - 100 F (06/06/1925, 06/26/1952 and 06/30/2021)
BDL - 100 F (06/26/1952, 06/30/1964)
PVD - 98 F  (06/25/1943, 06/15/1945 and 06/30/1945)
ORH - 98 F  (06/26/1952)

Most recent day of 100 F (or greater)

BOS - 100 F (07/24/2022)
BDL - 100 F (07/21/2019)
PVD - 100 F (07/28/2020)
ORH - 102 F (07/04/1911)*

* For ORH this is the only 100+ degree day in its period of record.

Daily High Temperature Records...

June 18th

BOS - 94 F (1907 and 1929)
BDL - 95 F (1957 and 1994)
PVD - 94 F (1929)
ORH - 93 F (1907 and 1929)

June 19th

BOS - 96 F (1923)
BDL - 95 F (1995)
PVD - 94 F (1923)
ORH - 93 F (1923)

June 20th

BOS - 98 F (1953)
BDL - 97 F (2012)
PVD - 95 F (1941)
ORH - 93 F (1953)

June 21st

BOS - 96 F (2012)
BDL - 96 F (1953 and 2012)
PVD - 96 F (1941)
ORH - 91 F (Multi-Years)

Daily Warmest Low Temperatures Records...

June 18th

BOS - 72 F (1929)
BDL - 70 F (1905)
PVD - 72 F (1929)
ORH - 69 F (1905 and 1994)

June 19th

BOS - 73 F (1995)
BDL - 72 F (1929)
PVD - 70 F (1995)
ORH - 72 F (1929)

June 20th

BOS - 78 F (1931)
BDL - 74 F (1931)
PVD - 74 F (1931)
ORH - 72 F (1931)

June 21st

BOS - 80 F (2012)
BDL - 73 F (1923 and 2012)
PVD - 75 F (2012)
ORH - 74 F (1923 and 2012)

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Excessive Heat Watch from Tuesday afternoon through Friday
     evening for CTZ002-003.
MA...Excessive Heat Watch from Tuesday afternoon through Friday
     evening for MAZ003-005-006-010-011-013-014.
RI...None.
MARINE...None.

&&

$$

SYNOPSIS...BW/BL
NEAR TERM...BW
SHORT TERM...BW
LONG TERM...BL
AVIATION...BW/BL
MARINE...BW/BL
CLIMATE...BL