-- Discussion containing changed information from previous version are highlighted. --
414
FXUS61 KBOX 152030
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
430 PM EDT Sat Jun 15 2024

.SYNOPSIS...

-- Changed Discussion --
High pressure will bring dry and pleasant Father`s Day weekend. Dangerous
heat and humidity arrives on Tuesday and peak 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 SUNDAY MORNING/...

-- Changed Discussion --
As low pressure continues to exit offshore of Nova Scotia high
pressure builds in further this evening and overnight bringing
continued clear skies and dry weather. Humidity is much more
comfortable for much of the region where (outside of Cape Cod)
dewpoints have dropped into the low 40s. This will make for quite a
cold night relative to last night (nearly 20 degrees colder in some
spots) thanks to radiational cooling. Thus, leaning on the MOS
guidance for the low temperature forecast with handles these
situations well. Lows will dip into the mid 40s to mid 50s (urban
centers).
-- End Changed Discussion --

&&

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

High pressure becomes centered over New England on Sunday as mid
level heights continue to rise. This means another dry and
comfortable day with highs in the 70s and dewpoints in the 40s
(though more humidity will be moving in from the south late in the
day on light southerly winds). Expect a mix of sun and high clouds
as a weak shortwave rounds the ridge, but nothing in the way of
precipitation. Overnight increased cloudcover and higher dewpoints
will limit low temperatures to the mid/upper 50s.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...

-- 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.

Monday...

A shortwave trough will be sliding across Quebec/northern New
England early in the day, while a ridge builds from the Carolinas
into the central/eastern Great Lakes.  The ridge builds into Mid
Atlantic/eastern Great Lakes by late in the day. High pressure
builds east of New England during the day, while a warm front lifts
through.

Dry and quiet weather expected through this timeframe, despite the
warm front lifting through. Think that this will add just a touch
more of mid/high cloud. Should see our 925 hPa temps increasing to
roughly 15-25 degrees Celsius. Think this flow will be strong enough
to keep the sea breeze at bay for eastern areas. The NBM looked
reasonable for high temps at this point with readings in the 70s
along the south coast and the 80s elsewhere.

Tuesday through Friday...

Dangerous Heat and Humidity expected through this timeframe 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 unusual weather event. Does appear that the ridge axis
planted over us begins to get shunted later on Wed, but especially
Thu/Fri as shortwaves slide across the 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. Tossed out the
idea given the higher than normal confidence for an Excessive Heat
Watch, but have held off for now. This will be something future
shifts need to look more into as though we may fall just shy of the
105 heat index in spots think that there is a significant risk for
heat issues 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. Should have a 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 below.

Next weekend...

Ridge axis gets shunted offshore, 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.

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 SATURDAY THROUGH THURSDAY/...

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. N winds 10 to 15 knots with a few gusts to 20 knots early this
afternoon.

Tonight...High Confidence.

VFR. Light N winds.

Sunday...

VFR. Light winds turn southerly with localized sea breezes.

Sunday night...

VFR. Light S winds.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Monday through Thursday/...

Monday through Monday Night: VFR. Breezy.

Tuesday through Tuesday Night: VFR.

Juneteenth: VFR. Slight chance SHRA, isolated TSRA.

Wednesday Night: VFR.

Thursday: VFR. Breezy. 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 generally light winds. Seas around 2-4
feet.

Sunday and Sunday night:

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

Outlook /Monday through Thursday/...

Monday: Winds less than 25 kt.

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

Tuesday through Wednesday Night: Winds less than 25 kt.

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

&&

.CLIMATE...

-- Changed Discussion --
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)
-- End Changed Discussion --

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

$$

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