Lexington Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 160149
AFDBOX

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

.SYNOPSIS...
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.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
10 PM Update...

Temperatures are quickly falling throughout the region with 
many locations already in the low 60s. Forecast remains on 
track. Given the strong radiational cooling anticipated tonight 
along with the light winds have lowered temps a bit further in 
latest update. Went with the 10th percentile of guidance, which 
brings readings down into the 40s for much of the interior. The 
immediate coastline will see readings in the low to mid 50s.

Previous 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 which handles these 
situations well. Lows will dip into the mid 40s to mid 50s 
(urban centers).

&&

.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/...
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.

&&

.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
Forecast Confidence Levels:

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

Tonight...High confidence.

VFR conditions with any gusty winds tapering off by 01Z the
latest as the boundary layer decouples. Winds shift to the N
with speeds around 5 kts or less.

Sunday...High confidence.

VFR with light N winds eventually turning to the S/SE by the
afternoon. Coastal areas will see localized sea breezes
developing roughly 15-17Z. 

Sunday night...High confidence.

VFR with S winds at 5-10 kts.

KBOS TAF...High confidence in TAF.

VFR through the forecast. Light N winds turning more NNE by the
AM push on Sun. Sea breeze developing around 15Z before we turn
more SE/S Sun Night.

KBDL TAF...High confidence in TAF.

VFR through the forecast. Winds becoming light and variable
tonight, but will eventually shift to the NNE before quickly
shifting to the S Sun afternoon.

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...
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...None.
MA...None.
RI...None.
MARINE...None.

&&

$$

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