Lexington Weather

Lexington, Massachusetts, USA

87°F
8/8/2022 6:48pm 
  • Lexington Conditions: Clear
  • Temperature: 86.9°F / 30.5°CColder 2.5°F than last hour.
  • Dew Point: 73.8°FDecreased 0.3°Fsince last hour.
  • Relative Humidity: 65%Increased 4.0% since last hour.
  • Wind: Wind from W W 6 mph, 10-min avg: 2 mph, gust: 14 mph
  • Barometer: 29.80 in Steady
  • Visibility: 10 miles
  • Rain Today: 0.00 in
  •   
Southeast Middlesex County, MA - Heat Advisory
 - SEE ALL NEARBY ALERTS -

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 052019
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
419 PM EDT Fri Aug 5 2022

.SYNOPSIS...

Heat and humidity will be the main weather story right into 
early next week. Heat Advisories have been extended through the
weekend and the threat of isolated to scattered thunderstorms
will remain possible as well. It may be Tuesday, or later, 
before this heat and oppressive humidity finally breaks in a 
significant way.

&&

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

410 PM Update...

Highlights...

* Isolated to scattered thunderstorms diminish this evening
* Muggy with fog developing overnight...locally dense 

A weakly capped environment coupled with a subtle shortwave 
and 1500-2000 J/KG of Cape was allowing isolated to scattered 
thunderstorms to develop this afternoon. Given the lack of deep 
synoptic scale forcing the activity is hit or miss and many 
locations will remain dry. The threat for severe weather is 
rather limited given very weak wind fields aloft, but you can 
never completely rule out an isolated wet microburst in this 
environment. Otherwise, given Pwats near 2 inches and the slow 
movement of any storm will result in a very localized heavy 
rain/brief street flooding threat. We should see this activity 
gradually wind down during the evening with the loss of diurnal
heating coupled with weak mid level lapse rates. 

Otherwise, generally dry weather expected later tonight but it 
will be quite muggy with an anomalous upper level ridge off the 
mid-Atlantic coast. Weak surface ridging will also result in 
light to calm winds tonight. This coupled with the high 
dewpoints in place and pockets of wet ground from today/s 
activity will likely lead to areas of fog. In fact...some of the
fog may become locally dense overnight. Low temps will only 
drop to between 70 and 75 in most locations with humidity too.

&&

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

Highlights...

* Heat & Humidity Continue Sat...Heat Headlines Extended
* Widely scattered diurnal t-storms again Sat, mainly NW of I-95

Saturday...

The overall hot and humid weather pattern will continue on
Saturday. This is being driven by an anomalous upper level ridge
of 596+ DM off the mid-Atlantic coast. 850T are still on the
order of +17C/+18C and given the warm start should see high
temps top off in the lower 90s in many locations away from the
very immediate south coast. A few locations may even see highs
reach the middle 90s. Regardless...the main story will be the
oppressive humidity given dewpoints near 70. This will allow heat
indices to reach between 95 and 102 degrees. Heat Advisories
have been extended for the entire region; excluding Nantucket
and Block Island.

The other issue will be for diurnally driven isolated to
scattered thunderstorms. A weakly capped environment coupled 
with Cape values of 1500-2500 J/KG will support isolated to 
scattered activity Saturday afternoon into the first half of the
evening. Main risk will probably be northwest of I-95 and 
especially further back to the north and west since they will be
somewhat further removed from the upper level ridging off the 
mid- Atlantic coast. Activity will be hit or miss and many 
locations will remain dry given the lack of synoptic scale 
forcing. In addition...the overall severe weather threat will be
rather limited given very weak wind fields. However, Pwats near
2 inches along with the slow movement of any activity will 
result in a localized heavy rainfall/very localized street 
flooding risk.

Saturday night...

Isolated to scattered thunderstorms should again wind down
during the evening with the loss of daytime heating and very
limited synoptic scale forcing. Otherwise...a strong upper 
level ridging off the mid-Atlantic coast will continue to result
a very mild and muggy Saturday night. Overnight low temps will
only bottom out in the lower to middle 70s. There will be a bit
more of a southwest flow in the boundary layer Saturday night.
This should limit the threat for much fog except near the
immediate south coast.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...

Highlights...

* Oppressive heat and humidity continues through early next week. 
  There is the chance for isolated showers and thunderstorms daily. 
* A slow-moving cold front could bring much needed rainfall to 
  portions of the region by later next week, but timing and areal 
  coverage remain uncertain at this time. 
  
Details...

Sunday...

Bermuda High continues to hold strong this weekend and support a 
deep southwest flow pattern into southern New England. As a result, 
above normal temperatures and humid conditions will persist. Whether 
individual locations meet the criteria for a heatwave, which is 
three consecutive days of 90 deg, the combination of air temperature 
and dew points in the mid 60s to mid 70s will yield heat indices in 
the mid 90s to low 100s. The elevated dew points also means muggy 
and uncomfortable nights. Current heat headlines will likely be 
extended with future forecast packages for this weekend, and perhaps 
into Cape Cod and the Islands. 

Precipitation wise, weak upper level short wave will bring some 
cloudiness and a chance for isolated showers and thunderstorms. 
While there will be sufficient instability for convection, little to 
no deep-layer shear will suppress severe thunderstorm development. 
However, abundant deep layer moisture and weak boundary layer winds 
could support slower moving thunderstorms with localized, brief 
heavy downpours. Unfortunately, short of widespread soaking 
rainfall, there will barely put a dent in the deteriorating drought 
situation, where the eastern half of our CWA is now in D2 severe 
drought category according to the US Drought Monitor. 

Monday into Friday...

No notable air mass change as we enter the new work week so high 
heat and humidity continues with a trend towards somewhat more 
seasonable temps later in the work week. For reference, typical 
highs for the second week of August are in the low to mid 80s. For 
those tired of the heat and humidity, we may get a reprieve sometime 
in the mid to late week time frame. But there remains plenty of 
uncertainty with regards to the timing. CIPS analog indicates that 
there is a somewhat better chance for stronger thunderstorms in the 
Tuesday or Wednesday time frame, but that is contingent on the 
strength and progression of the cold front. Given the plenty of 
uncertainty, mainly stuck to blended guidance for this part of the 
forecast.  While there may seem to be no end in sight to this heat, 
the good news is that we are now past the climatologically warmest 
time of the year and cooler days are not far away. 

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...

Forecaster Confidence Levels:

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

18z TAF Update...

This afternoon into tonight...Moderate Confidence.

VFR conditions persist outside the isolated to scattered 
thunderstorms that will develop into early this evening. This
activity should diminish with the loss of daytime heating. 
Otherwise...the main concern will be for areas of fog 
developing later tonight which may be locally dense in the
typically prone spots. The threat for widespread low clouds 
though will probably be confined to areas near the south coast 
with the best shot at Nantucket. Winds becoming Light/Calm 
tonight except more from the SW at 5-10 knots across the Cape 
and Islands.

Saturday...High Confidence.

Mainly VFR once the areas of fog burnoff shortly after sunrise.
However, isolated to widely scattered showers/t-storms will be
possible in the afternoon with the greatest risk in northern MA
and interior southern New England. S-SW winds 10 to 15 knots,
but there may be a couple hour window for sea breezes across the
eastern and especially northeast MA coast. Any sea breezes
should be overcome as the day wears along.

Saturday night...High Confidence. 

Mainly VFR and think the main threat for low clouds/fog will be
confined to areas near the south coast, Cape and Islands. Winds
will be from the WSW 5-10 knots. 

KBOS...Moderate Confidence in TAF. 

KBDL...Moderate Confidence in TAF.

Outlook /Sunday through Tuesday/...

Saturday Night: Mainly VFR, with local MVFR possible. Breezy.
Slight chance SHRA, isolated TSRA.

Sunday: Mainly VFR, with areas MVFR possible. Breezy. Chance
SHRA.

Sunday Night: Mainly VFR, with local MVFR possible. Breezy.
Slight chance SHRA.

Monday: Mainly VFR, with areas MVFR possible. Breezy. Chance
SHRA, isolated TSRA.

Monday Night through Tuesday: Mainly MVFR, with local IFR
possible. Breezy. Chance SHRA.

&&

.MARINE...

Forecaster Confidence Levels:

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

Tonight through Saturday night...High Confidence.

Upper level ridging off the mid-Atlantic coast will maintain a
S-SW wind of 10 to 15 knots with perhaps some 20 knot wind gusts
developing Sat into Sat night. Thinking is though winds/seas
will remain below small craft advisory thresholds through
Saturday night. We will have to watch for areas of fog...mainly
during the overnight into mid morning hours in the southern
waters.

Outlook /Sunday through Tuesday/... 

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

Sunday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of seas approaching 5 ft. 

Sunday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas up to 5 ft. Slight chance of rain
showers. 

Monday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Slight chance of rain showers, isolated thunderstorms. 

Monday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of
rain showers, isolated thunderstorms. 

Tuesday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain
showers. 

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory until 8 PM EDT Sunday for CTZ002>004.
MA...Heat Advisory until 8 PM EDT Sunday for MAZ002>023-026.
     Air Quality Alert until 11 PM EDT this evening for MAZ007-015-
     016.
RI...Heat Advisory until 8 PM EDT Sunday for RIZ001>007.
MARINE...None.

&&

$$
SYNOPSIS...Frank/Chai
NEAR TERM...Frank
SHORT TERM...Frank
LONG TERM...Chai
AVIATION...Frank/Chai
MARINE...Frank/Chai
      

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