Lexington Weather

Lexington, Massachusetts, USA

89°F

8/8/2022 5:57pm

Lexington Conditions: Partly cloudy
Temperature: 88.9°F / 31.6°C
Dew Point: 74.1°F
Relative Humidity: 62%
Wind: WSW 2 mph, 10-min avg: 4 mph, gust: 16 mph
Barometer: 29.79 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 061800
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
200 PM EDT Sat Aug 6 2022

.SYNOPSIS...
Heat and humidity will be the main weather story right into 
early next week. Heat Advisories have been extended through this
weekend, and the threat of isolated to scattered thunderstorms 
will remain as well. It may be Tuesday, or later, before this 
heat and oppressive humidity finally breaks in a significant 
way. Will have daily shots for showers and thunderstorms for
much of next week, but no washouts are anticipated at this time.

&&

.NEAR TERM /THROUGH TONIGHT/...
1 PM Update...

Temperatures have jumped up into the low 90s for most locations
this afternoon. Fog has dissipated over the Cape and islands 
but low stratus has been more stubborn over Nantucket. This low 
cloud deck may hold on through most if not all of the afternoon,
so the main change with this forecast was to extend the low 
clouds.



Previous discussion...

Not much change to the overall pattern and air mass over
southern New England, with the Bermuda High still pretty much in
control of our weather. Another day of heat and humidity is in 
store. Will also need to keep an eye on the sky this afternoon. 
Much like yesterday, overall wind fields remain weak, meaning 
widespread severe weather is not likely. However, steep low 
level lapse rates will lead to MUCAPE values of 1,500-2,500 
J/kg, which could result in an isolated strong to severe 
thunderstorm just by itself, mainly due to gusty winds. Local 
downpours will also be possible, which could result in nuisance
flooding of urban areas.

&&

.SHORT TERM /SUNDAY/...
Any showers and thunderstorms are expected to dissipate quickly
after sunset this evening, with much of the overnight remaining
rain-free. It will still be quite muggy, with yet another round
of stratus and fog expected towards southeast MA. 

Put the forecast on repeat for Sunday, with continued heat, 
humidity and a risk for afternoon showers and thunderstorms. At
this point, any rain will be beneficial to alleviate drought
conditions, but this is not typically the pattern to make much
progress in that regard. Any showers or thunderstorms will
remain of the hit-or-miss variety.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Highlights

* Daily opportunities for showers and thunderstorms as a slow
  moving cold front pushes in. Heavy downpours possible at 
  times. 

* Potential for oppressive heat to extend into Monday and
  perhaps Tuesday for parts of the region. Will be dependent on
  timing a cold front sliding through. 

* Temperatures near to cooler than seasonable mid/late in the week.

Caught in fairly zonal flow through much of the upcoming week 
with several waves sliding through. Mid, but especially late in 
the week we have a more amplified trough swinging into and 
perhaps through the region. Through much of this period will 
have a cold front slowly moving in. It may actually stall over 
the region before pushing offshore mid/late in the week.

Oppressive heat...

Main concern initially in the extended is the oppressive heat. 
Do have some uncertainty on both Monday and especially Tuesday. 
There will be a round of decaying showers/storms sliding through
Sunday night into early Monday. Depending on how quickly this 
slides through along with the mid/high clouds it leaves behind 
it could impact how warm we are able to get. Will also see more 
clouds Monday afternoon/evening as shower/storm chances
increase. Will still see W/WSW flow at 850 hPa with temps in 
the 18-21 degree Celsius range. Ensemble guidance minus the 
GEPS, show 60-90+ probabilities of 2m temps AOA 90 degrees. 
Confidence at this point would be highest across the Merrimack 
and CT River Valley. Given this, did bump up highs to the 75th 
percentile of guidance, which keeps high temps range from the 
mid 80s to low 90s. Do think the NBM is a tad bit too hot with 
the dew points given the downsloping and excellent mixing, but 
nonetheless will have dew points in the upper 60s to mid 70s. 
The result are Heat Index Values of 85-100 with the highest 
across the Merrimack and CT River Valley. Thinking that at least
part of the region will need the Heat Advisory extended into 
Monday, but have held off for now. 

May still have parts of the region in oppressive heat on 
Tuesday as well, but this will be dependent on the cold fronts 
location. The EPS is the most bullish with 2m temp probs AOA 90 
degrees compared to the GEFS and especially the GEPS. The EPS is
most similar to the operational ECWMF, which keeps the cold 
front to the N/NW of us. The GFS/GEM have the cold front either 
over or through the region. Will note the GEFS probabilities for
temps AOA 90 degrees has increased from the previous run. Given
the uncertainty stuck with the NBM dew points, which have 
values in the upper 60s to low 70s. Did nudge temps to the 60th 
percentile of guidance, which keeps us below Heat Advisory 
criteria. Not out of the question these temps need to be 
increased for future updates.

For the rest of the extended have stuck with the NBM for 
temperatures as there is just too much uncertainty with the 
front moving through. This brings temps to near/below seasonable
levels by mid/late in the week. 

Precipitation chances...

Given the pattern in place will pretty much see daily 
opportunities for showers and thunderstorms. Not looking like 
any washouts at this point, but there will likely be 
showers/storms around most afternoons into the evening hours. 
Does appear there is a higher risk for more widespread 
shower/storm activity mid/late in the week associated with the 
deeper trough lifting in. Could see a low ride along the front 
as it is over or just to the south/southeast of the region. 

Until the cold front slides through the region will be stuck in
a moisture laden airmass. Will have 70-90+ percent 
probabilities of PWATS AOA 1.5 inches per the EPS/GEFS/GEPS 
guidance until at least Wednesday. During that timeframe will 
even have 50-70 percent probs of PWATS AOA 2 inches. This 
couples with a few hundred to roughly 1500 J/kg of MUCAPE and 
warm cloud layer depths of 3-5 km. So, any activity will bring 
the risk of locally heavy downpours at times. At this point 
there does not appear to be a significant severe weather risk 
given the poor deep layer shear. Will need to monitor things 
mid/late in the week as the deep layer shear increases with the 
trough swinging in.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
Forecaster Confidence Levels:

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

...High confidence.

VFR save for ACK where stratus may hold on until 21Z or later.  
Pop up showers/storms expected in the afternoon. Confidence in 
the coverage is not high enough to add at VCTS. S-SW winds 10 
to 15 knots.

Tonight...High confidence. 

VFR for most with any lingering shower/storms tapering off
during the evening. Threat for IFR/LIFR stratus/fog returns across
the south coast but confidence is lower. WSW winds 5-10 kts.

Sunday...Moderate Confidence. 

Mixed bag of conditions. IFR stratus more likely to persist
towards the south coast. Still mainly VFR farther inland, with
brief periods of MVFR in any showers or thunderstorms.

Sunday Night: VFR. SW winds 5-10kt gusting to 20 kt along the
south coast. 

KBOS...Moderate confidence in TAF due to uncertainty as to
whether any TSRA makes it to the terminal this afternoon. 

KBDL...Moderate confidence in TAF due to uncertainty as to
whether any TSRA makes it to the terminal this afternoon. 

Outlook /Monday through Wednesday/...

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

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

Tuesday: Mainly VFR, with local IFR possible. Chance SHRA,
isolated TSRA.

Tuesday Night through Wednesday: MVFR/IFR conditions possible.
Chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Through Sunday...High Confidence.

Not much change to the overall forecast, with relatively light
winds and seas, and late night areas of fog with reduced
visibility.

Outlook /Sunday Night through Wednesday/... 

Sunday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers,
isolated thunderstorms. 

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

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

Tuesday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Chance of rain showers, isolated thunderstorms. 

Wednesday: Winds less than 25 kt. Chance of rain showers,
isolated thunderstorms.

&&

.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.
RI...Heat Advisory until 8 PM EDT Sunday for RIZ001>007.
MARINE...None.

&&

$$
SYNOPSIS...Belk/BL
NEAR TERM...Belk/BW
SHORT TERM...Belk
LONG TERM...BL
AVIATION...Belk/BL/BW
MARINE...Belk/BL