Lexington Weather

Lexington, Massachusetts, USA

87°F

8/8/2022 6:42pm

Lexington Conditions: Clear
Temperature: 87.1°F / 30.6°C
Dew Point: 73.9°F
Relative Humidity: 65%
Wind: W Calm, 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 021731
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
131 PM EDT Tue Aug 2 2022

.SYNOPSIS...
Becoming hot, muggy, with brief widely scattered showers and 
isolated thunderstorms develop ahead of an approaching cold 
front Tuesday afternoon. Dry and very warm again Wednesday 
albeit noticeably cooler along portions of the immediate coast. 
This will be followed by near record high temps and oppressive 
humidity Thursday some of which may linger into Friday. The 
threat for scattered showers and thunderstorms increases Friday 
and may persist at times this weekend into next Monday, but a
washout is not expected. Above normal temperatures continue as 
well, but not at the potential record breaking levels of 
Thursday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
1030 AM Update:

Earlier stratus has eroded in entirety giving way to full sun
and increasingly more humid weather on SW breezes. May have to
consider raising high tempratures a couple degrees in later
updates especially eastern MA/RI away from the coastline. 

Pre-frontal trough trailing through central NY should be a focus
for widely scattered SHRA/TSRA this afternoon, particularly in
the interior. Expect any convection to be very pulse-like in
character given weak low to mid-level wind fields. CAPE values 
tend to vary between the drier RAP at around 1000-1500 J/kg 
(due to lower dewpoints from a mixing PBL), while the NAM
doesn't mix its surface dewpoints (a known bias) and
contributing to 2000+ J/kg of CAPE. Suspect the RAP may be
closer to reality, leading to generally garden-variety, perhaps
SPSable type storms with gusty outflow and likely development of
cold pools/outflow for new storms to develop upon. Think the
main risk for scattered TSRA is across interior MA/CT, but do 
have to watch for the Route 6 corridor in CT-RI where both RAP 
and NAM show higher CAPEs and potentially greater storm vigor around
22-00z. Perhaps a stronger, marginally SVR storm in this 
corridor with gusty winds. Downdraft CAPEs are also closer to
the 800-1000 J/kg range in this general area too, which can be a
good predictor of strong gusts in weak shear/pulse-storm
environs. 

Previous Discussion:

Rather expansive area of stratus was located over 
the eastern 2/3 of southern New England this morning. This 
stratus should dissipate rather quickly after sunrise, only to 
be replaced with higher clouds later today.

Expecting another rather warm and humid day today, with the 
risk for some showers and a few thunderstorms as a cold front 
approaches. Given the timing of this front, these are more
likely across the western half of southern New England. There is
not a lot of shear to organize to modest CAPE values of
1,000-1,500 J/kg. Thus, not expecting a widespread severe
weather event today, but cannot rule out a strong storm or two.
These storms should weaken after sunset.

Expecting max temperatures to be about 5 degrees higher today
due to a persistent southwest wind ahead of a cold front. This
will also lead to much higher dewpoints. At this time, thinking
we will stay just under the threshold for a Heat Advisory, but
it will be close. This will need to be monitored by the day
shift, as a subtle increase of only a degree or two in either 
temperatures or dew points from the current forecast could make
all the difference. If you must work outdoors today, please
drink plenty of fluids and take frequent breaks out of the sun.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
A cold front will move offshore late this evening and overnight,
leading to less humid conditions Wednesday. A few locations
across eastern MA could also be slightly cooler, with seabreezes
developing by afternoon. Across the interior, max temperatures
should be similar to today.

Once showers dissipate this evening, rain-free weather should
persist through Wednesday.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Highlights

* Potentially record setting heat on Thursday with heat indices
  over 100.

* Oppressive humidity Friday with scattered showers and 
  thunderstorms Friday afternoon.

* Above normal temperatures continue this weekend

Thursday and Friday

Deep southwest flow is forecast to advect an anomalously warm 
and humid air mass into southern New England for Thursday and 
Friday. Temperatures at 850 hPa are expected to rise above 20 
Celsius on Thursday. With persistent 15-20 knot southwest winds 
expected in the boundary layer, we can expect diurnal mixing to 
850 hPa which will support high temperatures in the upper 90s to
perhaps 100 degrees across much of interior southern New 
England. Lower temperatures forecast across southeastern MA and 
the south coast in the upper 80s to low 90s. Dewpoints in the 
upper 60s to low 70s will result in heat indices in the low 100s
at some locations. Heat advisory headlines are likely at this 
time. Dry air in the mid-levels will keep the region dry on 
Thursday afternoon, but a spot shower/thunderstorm Thursday 
night can't be ruled out across the western zones.

Deep southwest flow continues into Friday and supports surging 
dewpoints into the low to mid 70s. Temperatures remain above 
normal, but increasing cloudiness Friday afternoon should limit 
high temperatures to the upper 80s and low 90s. Nonetheless, the
oppressive humidity will have us flirting with heat advisory 
criteria with heat indices in the upper 90s likely. 

Weak upper-level disturbance and surface frontal boundary moves
across the region late Friday. This will bring the potential 
for a few thunderstorms and some much needed rainfall across 
portions of southern New England. Weak boundary layer winds and 
PWATs close to 150 percent of normal will be supportive of 
locally heavy downpours. Not expecting any severe storms to 
develop as both deep-layer shear and synoptic forcing for ascent
will be very limited.

This Weekend

Southwest flow continues to support above normal temperatures 
this weekend. No strong signals for advisory level heat this 
weekend, but still hot with highs in the upper 80s to low 90s. 
Dewpoints remain elevated in the low to mid 70s making for some 
very uncomfortable sleeping weather. Can't rule out a few 
isolated convective showers or thunderstorms during the 
afternoon.

Next Week

Consensus among long-term models and ensembles if for the 
southwest flow pattern and above normal temperatures to continue
into Monday. Beyond Monday there is a signal for a frontal 
passage early next week that would bring the next opportunity 
for substantial rainfall.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels:

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

18z TAF Update:

Rest of the Afternoon (thru 00z Wed): High confidence. 

VFR, though SCT SHRA/TSRA develops in western MA/CT and moves 
ESE between 18-00z. Main risk is the interior airports and into
PVD; less clear if BOS or Cape airports see this activity. Since
storm type should be more cell type storms, have carried VCSH in
for airports with greatest risk and will TEMPO for a more
obvious risk. Storms capable of brief downpours with visby
reduction to MVFR-LIFR, lightning and brief strong wind gusts.
SW winds around 10-15 kt, gusts to 22-25 kt with shift to W
late for the western airports.

Tonight: High confidence. 

VFR for most; LIFR fog/stratus re-develops between 00-03z at ACK
and expands northward towards Cape airports. W winds 5-8 kt
shift to NW by daybreak. 

Wednesday and Wednesday Night: High confidence. 

VFR, with stratus/fog for Cape airports/ACK diminishing by mid
morning. Probable sea-breezes for the coastlines ~15-17z, 
otherwise winds become WSW 4-8 kt late. 

Continued VFR for most, though re-developing mist/fog and
stratus for the evening for at least the Cape and Islands but
also possible towards SE MA and PVD. S/SW winds 4-8 kt.

KBOS...High confidence in TAF. SHRA/TS possible 22-00z but too
low confidence to include in TAF. Will tempo if a direct hit
looks imminent.

KBDL...High confidence in TAF. 

Outlook /Wednesday Night through Saturday/...

Wednesday Night: VFR. 

Thursday: VFR. Breezy. 

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

Friday: Mainly VFR, with areas MVFR possible. Chance SHRA,
slight chance TSRA.

Friday Night: Mainly MVFR, with areas VFR possible. Chance
SHRA, slight chance TSRA.

Saturday: Mainly MVFR, with areas VFR possible. Breezy. Slight
chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Monday evening into Tuesday night...High confidence.

Poor visibility early this morning will improve during the day.
A cold front brings another chance for showers and slight 
chance for thunderstorms this afternoon and early evening. A
cold front will move across the waters tonight, with fair
conditions expected Wednesday.

Outlook /Wednesday Night through Saturday/... 

Wednesday Night through Thursday: Winds less than 25 kt. 

Thursday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Slight chance of rain showers. 

Friday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain showers, slight chance of thunderstorms. 

Friday Night: Winds less than 25 kt. Chance of rain showers,
slight chance of thunderstorms. 

Saturday: Winds less than 25 kt. Slight chance of rain showers.

&&

.CLIMATE...
August 4th daily record maximum high temperature.

BOS - 96F [1928]
ORH - 95F [1944]
PVD - 98F [1944]
BDL - 96F [1944]

August 4th daily record maximum low temperature.

BOS - 76F [1930] 
ORH - 72F [2002] 
PVD - 74F [2010] 
BDL - 74F [2006]

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory from 11 AM Thursday to 8 PM EDT Friday for 
     CTZ002>004.
MA...Heat Advisory from 11 AM Thursday to 8 PM EDT Friday for 
     MAZ002>021-026.
RI...Heat Advisory from 11 AM Thursday to 8 PM EDT Friday for 
     RIZ001>007.
MARINE...None.

&&

$$
SYNOPSIS...Belk/RM
NEAR TERM...Belk/Loconto/RM
SHORT TERM...Belk
LONG TERM...RM
AVIATION...Belk/Loconto/RM
MARINE...Belk/Loconto/RM
CLIMATE...