Lexington Weather

Lexington, Massachusetts, USA

85°F

8/8/2022 7:32pm

Lexington Conditions: Clear
Temperature: 84.9°F / 29.4°C
Dew Point: 74.1°F
Relative Humidity: 70%
Wind: SSW 1 mph, 10-min avg: 1 mph, gust: 9 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 021932
AFDBOX

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

.SYNOPSIS...

Heat and humidity will be the main weather story right through the 
weekend and into early next week. The heat and humidity will peak on 
Thursday and Friday with near record high temperatures and 
oppressive heat indices as well. The greatest potential for showers 
and thunderstorms will be on Friday with even some localized heavy 
rainfall possible.

&&

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

330 PM Update: 

Very warm to hot temperatures and humid dewpoints (upper 60s to mid 
70s!) continue as of mid-afternoon. Some modest relief is 
anticipated later tonight as a cool front moves eastward. In the 
interim, scattered showers and thunderstorms continue to develop on 
a pre-frontal trough moving through central MA into eastern/east-
central CT, with more shallow convection tied to the cold front now 
moving into the western Berkshires and eastern NY. Ongoing storms 
have been slow to develop given weak mid-level lapse rates that are 
at less than moist-adiabatic levels. A few have produced several 
instances of lightning across western MA along with short-lived, 
localized downpours. Environment is very much a weak shear/pulse 
environment with cores developing, then dissipating within about a 
half hour or so of time. Surface based CAPE values range from 1500-
2000 J/kg, and while downdraft CAPE values are generally 500 J/kg or 
less across most of MA, they are nearly double that across CT and RI 
into SE MA. Will have to watch CT-RI and SE MA as widely scattered 
cellular storms move eastward through sundown for locally stronger 
wind gusts, possible isolated SVR, but anticipate most convection to 
remain at sub-severe levels with lightning, brief downpours and sub-
severe gusts. 

Cool front moves through tonight, which should bring clearing skies 
and a drop in dewpoints into the low-mid 60s especially in the 
interior. Across the Cape and Islands, will still be quite humid 
with dewpoints upper 60s/locally near 70F. BUFKIT soundings showing 
radiation inversion developing near the South Coast, Cape and 
Islands with conditions favoring stratus and fog development for the 
overnight hrs. Lows mid 60s to lower 70s. 

&&

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

330 PM Update:

Wednesday through Wednesday Night: 

High pressure ridges into SNE as cool front moves offshore. Still 
will be quite warm but northerly flow as well as heating/mixing of 
drier air aloft should support lower to middle 60s dewpoints for 
most. So a little less humid, but plenty of sun and 850 mb temps in 
the mid teens C range should support highs at least as warm as today 
with mid 80s to low 90s in the interior and coastal plain. Should 
see local sea-breezes develop which will keep coastal areas a couple 
degrees cooler. Winds will shift from N/NW to S/SW as high pressure 
moves offshore later in the day. 

Dewpoints rise again back to uncomfortable levels (upper 60s/low 
70s) later Wed aftn into Wed night. As indicated by several guidance 
sources and the 12z HREF, developing fog/stratus near the South 
Coast/Cape and Islands looks to expand northwestward; it's not clear 
how far north and west fog may make it but could expand at least to 
the I-95 corridor and potentially into eastern CT/southern Worcester 
County. Lows mid/upper 60s to lower/mid-70s. 

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...

Highlights...

* Oppressive Heat & Humidity Thu and Fri with Heat Headlines Posted

* Heat Indices in 100 to 105 degree range Thu & Fri

* Main threat for showers & thunderstorms will be Fri with localized 
  heavy rainfall possible 

* Heat and humidity continue this weekend into early next week 
  with a few showers & thunderstorms possible 

Details...

Thursday and Friday...

Excellent model agreement in oppressive heat and humidity for both 
Thursday & Friday. The 500 MB height fields are on the order of 590 
to 594 DM which is outside the ECMWF climatological database. That 
is an excellent signal for an anomalous weather event; in this case 
being oppressive heat & humidity. 850T will be on the order of +19C 
to +21C over this time period along with southwest flow. 

Plenty of sunshine Thursday with good mixing should yield near 
record high temps in the 96 to 101 degree range. Dewpoints well into 
the 60s should bring Heat Indices on the order of 100 to 105 degrees.
By Friday...the surface cold front will be dropping down from the 
north. While high temps may end up a few degrees lower than Thu;
the dewpoints will be higher as moisture should pool along the 
cold front likely in the 70 to 75 degree range. High 
temperatures should still come up well into the 90s and it is 
not out of the question that a few spots hit 100 on Friday. 
Heat Indices should be on the order of 100 to 105 degrees. Given
the above we have opted to issue Heat Advisories for our entire
region...except for the Cape and Islands. We eventually may need
to include the Cape in the Heat Advisory for Friday. Lastly, 
given the potential for those very high dewpoints Friday...a 
few spots may see Heat Indices on the order of 105 to 107 so an 
upgrade to an Excessive Heat Warning is not out of the question.
Either way oppressive heat and humidity is on tap for the 
region.

Dry weather should prevail for much of Thursday given lack of 
synoptic scale forcing/deeper moisture. However, a few showers & 
t-storms can not be ruled out late Thu across our western 
zones. However, the main threat for scattered showers and 
thunderstorms will be on Friday as the cold front drops south 
into our region. The severe weather threat will be rather 
limited by weak wind fields. However, Pwats of 2+ inches coupled
with a slowing frontal boundary may result in localized heavy 
rainfall.

This Weekend Into Early Next Week...

Upper level ridging will remain anchored off the mid-Atlantic coast. 
This will result in continued above normal height fields and 
temperatures as well. In addition...this setup will result in quite 
a bit of humidity too. Highs in the upper 80s to the middle 90s 
along with humid conditions may result in the need for additional 
Heat Headlines. Perhaps some relief arrives by Tuesday. There also 
will be the potential for a few showers/t-storms at times, but not 
expecting a washout with dry weather dominating.

&&

.AVIATION /19Z 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 /Thursday through Sunday/...

Thursday: VFR. Breezy. 

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

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

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

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

Saturday Night: Mainly VFR, with local MVFR possible. Breezy. 

Sunday: Mainly VFR, with areas MVFR possible. 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.

Overall high confidence. 

Winds and seas to stay at sub-SCA levels through the period. 

SW winds near 20 kt late today shift to W and decrease early 
tonight, then becoming NW around 10 kt. Biggest concerns for tonight 
are potential for isolated/scattered thunder early tonight, then fog 
with significant reduction in visby overnight near the south 
coastal/nearshore waters. 

NW winds 10 kt shift to onshore with sea-breeze development Wed 
afternoon; then will trend S/SW Wed night with fog re-developing. 

Seas 3 ft or less all waters.

Outlook /Thursday through Sunday/... 

Thursday through Thursday Night: Winds less than 25 kt. 

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

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

Saturday: Winds less than 25 kt. 

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

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

&&

.CLIMATE...

August 4th daily record maximum high temperatures...

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

August 4th daily record maximum low temperatures...

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

August 5th daily record maximum high temperatures...

BOS - 100F [1955]
ORH - 96F  [1944]
PVD - 100F [1944]
BDL - 101F [1955]

August 5th daily record maximum low temperatures...

BOS - 76F [1938]
ORH - 73F [1938]
PVD - 77F [1938]
BDL - 76F [1938]

&&

.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...Loconto/Frank
NEAR TERM...Loconto
SHORT TERM...Loconto
LONG TERM...Frank
AVIATION...Loconto/Frank
MARINE...Loconto/Frank
CLIMATE...Simpson