Lexington Weather

Lexington, Massachusetts, USA

86°F

8/8/2022 7:16pm

Lexington Conditions: Clear
Temperature: 85.6°F / 29.8°C
Dew Point: 73.4°F
Relative Humidity: 67%
Wind: WSW Calm, 10-min avg: 2 mph, gust: 15 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 032037
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
437 PM EDT Wed Aug 3 2022

.SYNOPSIS...

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

&&

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

330 PM Update: 

While still rather humid across Cape Cod and the Islands, it's 
otherwise a warm but less humid afternoon across Southern New 
England, with local sea-breezes near the eastern and southern 
coasts. Shallow cumulus clouds dot the skies but otherwise mostly 
sunny skies with temperatures in the 80s to low 90s, though in the 
upper 70s to low 80s for coastal MA and RI.

A 1016 mb high pressure area over the northern portion of Cape Cod 
Bay will continue to move southeastward into the offshore waters 
tonight. Clear skies to prevail tonight, though increasing southerly 
to southwest flow will transport higher dewpoints (mid to upper 60s 
inland, low 70s toward southern waters) northward later tonight and 
especially overnight. This should result in re-developing mist/fog 
and stratus fields initially towards the southern coastal waters and 
the adjacent Islands toward late evening or midnight, then tending 
to expand north/northwest into the south coast. Its northwestern 
extent is a little uncertain given S/SW winds but we could see some 
expansion of mist/fog toward central and northern RI into SE MA. 
Lows mid 60s to low 70s.

&&

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

330 PM Update:

Thursday:  

Any overnight stratus/fog near southeast New England should 
dissipate by mid morning. 

Thereafter we are looking at hot and humid weather with temperatures 
expected to rise quickly under full sun and 850-925 mb warm 
advection. GFS is on the higher end of this range with 850 mb temps 
reaching around +21 to +22C. However in looking at the NAM and 
ECMWF, values are a couple degrees cooler. It really won't make much 
difference because southwest breezes will also add an element of 
downsloping and produce air temps in the mid to upper 90s and lower 
80s for southeast New England. Will also mention that skies could be 
rather hazy as HRRR-Smoke model vertically integrated smoke shows a 
plume of high-altitude smoke from wildfires in the western states. 

Heat Advisories were maintained with this forecast package with heat 
indices up to 104F. A few areas have a chance to meet or briefly 
eclipse excessive heat warning levels, mainly in the Hartford-
Springfield portion of the CT Valley and in the Merrimack Valley but 
confidence wasn't high enough for a large enough area to consider 
upgrading. Source air for dewpoints tomorrow looks to be across the 
central and southern Appalachians where current values are in the 
upper 60s to low 70s. While it still will be rather humid, WSW 
downsloping will help to reduce dewpoints a little, which cuts into 
how high heat indices get. There may be either convective cloud 
debris from convection over NY and/or isolated storms moving into 
western MA/CT later in the day. There is strong confidence in heat 
indices between 95 to 104 for most of Southern New England. So the 
message however is the same when it comes to the heat and we 
encourage everyone to practice appropriate heat-related precautions 
such as staying hydrated, taking frequent breaks in air conditioned 
rooms, and making sure pets and children are not left alone in cars.

Thursday Night: 

Any isolated garden-variety thunderstorms in western MA and western 
CT should weaken and fizzle shortly after sundown. A warm and muggy 
night is in store with continued southerly flow. This will also 
transport tropical low to mid 70s dewpoints northward. Re-developing 
fog and stratus seems likely as well near south coastal New England 
given the rising dewpoints. Other than the higher terrain where 
upper 60s are forecast, lows should only drop into the lower to mid 
70s.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...

Highlights

* Oppressive heat persists into Friday. Heat Advisory remains in 
  effect. 

* Could still have oppressive heat through the weekend into early 
  next week, but confidence is low/moderate. Additional heat 
  headlines may be needed.

* Daily shots for hit/miss showers and storms Friday through the 
  weekend into early next week. Locally heavy downpours possible at 
  times.

Friday through Saturday...

The Bermuda High will be firmly planted to the southeast of the 
region through this period. A weak shortwave will lift from the Mid 
Atlantic through New England by late Saturday. A cool front will 
slide toward southern New England during this timeframe, but may 
stall out as it is moving in. 

Main concern through this period is the oppressive heat. Will see 
850 hPa temps of 17-19 degrees Celsius on Friday and 16-19 degrees 
Celsius on Saturday. More confident in the heat risk for much of the 
region on Friday as opposed to Saturday at this point, which is why 
the Heat Advisory has not been extended yet. Main concern is the 
cold front may be over or just through the region on Saturday. 
Depending on the fronts location and cloud cover will impact the 
temps we realize. Did bump up highs on Friday toward the 75th 
percentile of guidance as deep westerly mixing within the boundary 
layer should allow most to get into the low/mid 90s. The exception 
will be along the immediate south coast and Islands where highs top 
out in the mid/upper 80s. The catch twenty two in this situation is 
the deep mixing will actually dry the dew points out a bit, so have 
knocked them down a bit from the default NBM. By late afternoon most 
will see dew points in the upper 60s to mid 70s. On Saturday given 
the uncertainty with the front have just stuck with the NBM, which 
keeps dew points in the low/mid 70s. Still anticipate Heat Index 
values of 95-103 for much of southern New England on Friday, so Heat 
Advisories continue. As for Saturday, will see Heat Index values 
range from roughly 90-100. Some spots may need the Heat Advisory 
expanded into Saturday.

Will have the shot for scattered showers and thunderstorms late 
Friday through Saturday. At this point the best shot to see any 
activity will be across the interior. Given the airmass in place 
could also have some heavy downpours at times. Will have PWATs of 
1.75-2+ inches on Friday and 1.8-2+ inches on Saturday. Warm cloud 
layer depths are roughly 3-4.5 km with a few hundred to roughly 1500 
J/kg of MUCAPE. Given the poor deep layer shear am not anticipating 
strong/severe storms, but there could be some locally heavy 
downpours with any showers/storms that develop as they will likely 
be slow moving.

Sunday through Tuesday...

Have generally stuck with the NBM guidance through this period as it 
seems reasonable. Will still have the Bermuda High firmly in place 
to the S/SE of New England through this period. Next deeper trough 
that lifts in is late on Monday into Tuesday. 

Anticipate for most that it will be dry and quiet through much of 
this period, but given the airmass in place will have daily shots of 
isolated to scattered showers and storms. Best chances will be 
across the interior. Expect the risk for more widespread activity 
comes late on Monday into Tuesday or perhaps into Wednesday with 
that trough lifting in. Still will see the risk for heavy downpours 
at times given the 1.75-2+ inch PWATs in place over southern New 
England. Could still be dealing with oppressive heat/humidity late 
in the weekend into early next week with Heat Index values ranging 
from 90-104 Sunday/Monday. We may finally turn more seasonable by 
Tuesday, but confidence at this point is low.

&&

.AVIATION /21Z WEDNESDAY THROUGH MONDAY/...

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 Thu): High confidence. 

VFR. S/SE winds (more SE near the eastern MA coast) around 5-10
kt. 

Tonight: High confidence in trends, moderate on extent of
fog/stratus. 

VFR early, then will start to see LIFR mist/fog and stratus develop
near ACK and spread northwestward toward at least the South 
Coast, Cape Cod, MVY and BID. Looks like IFR fog or stratus may 
advance as far northward as PVD, but how far north is a question
given S/SW flow. Most areas along/north of the Mass Pike to
stay VFR. 

Thursday: High confidence. 

Fog/stratus dissipates by 13z. VFR with hazy skies aloft. Low
prob of isolated TSRA in far western New England/Berkshires
after 22z. SW winds 8-13 kt gusts to 18-20 kt. 

Thursday Night: Moderate confidence. 

Generally VFR. Status/fog may return overnight to the South 
Coast, Cape and Islands.

KBOS...High confidence in TAF. 

KBDL...High confidence in TAF. 

Outlook /Friday through Monday/...

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

Friday Night: VFR. Chance SHRA, slight chance TSRA.

Saturday: VFR. Breezy. Chance SHRA, slight chance TSRA.

Saturday Night: VFR. Breezy. 

Sunday through Sunday Night: VFR. Breezy. Slight chance SHRA,
isolated TSRA.

Monday: VFR. Breezy. Chance SHRA, slight chance TSRA.

&&

.MARINE...

Forecaster Confidence Levels:

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

High confidence. 

Winds and seas to remain tranquil through the period. 

Winds become S/SW tonight around 10 kt with fog re-developing near 
the south coastal waters. SW gusts increase to 15 to 20 kt Thursday, 
with fog re-developing on the southern waters Thursday night. Seas 
continue at 3 ft or less for all waters.

Outlook /Friday through Monday/... 

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

Saturday Night: Winds less than 25 kt. 

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

Sunday Night through Monday: Winds less than 25 kt. Seas up to
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...BL/Loconto
NEAR TERM...Loconto
SHORT TERM...Loconto
LONG TERM...BL
AVIATION...BL/Loconto
MARINE...BL/Loconto
CLIMATE...