Lexington Weather

Lexington, Massachusetts, USA

72°F
9/22/2021 2:39pm 
  • Lexington Conditions: Overcast
  • Temperature: 71.8°F / 22.1°CColder 1.6°F than last hour.
  • Dew Point: 69.1°FIncreased 1.1°Fsince last hour.
  • Relative Humidity: 91%Increased 8.0% since last hour.
  • Wind: Wind from W W 2 mph, 10-min avg: 2 mph, gust: 10 mph
  • Barometer: 30.08 inFalling 0.02  inHg/hr Falling Slowly
  • Visibility: 10 miles
  • Rain Today: 0.00 in
  •   

Area Forecast Discussion
for Boston, MA

        
000
FXUS61 KBOX 160641
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
241 AM EDT Thu Sep 16 2021

.SYNOPSIS...
A cold front moves through later tonight, then stalls along the
south coast Thursday and Thursday night, resulting in 
additional showers or an isolated thunderstorm. A coastal low 
currently near the Bahamas may bring on and off showers, 
building waves and an increase in east winds Friday into 
Saturday for coastal New England as it recurves toward Atlantic 
Canada. High pressure then establishes itself on Sunday, leading
to dry weather and above average temperatures through at least 
the middle of next week.

&&

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

230 AM update...

Deep layer moisture continues to approach the region from
eastern NY, along with modest synoptic scale lift from RRQ of
upper level jet streak over SNE. This combination yielding a 
shield of showers with isolated thunder across western-central 
CT/MA. This precip shield will slowly slide east into RI and
eastern MA early this morning. Remaining mild this morning with
temps in the upper 60s and low 70s. 

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM FRIDAY/...
3 PM update...

Thursday...

Weak high pressure builds into northern New England, however 
the stalled frontal boundary will remain across CT,RI, and 
southeast MA. Despite weak height rises over the area, with 
abundant low level moisture, some instability and weak surface 
convergence, scattered showers are expected. Cannot rule out an
isolated thunderstorm. Could be some locally heavy downpours 
along the leftover boundary given high PWATs, marginal 
instability and light winds aloft. It will be noticeably cooler 
with highs only from 70 to 75. It will feel humid with dewpoints
still in the 60s. With Mild with highs in the 70s but humid as 
dew pts remain in the 60s. Cloudy skies are forecast along with
patches of fog and light northeast to east winds. 

Thursday night...
The front washes out over the region. But light northeast to
east flow continues, with cloudy skies and patchy fog. A few
lingering showers are possible.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...

3 PM update...

Highlights: 

* Monitoring low pressure northeast of the Bahamas that is likely to 
  become a tropical cyclone, but looks to stay far enough offshore 
  for minimal impacts to Southern New England. Off-and-on periods of 
  showers with cool and breezy conditions Friday into Saturday. 
  
* Dry weather and above normal temperatures likely heading into 
  middle of next week with high pressure in control. 

Details:

Friday into Saturday night...

Despite high pressure ridging in place for much of Southern New 
England Friday into Saturday, it remains a generally unsettled 
period. The main focus in this portion of the long-term forecast is 
the coastal low currently a few hundred miles northeast of the 
Central Bahamas. Per the National Hurricane Center latest 
discussion, conditions appear marginally favorable for development 
into a tropical depression, with 80 percent chance for formation by 
Friday. Model consensus takes the potential tropical cyclone near or 
just south of the 70W/40N benchmark later Friday into Saturday. This 
would mean best chances of rain across southeast New England, though 
rains in most areas may prove more intermittent. Otherwise, with 
onshore flow, expect mostly cloudy, breezy and cool conditions with 
interval of rain showers along with increased swells and risk of rip 
currents. Ultimately, effects and impacts will hinge on the track 
and intensity of the cyclone, but right now impacts to Southern New 
England appear minimal. Given the uncertainty regarding potential 
tropical development, stuck to NBM for this portion of the forecast. 

Heading into the weekend, looks like there may be some lingering 
showers for Saturday but as heights rise behind the exiting cyclone, 
it could be a decent weekend with seasonable temperatures, 
especially for the latter half with high pressure becoming the 
dominant surface feature.

Sunday into next Wednesday...

Following the passage of a moisture-starved cold front on Sunday, 
the main story will be a prolonged stretch of dry weather with above 
normal temperatures as mid-level ridging amplifies over the eastern 
US. Global guidance ensembles show 588+ Dm ridge building into 
Southern New England by middle of next week. With mean 850mb 
temperatures in the low to mid teens, expect daytime highs to reach 
the upper 70s to lower 80s, which would be 5 to 10 degrees above 
climatological normal. Have gone with NBM guidance for now given we 
are so far out but it is possible that daytime highs will be 
increased in future updates with southwest flow aloft boosting 
downsloping adiabatic warming. In fact, the Climate Prediction 
Center 6 to 10 day outlook features above 80 percent probability of 
above normal temperatures. So even as we head into astronomical fall 
for the Northern Hemisphere (beginning September 22), it will feel 
more like late August. PWATs look to be slightly below to near 
normal so expect generally mild days and cool nights given the dry 
air mass.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
Forecaster Confidence Levels.

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

06Z update: 

Today...high confidence.

A combination of MVFR/VFR (trending toward MVFR) in showers 
this morning, then drying trend for this afternoon, except south
coast especially Cape Cod, where showers may persist. Winds 
shifting to NW to NE with frontal passage.

Tonight...high confidence.

MVFR in the evening, then trending down to IFR/LIFR along with
patchy fog. Mainly dry weather. Light ENE winds. 


Friday...high confidence. 

IFR/LIFR to begin the day, but cigs lifting to MVFR/VFR during
the afternoon. Mainly dry weather with modest ENE winds. 

KBOS Terminal...Moderate confidence.

KBDL Terminal...Moderate confidence.

Outlook /Friday night through Sunday/

Friday Night: Mainly MVFR, with local IFR possible. Breezy.
Slight chance RA.

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

Saturday Night through Sunday: VFR.

&&

.MARINE...
Forecaster Confidence Levels.

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

Tonight...decreasing SSW winds. Scattered thunderstorms, a few 
strong storms possible across northern MA waters, then weakening 
after 8 pm. Humid airmass and light winds may yield areas of dense 
fog. 

Thursday...frontal boundary stalls or washes out over the MA/RI 
waters. Patchy fog in the morning lifts/improves during the 
afternoon but gives way to scattered showers/thunderstorms. 

Outlook /Friday Night through Monday/...

Thursday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Chance of rain showers. 

Friday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Chance of rain. 

Friday Night: Winds less than 25 kt. Local rough seas. Chance
of rain. 

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

Saturday Night: Winds less than 25 kt. Seas up to 5 ft. Slight
chance of rain. 

Sunday: Winds less than 25 kt. Seas up to 5 ft.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

$$
SYNOPSIS...Chai/GAF
NEAR TERM...Nocera
SHORT TERM...GAF
LONG TERM...Chai
AVIATION...Nocera/Chai
MARINE...Chai/GAF
      

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