Lexington Weather

Lexington, Massachusetts, USA

51°F

10/6/2024 2:19am

Lexington Conditions: Clear
Temperature: 51.1°F / 10.6°C
Dew Point: 44.4°F
Relative Humidity: 78%
Wind: Calm, 10-min avg: Calm, gust: None
Barometer: 30.12 in Steady
Visibility: 10 miles
Rain Today: 0.00 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 040529
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
129 AM EDT Fri Oct 4 2024

.SYNOPSIS...
Mild temperatures Friday with no precipitation. A weak cold 
front brings a brief wave of showers late Friday through early
Saturday. Decreasing cloud cover early Saturday gives way to a 
nice weekend in store with dry weather and seasonable 
temperatures. A cold front moves through Southern New England 
overnight Sunday evening into Monday, bringing a period of rain 
showers. This cold front will herald a cooler, Fall- like 
weather pattern as we move into the middle part of next week.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
10 PM Update...

Dewpoints approaching 60F, thanks to southerly flow, across the
south coast have supported patchy stratus/fog development for
the Cape and Islands. Most notably, MVY and ACK have reported
vsbys as low as ~2SM in the last hour or two. Will note that
dewpoints are currently running 2-3F higher than forecast, so
did an adjustment to the forecast with this update. 

While river valley fog remains possible in the CT River Valley,
some mid level clouds will delay fog development until after
midnight when the cloud deck finally pushes east. 

800 PM Update: 

No significant changes needed to the going forecast. Surface
high pressure continues to slowly sag southeast into the
offshore waters. Other than some high clouds streaming in from
the SW, mostly clear skies have allowed temps to cool off into
the lower to mid 60s for most. Good radiational cooling is
expected with lows bottoming out into the mid 40s to lower 50s
(mid 50s in the urban areas). Could see patchy fog develop in
the typical radiational fog-prone areas around NW MA, the CT
Valley, the I-495 corridor in MA. We also need to monitor for
patchy fog development toward early morning along the RI/MA
south coast as SE winds slacken off.

Previous discussion:

Southern New England remains under an area of surface high pressure 
tonight with light south/southwesterly surface winds. Lower clouds 
develop just off the Cape, potentially moving into those immediate 
shore areas. Across the interior, it will be a favorable night for 
cooling with lows dipping into the mid 40s and 50s. Model soundings 
show potential for patchy fog with ample cooling at the low levels 
and light winds. The best chances will be for the CT River Valley 
after midnight. Could see some spotty areas along the I-495 corridor 
as well leading up to sunrise. Higher clouds are possible overnight 
which will also help keep fog confined to the usual prone areas and 
less widespread.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/...
Weak upper level ridging overhead on Friday with a weak shortwave 
trough approaching from the west. Any lower clouds/patchy fog across 
the interior and offshore areas erode and scatter out. 850mb 
temperatures warm into the 10-12 degC range which will support a 
slightly warmer day. This could allow temperatures in the low to mid 
70s in most areas with some upper 70s readings possible for parts of 
the CT River Valley. Clouds pushing eastward ahead of the incoming 
shortwave trough may potentially dampen highs a degree or two. The 
Cape/islands will stay cooler with highs in the mid to upper
60s. 

A weak shortwave trough moves through the region Friday night into 
early Saturday. This will bring along a weak cold front with a wave 
of light showers overnight through early Saturday morning.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Key Points...

Highlights: 

* Early-Saturday light rain showers trend dry by mid morning 
  Saturday, with dry weather and seasonable temps for the weekend.

* Stronger cold front moves in overnight Sunday night into Monday, 
  bringing wetting rains but significant rainfall totals are not 
  expected.
  
* Pattern change toward cooler, Fall-like weather for early to mid 
  next week, with possible frost in some locations. 
    
Details:

Saturday and Sunday: 

Passing mid-level shortwave disturbance responsible for light rain 
showers during the overnight will continue to shift offshore as we 
move into the mid-morning hours on Sat. High pressure to then build 
in from NW NY and southern Ontario into Southern New England through 
the rest of Sat and continuing into the daytime hrs of Sunday. 

Early-Saturday low chance PoP will then trend to dry by the mid-
morning hours along with decreasing clouds and good diurnal ranges 
between high and low temps. Highs on Sat should reach into the low 
70s with increasing sun, and in the 60s to low 70s on Sunday, 
coolest near the coast. Lows Sat night in the 40s, to upper 
40s/around 50 in the urban centers. 

Sunday Night into Monday: 

500 mb height rises transitions to height falls later Sun night as a 
cold front brings our next chance for showers. PoPs increase into 
the Likely range for the overnight period into Monday. Rainfall amts 
do not appear to be too significant per 12z ensemble percentile 
analyses; however what we will need to monitor for is the potential 
for a weak low pressure area to develop along the front, as 
indicated more bullishly by recent ECWMF solutions. Net effect this 
would have, were it to develop, would be to delay the eastward 
progress of the front and perhaps continue lighter rain showers into 
eastern and southeastern sections of Southern New England into a 
greater part of Monday. With more clouds than sun for Monday, expect 
highs in the 60s. 

Tuesday through Thursday: 

Pretty significant pattern change toward cooler, Fall-like weather 
for Southern New England, as a pronounced closed low and cold pocket 
of air aloft settles in across the Northeast. 925 mb temps tumble to 
around +4 to +6C, representing an airmass that is slightly cooler 
than normal by early October standards. Highs may struggle to reach 
into the low 60s; we could also see nighttime lows cool down enough 
to the point where frost would be possible in the outlying valleys 
which radiate well. However there does appear to be at least some NW 
breeze that could keep nighttime temps from falling faster than they 
would in a clear/calm night. While the daytime hrs should feature a 
good deal of diurnal cloud cover, dry weather is expected.

&&

.AVIATION /05Z FRIDAY THROUGH TUESDAY/...
Forecast Confidence Levels:

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

06z TAF Update:

Through today... High Confidence

Patchy radiation fog yielding LIFR to IFR across the CT River
Valley will give way to VFR. VFR elsewhere except along the
immediate south coast where higher dewpoints and southerly flow
have led to some marine stratus/fog formation. By the lunch
hour, expect all terminals to be VFR. SSW winds today less than
10kt, with east coast seabreezes possible around 16Z. 

Tonight... Moderate confidence

Approaching cold front will deteriorate conditions from VFR to
MVFR with showers developing between 06-12Z. Light winds shift
to the NW behind the frontal passage. 

Saturday... Moderate Confidence

Rain showers most likely during the morning hours, tapering by
afternoon. MVFR improves to VFR, though isolated pockets of IFR
possible. Winds generally N, around 10kt with gusts to 15
possible. 

BOS TAF...High confidence in TAF.

VFR. For Friday, sea breeze develops likely in the 15-16z time 
frame with SSE/SE winds. Showers likely by 12Z Saturday. 

BDL TAF...High confidence in TAF. 

VFR, although localized patches of ground fog may come in and
out of the terminal through 13Z this morning. Light rain showers
possible by 06Z Saturday. Light SW/SSW winds Friday.

Outlook /Saturday Night through Tuesday/...

Saturday Night through Sunday: VFR. 

Sunday Night: VFR. Chance SHRA.

Monday: Mainly VFR, with local MVFR possible. Chance SHRA.

Monday Night: VFR. Slight chance SHRA.

Tuesday: VFR.

&&

.MARINE...
Forecaster Confidence Levels:

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

Tonight and Friday...High Confidence. 

Waves 2-4ft. SSW winds tonight, less than 15kt expected. Marine
stratus and patchy fog possible tonight across the southern 
waters. S/SE winds Friday through Friday night less than 15 
kts, waves 2-4 ft.


Saturday...High Confidence

NW winds less than 25 kts. Waves 2-4 ft.  

Outlook /Saturday Night through Tuesday/...

Saturday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. 

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

Sunday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of
rain showers. 

Monday: Winds less than 25 kt. Seas up to 5 ft. Rain showers
likely. 

Monday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of
rain showers. 

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

&&

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

&&

$$

SYNOPSIS...Loconto/Mensch
NEAR TERM...Loconto/Mensch/KS
SHORT TERM...Mensch/KS
LONG TERM...Loconto
AVIATION...KS
MARINE...Loconto/Mensch