Lexington Weather

Lexington, Massachusetts, USA

51°F

10/6/2024 2:35am

Lexington Conditions: Clear
Temperature: 50.5°F / 10.3°C
Dew Point: 44.2°F
Relative Humidity: 79%
Wind: Calm, 10-min avg: Calm, gust: None
Barometer: 30.11 in Steady
Visibility: 10 miles
Rain Today: 0.00 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 051415
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1015 AM EDT Sat Oct 5 2024

.SYNOPSIS...
An isolated shower early this morning gives way to plenty of sunshine
with very pleasant temperatures later this morning and afternoon. 
A cold front moves through Southern New England late Sunday night 
into Monday, bringing a period of rain showers. This 
cold front will usher in a cooler, fall-like weather 
pattern for the rest of the work week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

10 AM Update...

Some spotty showers moved through the Boston area over the last
hour and have since moved offshore. The rest of Saturday is 
expected to remain dry as a drier airmass settles in. Previous 
forecast continues to be on track, with highs still forecast to 
be in the lower to mid-70s throughout the region. No significant
changes were made aside from using updated guidance, which kept
the current trends essentially the same.

Previous discussion...

A shortwave/weak cold front was crossing the region early this
morning. There is not much deep layer moisture/forcing with this
weak front...so radar just indicated a brief isolated shower or
two during the early this morning. Most locations will not see
measurable rainfall. There was also some patchy fog mainly
towards the southeast New England coast...but this will burn off
fairly quickly in the next couple of hours.

Rapid clearing is expected behind the front by lunchtime which will 
set us up for a beautiful mid-fall afternoon. Abundant sunshine will 
aid in deep mixing, with 925mb temps between 8-10C, as temperatures 
warm again into the lower to middle 70s; with perhaps a few
upper 70s in the southern Connecticut River Valley. Also 
anticipating that winds will shift dramatically from the SSW to 
the NW and eventually north this afternoon and evening, which 
will allow a much drier airmass to trickle into SNE this 
afternoon and evening.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
Tonight...

With dry airmass in place, light northerly flow, and clear skies, 
tonight looks to be a textbook radiator. Dewpoints in the 40s will 
act as a lower bound to temps, and with strong radiation, it is 
quite likely that dews fall into the upper 30s across pockets of 
interior MA. Thus, opted to populate the overnight low temps with 
CONSMOS guidance, with the expectations that a few localities in the 
terrain of western MA dip below 40F. Urban heat islands will likely 
be the saving grace for Boston, which looks to remain in the 50s 
overnight. 

Sunday...

Pleasant and tranquil conditions will extend into Sunday morning. A 
few different mechanisms will increase cloud cover on Sunday, the 
first being developing onshore flow across eastern MA and the second 
being another approaching shortwave from the west. Thus, expect more 
clouds on Sunday compared to Saturday with some mid to low clouds 
possible for the immediate eastern MA coastline after ~16Z. As with 
many days over the last week, some isolated sprinkles may possibly 
accompany these lower ceilings, but are not expected to pose much of 
a threat to outdoor activities. By late Sunday afternoon and early 
evening, high clouds will develop from west to east, though any 
precipitation associated with the approaching front will hold off 
until well after 00Z. 

Temps will be seasonable to a few degrees above normal for likely 
the last time in the next several days, warming into the mid 60s to 
perhaps 70; warmest again in the CT River Valley.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Key Points...

* Showers late Sun night into Mon
* Mainly dry but cool/fall-like temps Tue through Fri 
* Some frost possible at times next week away from the urban centers

Details...

Sunday night and Monday...

An approaching shortwave/cold front will increase the forcing for 
ascent late Sun night into Mon. A modest southerly LLJ of 25 to 30 
knots at 925 mb with Pwats nearing 1.25 inches will result in a 
enough forcing/moisture for a period of widespread showers late Sun 
night into Mon. Guidance shows that much of the region may pickup 
between 0.25 and 0.75 inches rain. We will have to see how this pans 
out...but we could use the rain. We also can not rule out an 
embedded isolated t-storm or two with some marginal instability. The 
clouds and showers will probably hold high temps in the 60s...but 
may see a few areas near 70 in the CT River Valley.

Tuesday through Friday...

Amplifying closed upper level low across Quebec will allow a deep 
northeast trough to develop. The result will be our first real taste 
of cool fall-like weather. 850T will generally range from 
-2C to +2C...so high temps will generally range from the upper 50s 
in the high terrain to the lower to middle 60s elsewhere much of 
next week. Temps may even be a few degrees cooler than that on Thu 
with a reinforcing shot of cool air. It will also be a bit breezy 
during the daylight hours...so definitely a fall-like feel.

Overnight low temps should bottom out well down into the 30s a few 
of the nights in the outlying locations...where some frost is 
possible. Even the Urban Heat Islands of Boston and Providence 
should see overnight lows in the lower to middle 40s.

Generally dry weather is expected...but given shortwave energy and 
cold pool aloft expect a lot of strato-cu during the afternoons. 
There may be a brief spot shower or two...but for all intensive 
purposes it will mainly be dry.

&&

.AVIATION /14Z SATURDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:

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

12z TAF Update...

Today...High Confidence. 

Early morning patchy ground fog towards the southeast New
England coast will burn off quickly by mid-morning.
Otherwise...VFR with nothing more than a brief spot shower 
early this morning. Winds shift to the NW around
10 kts this morning and then N by afternoon...except NE along 
the coast.

Tonight...

VFR outside any very localized patchy ground fog late. N winds
generally less than 10 knots.

Sunday... 

VFR. Winds shift from the N/NE to the SE first across the 
interior around 17Z and eventually across coastal terminals by 
22z; except outer Cape terminals. Some MVFR possible for the 
outer Cape with lingering onshore flow Sunday afternoon. 

KBOS TAF...High confidence in TAF.

VFR. A cold front will shift winds to the NW/N around 10 knots 
this morning which probably will shift more to the NE during the
afternoon.

KBDL TAF... High Confidence in TAF. 

VFR. Outlook /Sunday Night through Wednesday/...

Sunday Night: Mainly VFR, with areas MVFR possible. Chance
SHRA.

Monday: Mainly MVFR, with areas VFR possible. Breezy. SHRA,
isolated TSRA.

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

Tuesday through Tuesday Night: VFR. 

Wednesday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels:

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


Saturday...High Confidence

Scattered showers possible early Saturday morning into Saturday
mid-day, though showers may linger across the eastern outer
waters into Saturday evening. Winds shift behind passing front
to the NW Saturday morning; winds less than 25 kts. Waves 2-4 
ft.

Saturday Night...High Confidence

Winds 10-20 kts with higher winds confined to the outer waters.
Seas grow to 5-6ft overnight tonight, prompting the issuance of
a SCA from 06Z and beyond. 

Sunday... High Confidence 

Winds less than 25kt but seas across the outer waters continue
to range from 4-6ft. SCA continues for the outer waters through
the day Sunday, and beyond. 

Outlook /Sunday Night through Wednesday/...

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,
isolated thunderstorms. 

Monday Night: Winds less than 25 kt. Areas of rough seas.
Chance of rain showers. 

Tuesday: Winds less than 25 kt. Local rough seas. 

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 2 AM Sunday to 8 AM EDT Tuesday for 
     ANZ250-254-255.

&&

$$

SYNOPSIS...Frank/KS
NEAR TERM...Frank/Hrencecin/KS
SHORT TERM...KS
LONG TERM...Frank
AVIATION...Frank/KS
MARINE...Frank/KS