Lexington Weather

Lexington, Massachusetts, USA

65°F

5/20/2024 5:06pm

Lexington Conditions: Clear
Temperature: 64.9°F / 18.3°C
Dew Point: 56.8°F
Relative Humidity: 75%
Wind: Calm, 10-min avg: Calm, gust: 3 mph
Barometer: 29.96 in Steady
Visibility: 10 miles
Rain Today: 0.00 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 141845
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
245 PM EDT Tue May 14 2024

.SYNOPSIS...
Warm and mainly dry today with some uncertainty regarding how 
mild Wednesday will be. Heading into a cloudier and unsettled 
weather pattern for late in the week into the weekend, as a 
series of slow-moving upper level disturbances move through 
Southern New England. While it is not likely to be raining the 
entire period, at least hit or miss showers can't be ruled out 
at any time. Temperatures for late in the week into the weekend 
trend slightly cooler than normal on high temperatures and 
milder than normal on the lows.

&&

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

2 PM Update:

Gorgeous spring weather in progress across SNE with abundant
sunshine and temps in the 70s to as warm as 81 at BDL and 80 at
BAF/CEF/FIT at 2 pm! Modest pressure gradient yielding SSW winds
gusting up to 25 mph. Dew points in the 50s helping to provide a
mild feel to the airmass. Previous forecast captures these
details nicely, therefore no changes to earlier forecast. 

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...

Showers remain possible for western MA and CT tonight but weak mid 
level height rises have dampened the signal overnight for any 
widespread precip. While dewpoint depressions will be quite small, 
southerly flow overnight should remain brisk enough, between 5-10kt, 
to keep widespread fog at bay. Lows will bottom out in the mid to 
even upper 50s region wide, coolest across the Cape. 

Wednesday's forecast proves to be a bit tricky as low pressure 
emerges off the mid-Atlantic coast. Overnight guidance took a 
significant step in the "drier and warmer" direction with low 
pressure remaining suppressed to our south for much of the day. With 
mid level ridge still in place, and 925mb temperatures still mild 
between 13-15C, the temperature forecast will be highly dependent on 
cloud cover and our mixing potential. Should sunshine break out for 
a good portion of the morning, it's very possible temps soar into 
the mid 70s region wide. With that said, anticipating cloud cover 
will be most robust across the CT River Valley, in part due to an 
eastward advancing weak boundary, so the warmest temperatures in our 
region will be across the Merrimack River Valley and across SE MA. 
Given the rather sudden shift in guidance, heavily weighted the 
temperatures forecast using NBM, but later forecasters may choose a 
more aggressive temperatures forecast should a sunnier trend 
continue. In order to derive warmer temperatures, also trended the 
PoP and Sky cover forecast in a more favorable (clearer and drier) 
direction that supports deeper mixing. 

Shower chances will increase late Wednesday from south to north as 
the precipitation shield associated with the low is able push across 
southern RI and the Cape. Again utilized NBM for the QPF
forecast.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...

Highlights: 

* Unsettled late week into the weekend, although below-average 
  confidence in temps and rain chances in this period.

* Won't be raining the whole time, with Fri offering some potential 
  for drier weather, but generally cloudy with periods of at least 
  possible showers.

* Seasonable to slightly cooler than normal highs, with milder 
  nighttime lows.

Details:

Global ensembles point to a generally unsettled and slow-evolving 
pattern through a large portion of this forecast period. Southern 
New England's weather looks to be governed by a weakening/filling 
upper low detached from the westerlies through late in the week, 
then right on its heels is another shortwave disturbance that is 
poised to approach and cross our area around the weekend. 
Unfortunately that's really all that can be said as there is quite a 
bit of uncertainty as far as the location and progression of these 
two trough features; thus, below-average forecast confidence in 
temps, PoP and rain amts in light of this uncertainty in mass field 
details. Took a pretty broad-stroked brush as far the forecast goes 
in this period; while most days have some mentionable PoP, it there 
will likely be periods of dry weather in between and it is not 
likely we're looking at significant rain amts. With a cloudier-than-
not forecast period and a few days of onshore breezes leading to 
shallower mixing depths, highs were seasonable or slightly cooler 
than normal and lows were milder than normal.  

Wednesday Night through Friday: 

Upper low initially over the OH Valley early Wed night progresses 
slowly offshore of the NJ coast and deamplifying as it does so; this 
puts SNE on the northern end of the upper-level circulation. These 
signals are not typically conducive to significant precip, with the 
better chances for steadier light rains on Thurs and mainly south of 
the Mass Pike. I do think the 00z GFS depiction regarding the 
eastward progression is still too progressive and leaned somewhat 
toward the slower ECMWF/GEM evolution. With E/SE onshore flow, highs 
in the upper 50s to low 60s near the coasts with highs well into the 
60s; however 850 mb temps are quite warm (around +8 to +10C) and 
would favor highs several degrees warmer if we can fully mix, but I 
just don't see that happening.

With weakening shortwave ridge axis poking NE into SNE around Fri, 
that could be a relatively drier day with lower (around 15-20%) PoP 
indicated for Fri. Highs Fri could reach into the lower to mid 70s 
in the CT Valley and western MA, with cooler 60s readings the 
further east one goes.  

The Weekend into Monday: 

This latter period perhaps is the most uncertain with guidance 
struggling with poor congruence both across modeling systems but 
also from run-to-run. Interaction, if any, between the slowly-
exiting late-weekday upper low and an approaching trough from the 
OH/TN Valleys probably is contributing to that run-to-run disparity. 
Opted to keep the forecast with a mention of PoP along with a 
considerable degree of cloud cover, but that will need to be better 
defined once models show better agreement in timing and placement of 
key features. While there are some solutions which indicate a dry 
weekend and favor better rain chances on Monday, it's probably too 
hasty to lock in that drier outcome just yet.

&&

.AVIATION /18Z TUESDAY THROUGH SATURDAY/...
Forecast Confidence Levels:

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

18Z TAF Update: 

Thru 00z...high confidence. 

VFR, dry weather and gusty SSW winds 15-25 kt. 

After 00z...moderate confidence. Some uncertainty on timing and
how far east MVFR cigs track tonight. 

VFR cloud bases along with SSW winds diminishing and becoming
south. Isolated to widely scattered showers across CT into
western-central MA. These showers likely accompanied by MVFR
cigs. Otherwise, mainly dry runways for RI and eastern MA. 

Wednesday...moderate confidence. Some uncertainty on coverage of
MVFR cigs and areal coverage of showers. 

Light south winds with widespread VFR cloud bases. Isolated
showers with marginal MVFR/VFR cigs across CT into western MA. 

Wednesday night...moderate confidence.

Light S-SE winds become east overnight. VFR conditions become
MVFR overnight, as rain shield comes onshore to the south coast
of CT/RI/MA. Forecast uncertainty in how far north this rain
shield tracks overnight. 

KBOS TAF...High confidence in TAF. Gusty SSW winds 15-25 kt
slowly slacken with sunset. 

KBDL TAF...High confidence in TAF. Gusty SSW winds 15-25 kt
diminish with sunset. 

Outlook /Thursday through Saturday/... 

Thursday: Mainly VFR, with local MVFR possible. Breezy. Chance
RA.

Thursday Night through Friday: VFR. Breezy. Slight chance RA.

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

Saturday: Mainly VFR, with local IFR possible. Breezy. Chance
RA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Update: 3 AM

Through Wednesday....


S/SW winds persist through Tuesday night before shifting to the
SE Wednesday afternoon. Gusts to 25kt possible this afternoon
for our far NE waters, though the short fused and small
zonal coverage nature of the conditions has prompted us to hold
off on a Small Craft Advisory between 15-03Z this evening. 
Generally dry on today with isolated shower chances for the 
eastern waters this morning. Shower chances increase for the 
southern waters late Wednesday as low pressure creeps north from
the mid- Atlantic coast.

Outlook /Wednesday Night 

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

Thursday: Winds less than 25 kt. Areas of rough seas. Chance of
rain. 

Thursday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of rough seas. Chance of rain. 

Friday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas up to 5 ft. Slight chance of rain. 

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

&&

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

&&

$$

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