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 140707
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
307 AM EDT Tue May 14 2024

.SYNOPSIS...

Mild and mainly dry today with some uncertainty regarding how
warm 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 trend 
slightly cooler than normal on high temperatures and milder than
normal on the lows.&&

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

Today is shaping up to be the warmest and brightest of the next 
several days as mid level ridging builds in from the west behind a 
warm front that lifted through overnight/early this morning. Some 
lingering showers associated with the warm front should come to an 
end quickly after sunrise yielding clearing skies for many through 
the afternoon. 

Anticipating very healthy mixing today, to as high as 750mb off 
model soundings, and with 925mb temperatures climbing to as warm as 
18C and 850mb temps between 9 and 11C, temps wont have any issues 
climbing well into the 70s and low 80s across interior southern New 
England. The caveat to the warm temperatures will be along the south 
coast and areas north of Narragansett Bay, as brisk southerly flow 
off the cool ocean (SSTs in the low 50s) will keep temps in the 60s. 

There will be a considerable amount of instability, with SBCAPE 
approaching 750-1000J/kg across upstate NY, that will fuel afternoon 
shower and thunderstorm activity, but with SB/MU CAPE struggling to 
climb to ~200 J/kg in our region, expecting most of the activity 
will stay to our north on the advancing edge of the mid level ridge, 
across VT/NH and NY. Hi-Res CAMs reflect this idea, with several SPC 
HREF members keeping all shower activity out of our area through 
00Z! With that said, can't rule out a stray shower or thunderstorm 
spilling over the Berkshires into far northwestern MA after 21Z this 
evening. 

&&

.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 /07Z TUESDAY THROUGH SATURDAY/...
Forecast Confidence Levels:

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

06Z TAF Update

Tonight...High confidence.

VFR. Scattered showers are possible across northern MA, with at
times briefly lower VFR CIGs 3-5k ft. Winds are south to
southwest 5 to 10 knots.

Today...High confidence.

VFR. Very isolated showers through 12Z, generally north of the
MA Turnpike, resulting in little more than a wet runway. Dry
through mid day before the chance for isolated shower/thunderstorm
redevelops after 22Z in far western MA. Most terminals will
remain dry through the duration of the day. Steady southwest 
winds with gusts developing in the afternoon 20 to 25 knots. 

Tonight...High confidence. 

VFR with lowering cigs to around 4000-5000ft in western MA/CT by
daybreak where isolated showers are possible. Winds remain
persistent from the S/SW overnight. 

Wednesday... Moderate Confidence 

Tricky forecast Wednesday with low pressure to our south, but
drier trend has developed. Generally VFR with pockets of MVFR. Isolated
shower chances persist for western MA/CT but a mix of sun and 
clouds for eastern terminals. Showers associated with low 
pressure will remain south until early evening but may impact 
Cape/Islands/srn RI terminals by 00Z. S/SW winds shift to the 
SE. 

KBOS TAF...High confidence in TAF. 

VFR. Isolated shower chance before 12Z this morning. Breezy 
southwest winds with gusts 20 to 25 knots fend off any sea-
breeze potential on Tuesday. 


KBDL TAF...High confidence in TAF. 

VFR. Increasing wind speeds Tuesday with gusts 20 to 25 knots 
possible. Isolated shower chances late this evening.

Outlook /Wednesday Night through Saturday/... 

Wednesday Night: Mainly VFR, with local MVFR possible. Breezy.
Chance SHRA.

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...KS
SHORT TERM...KS
LONG TERM...Loconto
AVIATION...KS
MARINE...Loconto/KS