Lexington Weather

Lexington, Massachusetts, USA

68°F

5/20/2024 2:03pm

Lexington Conditions: Few Clouds
Temperature: 67.6°F / 19.8°C
Dew Point: 58.3°F
Relative Humidity: 72%
Wind: SE 1 mph, 10-min avg: 1 mph, gust: 3 mph
Barometer: 30.00 in Steady
Visibility: 10 miles
Rain Today: 0.00 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 190133
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
933 PM EDT Sat May 18 2024

.SYNOPSIS...
Unsettled with periods of rain, drizzle and fog tonight.
Seasonably cool and brisk northeast winds for the coast. 
Trending drier with breaks of sunshine developing Sunday 
afternoon from northwest to southeast, as high pressure begins 
to nudge in from the southwest. Summerlike warmth arrives Monday 
through Wednesday, then a cold front brings the next chance of 
showers or thunderstorms Thursday. Drier and more seasonable 
weather follows for the end of the week.

&&

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

10 PM Update...

Rain continues to dissipate across central MA at this hour, but
moderate showers continue to blossom across eastern MA, with the
most widespread rain focused over the Boston metro area. Less
than a tenth of an inch of rain has fallen at Boston Logan
Airport over the last hour. 

Shower activity will continue to wane overnight with a bit of
clearing even possible in far NW MA by daybreak with cloud cover
across the Hudson River Valley already scattering out. Less
improvement expected for eastern MA/RI given persistent onshore
flow. As mentioned by the previous forecaster, will likely see
fog form tonight, and it may be dense at times across far
eastern MA.


715 PM Update:

Heavier rain that was focused near Worcester has begun to
diminish and will continue to do so this evening. Some decent
rainfall totals with several 1-2" amounts in eastern CT and
central MA (thanks everyone for your reports) and even a few 
over 2" per amateur radio including 2.51" in Rochdale 
(Leicester) and 2.31" in Spencer. This band of rain formed as 
onshore winds from offshore low focused activity along higher 
terrain and had added lift from couplet jets (850 mb and 250 
mb). High res models really struggled with this feature and only
NSSL WRF had somewhat of a clue. 


Meanwhile, another area of light rain was backing in off ocean 
and will affect much of eastern MA early tonight, before 
transitioning to patchy drizzle. Cloudy skies will prevail
tonight with areas of fog, especially in areas that saw rain
today, but also near coast where some dense fog is possible.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
320 PM update...

Sunday...

Rising heights slowly advect into SNE from west to east. This
subsidence combined with strong/high May sun will slowly erode
clouds from northwest to southeast during the afternoon.
However, persistent northeast winds will slow this trend for
eastern MA into RI, where only a few late day breaks of sunshine
may develop. This is where the forecast uncertainty is greatest. 

Duration of sunshine will be longest across western MA/CT where
highs should top out in the low 70s. 60s for most of the region,
except only 55-60 across eastern MA given clouds and onshore
flow, with NE winds 15-20 mph there.  

There could be some spotty light rain/drizzle and areas of fog
in the morning. 

Sunday night...

Low clouds and areas of fog may redevelop as blyr cools and
subsidence inversion remains over SNE, trapping low level
moisture. Less clouds and fog westward into CT and western-
central MA. Seasonably cool with lows in the upper 40s to lower
50s. Blended in some of the cooler MOS guidance given some
clearing during the evening hours. Winds will remain NE and
light.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Key Points:

 * Summerlike warmth early next week - Tue and Wed look warmest
 * Dry overall - scattered showers/storms Thu
 * More seasonable temps late week

Ensembles continue theme of warming trend Mon-Wed as upper ridge 
builds over New England in response to digging trough over western 
third of country. 

NBM probabilities for exceeding 80F are fairly high, especially Tue-
Wed where many locations away from South Coast are at or above 75%. 
Looks questionable in the Providence to Taunton to Plymouth corridor 
and points south due to prevailing SW flow. And on other side of the 
coin, NBM probabilities for 90+F are highest across interior MA from 
Greenfield to Amherst (40-65%) and in the Leominster and Lowell 
areas (40%), so it's not out of the question that we see some 90-
degree readings in those areas too. Fortunately dewpoints will stay 
on the lower side (50s) so it won't feel oppressive nor will heat 
index become a significant concern. Nonetheless, many of us are not 
yet accustomed to summertime temperatures, so it's something to be 
aware of if you're planning on spending time outdoors next week.

Pattern also favors dry weather for much of the week, though an 
approaching cold front should bring scattered showers or 
thunderstorms sometime in Thu-early Fri timeframe. Not looking at a 
big severe weather threat but Colorado State ML does show some low 
chances so it's something we'll follow in the coming days. Timing of 
front seems to be the biggest question, whether it approaches during 
peak daytime heating or closer to nighttime. Front heads offshore 
Fri which brings in more seasonable airmass for end of the week.

&&

.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
Forecast Confidence Levels:

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

00z TAF Update: Moderate confidence (40%).

Ceilings lower to MVFR across interior with mainly dry
conditions. Farther east, IFR in low clouds, drizzle, and fog 
from central MA to coastal areas, with LIFR possible closer to 
Cape Cod and Islands. Conditions slowly improve Sunday but
MVFR/IFR continue to prevail through Sunday night, though 
interior locations should improve to VFR Sunday afternoon and
remain that way into Sunday night.

N/NE winds persist through Sunday night, with 20-25kt gusts at
times near Cape Cod and Islands.

KBOS TAF...Moderate confidence (40%). Uncertainty on how fast
lower ceilings/visibilities arrive this evening, but higher
confidence on improvement Sunday.

KBDL TAF...High confidence (70%).  

Outlook /Monday through Thursday/...

Tuesday through Tuesday Night: VFR. 

Wednesday through Wednesday Night: VFR. Breezy. 

Thursday: VFR. Breezy. Slight chance SHRA, isolated TSRA.

Thursday Night: VFR. Chance SHRA.

Friday: Slight chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

320 PM update...

Tonight... High confidence.

NE winds 15-20 kt with gusts up to 25 kt this evening, slowly
easing overnight. However, long ENE fetch will keep seas up to
4-6 ft across the outer MA/RI waters. This combined with
marginal winds, SCA continue for the outer waters. Periods of
rain/drizzle and fog will yield poor vsby at times. Weak low
pressure southeast of 40N/70W benchmark is the culprit for NE
winds, combined with maritime high pressure. 

Sunday... High Confidence. 

Offshore low and maritime high move very little, thus morning
low clouds, fog and spotty light rain and drizzle expected. Some
improvement in the afternoon. NE winds 10-15 kt. 

Sunday night...high confidence. 

More of the same weather given offshore low and maritime high
persist. Lighter winds and maritime high slowly advects over the
MA/RI waters. 

Outlook /Monday through Thursday/... 

Tuesday through Tuesday Night: Winds less than 25 kt. Seas
locally approaching 5 ft. 

Wednesday: Winds less than 25 kt. 

Wednesday Night: Winds less than 25 kt. Seas locally
approaching 5 ft. 

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

Friday: Winds less than 25 kt. Slight chance of rain showers. 

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 2 AM EDT Monday for ANZ250-254.

&&

$$

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