Lexington Weather

Lexington, Massachusetts, USA

66°F

5/20/2024 3:06pm

Lexington Conditions: Clear
Temperature: 65.8°F / 18.8°C
Dew Point: 56.5°F
Relative Humidity: 72%
Wind: Calm, 10-min avg: Calm, gust: 3 mph
Barometer: 29.99 in Steady
Visibility: 10 miles
Rain Today: 0.00 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 181926
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
326 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/...

320 PM Update: 

This evening...

Rain shield from eastern CT into central MA continues to
decrease in areal coverage and intensity, as low level easterly
jet slowly wanes. Elsewhere, clouds dominate with areas of fog
across Cape Cod, islands and coastal plymouth county. Western MA
into northwest CT continuing to experience some partial sunshine
and temps in the upper 60s. Meanwhile, elsewhere temps are in
the upper 50s and lower 60s, low to mid 50s Cape Cod and
Islands. Although, raw and brisk along the coast with NE winds
10-15 mph, gusting up to 25 mph at times. 

Overnight...

Low pressure southeast of the 40N/70W benchmark will continue to
generate moist NE flow into SNE. Meanwhile, maritime high
pressure remains over SNE and this provides low level inversion
for moisture to become trapped. Thus, mostly cloudy to overcast
conditions, along with spotty light rain/drizzle and areas of
fog. Temps will be seasonable cool, with lows mainly from 50-55,
upper 40s across Cape Cod and the Islands. It will feel raw and
brisk there with NE winds 10-15 mph, gusting up to 20 mph at
times. 

&&

.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 /19Z SATURDAY THROUGH THURSDAY/...
Forecast Confidence Levels:

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

18z TAF Update: 

Through 00z...Moderate confidence. Uncertainty on arrival time
of IFR/LIFR over Cape and Islands advancing northwestward. 

Rain shield and intensity will be on the decrease this
afternoon. NE winds continue 10-15 kt. IFR/LIFR across Cape Cod,
Islands and coastal Plymouth county slowly spread inland into RI
and eastern MA 21z-00z. Elsewhere MVFR/VFR continues across CT
into western-central MA. 

After 00z...Moderate confidence. Uncertainty in arrival time of
IFR/LIFR spreading inland.

IFR/LIFR advance inland into RI and eastern MA, with MVFR across
CT into western-central MA. Drizzle and fog most common across
RI and eastern MA. NE winds continue 10-15 kt. 

Sunday...Moderate Confidence. Uncertainty on timing of
conditions improving from LIFR/IFR in the morning to MVFR/VFR in
the afternoon. 

IFR/LIFR in the morning lifts to MVFR/VFR in the afternoon
across CT into western-central MA. Timing across RI into eastern
MA more uncertain.  NE winds 10-15 kt.

Sunday night...moderate confidence. Uncertainty on timing and
how conditions will lower across RI and eastern MA. 

MVFR at 00z across RI and eastern MA, with VFR westward into CT
and western-central MA. Uncertain how quickly and how far west IFR
across Cape and Islands at 00z traverses overnight. IFR possible
across much of RI and eastern MA, as NE winds continue. 

KBOS TAF...High confidence on trends but lower on exact arrival
time of IFR/LIFR this evening, then departure time of improving
conditions Sunday afternoon. 

KBDL TAF...High confidence in trends, but uncertainty on timing
and duration of lower conditions tonight, then uncertainty on
exact timing of improving conditions Sunday. 

Outlook /Monday through Thursday/...

Monday Night 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. 

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/... 

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

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

Tuesday Night through Wednesday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 2 AM EDT Monday for ANZ250-254.
     Small Craft Advisory until 8 PM EDT this evening for ANZ255-
     256.

&&

$$

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