Lexington Weather

Lexington, Massachusetts, USA

69°F
8/17/2022 7:33pm 
  • Lexington Conditions: Overcast
  • Temperature: 69.4°F / 20.8°CColder 0.4°F than last hour.
  • Dew Point: 57.2°FDecreased 1.6°Fsince last hour.
  • Relative Humidity: 65%Decreased 3.0% since last hour.
  • Wind: Calm, 10-min avg: Calm, gust: None
  • Barometer: 29.84 inFalling 0.02  inHg/hr Falling Slowly
  • Visibility: 10 miles
  • Rain Today: 0.00 in
  •   

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 121725
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
125 PM EDT Fri Aug 12 2022

.SYNOPSIS...
Mainly dry, seasonable weather expected today with a low chance
for showers across southeast Massachusetts and Rhode Island.
Canadian high builds in this weekend ushering an early fall-like
air mass with mostly dry weather. Low pressure passing well
offshore could bring a few showers to southeast Massachusetts
and Rhode Island at times. An unsettled and slow- evolving 
weather pattern then develops into the middle of next week. 
While not yet set in stone, the potential exists for welcomed 
rains Tuesday through Thursday. Cooler than normal temps are 
likely this weekend into midweek.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
1:25 PM Update:

AN SPS has been issued for all of Massachusetts through 8pm for
elevated fire weather concerns. A dry airmass combined with severe
to extreme drought conditions will result in elevated fire weather
concerns today. RH values will drop to between 25 and 35 percent
across much of the interior this afternoon with northwest winds
10 to 15 mph. Clouds continue to clear from west to east, but 
as previously mentioned the main issue remains the stratus deck 
across the outer Cape and Islands. Low chance of an isolated
shower in places like Nantucket this afternoon, as KBOX has been
tracking a line off showers off shore but dry weather prevails 
much of the time.

Otherwise, high pressure ridging into interior Southern New 
England should yield plenty of sun and falling dewpoints into 
the upper 40s to mid 50s! Thus a refreshing air mass filtering 
into Southern New England. 

Previous discussion:

* Below normal temperatures today with mainly dry weather outside of 
  a few brief showers.

Except for a few sprinkles or spot showers, most locations will
stay mostly dry. Mesoanalysis shows a stalled front hung up
across central MA into CT. Areas to the west have dew points in
the 50s and mostly clear skies while areas east of the boundary
have dew points in the 60s and partly cloudy skies, with thicker
and lower cloud cover towards southeast MA into Cape
Cod/Islands. A thing to note is that despite dew point
depressions from 0-3F across the Cape/Islands, fog has struggled
to form the past couple of nights. Examining RAP model soundings
shows a very shallow mixed layer (below 500 ft) that has helped
stir up the boundary layer immediately above the surface. While
no widespread fog is expected through daybreak, areas of patchy
fog could still form in the next few hours in the typical fog
prone areas, including the interior river valleys. 

A potent upper trough will approach from the west today. This 
coupled with a distant offshore wave of low pressure, should 
provide modest but adequate convergence for shower activity and 
perhaps even an isolated thunderstorm. This is somewhat similar 
to an inverted trough setup that we often see in winter. 
However, baroclinicity is much weaker in mid August and the 
overall forcing is also quite limited. Therefore, we expect dry 
weather to dominate but a few showers may briefly impact parts 
of the region on Friday. Have gone with mostly slight chance
PoPs due to uncertainty with the northward extent of the
precipitation shield. Wouldn't be surprised if most locations
including those near the coast stay dry. Greatest risk for a few
hundredths of an inch of rain will be across eastern MA and RI.
Overall even if showers do materialize, any precipitation will 
be rather light with dry weather dominating for most locations. 

Temperatures wise, daytime highs should be mainly in the 70s to the 
low 80s depending on the amount of solar insolation. Greatest 
probability for more clouds and cooler temperatures will be across 
eastern MA and RI. Regardless, temperatures will be a little below 
normal, which is quite a dramatic shift from the oppressive heat and 
humidity that we experienced over the past several weeks.

&&

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

A cool night is in store with many locations falling into the 50s 
with 60s across southeast MA, and especially near the coast as well 
as the urban heat islands. Great opportunity to open the windows! A 
weak disturbance passing well offshore could bring some sprinkles or 
light showers into southeast MA and southern RI, but most locations 
should stay dry. 

Saturday...

Refreshing, almost fall-like weather is in store for Saturday with 
dew points falling into the 40s for much of the interior. There 
would be more cloudiness across eastern MA and RI, especially 
southeast MA as a offshore low pressure system passes outside the 
70W/40N benchmark during the day. With 925mb temps +12 to +15C and a 
light northerly flow across the interior and northeast flow across 
eastern MA/RI, highs should mainly be in the 70s, except low 80s 
across CT valley. These readings will be about 5 to 7 deg below 
normal, quite the change from the recent oppressive heat. Enjoy!

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Highlights: 

* Generally dry on Sunday with cooler than normal temps. 

* Unsettled early to midweek, and while not yet set in stone, 
  potential continues for rainy conditions Tue-Thurs.

* Cooler than normal temps continue into most of the upcoming week 
  with lower humidity levels.

Details:

While there remains some important detail differences to be ironed 
out, the large-scale pattern in this forecast period is little 
changed from that of previous forecasts. Longwave troughing to 
remain established, with an initial closed low Sat night moving 
northward into NH/ME on Sunday. Additional shortwave disturbances 
around the longwave trough early in the week to evolve into another 
closed-off low around Tues or Wed, setting up the potential for 
cloudiness and welcomed wet weather conditions for parts of or all 
of SNE Tue-Thurs. 

While most of the EPS/GEFS/GEPS ensemble means paint a closed low 
over central NY/northern PA around Tues, one source of uncertainty 
that appears to be leading to wider solution spread on daily rain 
chances in the deterministic guidance is how soon and/or how far to 
the west of SNE will the trough close off to a closed low. A rainier 
pattern would be favored by a closed low to our west; which would 
allow for more southerly flow around the east side of the closed low 
to facilitate several periods of rain. Important to point out that 
some guidance (e.g. the CMC and on some level the 00z ECMWF) is too 
far east and lead to less rain or a shutout entirely. However the 
ensemble consensus is that later Tue and into Wed offers the best 
rain chances (ensemble QPF probabilities of 0.50" of rain or greater 
in a 24-hr period are centered around 40-60%). This occurs as a 
surface low develops near the 40/70 benchmark Wed and moves slowly N 
into northern New England on Thurs. Given that we badly need the 
rain in protracted drought conditions, there still is optimism for a 
multi-day period of rains into midweek but there are now some 
outcomes that could lead to less rain.

Temperatures in the period are below-normal for mid-August. NBM 
temperatures seem reasonable for now (highs in the 70s/around 80, 
lows mid 50s-mid 60s). Given anticipated cloud cover trends, there 
may be need to undercut highs by a few degrees in later updates.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
Forecaster Confidence Levels:

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

18z TAF Update:

Today: High confidence.

Mostly VFR except for MVFR ceilings across the Cape terminals 
due to a passing offshore system. May have a few sprinkles or 
showers across southeast MA and southern RI. NW winds across 
western MA/CT/RI but NE winds across eastern MA. Wind speeds 
around 5-10 kt. 

Tonight...High confidence.

Mostly VFR. Best chance for MVFR/IFR ceilings and patchy fog across 
southeast MA. N winds at 5 to 10 kt. 

Saturday...High confidence. 

Mostly VFR. Best chance for MVFR/IFR ceilings across southeast MA. 
N/NE winds at 5 to 10 kt. 

KBOS...High confidence. NW winds shift to NE/ENE ~15-16.

KBDL...High confidence.

Outlook /Saturday Night through Tuesday/...

Saturday Night through Sunday Night: VFR. 

Monday: VFR. Slight chance RA.

Monday Night: VFR. Chance RA.

Tuesday: Mainly VFR, with areas MVFR possible. Breezy. Chance
RA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Today into Saturday...High confidence.

Mostly cool and cloudy with seas and winds below SCA thresholds. 
There will be periods of light showers at times, especially this 
afternoon and then on Saturday. NE winds on Friday turning N on 
Saturday. 

Outlook /Saturday Night through Tuesday/... 

Saturday Night through Monday: Winds less than 25 kt. 

Monday Night: Winds less than 25 kt. Chance of rain. 

Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Chance of rain.

&&

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

&&

$$
SYNOPSIS...Loconto/Chai
NEAR TERM...Loconto/Chai/Gaucher
SHORT TERM...Chai
LONG TERM...Loconto
AVIATION...Loconto/Gaucher
MARINE...Loconto/Chai
      

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