Lexington Weather

Lexington, Massachusetts, USA

71°F
9/22/2021 2:17pm 
  • Lexington Conditions: Light rain, Mist, Overcast
  • Temperature: 71.4°F / 21.9°CColder 3.6°F than last hour.
  • Dew Point: 68.9°FIncreased 0.5°Fsince last hour.
  • Relative Humidity: 92%Increased 12.0% since last hour.
  • Wind: Wind from W W 2 mph, 10-min avg: 2 mph, gust: 8 mph
  • Barometer: 30.08 inFalling 0.02  inHg/hr Falling Slowly
  • Visibility: 2 miles
  • Rain Today: 0.00 in
  •   

Area Forecast Discussion
for Boston, MA

        
000
FXUS61 KBOX 181948
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
348 PM EDT Sat Sep 18 2021

.SYNOPSIS...
A cold front will trigger scattered showers or thunderstorms 
through this evening. High pressure builds in Sunday and will 
bring sunny and dry conditions from Sunday through mid week, 
with a warming trend. An approaching cold front will be 
accompanied by showers and possible thunderstorms sometime 
Thursday into Friday, followed by dry and seasonably mild 
conditions Saturday.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
330 PM UPDATE...

Much of southern New England is now seeing clear skies as 
Tropical Storm Odette accelerates northeastwards well southeast 
of the 70W/40N benchmark. A broken line of showers and
thunderstorms is currently located along an Albany NY- 
Showhegan ME line, out ahead of a cold front sliding south. 
Clearing has allowed 500-1000 J/kg of surface- based CAPE to 
develop across the region but because there is non- existent 
shear or helicity as well as poor mid-level lapse rates, any 
storms that develop are expected to remain sub- severe. In 
addition, subsidence in the wake of the departing tropical 
cyclone has also entrained a layer of mid- level dry air, as 
hinted by the K index values in the mid 20s across the region.
In addition, mesoscale analysis shows that there could be an
area of wind convergence near the I-495 corridor so there could
be additional source of lift to ignite a few showers and 
scattered thunderstorms across Eastern MA and RI. So while we 
have chosen to maintain slight chance to chance PoPs this 
afternoon into early evening, not terribly bullish on convection
chances but enough to mention. Otherwise, forecast remains 
largely on track so only made minor changes to bring it up to 
date with current obs. In addition, beach goers should note the 
high rip current risk today as a result of the swells from 
Odette. 

Cold front then pushes offshore overnight, bringing an end to 
any lingering showers or isolated thunderstorm. Skies clear from
west to east, allowing for a few hours of radiational cooling. 
Blended in the MOS guidance to lower overnight minimum temps, 
although breezy conditions with gusts up to 20 mph at times 
should keep most locations in the upper 50s to lower 60s with 
pockets of mid 60s in urban centers like Boston. In addition, 
there should also be a period where low- level clouds could hang
tight and areas of fog could develop across eastern MA and RI 
before the cold front pushes through.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...

Sunday looks to be the start of several gorgeous late summer 
days. With high pressure building in, skies should be sunny. 
Highs will be in the 70s with pleasantly dry dewpoints in the 
upper 40s to low 50s. 

With high pressure moving overhead, conditions will be ripe for
excellent radiational cooling. Leaned heavily on MOS guidance to
derive overnight lows in the mid 40s to low 50s, except for mid
50s in the urban centers and immediate coast. Might be a good
idea to close the windows! 

In addition, have opted to hoist Rip Current Statements for the
entire eastern MA coast through tomorrow evening due to
remaining swells and lingering elevated rip current risks from 
Tropical cyclone Odette.


&&

.LONG TERM /MONDAY THROUGH SATURDAY/...

Highlights: 

* Pleasant, dry stretch of weather Mon into Wed with seasonably mild 
  day and cool nights

* Showers & scattered T-storms Thu into Fri

Overview...

Strong mid level ridge along the east coast into New Eng early next 
week moves slowly east Wed/Thu as a high amplitude trough moves into 
Gt Lakes with cut off low developing. GFS remains most progressive 
of the guidance envelope sweeping the trough and attending cold 
front through on Thu while ECMWF/GGEM have a much slower evolution 
with fropa not until Fri/Fri night. Given the GFS progressive bias 
in amplified patterns we will trend the forecast toward the slower 
ECMWF solution and its ensembles which favor mainly dry weather into 
Wed, then increasing risk of wet weather with showers and possible t-
storms Thu into Fri. Additionally, with ECMWF indicating upper low 
opening up and lifting well to the NW into eastern Canada, airmass 
behind the fropa will be modified so not expecting a significant 
cooling trend into next weekend.

Precipitation...

Strong high pres will maintain dry weather Mon and Tue and possibly 
into Wed as well. By Wed, the surface high will be well east of New 
Eng with increasingly moist southerly flow possibly bringing a few 
light showers in the west. However, much of the area should remain 
dry. Forecast confidence decreases beyond Wed due to timing 
differences on upstream trough and approaching cold front. ECMWF 
ensembles also vary a bit on timing so we will have chance showers 
Thu into Fri although there is uncertainty regarding which time 
period will have the greatest risk of showers. Pre-frontal PWAT 
plume approaching 2 inches suggests some heavy rainfall is possible 
with the front. Drying trend expected by Sat. 

Temperatures...

Despite strong mid level ridge, high pres from Maritimes with 
ridging extending into New Eng will result in seasonably mild days 
Mon into Wed with highs low/mid 70s. Cool nights Mon night and Tue 
night. Still mild and somewhat humid Thu ahead of the front and 
depending on timing of fropa, the mild weather could linger into 
Fri, especially eastern New Eng where highs could reach into the 
70s. Not much push of cool air in the post frontal airmass on Sat 
with 850 mb ensemble mean temps around 10C so highs should reach the 
70s again. 

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
Forecaster Confidence Levels.

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

1930z Update...

Overall moderate confidence in the forecast through tonight. 
High confidence Sunday.

Rest of today... VFR this afternoon except for Cape terminals. A
line of broken showers and scattered thunderstorms will cross 
the region between 22z and 05z. 

Overnight tonight... VFR western and central sections, but a 
line of scattered showers and thunderstorms is expected to sweep
across portions of MA, northern CT, and northern RI, with local
MVFR vsbys. IFR/LIFR overcast cloudiness will move back into 
the east coast between 22Z-00Z, impacting KBOS, KHYA, KFMH, and 
KACK until roughly 04Z-06Z. 

Sunday...Starting off MVFR for Cape terminals but improving to
VFR across all terminals by 15z. North winds 5-10 kt with gusts
up to 20 kt across Cape terminals. However, gusts gradually
diminish after 18z. 

Sunday night...VFR. Winds light and variable. 

KBOS Terminal...Moderate confidence through 10z Sun, then high 
confidence. MVFR conditions expected to develop after 16Z with 
VFR briefly possible after 20Z. IFR/LIFR redeveloping 22Z-00Z 
and lasting until 04Z-06Z Sunday.

KBDL Terminal...High confidence.

Outlook /Saturday night through Sunday/

Monday through Tuesday Night: VFR. 

Wednesday: Mainly VFR, with local MVFR possible. 

Wednesday Night: Mainly MVFR, with local IFR possible. Slight
chance SHRA.

Thursday: Mainly MVFR, with local IFR possible. Breezy. Chance
SHRA.

&&

.MARINE...
Forecaster Confidence Levels.

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

Generally high confidence in the forecast. Even as Tropical 
cyclone Odette continues to pull further away into the Atlantic 
Ocean, lingering swells and 4-7 ft seas warrants the
continuation of Small Craft Advisories for most outer waters
through a good part of Sunday.

Chance of a shower or thunderstorm this evening. Areas of dense
fog over the waters east of Massachusetts overnight tonight, 
reducing visibility to less than 1 nm at times.

High pressure moves overhead late Sunday, resulting in light and
variable winds and seas falling below 5 ft overnight Sunday. 

Outlook /Monday through Thursday/...

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

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

Wednesday: Winds less than 25 kt. Seas up to 5 ft. 

Wednesday Night: Winds less than 25 kt. Seas up to 5 ft. Slight
chance of rain showers. 

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...High Rip Current Risk through Sunday evening for MAZ007-019-
     022-024.
RI...None.
MARINE...Small Craft Advisory until 11 PM EDT this evening for ANZ235-
     237.
     Small Craft Advisory until 8 PM EDT Sunday for ANZ250-254.
     Small Craft Advisory until 2 PM EDT Sunday for ANZ255-256.

&&

$$
SYNOPSIS...KJC/Chai
NEAR TERM...Chai
SHORT TERM...Chai
LONG TERM...KJC
AVIATION...KJC/Chai
MARINE...KJC/Chai
      

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