Lexington Weather

Lexington, Massachusetts, USA

71°F

9/22/2021 2:13pm

Lexington Conditions: Light rain, Mist, Overcast
Temperature: 71.4°F / 21.9°C
Dew Point: 69.3°F
Relative Humidity: 93%
Wind: W 4 mph, 10-min avg: 2 mph, gust: 7 mph
Barometer: 30.09 in Steady
Visibility: 2 miles
Rain Today: 0.00 in

Area Forecast Discussion
for Boston, MA

        
000
FXUS61 KBOX 210727
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
327 AM EDT Tue Sep 21 2021

.SYNOPSIS...
High pressure nearby will maintain another dry day across
southern New England. This high pressure moves slightly farther
offshore Wednesday, resulting in increasing humidity and a risk
for showers. A slow-moving front approaching from the west will
be accompanied by widespread showers at times Thursday into at
least Friday. Improving conditions expected Saturday, but
uncertainty increases for the weekend. No big warm ups or cool 
downs are expected.

&&

.NEAR TERM /THROUGH TODAY/...
Strong high pressure centered south of the Maritimes will
maintain a SE to S flow across southern New England. This high
pressure will be close enough to keep it dry today, with some
scattered diurnal fair-weather clouds at times. The exception 
could be some low clouds and fog in the CT River Valley early 
this morning. Any stratus and fog should dissipate rather 
quickly after daybreak. The slight decrease in sunshine will 
mean slightly lower temperatures this afternoon compared to
Monday.

&&

.SHORT TERM /TONIGHT THROUGH 6 PM WEDNESDAY/...
This high pressure moves farther offshore tonight into
Wednesday. As it does, the light SE flow tonight will increase
Wednesday. With the core of the subsidence departing to the 
east, and the increased humidity, expecting more clouds and a
chance for showers tonight into Wednesday. The greatest risk for
showers will be across the western half of southern New England.
Limited instability, so not thinking thunderstorms will be an
issue. Slightly above normal temperatures expected due to
increased cloud cover and southerly flow.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Highlights...

* Increasing temperatures and humidity mid-week

* Slow moving low-pressure system brings periods of unsettled 
  weather Wednesday, potentially through the weekend 

Details...

Wednesday night through Friday...

Late Wednesday through much of the latter half of the week a 
slow moving and negatively tilted upper level low will linger 
over the Ohio Valley with a strengthening surface low at the 
surface. This places southern New England in moist SSE flow 
between high pressure to the east and low pressure to the west. 
The warm front lifts north through the region on Thursday 
bringing surface dewpoints back up into the upper 60s. This, 
together with a 30-40 kt low level jet and placement beneath the
right entrance region of a 100 kt upper level jet will bring 
widespread scattered shower showers Wednesday night into 
Thursday. A few thunderstorms are possible during the day on 
Thursday as soundings indicate several hundred J/kg of CAPE 
coincident with modest bulk shear. The cold front slowly 
approaches around Friday which will provide more focused lift in
the lower levels for heavier rainfall. However, a great deal of
uncertainty remains as to how the front evolves and when it may
cross on Friday, or potentially stall out in our vicinity. 
Temperatures remain on the high side of normal, in the upper 70s
on Thursday, cooling off a few degrees on Friday if the front 
makes it through. 

This weekend...

For now we've lowered POPs from an initial blend of guidance, 
leaning away from the slower ECMWF guidance which wants to hang 
up the front through at least Saturday and keep rain in the 
forecast for the first half of the weekend. For now, though 
broad troughing continues over much of the east coast, keeping 
the forecast largely dry but with widely scattered showers 
possible beneath the upper level cold pool. We're still waiting 
on that first sub-70 F high temperatures in Boston; temperatures
remain largely in the 70s through the forecast period.

&&

.AVIATION /07Z TUESDAY THROUGH SATURDAY/...
Forecaster Confidence Levels.

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

High confidence. VFR overnight with a short period of MVFR
visibilities at BAF/BDL due to the development of radiation fog
and stratus. Also may see a brief period of MVFR ceilings across
portions of RI and southeast MA this morning. VFR everywhere 
by this afternoon. Modest southeasterly winds.

Conditions lowering to MVFR/IFR across the western half of
southern New England tonight into Wednesday, mainly from low 
clouds. Scattered showers possible, mainly after 22/04Z. 
 
KBOS Terminal...High confidence. VFR.

KBDL Terminal...High confidence. VFR.

Outlook /Wednesday Night through Saturday/...

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

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

Thursday Night through Friday: VFR. Breezy. Chance SHRA.

Friday Night: VFR. Breezy. Slight chance SHRA.

Saturday: VFR. Slight chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels.

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

Through Wednesday...High Confidence

Rather tranquil winds and seas expected through Wednesday with
high pressure over the waters. Mainly dry weather across the 
waters will good visibility.

Outlook /Wednesday Night through Saturday/...

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

Friday through Friday Night: Winds less than 25 kt. Areas of
rough seas. Slight chance of rain showers. 

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

&&

.CLIMATE...
The latest first sub-70 degree high temperature heading into 
astronomical Autumn for BOS was September 20, 1947. Still
waiting on the first sub-70 max temperature after Summer.

The latest first sub-70 degree high heading into astronomical
fall for PVD is September 26, 2015.

Both BDL and ORH have already recorded sub-70 degree highs
earlier this month.

&&

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

&&

$$
SYNOPSIS...Belk/BW
NEAR TERM...Belk
SHORT TERM...Belk
LONG TERM...RM
AVIATION...Belk/BW
MARINE...Belk/BW
CLIMATE...Staff