Lexington Weather

Lexington, Massachusetts, USA

72°F

9/22/2021 2:29pm

Lexington Conditions: Overcast
Temperature: 71.8°F / 22.1°C
Dew Point: 69.1°F
Relative Humidity: 91%
Wind: SE 9 mph, 10-min avg: 3 mph, gust: 13 mph
Barometer: 30.08 in Falling Slowly
Visibility: 10 miles
Rain Today: 0.00 in

Area Forecast Discussion
for Boston, MA

        
000
FXUS61 KBOX 202315
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
715 PM EDT Mon Sep 20 2021

.SYNOPSIS...
Dry and cool once again this evening. The ridge of high 
pressure continues to give us pleasant weather Tuesday along 
with comfortable temperatures. The high begins to drift 
offshore Wednesday, with increasing humidity and scattered 
showers possible. A slow moving frontal system approaching from 
the west will be accompanied by widespread showers at times 
Thursday into Friday. Improving conditions expected Saturday but
a few showers could linger in eastern Massachusetts and Rhode 
Island.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
630 PM Update

Forecast remains on track and no changes are needed at this
time. Center of surface high pressure has moved off shore but
remains firmly in control. Clear skies and radiational
cooling overnight should support fog development prior to
sunrise as low-level moisture increases in response to more
southeasterly flow. See previous discussion for further 
details.

Previous discussion

It's a magnificent Monday for southern New 
England! A mid level ridge of high pressure continues to 
amplifies across the northeast and this is our driving force for
the pleasant weather. This afternoon was rather comfortable 
with temperatures in the low to middle 70s, and dew points in 
the 50s. Wrapping up Monday afternoon we are are left with fair 
weather cumulus clouds, though these clouds will fade away 
around sunset. 

With clear skies overnight, similarly to Sunday evening, we expect 
another night of radiational cooling. In addition, winds are 
forecast to be nearly calm and this will lead to areas of fog in 
valleys and other fog prone areas. For temperatures, we went with 
the cooler MOS guidance. Temperatures will once again drop into the 
50s with a few areas reaching the mid-40s in the cooler spots. 

Areas of valley fog will dissipate by mid to late Tuesday morning.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
Tuesday: 

The anomolous mid level ridge and 1030 surface high east of southern 
New England will allow for another quiet day. The only difference 
will be the added cloud cover. The deterministic models point to low 
and mid level moisture moving into the northeast during the late 
morning and early afternoon. By no means will this be an overcast 
day, but there will be more clouds about than there were on Monday. 
925mb temperatures Tuesday afternoon are forecast to reach between 
+14C and +15C - that would give us a mix down temperature between 
71F to 74F. Given the amount of cloud cover and lower sun angle we 
went with the NBM guidance which gave temperatures in the upper 60s 
across the higher terrain of the east slopes of the Berkshires and 
low 70s for the coastal plain. 

Tuesday Night:

The surface high and mid level ridge do slide further off shore 
which will allow for more cloud cover overnight. With the added 
insulation of the clouds we shouldn't see any radiation cooling 
Tuesday night/Wednesday morning. In fact temperatures will likely 
only fall to the upper 50s to lower 60s. There is a low chance we 
could see an isolated shower before day break on Wednesday as a 
weak warm front lifts north.

&&

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

* Increasing temperatures and humidity mid-week
* Slow moving low-pressure system brings periods of unsettled 
  weather Wednesday through Saturday

Wednesday

Surface high pressure system positioned to the east of southern New 
England on Wednesday afternoon will result in moderate southerly 
flow and moisture advection into the region. This will bring an 
increase in both temperatures and humidity on Wednesday. Warm 
temperature advection aloft will support weak height falls and 
forcing for ascent on Wednesday afternoon. With increasing deep-
layer moisture this should support some scattered showers on 
Wednesday over portions of southern New England. 

Thursday through next weekend.

As we head into Thursday a surface-low pressure system approaching 
from the west will induce a period of unsettled weather for southern 
New England. A surface warm front  will lift through southern New 
England sometime Thursday. This will bring scattered showers and 
perhaps a few thunderstorms as there will be a few hundred J/kg of 
CAPE along with moderate deep layer shear on the order of 30-40 
knots in the 0-6km layer. The associated cold front will then slowly 
move through the region early Friday morning through Friday evening. 
There is still some uncertainty in the timing/speed of the cold 
frontal passage, but models have been trending toward a slower 
moving boundary with a later arrival. This is in large part due to 
the development of a closed upper-level low developing aloft. 
Furthermore, the upper-level low is forecast to take on a negative 
tilt supporting a slower moving system. Should a slower moving 
system to develop, we could see showers associated with the cold 
front linger into Saturday morning for the eastern portions of 
southern New England. This will be followed by drier and more 
seasonable conditions for the remainder of next weekend, followed by 
the possibility of another frontal passage early next week.

&&

.AVIATION /23Z MONDAY THROUGH SATURDAY/...
Forecaster Confidence Levels.

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

00Z TAF Update: High confidence.

VFR overnight with a short period of MVFR visibilities at 
BAF/BDL due to the development of radiation fog. Also may see a 
brief period of MVFR ceilings at PVD between 14-16Z. VFR
everywhere tomorrow afternoon through the remainder of the TAF
period with modest southeasterly winds.

 
KBOS Terminal...High confidence. VFR.


KBDL Terminal...High confidence. VFR.

Outlook /Tuesday night through Thursday/

Wednesday: Mainly VFR, with local IFR possible. Breezy. Slight
chance SHRA.

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.

19z Marine Forecast: High Confidence: 

Monday Night through Tuesday Night...

Great near end of season boating weather thanks to an 1030 mb 
high stretching from the Maritimes to New England. Light east
winds tonight will become light southeast wind Tuesday. Dry 
weather and good visibility through the period. 

Outlook /Wednesday through Saturday/...

Wednesday: Winds less than 25 kt. Areas of seas approaching
5 ft. 

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 heading into astronomical 
fall for BOS is September 20 1947. It is possible we may break 
the record by tomorrow. 

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...Gaucher/RM
NEAR TERM...Gaucher/RM
SHORT TERM...Gaucher
LONG TERM...RM
AVIATION...Gaucher/RM
MARINE...Gaucher/RM
CLIMATE...