Lexington Weather

Lexington, Massachusetts, USA

7/31/2021 9:18pm 
  • Lexington Conditions: Clear
  • Temperature: 64.9°F / 18.3°CColder 1.8°F than last hour.
  • Dew Point: 54.5°FDecreased 0.2°Fsince last hour.
  • Relative Humidity: 69%Increased 4.0% since last hour.
  • Wind: Calm, 10-min avg: Calm, gust: 1 mph
  • Barometer: 29.89 inRising 0.02  inHg/hr Rising Slowly
  • Visibility: 10 miles
  • Rain Today: 0.00 in

Area Forecast Discussion
for Boston, MA

FXUS61 KBOX 010033

Area Forecast Discussion
National Weather Service Boston/Norton MA
Issued by National Weather Service New York NY
833 PM EDT Sat Jul 31 2021

High pressure shifts offshore tonight into Sunday. Low pressure
moves out of the Great Lakes and from the southwest producing
showers late Sunday into Sunday night. High pressure returns 
with mainly dry weather for the first half of the upcoming work 
week. Unsettled weather looks to return by the second half the 


Updated for current conditions.

A ridge of high pressure will slide to the south of our region 
tonight. The result will be mainly clear skies, light winds and 
cool temperatures. It probably will be a couple of degrees 
milder than early this morning. Nonetheless, low temps should 
still bottom out in near 50 in the coolest outlying locations 
and the middle 50s to near 60 elsewhere.


A shortwave dropping southeastward from the Great Lakes, and a
wave of low pressure passing to the south, will result in
increasing cloudiness through the day and developing showers
Sunday afternoon, with the better chances Sunday night.

The deeper moisture/forcing will remain to our northwest; so 
expect the vast majority of the day to remain dry.



* No big warm ups in sight and the return of humidity. 
* Generally fair weather through mid week but turning unsettled late 
  week, where there is increased potential for heavy rainfall and 
  possible flooding concerns given antecedent conditions.  


We are currently under a positive PNA and neutral NAO regime. This 
means a highly amplified ridge over Western US (the Pacific 
Northwest are about to have the season's second major heat wave). 
But because there is a lack of blocking downstream, H5 troughs are 
either positively tilted or at best neutral which means surges of 
cooler/drier air and/or storm systems would be relatively transient 
or progressive. Putting things together, the CPC's 6-10 and 8-14 day 
outlooks of near normal temperatures and near normal precipitation 
make a lot of sense. 

Then by middle of next week, the PNA is forecast to go neutral 
and the jet stream flattens out, allowing for the Bermuda High 
to exert a greater influence and higher heights to build back 
into the Eastern seaboard. Yet warm weather fans should not 
rejoice prematurely. Troughing persists over the eastern United 
States with an upper level low expected to develop over the 
Ohio/Tennessee Valleys by mid-week even as the ridge over the 
western Atlantic strengthens and builds westward toward the east
coast. This would result in a predominantly meridional flow for
Southern New England. In fact, meteograms from ensemble 
guidance suggest that most days would feature rather seasonable 
temperatures (upper 70s to low 80s) with no strong signal for 
big warmups until perhaps late next week at the earliest. Of 
course, if we were able to get a more zonal component on one of 
these days, we could pop into the mid to upper 80s but it is 
nearly impossible to determine which day could feature summer 

In addition, with the meridional flow comes tropical moisture 
(with PWATs rising to 2 inches or maximum of sounding 
climatology!) and the risk for moderate to heavy rainfall along 
the axis of convergence, especially towards late week. And with 
antecedent conditions, there is increased potential for flooding
where the stalled boundary sets up but it is too premature to 
pin down any more geographic details.


Weak high pressure works across the area overnight and then 
passes to the east in the morning. A weak area of low pressure 
will then move off the Mid Atlantic coast Sunday afternoon, 
passing south and east of the area Sunday night. 

Light and/or variable winds overnight will shift to the S in 
the morning at 5 to 10 kt. 

There is a low chance of MVFR conditions with scattered showers
in the late afternoon and evening.

.Sunday Night...Chance of MVFR in showers through about 06Z.
.Monday through Tuesday...VFR.
.Wednesday and Thursday...Mainly VFR with a chance of showers. 


Forecaster Confidence Levels.

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

Tonight through Sunday...High Confidence. High pressure sliding
to our south tonight and Sunday will keep winds/seas below 
small craft advisory thresholds through Sunday. As this high 
passes to our south the winds will shift to the SSE at 10 to 15 
knots with a few gusts near 20 knots on Sunday; but below small 
craft advisory criteria.

/Outlook /Monday through Thursday/...

Sunday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Chance of rain showers. 

Monday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Slight chance of rain showers. 

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

Tuesday through Tuesday Night: Winds less than 25 kt. Seas
locally approaching 5 ft. Chance of rain showers. 

Wednesday through Wednesday Night: Winds less than 25 kt. Areas
of seas approaching 5 ft. Chance of rain showers.






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