Lexington Weather

Lexington, Massachusetts, USA

65°F

5/20/2024 4:56pm

Lexington Conditions: Clear
Temperature: 64.8°F / 18.2°C
Dew Point: 56.7°F
Relative Humidity: 75%
Wind: Calm, 10-min avg: Calm, gust: 1 mph
Barometer: 29.97 in Steady
Visibility: 10 miles
Rain Today: 0.00 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 170543
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
143 AM EDT Fri May 17 2024

.SYNOPSIS...
Rainfall tapering off for most late this afternoon, but may not
be until this evening for parts of the south coast. Patchy fog
spreading into the eastern half of southern New England. Could
perhaps be dense at times in a few spots. Temperatures rebound
nicely on Friday after the AM fog burns off. The weekend 
features generally dry weather and onshore breezes, but still a 
good amount of cloud cover. A warming trend then develops Monday
through Wednesday, and we could see a couple days of high 
temperatures in the low 80s over interior sections of Southern 
New England. After today, our next chance for rain develops late
next week.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
10 PM Update...

A last gasp of light showers has been impacting the islands over
the last few hours, the greatest impact of which is persistent
low stratus and a few hundredths of QPF, as low pressure
continues to draw south of souther New England. Many localities
away from the immediate south coast were able to break out into
sunshine before sunset this evening, allowing for pretty quick
radiation where winds calmed quickly. As mentioned by the 
previous forecaster, fog and stratus redevelopment overnight 
will be fueled by residual moisture and onshore flow. The 
question remains on if NNE/ENE will be strong enough to advect 
low clouds into the Boston metro area, which will be something 
we watch closely overnight. 

Otherwise, very seasonable night expected. Many towns have
already fallen back into the mid-50s. Should start to see fog
form over the next few hours, with Tds in the low to mid 50s, as
dewpoint depressions drop below 3F across the interior. Winds, 
still gusting as high as 25mph along the south coast/in RI, will
delay fog formation in these locations. 

Previous Update...


* Marine stratus/fog possibly dense at times spreading into 
  central MA/RI eastward tonight.

A cutoff low will meander from south of southern New England
late tonight to the southeast of our region by early Fri. Behind
the cutoff a ridge slides from the Mid Atlantic/eastern Great
Lakes into western New England by early Fri. Low pressure south
of Long Island late today will rotate southeastward tonight,
while high pressure nudges in from Upstate NY.

Main change to the forecast was slightly slow down precipitation
tapering off from the low meandering offshore. Think for the
MA-Pike northward things should end by this evening, but may not
be until 10 PM to midnight for precip to cease for the MA-Pike
southward. This will take the longest for MVY/ACK. Fortunately
the heaviest precipitation is over with as the mesoscale band
that set up is falling apart. This axis of precip will slide
southeastward. Leaned pretty heavily on the previous ARW and
current NSSL WRF as it is handling this band quite well based on
observations.

The other main concern to the forecast for tonight is given the
onshore flow am anticipating marine stratus/fog along with some
drizzle to spread into southern New England. This has been
hinted at by the past two cycles of the HREF and several GLAMP
runs. Have trended the forecast in this direction tonight for
central MA/RI eastward. Not out of the question there could be
some spots where the fog is dense, but not completely certain on
this risk at this junction as guidance is all over the place.
Something we will need to monitor given the prolonged ENE to NE
flow as it could linger into the Fri AM commute. 

Cloud cover will be slow to clear for most other than portions
of western MA/CT as this is closer to the high nudging its way
in. Not expecting much radiational cooling and think the 50th
percentile of guidance looks reasonable at this point. Lows in
the low/mid 50s.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/...
Highlights

* Any stratus/fog anticipated to erode Fri AM. Mix of sun and
  clouds through Fri.

* Increasing clouds Fri Night into early Sat. Could see the
  stratus/fog returning to portions of eastern MA.

Ridge axis over western New England early on Fri builds over
southern New England and into the Gulf of ME by late in the day.
The ridge essentially remains in place as we head into Fri
Night, but may flatten out a bit as a shortwave lifts across the
eastern Great Lakes into northern New England. A weak high
nudges into New England on Fri and Fri Night.

Dry and quiet weather anticipated on Fri with high pressure in
control. Should see any of the lingering stratus/fog burning off
by mid to perhaps late AM. Will still have prolonged ENE to NE
winds, but think given the breaks of May sun we should warm up
quite nicely. Should see 925 hPa temps of 11-15 Celsius. The
result should be widespread highs in the 60s with some mid 70s
across the CT River Valley. Still may struggle to hit 60 degrees
for portions of the east coast given the onshore winds, but will
still have roughly 15-30 kt ENE to NE LLJ at 925. Should result
in a fairly well mixed boundary layer, which should keep our
temps up. It will be a bit breezy into the afternoon.

Still anticipating dry and quiet weather to persist as we head
into Fri Night/Sat AM. Though we will see increasing cloudiness
as the ridge axis gets shunted to the south due to the shortwave
lifting in. Not a whole lot of moisture to work with in the mid
levels, but there is increasing low level moisture per 1000-850
hPa RH fields. Should have PWATs of 0.75 to roughly 1 inch. At
this point leaning on a dry forecast, but the ECMWF does eek out
some spotty showers across the interior. Think there is a better
shot given prolonged ENE to NE winds that we see another round
of marine stratus/fog/drizzle across eastern areas heading into
Sat AM.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Key messages...

* Outside of a spot shower, mainly dry weather is expected through 
  at least the middle of next week.

* After a slightly cooler than average weekend a big warm-up arrives 
  for early next week with 80s possible by Tuesday. 

Details...

Saturday and Sunday...

Overall a welcome trend in the forecast for the weekend over the 
last 24-48 hours for anyone with outdoor activities as, even though 
the clouds will stick around, things should be dry on the whole. 
This is thanks to a ridge of high pressure which will extend SW from 
Nova Scotia further into SNE each day. The positioning of that high 
will continue to direct cool, moist NE flow into the region. Thus, 
Saturday should be mostly cloudy, and Sunday, while drier air does 
start to work in from the upper levels down for lessening clouds, 
will still be at least partly cloudy. Besides keeping the clouds 
around this wind direction also keeps temperatures below normal; 
highs will be coolest in eastern MA (upper 50s/low 60s) and warmest 
in the CT Valley (low 70s). 

Next week...

A pleasant week is setting up through at least Wednesday as high 
pressure continues to center overhead pushing one low pressure 
further to our east and suppressing one to the south over the 
Carolina coast. Surface flow eventually veers to the SW while at the 
same time we'll be seeing more insolation (thanks to less clouds) 
and a warming mid level airmass. 850 mb warm from +8C on Sunday to 
+15C on Tuesday which looks to be the hottest day of the week; 
expecting temps well into the upper 70s for many locations and even 
low 80s for places like the CT and Merrimack Valleys. EPS and GEFS 
ensemble guidance currently outline a 40-50% chance of temps AOA 80F 
on Tuesday afternoon for those locations. It's not until around 
Thursday that we could see this dry pattern breaking down with the 
arrival of our next shortwave, but confidence is low at this 
distance in time.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
Forecast Confidence Levels:

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

Through Today...High Confidence

Mainly VFR with some MVFR across the Cape and Islands associated
with patchy rain showers. Patchy fog will result in localized 
IFR across the interior through 13Z this morning. VFR will
prevail for much of the area after 13Z, though MVFR/marine
stratus likely to stick around for the Cape and Islands all day.
E/NE flow between 5-10kt with gusts to 20kt possible along the
immediate coastline. 

Friday Night... Moderate Confidence

VFR, away from the Cape and Islands where MVFR persists, to 
start before patchy fog development drives categories down to
locally IFR. Persistent E/NE flow.

Saturday... Moderate Confidence

VFR across the CT River Valley with MVFR for eastern MA RI
Saturday morning falling to MVFR/IFR during the afternoon as
showers develop mid day. Onshore flow will drive cigs to as low
as 003ft along the coast. Winds 5 to 15kt. 

KBOS TAF...Moderate Confidence

VFR today with onshore NE winds, gusting as high as 20kt for a
brief period this afternoon. Patchy fog across the interior
should remain clear of the terminal. MVFR develops overnight
tonight as stratus and fog redevelops given onshore flow.
Showers possible by early Saturday morning. 

KBDL TAF...High confidence in 
TAF.

Patchy fog this morning may briefly deteriorate VFR to IFR. VFR
through the day before fog redevelops tonight. Light E/NE winds
today, generally less than 10kt. 

Outlook /Saturday Night through Tuesday/...

Saturday Night: Mainly VFR, with local MVFR possible. 

Sunday through Tuesday: VFR. 

&&

.MARINE...
Forecaster Confidence Levels:

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

Tonight...High confidence. 

Rain tapering off across the southern waters north to south for
most before midnight, though the far outer southern waters may
not be until daybreak. Winds ENE to NE at 10-20 kts with gusts 
20-30 kts gradually easing heading into Fri AM. Patchy to areas
of stratus/fog with visibility's of 1/2 to 4 SM. Could even see
some spot where fog is dense at times.

Friday... High Confidence.

Any pockets of fog burning off by mid to late Fri AM. E/ENE 
winds 15-20 kt with 20-25 kt gusts. Seas remain elevated across
the outer waters, so the SCA remains.

Friday Night...High confidence.

Winds remain out of the NE at 10-20 kts. Could see a return of
stratus/fog across the waters late. Visibilities of 1-4 SM with
the lowest across the eastern waters. Seas remain elevated so
have extended the SCA through the period.

Outlook /Saturday Night through Tuesday/...

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

Sunday through Monday: Winds less than 25 kt. Seas up to 5 ft. 

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

Tuesday: Winds less than 25 kt. Seas locally approaching 5 ft. 

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 2 AM EDT early this morning for 
     ANZ235-237.
     Small Craft Advisory until 8 AM EDT Saturday for ANZ250-
     254>256.

&&

$$

SYNOPSIS...BW/BL
NEAR TERM...BW/BL/KS
SHORT TERM...BL
LONG TERM...BW
AVIATION...KS
MARINE...BW/BL