Lexington Weather

Lexington, Massachusetts, USA

66°F

5/20/2024 3:00pm

Lexington Conditions: Clear
Temperature: 65.8°F / 18.8°C
Dew Point: 56.5°F
Relative Humidity: 72%
Wind: Calm, 10-min avg: Calm, gust: 3 mph
Barometer: 29.99 in Steady
Visibility: 10 miles
Rain Today: 0.00 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 161906
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
306 PM EDT Thu May 16 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 FRIDAY MORNING/...

* Rain tapering off from NW to SE as low pressure slides further
  offshore.

* 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 FRIDAY MORNING THROUGH FRIDAY NIGHT/...

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 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 /19Z THURSDAY THROUGH TUESDAY/...

Forecast Confidence Levels:

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

Through 00Z...High confidence.

MVFR to IFR conditions with rain tapering off from NW to SE for
most. Though spotty rain may continue across portions of the
south coast into this evening. Winds out of the ENE to NE at
10-20 kts with gusts of 20 to 35 kts. Should see those strongest
speeds/gusts along the immediate south coast.

Tonight...Moderate confidence.

Western interior terminals may briefly improve to VFR this
evening before lowering to MVFR/IFR as stratus spreads in.
Leaned more pessimistic for central MA/RI eastward due to
prolonged ENE to NE winds (onshore flow). Anticipating that the
marine stratus/fog layer spreads in lowering us to IFR and LIFR
conditions. Could even see some dense fog in spots, especially
across portions of Cape/Islands. For now kept things no worse
than 1/2 SM, but may need to be adjusted in future updates.
Winds out of the ENE to NE at 5-15 kts. Still could see 20-30
kt gusts across MVY/ACK. 

Friday...High confidence in trends, moderate in timing.

Widespread VFR after any stratus/fog burns off by roughly mid to
late AM. Though may not be until the afternoon for ACK. Winds
out of the ENE to NE at 5-15 kts with gusts of 20-25 kts across
the Cape/Islands.

Friday Night...Moderate confidence.

VFR for most with increasing mid/high clouds. The only exception
is across eastern MA, but especially SE MA where MVFR/IFR
stratus/fog spreads in late. NE winds at 5-15 kts.

KBOS TAF...High confidence through 00Z, moderate afterward.

MVFR conditions persist with light rain gradually tapering off.
Gusty NE to ENE winds continue through roughly 01Z. Prolonged
onshore flow will advect IFR to LIFR stratus onshore tonight
along with some spotty drizzle. Uncertainty highest in the
vsby as there are some indications that the fog could be dense 
for a few hours 04-09Z window. May not be until 13-15Z where the
stratus/fog burns off due to the prolonged onshore flow.

KBDL TAF...High confidence in TAF.

Rains tapering off with MVFR persisting into the evening. Could
have brief improvement to VFR this evening before borderline
MVFR/VFR ceilings spread in late. Should see this lift to VFR
early on Fri as the boundary layer grows.

Outlook /Saturday through Tuesday/...

Saturday through 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 through Tuesday/...

Saturday: Winds less than 25 kt. Local rough seas. Slight
chance of rain showers. 

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 8 PM EDT this evening for ANZ231-
     233-234.
     Small Craft Advisory until 11 PM EDT this evening for ANZ232-
     236.
     Small Craft Advisory until 2 AM EDT Friday for ANZ235-237.
     Small Craft Advisory from 7 PM this evening to 8 AM EDT 
     Saturday for ANZ250.
     Small Craft Advisory until 8 AM EDT Saturday for ANZ254>256.

&&

$$

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