Lexington Weather

Lexington, Massachusetts, USA

54°F

5/11/2024 12:22pm

Lexington Conditions: Mostly cloudy
Temperature: 54.1°F / 12.3°C
Dew Point: 44.2°F
Relative Humidity: 69%
Wind: Calm, 10-min avg: Calm, gust: 3 mph
Barometer: 29.82 in Steady
Visibility: 10 miles
Rain Today: 0.00 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 101917
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
317 PM EDT Fri May 10 2024

.SYNOPSIS...

Low pressure tracks well south and east of New England through 
Saturday as high pressure builds in from the north. This will bring 
drier conditions but cool temperatures as a persistent NE wind 
prevails. Continued cooler than normal Sunday with chance of showers 
as an upper level low pressure moves into the region. Milder 
temperatures return next week but an unsettled pattern persists 
through midweek.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...

The main change was to decrease cloudcover this afternoon especially 
over eastern MA where drier air has really scoured out the mid level 
clouds on NE flow. A midlevel shortwave digging into the mid-
Atlantic is already bringing an increase in mid/upper clouds from 
the SW (good directional shear visible on satellite given our NE 
flow at the surface). Some light radar returns continue to show up 
on the vicinity of the region to the south and west; even so, with 
PWATs even lower (<0.5") over SNE these shouldn't survive for long 
and the thinking is that this remains the case overnight with the 
better moisture and any showers staying south and west of the 
region. Cloudcover is expected to fill back in this evening but for 
those looking to catch a glimpse of the possible aurora after 
midnight, there is hi-res guidance suggesting a window between 2-5am 
where we'll see partial to full clearing outside of far southeast MA 
and northwest MA. Low temps in the interior where clearing allows 
for it may benefit from radiational cooling and dip into the low 40s 
while the rest of the region is in the mid 40s. 

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...

The forecast for Saturday looks better than it did a few days ago as 
guidance has converged on a weak mid level ridge keeping things dry. 
The exception would be a spot shower over eastern MA thanks to 
moisture off the ocean and cooler temps aloft but vast majority will 
stay dry. It will be a similar setup to today in that we'll have 
cool NE flow at the surface bringing scattered to broken cloudcover 
moving in while mid and high clouds stream in aloft from the 
opposite direction. Thus, expect a mix of clouds and sun but 
continued northeast flow keeps highs cooler than normal for mid May, 
in the mid 50s (east) to mid 60s (CT valley). Overnight cloudcover 
increases ahead our next shortwave over NY. However, forcing is 
quite weak and so while cyclonic flow with the cold pool overhead 
will drive some showers, they will be widely scattered and should 
hold off until toward daybreak, mainly over the interior where 
orographic lift will provide some additional lift. 

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Key Points:

* Unseasonably cool and mainly dry Sunday 

* Temps become more seasonable Monday and Tuesday

* Unsettled wet weather Monday - Wednesday, but uncertainty remains 
  high.

Sunday:

Upper level closed low becomes centered over SNE. This leaves the 
region under cyclonic flow along with a cold pool aloft. The best 
forcing with the closed low remains south of SNE. There is a low 
chance for a weak hit or miss diurnally driven showers Sunday, 
however, guidance doesnt show much if any instability and bufkit 
soundings show a rather capped atmosphere with some warming at 
700mb. Skies look to turn mostly cloudy Sunday with onshore flow and 
a moist column. High temps remain unseasonably cool in the upper 50s 
to low 60s with 850mb temps still around -1C.

Monday - Wednesday

Upper level closed low and cold pool finally move to the NE. 850mb 
temps quickly begin to warm to +7C by Monday. This will allow 
temperatures to become more seasonable with highs in the low to mid 
70s. Precipitation is rather messy during this time period with 
considerable uncertainty. Monday should be mainly dry for the most 
part with rising heights. However, WAA and PWATS near 1.1 inches 
enter the region and could bring a few weak showers late in the day. 
Better forcing doesnt look to arrive until late Tuesday night into 
Wednesday as a weakening shortwave exiting the Great Plains sends 
weak impulses of energy along with falling heights to the region. 
The best forcing from this shortwave once again looks to stay south 
of the region sending most of the widespread rain south as well. 
Ensemble guidance remains very spread out with this system with very 
little agreement between the GEFS and Euro members.  Using the LREF, 
which combines the GFS, Euro, and Canadian ensembles, 24 hour 
probabilities for 0.5 inches of rain max out Wednesday at 40-50% 
along the south coast, with 30% or less further north.  

Thursday and Friday

A very dry airmass looks to follow behind the shortwave with PWATS 
falling below 0.4 inches. An upper level ridge and rising heights 
should allow skies to be mostly sunny. Weak CAA and NW winds should 
keep daytime high temps in the low to mid 70s.

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:

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

18z Update:

This afternoon...High confidence.

VFR. NE wind 10-20 kt with higher gusts over the Islands.

Tonight...High confidence.

VFR with the exception of ACK where low clouds to the south will
lift far enough north to impact the terminal...low prob of
-SHRA there. NE wind 5-15 kt becoming N overnight.

Saturday...High confidence.

VFR, but areas of MVFR cigs developing across portions of eastern
MA and Cape/Islands where a spot shower possible. NE wind 10-20
kt.

Saturday night...High confidence. 

VFR except for chance of MVFR/IFR over ACK and potentially
FMH/HYA. Light E winds to start becoming NE/N. 

KBOS TAF...High confidence in TAF. 

KBDL TAF...High confidence in TAF. 

Outlook /Sunday through Wednesday/... 

Sunday: Mainly VFR, with local MVFR possible. Slight chance
SHRA, isolated TSRA.

Sunday Night: VFR. 

Monday: VFR. Breezy. Slight chance SHRA.

Monday Night: Mainly VFR, with local MVFR possible. Breezy.
Slight chance SHRA.

Tuesday: VFR. Breezy. Chance SHRA, isolated TSRA.

Tuesday Night: Mainly VFR, with local IFR possible. Breezy.
SHRA likely, isolated TSRA.

Wednesday: MVFR/IFR conditions possible. Breezy. Chance SHRA,
isolated TSRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Through Saturday night...

Low pres tracking south and east of the waters will bring NE 
winds 10-20 kt with occasional 25 kt gusts over southern waters
through Sat night with seas building to 5 ft. Extended the SCA 
for outer southern waters through Sat night for southeastern
waters. 

Outlook /Sunday through Wednesday/... 

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

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

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

Monday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of seas approaching 5 ft. Slight
chance of rain showers. 

Tuesday: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas up to 5 ft. Slight chance of rain
showers. 

Tuesday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 25 kt. Seas up to 5 ft. Rain showers likely,
isolated thunderstorms. 

Wednesday: Low risk for Small Craft Advisory winds with gusts
up to 25 kt. Seas up to 5 ft. Rain showers likely, isolated
thunderstorms. 

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 AM EDT Sunday for ANZ254-255.
     Small Craft Advisory until 8 PM EDT Saturday for ANZ256.

&&

$$

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