Lexington Weather

Lexington, Massachusetts, USA

41°F

5/12/2024 4:27am

Lexington Conditions: Clear
Temperature: 40.6°F / 4.8°C
Dew Point: 37.6°F
Relative Humidity: 89%
Wind: Calm, 10-min avg: Calm, gust: None
Barometer: 29.83 in Steady
Visibility: 10 miles
Rain Today: 0.00 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 061732
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
132 PM EDT Mon May 6 2024

.SYNOPSIS...
Partial sunshine develops today with much warmer temperatures. 
A brief band of scattered showers is expected Monday afternoon/ 
evening...but the majority of the time will feature dry weather.
Tuesday will be the pick of the week with abundant sunshine and
above normal temperatures. Then an unsettled weather pattern 
develops Wednesday and beyond, with cooler than normal 
temperatures and the risk of showers at times. However, there 
will also be periods of dry weather. The weekend may feature a 
drying trend, with shower potential not as widespread and 
limited to the afternoon/evening hours.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

The back edge of the rain shield has finally exited the islands
and we expect mostly dry weather to persist through the rest of
the day. The biggest question this morning is how quickly those
clouds can erode and allow the temperatures to jump up. We're
currently sitting in the in the upper 50s across much of the 
region but where those breaks in the clouds have started we see 
low 60s. The next few hours should see some continued clearing 
and temperatures climbing. No significant changes to thinking 
for this afternoon. 

Previous Discussion...

Today

Short-wave energy and associated showers at the surface 
exit east off the coast of southern New England this morning. 
This will be followed by increasing temperatures and dewpoints 
today as southerly flow advects a more warm/moist air mass over 
southern New England. 925 hPa temps rise close to 15 Celsius, so
we should experience very warm temperatures in the low to mid 
70s across the interior this afternoon. While the sun is likely 
to break out at times, there will continue to be a fair amount 
of low clouds in place as well, especially over the south coast,
Cape, and Islands where the sun may not break out at all with 
low-stratus persisting into tonight. With not as much sunshine 
and the expectation that sea-breezes will develop, these 
locations near the coast will be noticeably cooler than across 
the interior with highs in the low to mid 60s more common. While
most areas should stay dry today, there will be chances for 
some mid-afternoon showers to develop as another embedded short-
wave traverses over the region. Can't rule out a rumble of 
thunder either as there will be modest amounts of instability in
the atmosphere to the tune of 100-300 J/kg of CAPE. Expect any 
shower/thunderstorm activity to be limited to the interior as 
sea-breezes would be expected to stabilize the atmosphere near 
the coast.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
Tonight

Low clouds fill back in after sunset tonight as the boundary layer 
cools. Light winds and high dewpoints will likely result in areas of 
fog developing this evening as well. However, low-level winds in the 
925-850 hPa layer shift northwest as a mid-level trough axis shifts 
east of the region. This will support winds shifting to the north at 
the surface which will allow drier air to displace the fog/low-
stratus gradually overnight. Expect clearing skies by sunrise. Low 
temps in the low to mid 50s.

Tomorrow

Beautiful day on tap for Tuesday. High pressure and a dry air mass 
will support very warm and sunny conditions. 925 hPa air temps in 
the mid to upper teens will support another afternoon with temps in 
the mid to upper 70s. Can't rule out a few locations in  the CT 
River Valley topping 80. Light northerly winds to start will become 
more westerly as the day progresses. By far the pick of the week if 
you enjoy warm/sunny weather.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
* Progressively cooler this period, especially Fri and Sat

* Wet weather at times Wednesday through Friday, but also 
  periods of dry weather too

* Possibly trending drier next weekend, with showers not as 
  widespread and limited during the afternoon/early evening

Synoptic Overview...

By late Tue/Tue night, a high amplitude closed low will be located 
over the Dakotas. Models, including ensembles then differ on the 
evolution of jet energy ejecting eastward from this closed low 
eastward into New England. This will impact frontal position across 
SNE, along with timing and amplitude of frontal waves. Hence, a low 
confidence forecast this period. Forecast confidence increases 
slight for next weekend, as ensembles in better agreement, with mean 
trough axis over SNE, displacing deep layer moisture well offshore. 
This will favor drier weather with shower threat more diurnally 
driven across SNE. 

Precipitation...

As mentioned above, anomalous closed low over the Dakotas late Tue 
moves slowly east mid to late week. Models, including ensembles 
displaying a large spread in the timing of jet energy ejecting 
eastward out of this low and eventually into New England. This 
results in a low confidence forecast this period, specifically in 
regards to frontal boundary placement, including magnitude and 
timing of frontal waves traversing this boundary. Hence, rain likely 
at times, although periods of dry weather too. Unfortunately, given 
model spread, too difficult at this time range to nail down exact 
timing of specifics. Ensembles offer some support of drier weather 
for the weekend, with mean trough axis over SNE. This will shift 
deep layer moisture and frontal wave offshore. However, cyclonic 
flow aloft and cold pool will yield a risk of diurnal instability 
showers. Not widespread, but unfortunately timing will be in the 
afternoon and evening hours. 

Temperatures...

High forecast confidence on a cooler temperature regime this period, 
in response to lowering heights across New England. Seasonably cool 
Wed with highs in the 60s, but then cooling off into the 50s Thu, 
especially in eastern MA behind departing wave with N-NE winds 
across SNE. Coolest weather could arrive Fri pending track and 
intensity of surface wave tracking SE of New England. Depending on 
amplitude of wave, could be chilly with onshore only yielding highs 
in the 50s. Ensemble 850 mb temp anomalies are impressive, about -6C 
cooler than normal. In fact, ensemble probs of 50+ highs Friday drop 
to less than 50% across northern MA. Hence, could see highs only in 
the 40s there. Chilly weather likely lingers into Saturday given 
below normal heights/cold pool aloft. Temps may moderate to seasonal 
levels by Sunday, as flow becomes NW aloft and cold pool moves 
offshore.

&&

.AVIATION /18Z MONDAY THROUGH FRIDAY/...
Forecast Confidence Levels:

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

18Z TAF Update

This afternoon...high confidence. 

Conditions have improved to VFR for most of the region. The
exception is the Cape and islands where stubborn low clouds may
hang on for the whole day. Mainly a dry day today, however 
widely scattered showers develop this afternoon and early 
evening. 10-20% chance of an isolated thunderstorm. Light WSW 
winds with local seabreezes along the eastern MA coast.

Tonight...Moderate Confidence

MVFR/IFR conditions fill back in across the interior and persist
over the south coast, Cape, and Islands through about 06Z. Winds
shift to the north after that time frame and allow ceilings to
gradually improve to VFR by 09-12Z.

Tomorrow...High Confidence

VFR. Light northerly winds becoming light out of the west. Sea-
breezes likely along the coast with very warm temps forecast
over land. 

Tomorrow night...Moderate Confidence. 

Rain arrives to western terminals by 12z with VFR conditions
throughout the night. Winds light and variable. 


KBOS TAF...Moderate Confidence in TAF. Biggest question is if
enough clouds fill back in to have the sea breeze flip back to
west winds at 21z.  

KBDL TAF...High Confidence in TAF.

Outlook /Tuesday Night through Friday/... 

Tuesday Night: VFR. Slight chance RA.

Wednesday: Mainly MVFR, with local IFR possible. Chance RA.

Wednesday Night: Mainly VFR, with local IFR possible. Chance
RA.

Thursday: Mainly VFR, with areas MVFR possible. Breezy. Chance
RA.

Thursday Night: Mainly MVFR, with areas IFR possible. Breezy.
Chance RA.

Friday: Mainly VFR, with areas IFR possible. Breezy. Chance RA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Today through Tomorrow...High Confidence

Modest winds and seas continue today and tomorrow. Expect areas of 
fog over the coastal waters this morning and this afternoon as 
moisture increases from southerly winds. Fog should dissipate 
tonight into tomorrow as a weak cold front ushers drier air over the 
coastal waters.


Outlook /Tuesday Night through Friday/... 

Tuesday Night: Winds less than 25 kt. 

Wednesday: Winds less than 25 kt. Chance of rain. 

Wednesday Night: Winds less than 25 kt. Slight chance of rain. 

Thursday: Winds less than 25 kt. Chance of rain. 

Thursday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of seas approaching 5 ft. Chance of
rain. 

Friday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas up to 5 ft. Chance of rain.

&&

.TIDES/COASTAL FLOODING...
.Coastal Flooding...

High astro tides this week and concern becomes late Thu into Fri 
with potential frontal wave tracking south of New England, 
generating onshore flow into eastern MA. Magnitude of potential 
inundation and erosion will depend on strength and timing of surface 
low. Too early for specifics with any certainty, but given astro 
tides are already over 11 ft at Boston, it will only take a 1 ft 
storm surge and modest wave action to yield minor inundation and 
erosion. Stay tuned throughout the week for updated information.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

$$

SYNOPSIS...Nocera/RM
NEAR TERM...Nocera/BW/RM
SHORT TERM...RM
LONG TERM...Nocera
AVIATION...Nocera/BW
MARINE...Nocera/RM
TIDES/COASTAL FLOODING...