Lexington Weather

Lexington, Massachusetts, USA

53°F

5/11/2024 6:19pm

Lexington Conditions: Partly cloudy
Temperature: 52.5°F / 11.4°C
Dew Point: 41.9°F
Relative Humidity: 67%
Wind: Calm, 10-min avg: Calm, gust: 1 mph
Barometer: 29.83 in Steady
Visibility: 10 miles
Rain Today: 0.00 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 061101
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
701 AM EDT Mon May 6 2024

.SYNOPSIS...
Partial sunshine develops Monday 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/...

7 AM update...

Back edge of rain shield at 645 AM is across RI and southeast 
MA, continuing to advance east and should be offshore by 8 AM.
Water vapor satellite imagery shows dry slot aloft moving across
the area and visible satellite already showing breaks in the
overcast across northern MA. These breaks will allow strong/high
May sun angle to continue to erode and mix out low level
moisture, while also mixing downward dry air aloft to the
surface. Also, westerly flow aloft will also mix down to the
surface and help the drying out process. Therefore, expecting
partial sunshine to combine with warm airmass aloft to result in
surface temps soaring into the low and mid 70s away from the 
coastline.

Dry weather much of the day, however, as trailing short wave
energy approaches from the west, combined with surface trough, a
few widely scattered showers and perhaps an isolated
thunderstorm move across the area this afternoon. Previous
forecast captures these details, therefore no wholesale changes
with this update. Earlier discussion below. 

-----------------------------------------------------------------

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 /12Z MONDAY THROUGH FRIDAY/...
Forecast Confidence Levels:

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

12Z TAF Update...high confidence in trends, but some uncertainty
on exact timing. 

Forecast theme remains for upward trends today with IFR/MVFR
conditions lifting to VFR bases by late morning and continuing
into the afternoon. Rain across RI and southeast MA at 11z will
exit offshore by 12z. Then mainly a dry day, however widely
scattered showers develop this afternoon and early evening.
10-20% chance of an isolated thunderstorm. Light WSW winds with
local seabreezes possible along the eastern MA coast. 

-----------------------------------------------------------------

Tonight...High 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. 


KBOS TAF...Moderate Confidence in TAF. BOS should scatter out
for a few hours this morning into early afternoon before
returning to MVFR by early to mid afternoon. Moderate 
confidence in a sea- breeze circulation developing today between
14 and 16Z. Higher confidence in a sea- breeze for Tuesday.

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