Lexington Weather

Lexington, Massachusetts, USA

27°F

12/3/2024 12:45am

Lexington Conditions: Few Clouds
Temperature: 27.1°F / -2.7°C
Dew Point: 19.6°F
Relative Humidity: 73%
Wind: Calm, 10-min avg: Calm, gust: None
Barometer: 30.08 in Steady
Visibility: 10 miles
Rain Today: 0.00 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 030520
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1220 AM EST Tue Dec 3 2024

.SYNOPSIS...

Mainly sunny and dry weather is expected through Tuesday, 
although a cold airmass will continue to yield below normal 
temperatures and periods of ocean effect cloudiness for the 
Cape and Islands. Next chance for precipitation comes Wednesday
night into Thursday, as a clipper system brings rain near the 
coast and accumulating snowfall in the interior. An colder 
airmass moves in Friday and into the weekend, likely with the 
coldest air of the season thus far.

&&

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

Sct-bkn strato-cu lingering across portions of SNE but these
clouds are expected to clear tonight. Otherwise, ocean effect
strato-cu developing over the ocean north of Cape Cod and these
clouds expected to fill in across the outer Cape and Nantucket 
through the night. Otherwise, a mainly clear night with light
WNW winds becoming near calm overnight. This means another very
chilly night is in store with strong radiational cooling 
expected. With little change in thermal airmass, largely used 
persistence as a basis for tonight's lows. The lone exception is
across the Mid-Cape and Outer Cape where an increasing coverage
of ocean effect stratocumulus and modest NW breeze should limit
radiational cooling and bring lows closer to the mid/upper 20s.
The larger metro cities should stay in the lower 20s but most 
areas elsewhere should dip into the teens.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM WEDNESDAY/...
120 PM Update:

Little change in the governing synoptic regime for Tues, with 
high pressure to our south supplying continued dry weather and a
light westerly wind. The shift in the winds to more of a 
westerly flow, a less favorable direction for ocean effect over 
land, should in turn shut off ocean effect cloudiness over the 
Outer Cape early in the day. Thus mostly clear skies but still a
rather chilly and dry day with highs in the 30s, but may 
struggle to reach the freezing mark over the higher terrain of 
the Berkshires and hills in Worcester and Tolland Counties. 

For Tues night, modest change takes place with 500 mb longwave 
trough axis and associated 925-850 mb thermal trough moving
eastward and offshore. Although we still expect clear skies and 
light winds favoring efficient radiational cooling, we will see 
more in the way of lower- tropospheric warm advection. Still 
ends up being another rather cold night, and though it may not 
necessarily feel much different, lows should be a couple degrees
warmer in the upper teens to the mid 20s.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Key Messages...

* Accumulating snowfall likely Wed night into early Thu,
  especially west of I-495 with mainly rain in the coastal 
  plain.

* Turning colder Thu night into the weekend with temps well below 
  normal

* Strong wind gusts developing Wed night Cape/Islands and late Thu 
  into Fri rest of SNE


Wednesday...

Surface ridging moves across SNE then to the east by days end ahead 
of next approaching system from the Gt Lakes. Plenty of sunshine to 
start the day, then developing warm advection pattern within SW flow 
will bring increasing clouds in the afternoon. However, it should 
remain dry through the day with precip holding off until evening. 
Highs will range from the mid 30s to lower 40s with increasing SW 
winds 10-20 mph in the afternoon. 

Wednesday night into Thursday...

Deep upper level low dives into the Gt Lakes Wed night before moving 
across New Eng on Thu. Diffluent flow aloft Wed night ahead of the 
trough with favorable left exit region of the upper jet will provide 
strong large scale forcing for ascent. Decent SW low level jet will 
bring increasing moisture with saturated column developing through a 
deep layer. This will bring a period of widespread precip Wed night 
into early Thu with expected QPF amounts of 0.25 to 0.50". The 
column is cold enough for snow in the interior west of I-95 with 
mostly rain along and SE of I-95, although a rain-snow mix is 
possible along the I-95 corridor. Highest snow amounts will be over 
higher elevations where temps will be coldest. Preliminary forecast 
accums of 3-6 inches is possible over the Berkshires and Worcester 
Hills, with 1-3 inches across the rest of the interior. This is line 
with ECWMF and GEFS ensembles showing high probs (60-90%) of 3+ 
inches over the elevated terrain, with high probs (90%+) of 1 inch 
across the interior. No snow accums are expected near the coast. 
Fortunately, the bulk of the snow will begin after the Wed evening 
commute although the morning commute will be impacted. 

Best moisture will be lifting out Thu morning so interior snow will 
begin to taper off, although scattered rain and higher elevation 
snow showers likely to continue as the upper low and arctic front 
moves into the region. Clearing Thu night and windy and colder with 
lows dropping into the upper teens to mid 20s. 

Decent SW low level jet developing Wed night will likely bring a 
period of strong wind gusts across the Cape/Islands. Model soundings 
suggest potential for a period of 40-50 mph gusts here and wind 
advisories may eventually be needed. Then strong W wind gusts will 
develop across rest of SNE late Thu and especially Thu night in the 
cold advection with marginal wind advisory criteria possible. 

Friday through Monday...

Blustery and cold Fri as 850 mb temps bottoming out near -14C. Highs 
will range from the upper 20s to mid 30s and the cold conditions 
will continue into Sat but with less wind. Another fast moving 
northern stream shortwave and clipper may bring some light snow 
sometime Sat or Sat night but low confidence on timing. Drying out 
Sunday, then next system approaches next Monday with rain or a mix 
as milder air will be moving in as southerly flow develops.

&&

.AVIATION /05Z TUESDAY THROUGH SATURDAY/...
Forecast Confidence Levels:

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

06z TAF Update: 

Today and tonight: High confidence. 

VFR. Light WNW winds early this morning except 5-8 kt for BOS 
and the Cape airports. For today, winds become more WNW to W, 
then become light W to WSW for tonight. 

Wednesday: High confidence. 

VFR. Light W winds increase to 5-10 kts becoming SW then S. 

KBOS Terminal...High confidence in TAF. 

KBDL Terminal...High confidence in TAF.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: MVFR/IFR conditions possible. Windy with gusts
up to 35 kt. SN, RA.

Thursday: Mainly MVFR, with local IFR possible. Windy with
gusts up to 35 kt. Chance SHRA, chance SHSN.

Thursday Night: VFR. Windy with gusts up to 35 kt. 

Friday: VFR. Windy with gusts up to 30 kt. 

Friday Night: VFR. Breezy. 

Saturday: VFR. Breezy. Slight chance SHSN.

&&

.MARINE...
Forecaster Confidence Levels:

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

Generally tranquil winds and sea conditions for boaters through
Tuesday night. WNW to W winds around 10-15 kt thru Tue, then
becoming W/WSW around 15 kt for Tue night. Seas thru Tue night 3
ft or less all waters. Dry weather is expected, although ocean 
effect cloudiness over the eastern waters could produce a 
sprinkle or flurry over the outer waters.

Outlook /Wednesday Night through Saturday/...

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

Wednesday Night: Low risk for gale force winds with gusts up to
35 kt. Areas of rough seas. Rain. 

Thursday: Moderate risk for gale force winds with gusts up to
40 kt. Rough seas up to 14 ft. Rain showers. 

Thursday Night: gale force winds with gusts up to 40 kt. Rough
seas up to 14 ft. Slight chance of rain showers. 

Friday: Strong winds with gusts up to 35 kt. Rough seas up to
11 ft. 

Friday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Areas of rough seas. 

Saturday: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of rain showers, slight chance of snow
showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Gale Watch from Wednesday evening through Thursday evening for 
     ANZ232>235-237-255-256.

&&

$$

SYNOPSIS...KJC/Loconto
NEAR TERM...KJC/Loconto
SHORT TERM...Loconto
LONG TERM...KJC
AVIATION...KJC/BW
MARINE...KJC/Loconto