Lexington Weather

Lexington, Massachusetts, USA

26°F

12/3/2024 1:24am

Lexington Conditions: Partly cloudy
Temperature: 26.4°F / -3.1°C
Dew Point: 19.2°F
Relative Humidity: 74%
Wind: Calm, 10-min avg: Calm, gust: None
Barometer: 30.08 in Steady
Rain Today: 0.00 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 300216
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
916 PM EST Fri Nov 29 2024

.SYNOPSIS...
A cold front aloft will pass through Southern New England early
tonight, bringing an increase in clouds along with hit or miss
rain or snow shower, but many areas stay dry. Blustery and dry 
weather then prevails for Saturday. Generally dry weather then 
follows for Sunday into most of next week, with colder than 
normal temperatures. Scattered snow showers (rain showers south 
coast) are possible midweek, followed by possibly the coldest 
air of the season thereafter into next weekend.

&&

.NEAR TERM /THROUGH SATURDAY/...
9PM Update:

Pretty impressive area of snow moving across northern MA at this
hour in response to a weak cold front moving west to east
through the region. Pretty impressive estimated snow ratios 
between 15-1 and 20-1. With temperatures below freezing, it wont
take much QPF to get a quick coating to inch of snow. Have seen
several reports of grassy surfaces being covered with snow and 
even some pavement. This area of snow is moving ENE and should 
be offshore by midnight.


6 PM Update: 

Short wave trough moving across PA this evening and generating
scattered rain/snow showers downstream across eastern NY into
western CT/MA. Lots of low level dry air across SNE with current
dew pts in the 20s, yielding cloud bases in the 5000-8000 ft.
Thus, much of this activity is drying up as it traverse SNE.
Hence, most locations remain dry this evening, with little if
any impacts (sprinkles and/or flurries).  

Winds across the region this evening are WSW ahead of the short
wave. Later tonight, behind the short wave, winds will shift to
the WNW and CAA will commence, yielding a chilly night with lows
in the 20s most of the region, along with blustery west wind
developing late. Earlier discussion below. 

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

Current temps in the lower to mid 40s along with WSWly breezes 
to 25 mph. However cloud cover is starting to increase into the 
Berkshires and the I-91 corridor in MA/CT ahead of a lower-level
cold front, which heralds the arrival of colder 925-850 mb 
temps. Composite radar trends over central NY shows scattered 
convective showers driven by shallow convective instability 
(CAPEs around 50 J/kg per proximity BUFKIT soundings), and there
have been some reports of graupel in some of these showers 
indicative of convective processes. So we should see an increase
in cloud cover from west to east as the cold front aloft 
approaches over the next several hours, along with widely 
scattered showers or flurries. Potential exists for some graupel
mixing in with the showers, but overall these should be more 
novelty than anything significant and certainly not impactful. 
Passage of the cold front aloft will bring about a windshift 
from SW to WNW with easing speeds, along with some ocean effect 
cloudiness over the Islands. Otherwise, looking at dry weather 
with lows in the 20s, with the cities running in the upper 20s 
to the freezing mark.

&&

.SHORT TERM /SATURDAY NIGHT/...
130 PM Update: 

Broad cyclonic flow aloft still maintained through Saturday,
with a WSWly pressure gradient with high pressure to our south.
We'll be more entrenched in the colder air compared to today
though, with 925 mb temps -3 to -6C. This will steepen lapse
rates and lead to W/WSW breezes with gusts around 20 to 25 mph.
Should see mostly full sun; the interior higher terrain could 
see some stratocu during the aftn hrs, as well as over the 
Islands with the WSW flow and colder air aloft over the milder 
waters supporting continued ocean effect cloudiness. With the 
colder air, highs upper 30s to low 40s, though the terrain may 
struggle to reach the freezing mark. 

Clear skies promoting good nocturnal cooling for Sat night will
set the stage for a pretty cold night for the last evening of 
November 2024. Didn't go quite as low as some of the coldest
guidance as there might be some light westerly wind around.
Widespread 20s should be common, though upper teens are possible
in the typical sites which radiate well.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Updated 225 pm...

Key Points

 - About 10 degs colder than normal most days this period, then
   possibly the coldest air of the season arriving late next
   week/weekend

 - Dry weather prevails thru Tue, then scattered snow showers (rain 
   showers south coast) Wed-Thu timeframe

Teleconnections indicating a strong positive PNA emerging this 
period, with high amplitude ridge from the Pacific Northwest through 
western Canada. This yields below normal heights downstream across 
the Northeast and New England.  Hence, temps will average around 10 
degs colder than normal much of this period, with highs 35-40 most 
days, along with overnight lows in the teens and 20s. Ensembles and 
deterministic guidance in good agreement that the mean trough axis 
will likely be too far east for any wave development near the coast, 
hence storm track too far offshore for significant precip to impact 
SNE. Thus, each passing northern stream short wave and attending dry 
cold front, will just offer a reinforcing surge of CAA into SNE. 
Given CAA will be streaming across the region on WSW flow, it's 
possible we see some ocean effect rain/snow showers along the south 
coast and Islands Sunday. 

By middle of next, good ensemble agreement that a polar short wave 
dives southeast and may be accompanied by scattered snow showers 
(rain showers possible south coast) in the Wed/Thu timeframe. Again, 
mean trough axis appears too far east for any wave development to 
impact SNE. Behind the departing polar short wave, probably the 
coldest air of the season overspreads SNE late next week and/or next 
weekend.

&&

.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:

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

00z TAF Update: no change from previous TAFs. Earlier discussion
below. 

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

Through Tonight: High confidence. 

Largely VFR, though there could be some MVFR decks at times at
BAF, BDL and over the Islands (indicated with TEMPOs). A cold
front aloft comes in 21z Fri-03z Sat, which could bring an
increase in cloud cover and perhaps a hit or miss sprinkle or
flurry but not enough to restrict visbys. SW winds around 10-12
kt with gusts to 20 kt, easing by sundown, then passage of the
front will shift winds to W/WNW around 10 kt. 

Saturday and Saturday Night: High confidence. 

VFR, though there could be continued ocean effect clouds at
borderline VFR/MVFR levels at ACK. W to WSW winds around 10 kt,
then easing to light W Sat night. 

KBOS Terminal...High confidence in TAF. VFR. SW winds around 10
kt with gusts below 20 kt today; windshift to WNW with less 
gustiness expected 02-04z with dry cold frontal passage. 

KBDL Terminal...High confidence in TAF. Mainly VFR, though can't
rule out a BKN030 deck after 20z with a cold frontal passage.
Sprinkles or flurries ~ 20z to 00z but not to restrict visbys.

Outlook /Sunday through Wednesday/...

Saturday Night through Sunday: VFR. Breezy. 

Sunday Night through Tuesday: VFR.

&&

.MARINE...
Forecaster Confidence Levels:

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

130 PM Update: 

Westerly gusts around 20 kt expected through Sat, then easing 
to around 15 to 20 kt overnight Sat night. Seas 4-6 ft over the
southern outer waters will take time to lower, and have extended
the SCA on those waters until 12z Sunday.

Outlook /Sunday through Wednesday/...

Saturday Night: Winds less than 25 kt. Local rough seas. 

Sunday: Winds less than 25 kt. Local rough seas. Chance of rain
showers. 

Sunday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain showers. 

Monday: Winds less than 25 kt. Slight chance of rain showers. 

Monday Night: Winds less than 25 kt. Chance of rain showers,
slight chance of snow showers. 

Tuesday: Winds less than 25 kt. Slight chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 7 AM EST Sunday for ANZ254>256.

&&

$$

SYNOPSIS...Loconto/Nocera
NEAR TERM...Loconto/KP/Nocera
SHORT TERM...Loconto
LONG TERM...Nocera
AVIATION...Loconto/Nocera
MARINE...Loconto/Nocera