Lexington Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 141120
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
620 AM EST Sun Dec 14 2025

.SYNOPSIS...

Fast moving low pressure will bring accumulating snow to the
region into midday especially south of the Massachusetts
turnpike. The snow will linger into the afternoon across Rhode 
Island and especially across far eastern Massachusetts where it
may persist into this evening. A brief shot of arctic
air follows tonight into Monday, with wind chill values 
dropping to between 0 to 10 below zero. Cold weather continues 
Monday night into Tuesday but with much lighter winds. A warming
trend begins Wednesday and especially by Thursday when high 
temperatures of 50+ are possible. Unseasonably mild temperatures
will be accompanied by a round of showers sometime later 
Thursday into early Friday with perhaps a period of strong 
southerly winds and heavy rain. A brief shot of much colder 
weather with another period of strong winds possible later 
Friday into Saturday.

&&

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

Key Messages...

* Accumulating snow ends by lunchtime across western MA/CT, but
  persists into the afternoon especially across eastern MA

* Hourly snowfall rates generally on the lighter side...but
  brief bursts of moderate snow possible near the south coast

Trend in high res guidance has been to shift the timing of the end 
of the steadiest snow from mid morning to the afternoon for much of 
Rhode Island and Eastern Massachusetts. Model guidance, namely the 
HRRR and NAM3km have also begun to resolve an inverted trough and 
wrap around ocean effect snow extending from low pressure as it 
pulls away. Trough will be a good focus for vertical motion and 
moisture as omega increases to -10 to -15 ubar/sec. Sharply colder 
air filtering behind departing low pressure will introduce non-zero 
MLCAPE values which could help with ocean enhancement of any 
snowbands. Despite these favorable parameters, daytime will likely 
be limited by marginal sfc temps in the mid and even upper 30s. 
Temps may be locally lower under any ocean effect bands but its 
really going to take considerable rates to cool the PBL from the 
influence of 45-47F water temps. As a result, still think that 
advisory level snow totals 2-4" for RI/SE MA with localized 5-6"
amounts possible near the south coast and Cape Cod.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...

Key Messages...

* Very cold with wind chill values near or below zero

* Windy conditions with gusts up to 40 mph Sunday Night and Monday

The coldest airmass of the season thus far will move in behind the 
snow for Sunday night as 850mb temps crash into the -15C to 
-20C range. This will result in overnight low temperatures bottoming 
out in the single digits across the interior, to the low teens near 
the coastal plain. A strong pressure gradient will result in gusty 
winds overnight, around 25-40 mph. This will bring the windchill 
index/feels-like temperatures down to the 0F to -5F range, with -5F 
to -15F in the high terrain. 

MONDAY 

High pressure helps to keep an Arctic air mass in place through the 
day on Monday as GFS and Euro ensembles keep temperature anomalies 
near 10 degrees colder than normal. Other story Monday will be a 
steep pressure gradient keeping a stiff NW wind in place for the 
region. Wind gusts between 25 and 35 mph will make high temperatures 
in the teens (at higher elevations) and 20s elsewhere feel more like 
the single digits to lower teens at their warmest.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...

Key Messages...

* A few brief snow showers possible Mon night, otherwise diminishing 
  winds with low temps mainly in the teens

* Dry & chilly Tue...Highs mainly in the lower to middle 30s

* Turning milder Wed with continued dry weather & highs into the 40s

* Showers with heavy rain & potential briefly strong southerly wind 
  gusts later Thu into early Fri with unseasonably mild temps

* Brief shot of much colder temps returns behind the front later Fri 
  into Sat with another round of strong winds possible

Details...

Monday night into Tuesday...

A weak shortwave may bring a few brief snow showers to the region 
Monday night. Otherwise...still chilly Mon night into Tue but with 
light winds. Low temperatures Mon night will mainly be in the teens. 
Highs on Tue will range from the upper 20s in the highest terrain to 
mainly the lower to middle 30s elsewhere. 

Wednesday...

The developing -PNA and high pressure to our south sliding further 
east will allow for the beginning of a pattern change and milder 
temperatures. While it will remain dry on Wed, gusty southwest winds 
developing will push high temperatures well into the 40s.

Thursday into Friday morning...

Strong shortwave energy over the northern plains will move eastward 
into the Great Lakes. As this happens...strong surface low pressure 
perhaps sub 980 mb will pass well to our north across Quebec. Given 
the potential strength of the surface low pressure system...the long 
range guidance is indicating a strong southerly LLJ nearly 3 
standard deviations outside climatology. Not only will this bring up 
unseasonably mild temperatures and Pwats exceeding 1 inch. This will 
combined with strong forcing ahead of the cold front and bring 
showers with perhaps brief heavy rain sometime later Thu into Fri. 
In addition...given the magnitude of the southerly LLJ we will have 
to watch for a brief period for strong surface wind gusts if the 
inversion is able to mix out. It is way too early to assess 
that...but depending on the timing temperatures may rise well into 
the 50s Thu night/early Fri and may even flirt with 60 degrees. If 
we are able to get mild enough...the potential for a period of 
strong winds to be realized will increase. Again...way too early to 
say much more than that but something to watch in the coming days.

Later Friday into Saturday...

Briefly turning much colder later Friday into Saturday behind the 
cold front. Mainly dry weather expected, but another period of strong 
winds this time from the west is possible immediately behind the 
cold front.

&&

.AVIATION /12Z SUNDAY THROUGH THURSDAY/...

Forecaster Confidence Levels...

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

12z TAF Update..

Today...Moderate Confidence 

Light snow will result in a lot of IFR conditions this morning
with vsbys in the 1-3 mile range. Bands of moderate snow and and
LIFR conditions should mainly be confined to RI/SE MA. The light
snow will end across western MA/CT by lunchtime, but linger into
the afternoon east of the CT River Valley especially across
eastern MA. So improvement to MVFR and even VFR conditions will
be confined to mainly interior southern New England this
afternoon.

Tonight...High Confidence 

MVFR-IFR and even brief LIFR conditions are expected in areas
towards the Cape and Islands in ocean effect snow showers. This
activity should dissipate though after midnight. Otherwise, NW 
wind gusts of 20 to 25 knots with a few gusts near 30 knots 
across the high terrain and near the coast develop tonight.

Monday...High Confidence 

Mainly VFR with NW gusts of 30-35 knots. A few CU but should be 
above MVFR ceilings. 

KBOS Terminal...Moderate confidence in TAF. Light snow continues
much of the day with vsbys generally in the 1-3 mile range. The
steady light snow should finally come to an end by late
afternoon/early evening. Total snow accumulations of 1-3".

KBDL Terminal...Moderate confidence in TAF. Light snow ends by
lunchtime with snow accumulations of 1-2" expected.

Outlook /Monday Night through Thursday/... 

Monday Night: VFR. Breezy. Slight chance SHSN.

Tuesday: VFR. 

Tuesday Night: VFR. Breezy. 

Wednesday: VFR. Windy with areas of gusts up to 30 kt. 

Wednesday Night through Thursday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels...

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

Today Through Monday Night  ...High confidence.

Light N/NW winds through the early afternoon. Winds quickly increase 
to gales around 21z and gales continue through 20z Monday. Strong 
cold advection allows for ample mixing resulting in wind gusts 
between 35-40kts Sunday evening through Monday afternoon. Areas of 
very light freezing spray possible 00z Monday - 19z Monday. 
Elsewhere, small craft advisory conditions expected in Narragansett 
Bay and Boston Harbor.

Outlook /Monday Night through Thursday/...

Monday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Local rough seas. Slight chance of snow
showers. 

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

Tuesday Night: Low risk for Small Craft Advisory winds with
gusts up to 30 kt. Seas locally approaching 5 ft. 

Wednesday: Strong winds with gusts up to 30 kt. Areas of rough
seas. 

Wednesday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Local rough seas. 

Thursday: Low risk for Small Craft Advisory winds with gusts up
to 30 kt. Areas of seas approaching 5 ft.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Winter Weather Advisory until 7 PM EST this evening for 
     MAZ017>024.
RI...Winter Weather Advisory until 7 PM EST this evening for 
     RIZ001>008.
MARINE...Small Craft Advisory from 4 PM this afternoon to 3 PM EST 
     Monday for ANZ230-236.
     Gale Warning from 7 PM this evening to 1 PM EST Monday for 
     ANZ231>235-237-250-251-254>256.

&&

$$

SYNOPSIS...FT/Frank
NEAR TERM...FT
SHORT TERM...FT
LONG TERM...Frank
AVIATION...FT/Frank
MARINE...FT/Frank