Lexington Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 181132
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
632 AM EST Sun Jan 18 2026

.WHAT HAS CHANGED...

Snow accumulations increased and winter weather advisories 
expanded to include the rest of southern New England except 
Nantucket. Total snow accumulations of 2-6" expected with
localized 7" amounts possible across eastern MA/RI. Heaviest
snow occurs between 5 pm this evening and 1 am Monday...but 
some snow showers may linger into the Monday morning commute
especially across eastern Massachusetts. No other significant
changes made to the forecast.

&&

.KEY MESSAGES...

- Plowable snow today-tonight with total accumulations of 2-6"
  with localized 7" amounts possible across eastern MA/RI.
  Heaviest snow/worst of the travel conditions between 5 pm and
  1 am...but snow showers may linger for the Mon am commute.

- Arctic cold front sweeps across the region Mon night bringing
  well below normal temperatures and bitterly cold wind chills &
  temps. The peak of the cold weather will be Tue into Wed am.

- Milder temps arrive Wed night-Thu with perhaps a brief period
  of light snow showers or even light rain showers near the
  coast.

- Another shot of very cold air works into the region behind 
  a cold front Thu night into Fri.

&&

.DISCUSSION...

KEY MESSAGE 1...Plowable snow today-tonight with total accumulations 
of 2-6" with localized 7" amounts possible across eastern 
MA/RI. Heaviest snow/worst of the travel conditions between 5 pm
and 1 am...but snow showers may linger for the Mon am commute.

Deepening shortwave near a strong thermal boundary over the south 
triggers cyclogenesis off the coast of the Carolinas early this 
morning. Surface low quickly tracks northeast as the parent trough 
becomes negatively tilted over the Great Lakes. Low pressure will be 
slow to deepen as upper level energy will be somewhat stretched and 
elongated along a broad baroclinic zone offshore. Some modest 
deepening of the low center will occur as the trough goes negative 
and the right entrance region of a 180kt jet moves over the low 
center. Models have come into better agreement on the track of the 
storm, taking the center of the low SE of the 40 70 benchmark from 
00z-06z Monday. Despite the weaker low center (~995mb) guidance 
continues to increase QPF across the region with 0.5-0.7" for SE MA 
and the Cape/Islands and 0.2-0.5" along and NW of I-95. Periods
of mainly light snow develop this morning and continue at times
into the afternoon...but a lull in the activity is possible
especially north of I-90. The steadier/heavier snowfall will
arrive late this afternoon and especially tonight across eastern
MA/RI. 

Looking at some strong midlevel frontogenesis resulting in 
ample lift in the DGZ. Guidance shows mid level cooling NW of 
the 850mb low as it tracks SE of the region. This cooling 
results in the DGZ growing a depth of 2kft during the afternoon 
to around 6kft through the evening and overnight. At the same 
time, 700mb omega of -10 to -15 ubar/sec means vigorous lift 
will be present resulting in bands of moderate to perhaps heavy 
snow overnight. Highest chance of more consistent moderate/heavy
snowfall rates will be across eastern MA/RI. The highest snow 
totals are still expected across eastern MA/RI, where strong 
mid-level forcing and temperatures near or below freezing will 
overlap for the longest duration. Snow totals in this area will 
range from 3-6 inches, with localized 7" amounts possible. Would
not be surprised if this band extended into parts of central 
MA/northeast CT where temps are colder and there will be better 
snow ratios. 

While there will be good forcing over Nantucket and Block Island, 
temperatures will likely be too warm for significant accumulations, 
but a slushy inch remains possible. Across CT and into western MA,
the mid-level forcing is not quite as strong, but lower 
temperatures will allow for 2-5 inches. Have opted to include 
the rest of western and north central MA in the advisory. While
forcing will be less in these areas, higher ratios will 
contribute to greater snowfall accumulations.

While the steady snow ends before daybreak Mon, a period of 
lingering snow showers are possible especially across eastern MA
through 15z. Guidance shows low level convergence and a bit of 
instability which could pair to produce areas of snow showers 
and light snow into MLK day. 

In summary...periods of snow overspread the region this morning
and continue at times this afternoon but a lull in the activity
is possible for a time especially north of I-90. Heaviest snow 
rates arrive later in the afternoon and especially tonight with
the potential of 1"+ per hour snow fall rates. 

Otherwise...becomes breezy with partial sunshine returning by 
Monday afternoon ahead of an arctic cold front. High temps will
be in the upper 20s to the middle 30s

KEY MESSAGE 2...Arctic cold front sweeps across the region Monday
night bringing well below normal temperatures and bitterly cold
wind chills & temps. The peak of the cold weather will be Tue 
into early Wed morning.

The models are still in very good agreement in an arctic cold front 
crossing the region Mon night. This will bring a shot of arctic air 
and well below normal temperatures to the region. 850T will drop to 
between -18C and -20C with the cold peaking Tue into early Wed. 
Gusty west winds will result in wind chills below zero to the single 
digits. High temps Tue will only be in the upper teens to the
middle 20s with low temps Tue night mainly in the single digits
to the lower teens. This shot of arctic air will be short-lived
as high pressure shifts to our east by Wed. We should see high 
temps recover into the middle 20s and lower 30s by Wed 
afternoon...which is still below normal. 

KEY MESSAGE 3...Milder temps arrive Wed night-Thu with perhaps 
a brief period of light snow showers or even light rain showers 
near the coast. 

Low pressure tracking across Quebec will result in much milder 
air working back into the region on southwest flow. We may see 
a period of light snow showers in the warm air advection pattern
and perhaps even light rain showers near the coast as the 
boundary layer warms. Regardless...these rain/snow showers will 
likely be short-lived and not expecting a significant 
precipitation event. 

KEY MESSAGE 4...Another shot of very cold air works into the 
region behind a cold front Thu night into Fri.

Another shot of very cold air works into southern New England
behind a strong cold front Thu night into Fri. Highs may be held
in the upper 20s and lower 30s on Fri but with mainly dry
weather.

&&

.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 and tonight...Moderate confidence.

Periods of mainly light snow develop this morning and continue
at times this afternoon. This will result in MVFR conditions 
but localized IFR conditions are possible too in steadier snow.
The initial mainly light snow this morning may temporarily end 
this afternoon especially north of I-90...before the more 
significant snow arrives between 21z and 00z and continues 
tonight. This is where we expect the bulk of the accumulations 
to occur along with widespread IFR-LIFR conditions. Ptype mainly
snow except parts of the Cape and especially the Islands where 
some rain will mix in at times.

Monday...Moderate confidence.

Lingering snow showers expected into Mon morning especially
across eastern MA. MVFR to even localized IFR early in the
morning will improve to VFR by afternoon. SW wind gusts of
20 to 25 knots develop in the afternoon.


KBOS Terminal...Moderate confidence in TAF.

Areas of light snow this morning into the afternoon with the
steady/heavier snow expected to arrive after 21z/22z.

KBDL Terminal...Moderate confidence in TAF.

Areas of light snow this morning into the afternoon with the
steady/heavier snow expected to arrive after 21z/22z.

Outlook /Monday Night through Thursday/...

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

Tuesday through Wednesday: VFR. Breezy. 

Wednesday Night: VFR. Breezy. Chance SHSN.

Thursday: VFR. Breezy. Chance SHSN, slight chance SHRA.

&&

.MARINE...
Today and tonight...High Confidence.

Residual seas of 5-8 feet on the southern waters and 3-6 feet on the 
eastern waters is the basis for a continued Small Craft Advisory on 
the outer waters, which is in effect through Sunday morning. Coastal 
storm passes off shore today, bringing a rain/snow mixture and 
poor visby conditions. Brief lull in advisory level conditions, 
seas fall below 5 feet with light winds. Increasing wind 
speed/gusts with seas coming up late tonight into early Monday,
likely will need to be handled with a renewed Small Craft 
Advisory.

Outlook /Monday Night through Thursday/...

Monday Night: Moderate risk for gale force winds with gusts up
to 40 kt. Rough seas up to 12 ft. Freezing spray. 

Tuesday: Low risk for gale force winds with gusts up to 30 kt.
Areas of rough seas. Freezing spray. 

Tuesday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Local rough seas. Freezing spray. 

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

Wednesday Night: Strong winds with gusts up to 30 kt. Areas of
rough seas. Chance of rain showers. 

Thursday: Strong winds with gusts up to 30 kt. Areas of rough
seas. Slight chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Winter Weather Advisory until 7 AM EST Monday for CTZ002>004.
MA...Winter Weather Advisory until 7 AM EST Monday for MAZ002>023-
     026.
RI...Winter Weather Advisory until 7 AM EST Monday for RIZ001>007.
MARINE...Small Craft Advisory until 10 AM EST this morning for ANZ235-
     237-250.
     Small Craft Advisory until 7 PM EST Monday for ANZ254>256.

&&

$$

DISCUSSION...FT/Frank
AVIATION...FT/Frank
MARINE...FT/Frank