Lexington Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 121112
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
712 AM EDT Thu Mar 12 2026

.WHAT HAS CHANGED...
Increased snow/sleet accumulations for this afternoon into tonight 
to up to 2 inches, although much of this should fall on grassy non-
paved surfaces. Wind gusts were increased for Saturday and could
warrant wind headlines. Growing confidence in heavy rain and 
strong winds early next week.

&&

.KEY MESSAGES...

- Rain showers/embedded thunderstorms end early this morning,
  then passage of a sharp cold front allows for breezy northwest
  winds and falling temperatures today. 

- Light rains change to a mix of rain/sleet and then to wet 
  snow this afternoon into early tonight. Reduced visibilities 
  likely during the PM commute. Minor accumulation (up to 2", 
  locally more possible) but pavement should be mostly wet.

- Scattered rain and elevation snow showers late Fri and Fri 
  night, then drying out and becoming windy Sat.

- Widespread showers with locally heavy rainfall possible 
  Sunday night into Monday night which may lead to minor river 
  flooding. Strong winds possible late Monday and Monday 
  evening. 

- Dry and trending colder Tue into Wed.

&&

.DISCUSSION...
KEY MESSAGE 1...Rain showers/embedded thunderstorms end early this 
morning, then passage of a sharp cold front allows for breezy 
northwest winds and falling temperatures today. 

Looking like we'll be experiencing two seasons today. 

A strong cold front is working its way through central NY. Ahead of 
it is a moist and anomalously mild warm sector with temps in the 50s 
to near 60 and dew pts in the upper 40s to mid 50s in most of 
Southern New England. Areas of showers and even a few garden-variety 
thunderstorms are around early this morning due to elevated 
instability (MUCAPE values as high as 1000 J/kg per SPC's 
mesoanalysis). The shower and embedded thunderstorm activity should 
come to an end by the pre-dawn hours but could make for some 
difficult travel for morning commuters. 

The cold front will then surge through Southern New England during 
the morning hours. Mainly light (if any) showers take place and some 
areas could end up dry for short intervals will accompany the 
front's passage. But this is a cold front that has quite a punch of 
shallow cold advection - temperatures then stand to fall beginning 
this morning and through the day, and will also be accompanied by 
northwesterly wind gusts 25-40 mph. More shallow mixing really 
will cap how strong the gusts will get. Gusts could punch as 
high as near- Advisory level for a couple hours in the 
Berkshires early this morning immediately after frontal passage.
But either way, expect a cloudy, breezy and raw day once the 
winds turn northwesterly, with highs occurring before the 
frontal passage and then steadily dropping into the 30s through 
the day.

This then leads in to what takes place this afternoon... 

KEY MESSAGE 2...Light rains change to a mix of rain/sleet and 
then to wet snow this afternoon into early tonight. Reduced 
visibilities likely during the PM commute. Minor accumulation 
(up to 2", locally more possible) but pavement should be mostly 
wet.

Although the cold front will have moved offshore by around noontime, 
a southern-stream trough over the lower MS Valley will help to 
draw another round of precipitation northeastward from the mid- 
Atlantic into the Northeast in an ana-frontal configuration, 
falling into the increasingly colder air. This should facilitate
rain to change to wintry precipitation as soon as early 
afternoon before moving offshore early tonight. Precip falls as 
rain initially, but the strength of the shallow cold airmass 
suggests that as we move through the afternoon...rain ends up 
mixing with sleet/ice pellets as model soundings show 
temperatures aloft not cooling off as fast as the lowest 100 mb 
to surface do, but then eventually ending as a few-hour period 
of snow (or snow mixed with rain near the eastern coast). 

There are a few moving parts here which cast some degree of 
uncertainty on how this scenario ultimately unfolds. One is when the 
precip begins to advance northeastward into the colder airmass;
it doesn't look to be much QPF but when it begins will dictate 
how long changeovers occur, which of course also affects how 
much of what type of precip falls. Finally, it's important to 
recognize that early- March wintry accumulations on pavement 
tend to be governed by time of day and if rates become intense, 
and that's especially true as just two days ago, many areas saw 
temperatures in the 70s. Confidence in specific accumulations 
is not especially high and could be subject to adjustments given
the above uncertainties and moving parts to the forecast, 
either up or down. We opted for coatings to an inch for most, 
but as much as 2 inches of snow/sleet in interior Southern New 
England. Pavement should be mostly wet vs wintry though. But 
with that said, I'd plan on the afternoon commute to be a pretty
sloppy one due to wet roads and reduced visibilities...with 
precip ending by early tonight.

Even though low temperatures drop to around 25-30 degrees tonight, 
the risk for black ice looks minimized by strong
drying/evaporation. 

KEY MESSAGE 3...Scattered rain and elevation snow showers late 
Fri and Fri night, then drying ou 
totalt and becoming windy Sat.

Quick moving northern stream shortwave and clipper low pass to the 
north Fri night. Bulk of precip with this system will be focused 
across northern New Eng, but decent warm advection enhanced by a low 
level jet will support scattered rain or elevation snow showers late 
Fri and Fri night. Any snow accum will likely be focused across the 
Berkshires and Worcester Hills where up to an inch is possible. The 
low level jet will bring some gusty pre-frontal S-SW winds to the 
south coast Fri evening, then the low pres will push a cold front 
through SNE overnight with potential for strong post-frontal wind 
gusts Sat in the cold advection pattern. Forecast soundings show a 
well mixed boundary layer supportive of gusts to 35-45 mph with a 
few 50 mph gusts possible. Wind advisories may eventually be needed. 

KEY MESSAGE 4...Widespread showers with locally heavy rainfall 
possible Sunday night into Monday night which may lead to minor 
river flooding. Strong winds possible late Monday and Monday 
evening. 

High amplitude trough approaches from the Gt Lakes Mon before 
lifting across New Eng Tue. Strengthening low level jet ahead of the 
trough will bring anomalous moisture northward into SNE. PWAT and 
wind anomalies are favorable for a heavy rainfall event, which is 
likely to come in 2 waves. First late Sun night into Mon AM with the 
initial low level jet, then another period late Mon and Mon night 
with the main LLJ ahead of the cold front. Strong forcing for ascent 
along with elevated instability will support some heavy convective 
showers along with a few t-storms. Ensemble guidance suggests 
potential for 1-2 inches rainfall given high probs (70-90%) of 
greater than 1" rainfall focused across CT/RI and SE MA. 90th 
percentile of the ensemble distribution is showing 2-3 inches which 
would represent a localized worst case scenario. MMEFS ensemble 
guidance from the NAEFS continues to show moderate probs (50-70%) 
for river levels reaching minor flood along the Pawtuxet, Pawcatuck 
and Wood Rivers in RI, and there are even some low probs for 
moderate flooding. Along the lower reaches of CT river from Hartford 
to Middle Haddam there are lower probs (35-45%) of reaching minor 
flood. 

Strong wind across SE New Eng is the other concern with this event, 
especially late Mon and Mon night ahead of the cold front as LLJ 
lifts across the region. Details at this time range are uncertain as 
the strong wind will depend on the extent of mixing which is always 
a challenge with these southerly LLJ events. It will be mild Mon 
into Mon evening ahead of the cold front with temps possibly 

KEY MESSAGE 5...Dry and trending colder Tue into Wed.

Cold front is forecast to be east of New Eng by 12z Tue with much 
drier air moving in from the west. Mainly dry conditions expected 
Tue but blustery and cooler weather in the cold advection pattern. 
Coldest day will be Wed as the upper trough and core of the coldest 
air aloft settles over New Eng with expected temps several degrees 
below normal.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
Forecaster Confidence Levels...

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

12z TAF Update: 

Today: Moderate confidence. 

A pretty active, changeable aviation forecast period.

Mix of flight categories from VFR to LIFR, lowest along the
south coast due to dense fog. Southerly winds around 10-15 kt 
with gusts 20-25 kt with continued low level wind shear.

A cold front will be moving through SNE between 12-16z Thurs 
west to east, which will bring a gusty windshift to WNW around 
15-18 kt with gusts 25-30 kt. Cooling temperatures will allow 
for initial rain, but rain should then mix with PL and then SN 
with MVFR visby/MVFR-IFR ceilings from ~18-00z. Up to an inch of
snow accum possible on grassy surfaces although runways should 
be wet given preceding spell of warm temperatures. 

Tonight: High confidence. 

Rapid improvement to VFR early tonight. NW winds around 10 kt
with occasional gusts to 20 kt. Even though temperatures will 
be subfreezing, rapid drying should limit any freeze-up on 
runways.

Friday: High confidence. 

VFR, though with increasing midlevel clouds late in the day. NW
winds become light and then shift to SW around 5-10 kt.

KBOS Terminal...Moderate confidence. SHRA thru 09z Thurs with
period of brief dry weather but MVFR/VFR ceilings around. A
gusty windshift to NW takes place 13-15z. Cooling temps after 
18z then brings a risk for rain mixed with PL then brief SN.
Visbys 2-4 SM in wintry precip, although runways should be wet.
Rapid VFR improvement by early this evening.

KBDL Terminal...Moderate confidence. SHRA, embedded TS possible
thru 08z. VFR/MVFR ceilings after 08z before cold front brings 
resuming risk for rain and a gusty NW windshift after 13z. 
Cooling temps could support mixover to PL then SN after 17z 
Thurs, ending by 00z.

Outlook /Friday through Monday/...

Friday: VFR. Breezy. 

Friday Night: Mainly VFR, with local MVFR possible. Breezy.
Slight chance RA.

Saturday: VFR. Strong winds with local gusts up to 40 kt. 

Saturday Night: VFR. Windy with local gusts up to 30 kt. 

Sunday: VFR. Breezy. Slight chance RA, slight chance FZRA.

Sunday Night: Mainly VFR, with local IFR possible. Windy with
gusts up to 35 kt. Chance RA, slight chance FZRA.

Monday: Mainly MVFR, with areas IFR possible. Strong winds with
local gusts up to 40 kt. RA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Rough seas linger across the outer coastal waters into Friday
morning. A cold front moving across the waters Thursday will 
also generate gusty SW winds at times until it passes. Becoming 
clearer with gusty W to NW winds Thursday into Thursday night.

Outlook /Friday through Monday/...

Friday: Winds less than 25 kt. Seas up to 5 ft. 

Friday Night: Strong winds with local gusts up to 30 kt. Areas
of rough seas. Slight chance of rain. 

Saturday: Moderate risk for gale force winds with gusts up to
35 kt. Rough seas up to 12 ft. 

Saturday Night: Low risk for Small Craft Advisory winds with
gusts up to 30 kt. Local rough seas. 

Sunday: Winds less than 25 kt. 

Sunday Night: Strong winds with gusts up to 35 kt. Areas of
rough seas. Chance of rain. 

Monday: gale force winds with gusts up to 40 kt. Rough seas up
to 17 ft. Rain.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 2 AM EDT Friday for ANZ230.
     Small Craft Advisory until 8 AM EDT Friday for ANZ231-232-250-
     251-254>256.
     Small Craft Advisory until 5 AM EDT Friday for ANZ233>235-237.
     Small Craft Advisory until 8 PM EDT this evening for ANZ236.

&&

$$

DISCUSSION...KJC/Loconto
AVIATION...KJC/Loconto/BW
MARINE...KJC/Loconto