Lexington Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 041917
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
217 PM EST Wed Mar 4 2026

.WHAT HAS CHANGED...
Winter Weather Advisories have been issued for Thursday late 
afternoon into noontime Friday as initial rain changes to a wintry 
mix of freezing rain, sleet and light-accumulating snow. Slippery 
roads can be expected, with tree and powerline damage also possible 
where ice totals are higher. Mild weather this weekend into early 
next week could cause river rises due to snowmelt.

&&

.KEY MESSAGES...

- Patchy fog possible tonight across the region with light to 
  calm winds. Black ice will likely be an issue again Thursday 
  morning.

- Rain Thursday changes to a wintry mess of freezing rain, sleet
  and even some snow Thursday night into Friday in most areas
  away from southeast New England. Slippery roads are likely,
  and the potential exists for tree and powerline damage in
  interior high terrain if greater ice accretions materialize. 

- Pattern change toward milder temperatures remains in the cards
  for the weekend. Snowmelt could cause within-bank rises on
  streams, creeks and larger rivers into early next week.

&&

.DISCUSSION...
Key Message 1...Patchy fog possible tonight across the region 
with light to calm winds. Black ice will likely be an issue
again Thursday morning.

Fog finally cleared out in the CT Valley this afternoon, and as a 
result, high temperatures there this afternoon may reach the mid 40s 
at the highest. Temperatures fall quickly tonight across the region 
after sunset as winds go light to calm along with the effects of the 
snowpack. The snowpack across the region in combination with 
dewpoints and air temperatures in the 20s and upper teens will 
likely lead to patchy fog developing late tonight, especially after 
midnight. Freezing fog will also be a concern with temperatures 
falling below freezing, so black ice will be a concern once more 
tomorrow morning. 

Key Message 2...Rain Thursday changes to a wintry mess of freezing 
rain, sleet and even some snow Thursday night into Friday in most 
areas away from southeast New England. Slippery roads are likely, 
and the potential exists for tree and powerline damage in interior 
high terrain if greater ice accretions materialize. 

An elongated, west-east oriented surface warm front with parent 500 
mb shortwave disturbance will be attempting to build northward from 
the mid-Atlantic/Ohio Valley region Thurs into early Fri. As it does 
so, it will be running into a shallow sub-freezing airmass building 
southward from NH/ME on increased NE winds. While initial plain rain 
will develop in many areas Thurs, falling temps through the 30s into 
the mid/upper 20s will be enough to facilitate a transition from 
rain to a wintry mess of freezing rain, sleet and now even some 
light accumulating snow starting early Thurs night through Fri 
morning away from southeast New England. From a travel standpoint, 
this is likely an especially problematic precip type changeover 
evolution, given rain to wintry mix, which lends itself to slippery 
roads. Winter Weather Advisories have been posted starting 5 PM 
Thursday through noon Friday.

Forecast guidance has trended a little colder with 925-850 mb temps 
today, which results in a larger portion of Southern New England to 
experience a rain to wintry mix than previous indications, while at 
the same time opening the door for some accumulating snow along the 
NH/MA border. Although ice accretions of at least a light glaze are 
expected in much of the Advisory area, tried to hit the higher 
terrain in CT and MA as having the greatest ice accretions, which 
are up to around a quarter to third of an inch. If those higher 
totals materialize, the risk for tree and powerline damage would 
increase and feel those are possible in the higher terrain. Up to 2 
inches of combined sleet and snow accumulation are forecast along 
the Route 2 corridor into the North Shore. But because of the cooler 
trend in guidance and that very subtle changes in surface to lower-
atmospheric temperatures will drive the duration of precip types and 
accumulations, I wouldn't rate confidence in specific snow/ice 
accumulations as being high; future adjustments in either/both are 
possible. But strong confidence exists in the impacts being at least 
slippery/icy roads, but could also include a risk for tree and 
powerline damage if higher ice totals over a quarter-inch develop, 
and that was the rationale for the Winter Weather Advisories. 

Precipitation comes to an end Friday mid to late morning; but of 
some concern is that there could be lingering freezing mist/freezing 
drizzle even after precip ends in some interior locations Friday 
afternoon. If that develops, it could lead to continued slippery 
roads into a good part of Friday. Nonetheless, expect a cloudy, 
chilly and raw Friday with highs only in the 30s, with highs in the 
low 30s around the interior higher terrain. 

Key Message 3...Pattern change toward milder temperatures remains in 
the cards for the weekend. Snowmelt could cause within-bank rises on 
streams, creeks and larger rivers into early next week.

Significant pattern change takes place for the weekend as 
anomalously strong SWly flow aloft advects in well above normal 850 
mb temperatures Sat/Sun, as high as 10-13C. These would be some 15 
degrees Celsius warmer than climatological 850 mb temps for early 
March. Mixing looks shallow despite the very warm 850 mb temps on 
Saturday, which could keep highs closer to the mid 40s to lower 50s. 
Still, highs some 10-15 degrees above normal should develop Sun with 
highs in the 50s to even some spot 60s. Rising dewpoints into the 
mid 40s/around 50 will also eat away at the standing snow depth, 
too. There is a frontal system which looks to move in around 
Saturday night into Sunday, bringing light rains. Some rises on 
rivers are anticipated from melting snow during the weekend to early 
next week based on GEFS/NAEFS hydrologic forecasts. Will have to 
monitor the western watersheds for at least within-bank rises into 
early next week, though potential for some to reach flood stage if 
we get any rainfall on top of the melting snow.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
Forecaster Confidence Levels...

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

18z TAF Update...

Rest of Today...High confidence. 

Lingering IFR conditions in the CT Valley are finally starting
to clear and should continue to lift to VFR within the next
hours or so. Otherwise, VFR for the rest of today across 
southern New England with light SW winds for most (winds more N 
to NE in the CT Valley), aside from localized sea breezes along 
the immediate coast for some terminals.

Tonight...Moderate confidence.

VFR this evening, but areas of low clouds and fog may develop 
late resulting in MVFR-IFR conditions with even localized LIFR 
cigs/vsbys. While low clouds and fog patches are possible 
anywhere late tonight, guidance continues to indicate the 
greatest risk for it being most widespread across CT/RI and 
southeast MA. Light/calm winds.

Thursday...Moderate confidence.

The initial morning low clouds/fog patches may briefly burn off. 
Widespread MVFR to localized IFR conditions expected to 
overspread the region from southwest to northeast, particularly
in the evening hours into Thursday night with rain mixed with
some sleet moving in. Light NE winds.

Thursday Night...Moderate confidence.

IFR/LIFR ceilings with IFR/MVFR visbys. FZRA and RA expected
across the region, moving in from SW to NE starting in the
evening hours. NE winds pick up slightly to be around 6-12 kt
sustained with occasional gusts to 20 kt possible in higher
elevations and towards the Cape/Islands. 

KBOS Terminal...Moderate confidence in TAF. Main uncertainty is
timing of category improvments tomorrow. Confidence in any
seabreeze for the rest of this afternoon is very low.

KBDL Terminal...Moderate confidence in TAF. Main uncertainty is
timing of category improvements tomorrow.

Outlook /Friday through Monday/...

Friday: MVFR/IFR conditions possible. Breezy. Chance RA, chance
FZRA.

Friday Night: MVFR/IFR conditions possible. Slight chance RA.

Saturday: Mainly VFR, with areas IFR possible. Breezy. Slight
chance RA.

Saturday Night: Mainly VFR, with local IFR possible. Breezy.
Chance RA.

Sunday: VFR. Breezy. Slight chance RA.

Sunday Night: VFR. 

Monday: 

&&

.MARINE...
Forecaster Confidence Levels...

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

Through Thursday Night...High confidence.

Lingering southerly swell will result in small craft seas lingering 
across our southern waters into the first half of the evening before 
dropping below criteria. High pressure tonight will keep 
sustained winds generally 10 knots or less. Low pressure 
approaching from the west will allow NE winds to increase to 
between 10 and 20 knots on Thu. Wintry mix moves over the waters
for Thursday night and seas in the northern waters begin
building again heading into Friday morning. NE winds 10-20 kt
continue through Thursday night with occasional gusts to 25 kt.
Small craft advisories may be needed then.

Outlook /Friday through Monday/...

Friday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of rough seas. Chance of rain. 

Friday Night: Winds less than 25 kt. Areas of rough seas. 

Saturday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of rough seas. 

Saturday Night: Moderate risk for Small Craft Advisory winds
with local gusts up to 30 kt. Areas of rough seas. Chance of
rain, isolated thunderstorms. 

Sunday: Winds less than 25 kt. Seas up to 5 ft. Slight chance
of rain. 

Sunday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of rain. 

Monday: Winds less than 25 kt. Areas of seas approaching 5 ft. 

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Winter Weather Advisory from 5 PM Thursday to noon EST Friday 
     for CTZ002>004.
MA...Winter Weather Advisory from 5 PM Thursday to noon EST Friday 
     for MAZ002>015-026.
RI...Winter Weather Advisory from 5 PM Thursday to noon EST Friday 
     for RIZ001-003.
MARINE...Small Craft Advisory until 10 PM EST this evening for 
     ANZ254>256.

&&

$$

DISCUSSION...Loconto/Hrencecin
AVIATION...Loconto/Hrencecin
MARINE...Loconto/Hrencecin