Lexington Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 051951
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
251 PM EST Thu Mar 5 2026

.WHAT HAS CHANGED...
Snowfall amounts across NE MA were increased slightly. Otherwise, no 
significant changes to the forecast..

&&

.KEY MESSAGES...

- Rain ongoing today will transition to sleet and freezing rain
  across the higher terrain heading into the evening hours,
  along with areas north of I-90. Precipitation expected to last
  through Friday morning. Greatest risk for 0.25"+ ice accretion
  remains in the high terrain of the southern Worcester Hills
  and southern Berkshires. Plowable snow more likely in far NE
  MA. Lingering drizzle as precip tapers off Fri afternoon.

- Turning milder with a warming trend this weekend and
  increasing risk for showers Sat night into early Sun as a cold
  front approaches.

- Potential for a few days of unseasonably mild conditions next
  week but have to watch a backdoor front to the north which
  would bring much cooler temps. Accelerated snowmelt will lead
  to steady rises on rivers and streams through the week. A
  period of showers accompany a cold front late Wed-Thu, then
  turning cooler towards the end of the week.

&&

.DISCUSSION...
KEY MESSAGE 1...Rain ongoing today will transition to sleet and 
freezing rain across the higher terrain heading into the evening 
hours, along with areas north of I-90. Precipitation expected to 
last through Friday morning. Greatest risk for 0.25"+ ice accretion 
remains in the high terrain of the southern Worcester Hills and 
southern Berkshires. Plowable snow more likely in far NE MA.

A low from the west will continue tracking towards the south coast 
today into tonight, bringing with it a mix of rain, snow, sleet, and 
freezing rain.

Rain is making its way through southern New England at this time, 
with rain slowly moving north and east, being somewhat suppressed in 
northern parts of the region by lingering dry air aloft. More rain 
will move in during the evening hours and into tonight where the 
forecast becomes a bit messier, as ptype will transition from mostly 
rain to more sleet and freezing rain. This mix will mostly impact 
areas north of I-90 along with the higher terrain in the southern 
Worcester Hills and Berkshires, where the colder temperatures 
towards the surface resulting from the shallow cold air will allow 
for refreezing of falling precip. As a result, the chances for ice 
accretions reaching 0.25"+ are highest there, which could lead to 
power outages in these areas.

Latest guidance continues to support more of a glaze of ice and 
sleet for northern MA, as 925 mb temperatures remain around -3C 
to -5C, but 850 mb temperatures are closer to and above 0C. 
Latest forecast soundings still have air below freezing 
extending up to around 5000 ft for northern MA for the first 
half of tonight, favoring more sleet. Past midnight, the 
guidance shifts to more snow as the air around 850 mb falls 
below 0C and the column becomes isothermal. Some sleet being
mixed in with this snowfall cannot be completely ruled out. The
latest HREF showed this trend well, favoring more snow for NE 
MA and down into Boston. Snow totals in NE MA could reach up to 
4"; snow and sleet accumulations further south into the Boston 
area could range between 2-3".

Precipitation is expected to taper off heading into the afternoon 
Friday, but light rain/drizzle and some fog will likely stick 
around, especially in the eastern half of southern New England due 
to continued onshore flow. These NE winds will keep the lower level 
moisture in place over the area, leading to a mostly dreary day 
Friday.

KEY MESSAGE 2...Turning milder with a warming trend this weekend and 
increasing risk for showers Sat night into early Sun as a cold front 
approaches.

Surface ridge across New Eng Sat will move offshore with a S-SW flow 
developing in the afternoon. This will bring milder temps than Fri 
but certainly not as mild as 925/850 mb temps would suggest. 
Soundings show a rather strong inversion just off the deck with 
abundant low level moisture so expect lots of clouds with very 
shallow/limited BL mixing. So while it will be milder, the shallow 
cooler air will linger likely holding temps in the low-mid 40s. A 
cold front approaches from the NW Sat night and moves into SNE 
during Sun. A modest pre-frontal LLJ develops which advects higher 
PWATs exceeding 1" into SNE leading to some showers later Sat night 
into Sun morning, but widespread rain not expected. Then it should 
dry out by the afternoon with sunshine developing from NW to SE as 
the column dries out from the north. However, clouds should persist 
along the south coast as the moisture plume lingers here. Still a 
shallow mixed layer Sun but it's drier with westerly flow which 
should help to boost temps into the 50s. 

KEY MESSAGE 3...Potential for a few days of unseasonably mild 
conditions next week but have to watch a backdoor front to the north 
which would bring much cooler temps. Accelerated snowmelt will lead 
to steady rises on rivers and streams through the week. A period of 
showers accompany a cold front late Wed-Thu, then turning cooler 
towards the end of the week.

A quasi-zonal flow sets up across the northern CONUS with a series 
of low amplitude shortwaves moving through the flow. A broad SW flow 
will allow further warming Monday with the potential for 
unseasonably mild to perhaps warm conditions on Tue and Wed. 
However, this is not a certainty as high pres will be across eastern 
Canada with a backdoor front lurking to the north. GFS is trying to 
push the front southward with shallow cool air draining south into 
SNE later Tue into Wed and GEFS overall is leaning on the cooler 
side. Meanwhile ECMWF keeps the front to the north with unseasonably 
mild temps. Interesting that AIGFS is all in on the warmth for Tue-
Wed. We followed the NBM temps which has temps in the 60s away from 
the south coast. Confidence in temps is moderate and warmer temps 
will depend on front remaining to the north. 925 mb temps are pretty 
mild and it's not out of the question we could see a few 70+ 
readings in the CT and Merrimack valley both Tue and Wed if the 
front stays to the north. EC ENS indicate 20-40% prob of 70+ Tue & 
Wed. These warmer temps combined with dewpoints climbing through the 
40s and possibly some 50s by Wed will promote accelerated snowmelt 
with steady rises on rivers and streams. In addition, a period of 
showers will likely accompany a cold front late Wed into Thu. MMEFS 
ensemble guidance from the NAEFS and GEFS indicate a low risk for 
some rivers reaching minor flood next week so we will have to 
monitor this closely. The cold front is expected move through 
sometime Wed night into early Thu followed by cooler and drier 
conditions.

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
Forecaster Confidence Levels...

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

18z TAF Update...

Rest of Today...Moderate confidence.

Widespread MVFR-IFR with localized LIFR conditions expected to 
overspread the region from southwest to northeast as the
afternoon goes on, but mostly VFR north of the MA/RI/CT border 
at this time. Pockets of light rain already impacting CT/RI/SE 
MA. The rain is slowly to advancing north, and some showers are 
already making their way into Middlesex Co. in MA. ORH is 
currently reporting rain as well, but still seeing VFR 
conditions that may deteriorate over the next few hours. The 
rain may also begin to mix with sleet this evening near and 
north. NE winds increasing to between 5 and 15 knots during the 
afternoon with the strongest of those winds near the coast.

Tonight and Friday...Moderate confidence.

IFR/LIFR conditions dominate in freezing rain and sleet in areas
north of I-90 as well as parts of the high terrain tonight. Sleet
will probably be favored over freezing rain to the north of 
I-90 by the mid evening hours. South of I-90 in the lower 
elevation, ptype mainly will be rain but some sleet may be 
mixed in at times. Ptype may mix with or change to snow late 
tonight into Fri morning for northern MA with the greatest risk 
north of route 2 into into northeast MA near the NH border. The
risk for snow has also shifted slightly south into BOS after
midnight. Precipitation tapers to mainly light rain/drizzle by 
Friday afternoon but IFR/LIFR conditions likely persist along 
with areas of fog due to continued onshore flow. NE winds 5 to 
15 knots with some 20-25 knot gusts possible near the coast.

Friday Night...Moderate confidence.

Mostly IFR. Winds weaken, but remain NE. With all the moisture
left behind by the Thu night/Fri system, widespread areas of fog
are a possibility overnight. Low chance for some precip for 
northern and western MA into central CT in the early morning
hours of Saturday.

KBOS Terminal...Moderate confidence in TAF. 

KBDL Terminal...Moderate confidence in TAF.

Outlook /Saturday through Tuesday/...

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

Saturday Night: MVFR/IFR conditions possible. Breezy. Chance
RA.

Sunday: Mainly VFR, with local MVFR possible. Breezy. 

Sunday Night: VFR. 

Monday: VFR. Breezy. 

Monday Night through Tuesday: VFR. 

&&

.MARINE...
Forecaster Confidence Levels...

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

Through Friday Night...High confidence.

Low pressure continues to approach from the west this afternoon
and will pass to our south Friday morning. At the same time, a 
1040+ mb high pressure system will build across Quebec.
Increasing NE winds this afternoon will continue through Friday
before easing up Friday night as high pressure shifts more south.
NE wind gusts of 20 to 30 knots expected this evening will 
continue at times into Friday, so Small Craft Advisories remain
in effect. Seas will also become quite choppy, ranging between
6-8 ft.

Outlook /Saturday through Tuesday/...

Saturday: Winds less than 25 kt. Areas of rough seas. 

Saturday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Rough seas up to 8 ft. Chance of rain. 

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. 

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Winter Weather Advisory until noon EST Friday for CTZ002>004.
MA...Winter Weather Advisory until noon EST Friday for MAZ002>015-
     026.
RI...Winter Weather Advisory until noon EST Friday for RIZ001-003.
MARINE...Small Craft Advisory until 7 PM EST Friday for ANZ231>235-237-
     254>256.
     Small Craft Advisory until 7 PM EST Friday for ANZ250-251.

&&

$$

DISCUSSION...KJC/Hrencecin
AVIATION...KJC/Hrencecin
MARINE...KJC/Hrencecin