Lexington Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 151744
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
144 PM EDT Sun Mar 15 2026

.WHAT HAS CHANGED...

A Wind Advisory was issued for the portion of Southern New England 
not within the High Wind Watch. The Storm Watch has been converted 
to a Storm Warning for all waters. A Flood Watch has been issued for 
the potential of some minor river and stream flooding as well as 
localized poor drainage flooding in urban areas. 

&&

.KEY MESSAGES...

- Periods of heavy rain with embedded t-storms Monday,
  especially Monday night, may lead to some river and small 
  stream flooding. Poor drainage in urban areas could flood as 
  well.

- A period of strong to damaging winds expected across portions
  of SNE Monday night. 

- Mainly dry and trending colder Tue into Wed, then moderating 
  temperatures Thu and especially Fri.

- Period of showers possible sometime Fri night and/or Sat with
  a trend to drier/chillier weather Sun or Sun night.

&&

.DISCUSSION...

KEY MESSAGE 1...Periods of heavy rain with embedded t-storms Monday, 
especially Monday night, may lead to some river and small stream 
flooding. Poor drainage in urban areas could flood as well.

The upcoming storm system will pose two hazards for southern New 
England, the first of which we'll address is potential for heavy 
rain, flooding, and some embedded thunderstorms. A deepening low 
pressure system crossing the Great Lakes on Monday will direct a 
plume of deep moisture out ahead of it while strong dynamics both at 
the surface and in the middle/upper atmosphere will together bring a 
prolonged period of rain, heavy at times. As the warm front lifts 
north on Monday SNE will be placed in the warm sector featuring 
temperatures as warm as the low 60s and dewpoints well into the 
upper 50s! Warm advection showers will begin to overspread the 
region in the pre dawn hours on Monday. The environment is conducive 
to widespread light to moderate rain with embedded convective 
elements given 200-500 J/kg of elevated MUCAPE. These would 
contribute to localized heavy downpours as well as thunder. It 
should feel like a true Spring day, especially in those locations 
that make it into the 60s. Rainfall continues through the day and 
overnight hours, coming to a head with a potential fine line of 
convection (depicted in most hi-res guidance) ahead of the cold 
front which moves through between midnight and 5am. Anomalous 
moisture content in the atmosphere (PWATs near 1.5" or 3-4 SD above 
normal) combined with similarly anomolous jet dynamics (80-90kts at 
925mb) will squeeze out a good soaking of rain, widespread 2" likely 
with as much as 3+" possible under any soaking t-storms. A Flood 
Watch has been issued for the area, given recent snowmelt combined 
with a decent rainfall will likely lead to rises to minor flood 
stage on some rivers and streams as early as Tuesday morning. Can't 
rule out some localized poor drainage flooding under t-storms as 
well. 

KEY MESSAGE 2...A period of strong to damaging winds expected across 
portions of SNE Monday night. 

The other (and likely more impactful) threat from this storm system 
is that those impressive jet dynamics make their way to the surface 
as damaging wind gusts during a ~6 hour window Monday night with the 
passage of the cold front. As mentioned above, the wind will be 
screaming just overhead with some guidance indicating as much as 80-
90 kts at 925mb between 03 and 09Z. The difficulty, as is usually 
the case with southerly flow events like this, is that we'll have a 
stout inversion in place to about 950mb which will have to be 
overcome to bring the strongest of those winds down. This will 
depend heavily on just how warm temperatures get late Monday. 
Regardless, winds will ramp up on Monday gusting 35-45 mph. The best 
shot at the damaging winds comes along and ahead of the cold front, 
especially if that fine line of convection forms and can help to 
drag the strongest gusts down. A High Wind Warning is in effect for 
RI and eastern MA which has the best shot at a ~3 window in any 
given location for damaging gusts of 60-70 mph. Best case scenario 
if we don't reach these speeds, gusts of 45 to 55 mph are likely so 
Wind Advisories have been issued for the rest of the region.

KEY MESSAGE 3...Mainly dry and trending colder Tue into Wed, then 
moderating temperatures Thu and especially Fri.

Strong cold air advection aloft works into the region Tue morning 
behind the cold frontal passage. This will be offset somewhat by some 
mid March sunshine...although we do expect some diurnal CU too in 
especially across the interior and can not rule out a passing brief 
spot flurry/snow shower. Tue afternoon temps will mainly be in the 
lower to middle 40s in the lower elevations with 30s in the higher 
terrain. It will also be blustery with westerly wind gusts on the 
order of 25 to 35 mph...so it will feel colder. The cold air peaks 
Tue night into Wed with 850T dropping to between -15C to -18C. This 
is a decent shot of cold air for the second half of March. Low temps 
Tue night will bottom out in mainly in the teens with a few urban 
centers in the 20-25 degree range. Wind chills early Wed morning 
will be in the single digits to the lower teens! Despite plenty of 
sunshine Wed...Highs will be held mainly in the 30s but with much 
less wind as high pressure builds overhead. 

After a rather cold start early Thu morning...temps will begin to 
moderate as high pressure moves east of the region allowing return 
southwest flow to develop. Highs Thu will still be in the 40s...But 
expect highs to reach into the 50s on Fri ahead of an approaching 
cold front. 

KEY MESSAGE 4...Period of showers possible sometime Fri night and/or 
Sat with a trend to drier/chillier weather Sun into Sun night.

A cold front approaching from the west may bring a period of showers 
sometime Fri night and/or Sat depending on the specific timing. 
Behind this cold front...think things will trend drier and chillier 
sometime Sun or Sun night. Quite the ways out though so this is 
certainly subject to change. 

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...

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

18Z update...

This afternoon...High Confidence

VFR. Winds E/SE 5 to 10 knots.

Tonight...High Confidence

Deteriorating conditions tonight into Monday as a warm front 
lifts north over the region. MVFR/IFR ceilings and visibility 
develop after 05/7Z as light to moderate rain overspreads 
southern New England.

Monday...High Confidence

IFR in expanding RA. Winds increase through the day, shifting 
to become more southerly, gusting 30-35 kts late afternoon and
evening. Scattered TSRA is increasingly likely particularly in 
CT and RI. 

Monday Night...High Confidence. 

Peak of the winds, gusting gusting 40-55kts for several hours. S
winds become more SW and W by 12Z. RA/TSRA possible through
07-12z, ending from west to east. 

KBOS Terminal...High confidence.

KBDL Terminal...High confidence

Outlook /Monday Night through Friday/...

Tuesday: VFR. Windy with gusts up to 35 kt. 

Tuesday Night through Wednesday: VFR. Breezy. 

Wednesday Night through Thursday Night: 

Friday: Slight chance RA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Through Monday Night

Seas calm to 1-3 ft through the day afternoon as high pressure 
settles overhead. Winds today over the waters shift more to the SE 
into the afternoon but remain around 10-15 kt, occasionally gusting 
to 20 kt over the southern waters. Winds ramp back up tonight into 
Monday as a powerful low pressure system approaches from the west. 
Seas increase considerably headed into Monday night, reaching up to 
15 ft and even close to 20 ft in the southern waters by 06z Tuesday. 
Seas 7-10 ft will be more common in the eastern waters. Winds will 
likely approach storm conditions Monday night. Storm Watches have 
been upgraded to Storm Warnings for all waters. 

Outlook /Tuesday through Friday/...

Tuesday: Strong winds with gusts up to 35 kt. Rough seas up to
14 ft. 

Tuesday Night: Moderate risk for Small Craft Advisory winds
with local gusts up to 30 kt. Rough seas up to 12 ft. 

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

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

Thursday through Thursday Night: Winds less than 25 kt. Seas
locally approaching 5 ft. 

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Flood Watch from late tonight through Tuesday morning for 
     CTZ002>004.
     Wind Advisory from 2 PM Monday to 8 AM EDT Tuesday for 
     CTZ002>004.
MA...Flood Watch from late tonight through Tuesday morning for 
     MAZ002>022-026.
     Wind Advisory from 2 PM Monday to 8 AM EDT Tuesday for 
     MAZ002>004-008>012-026.
     High Wind Watch from Monday afternoon through late Monday 
     night for MAZ005>007-013>024.
RI...Flood Watch from late tonight through Tuesday morning for 
     RIZ001>007.
     High Wind Watch from Monday afternoon through late Monday 
     night for RIZ001>008.
MARINE...Storm Warning from 8 PM Monday to 5 AM EDT Tuesday for ANZ230-
     236.
     Storm Warning from 5 PM Monday to 8 AM EDT Tuesday for 
     ANZ231>235-237-250-251-254>256.

&&

$$

DISCUSSION...Frank/BW
AVIATION...Frank/BW
MARINE...Frank/BW