Lexington Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 141918
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
318 PM EDT Wed Oct 14 2026

.WHAT HAS CHANGED...
Gale Watches have been issued for all waters due to the potential 
for strong post-frontal northwest wind gusts Friday evening through 
Saturday.

&&

.KEY MESSAGES...

- Isolated shower possible this afternoon, but otherwise mainly
  dry and warm. Dry Thursday with seasonably cool temperatures.
  
- Fast-moving system to bring periods of rain Friday, followed 
  by drier and much colder conditions Saturday.

- Quiet and seasonable weather Sunday through Tuesday.

&&

.DISCUSSION...
KEY MESSAGE 1...Isolated shower possible this afternoon, but 
otherwise mainly dry and warm. Dry Thursday with seasonably cool 
temperatures. 

For the rest of the afternoon, expect dry conditions overall with 
the exception of an isolated shower through the evening. Tonight 
will be dry with mainly clear skies with temperatures falling into 
the 40s. Cooler air advects in from the north overnight while 
surface high pressure shifts eastward into the region. The tightened 
pressure gradient along with steeper lapse rates should support some 
mixing to bring down gusts around 20 kts, perhaps a little stronger 
for the Cape where the gradient is tighter. 

Surface high pressure settles over southern New England on Thursday. 
 As it builds in, the pressure gradient will relax, allowing winds 
to decrease through the morning. Large scale subsidence will 
maintain dry conditions alongside light northerly flow. A cooler 
airmass will be in place characterized by 925mb temperatures +6-
8(approx 10C cooler than Wed). This will bring a seasonably cool day 
with high temperatures in the upper 50s and low 60s.  

KEY MESSAGE 2...Fast-moving system to bring periods of rain Friday,
followed by drier and much colder conditions Saturday.

Forecast trends continue to indicate a rather soggy end to the week. 
The good news is that this is a fairly progressive system, with rain 
clearing out in time for the weekend. High pressure drifts east and 
offshore overnight into early Friday. Meanwhile, to our west, a low 
pressure system develops across the eastern Great Lakes and deepens 
as it travels northeast through the Saint Lawrence Valley. The low 
is expected to deepen by roughly 10 to 15 mb within 24 hours, 
reaching around 995 mb by late Friday evening. Out ahead of the low, 
a warm front brings an initial band of rain to southern New England 
during the early morning hours Friday, beginning during the predawn 
hours and spreading from west to east. There is the potential for a 
lull in activity between late morning and early afternoon. While in 
the warm sector, anticipate mild, muggy, and breezy conditions with 
south-southwesterly winds. A second round of showers, with the 
potential for thunder, is expected late Friday afternoon through the 
evening with the passage of a strong cold front. Drier and cooler 
conditions follow beginning Saturday morning.

In terms of precipitation, PWATs are quite elevated for mid-October, 
with values ranging between 1.5 and 1.8 inches, roughly 2 to 3 
standard deviations above normal. Locally heavy downpours are 
possible, though the flooding threat is minimal considering the 
progressive nature of the system. As mentioned, warm frontal showers 
are expected during the predawn hours Friday. There will be less 
lift during the daytime; however, spotty showers may continue due to 
ongoing WAA. As the surface low tracks closer to Quebec City, a cold 
front brings strong forcing during the late afternoon and evening, 
with a final round of showers and embedded thunderstorms. While we 
do not anticipate widespread severe weather, there is a fair amount 
of bulk shear, ranging from 50 to 80 knots, and MUCAPE values around 
500 J/kg. It could be one of those days where the higher shear 
compensates for the relatively limited instability. This is 
something we will continue to monitor. As for rainfall amounts, 
there is still a bit of spread among the guidance, though consensus 
is leaning toward 0.3 to 0.8 inches. That being said, locally higher 
amounts are possible, with the greatest potential for more than an 
inch of rainfall across northwestern Massachusetts, where DESI 
probabilities are 15 to 25 percent.

As mentioned, it will be breezy on Friday, with a 30 to 40 knot low-
level jet. However, the low-level thermal inversion will play a 
significant role in determining how much of that wind can mix down 
to the surface. Given a neutral inversion, did not want to mix the 
full strength of the low-level jet to the ground. Therefore, gusts 
of 25 to 35 mph on Friday seem the most reasonable. Behind the 
front, strong CAA aloft sends 850 mb temperatures falling from +17C 
on Friday to -5C on Saturday. With steep low-level lapse rates, 
there will be efficient mixing through the lower levels. Gusts 
Saturday afternoon may approach 30 to 40 mph. Mixing may be further 
enhanced over the warmer ocean waters; thus, Gale Watches have been 
issued for all waters from Friday evening through Saturday evening. 
While temperatures will be mild on Friday, the bigger story will be 
the cold on Saturday. As mentioned, temperatures aloft will be in 
free fall. Highs will struggle to reach the upper 40s to lower 50s. 
However, when factoring in the wind, it will likely feel as though 
temperatures are in the upper 30s to middle 40s Saturday afternoon. 
Saturday night will be quite cold, with many areas falling into the 
lower 30s and upper 20s. Thus, frost is possible, though lingering 
breezy conditions may limit its development. Nevertheless, our 
frost/freeze program has ended for the growing season as of October 
11, and no frost or freeze headlines will be issued.


KEY MESSAGE 3...Quiet and seasonable weather Sunday through 
Tuesday.

A broad area of high pressure builds into the region Sunday through 
Tuesday, leading to a period of quiet and dry weather. The stronger 
winds from Saturday diminish on Sunday as the pressure gradient 
relaxes with the return of high pressure. During this time, 
temperatures begin to moderate and return to more seasonable levels, 
with highs in the upper 50s to lower 60s and overnight lows ranging 
from the upper 30s to middle 40s.


&&

.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:

Today: High confidence. 

VFR with SCT to BKN decks between 035-150. Isolated light
SHRA/sprinkle possible through 23z as showers moves west to east.
Coverage is very limited with little hitting the ground so threw
in as a VCSH for the east terminals. Winds WNW this afternoon 
at 8-15 kts. Gusts 20-25 kts. Gusts diminish after 21Z. Although
a few lighter gusts up to 20 kts may linger for the Cape 
terminals. Winds shift to the NW this evening.

Tonight: High confidence. 

VFR. Gusts 20-25 kt for most developing 02-04Z; 20-25 kt gusts,
highest for the Cape and Island terminals.  

Thursday...High confidence.

VFR. Winds diminish 12-15Z for most terminals with high 
pressure settling overhead. Gusts around 18kts may linger
through 16/17Z for HYA/ACK. Winds NNW shifting to the N at 5-10
kts. Winds may shift around to the NE-E in the afternoon/early
eve for the coastal terminals. 



KBOS Terminal...High confidence in TAF. 
Chance of an isolated shower or sprinkle mainly between 18-21Z.
It's likely that little hits the ground.


KBDL Terminal...High confidence in TAF.

Outlook /Thursday Night through Monday/...

Friday: MVFR/IFR conditions possible. Windy with areas of gusts
up to 30 kt. SHRA, patchy BR.

Friday Night: Mainly VFR, with local IFR possible. Windy with
gusts up to 35 kt. SHRA, patchy BR.

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

Saturday Night through Sunday: VFR. Breezy. 

Sunday Night: VFR. 

Monday: VFR. Breezy. 

&&

.MARINE...
Forecaster Confidence Levels...

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

Small craft advisories were extended and/or hoisted for tonight
for the eastern waters into 18z Thursday as a period of enhanced
NW gusts of 25-30 kt are expected to develop early tonight. Seas
around 3-5 ft on most waters through Thursday, with dry weather
and good visibility expected. Gusts should subside below SCA
criterion by Thursday night.

A frontal system brings returning SW winds into the SCA range on
Friday (25-30 kt), which will also bring periods of light to
moderate rain reducing visibility through Friday early evening.
A short period of small craft advisories will likely be needed 
once the existing SCAs expiring Thursday afternoon expire.

Looking ahead into Friday night and into Saturday...a period of
strong northwest winds are forecast. We've issued a Gale Watch 
on most waters for Friday night into Saturday, with seas 
becoming increasingly rough at up to 12 ft. Dry weather is 
expected by Saturday.

Outlook /Thursday Night through Monday/...

Friday: Moderate risk for Small Craft Advisory winds with gusts
up to 30 kt. Areas of rough seas. Rain showers, patchy fog. 

Friday Night: Strong winds with gusts up to 35 kt. Rough seas
up to 12 ft. Rain showers likely. 

Saturday: Strong winds with gusts up to 35 kt. Rough seas up to
12 ft. Chance of rain showers. 

Saturday Night: Strong winds with local gusts up to 30 kt.
Rough seas up to 11 ft. 

Sunday: Winds less than 25 kt. Local rough seas. 

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

Monday: Winds less than 25 kt. 

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 8 PM this evening to 2 PM EDT 
     Thursday for ANZ230>234-250-251.
     Gale Watch from Friday evening through Saturday evening for 
     ANZ230>237-250-251-254>256-280>283.
     Small Craft Advisory until 2 PM EDT Thursday for ANZ254-255.
     Small Craft Advisory until 8 PM EDT this evening for ANZ256.

&&

$$

DISCUSSION...Dooley/Mensch
AVIATION...Dooley/Mensch
MARINE...Loconto/Dooley/Mensch