Lexington Weather

Lexington, Massachusetts, USA

46°F
3/28/2024 4:32am 
  • Lexington Conditions: Rain, Mist, Overcast
  • Temperature: 46.0°F / 7.8°C 
  • Dew Point: 44.4°FIncreased 0.3°Fsince last hour.
  • Relative Humidity: 94%Increased 1.0% since last hour.
  • Wind: Calm, 10-min avg: Calm, gust: None
  • Barometer: 29.98 in Steady
  • Visibility: 2½ miles
  • Rain Today: 0.04 in
  •   

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 211952
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
352 PM EDT Thu Mar 21 2024

.SYNOPSIS...
Gusty winds diminish overnight leading to a dry/sunny day
Friday. Though southern New England is located between two 
pressure systems and will experience strong west/northwest gusts
through this evening, before diminishing on Friday. A more 
active weather pattern then evolves for Friday night into the 
weekend. A strong frontal system may bring the risk for minor 
accumulating snow in the interior late Friday night, but 
transition to widespread soaking rain Saturday into Saturday 
evening, capable of poor drainage flooding and rises on rivers 
and streams. Drying out Sunday into early next week but 
temperatures will average below normal with persistent onshore 
flow.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

Tonight

Gusty westerly winds from this afternoon remain elevated tonight, 
but weaken slightly in response to a slight weakening in the 
pressure gradient. We should still experience steady westerly winds 
from 10 to 20 mph with gusts up to 30 mph possible at times. Despite 
clear skies overnight, radiational cooling will be limited 
thanks to mechanical mixing. Nonetheless, overnight lows will 
still be substantially below normal and cooler than last night 
with most locations in the upper teens/low 20s just before 
sunrise. Coastal areas will be slightly more mild in the mid 
20s. For reference, the average low temperature for Boston for 
this time of year is about 32 degrees. This is consistent with 
an anomaly of about 10 degrees below normal. 

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...

Tomorrow

Surface high pressure builds over southern New England tomorrow 
bringing an end to the period of gusty westerly winds. There still 
remains a modest pressure gradient in place however, so steady 
westerly winds are still forecast but with more modest speeds in the 
5 to 10 mph range. This should be enough to support diurnal mixing 
during the afternoon. Mixing -5 Celsius temps at 925 hPa down to the 
surface would translate to surface high temps in the low to mid 40s 
F tomorrow afternoon. Overall a quiet/sunny day and very dry with 
single digit to negative single digit dewpoints. Despite excessive 
dry air, winds are not looking strong enough to raise fire weather 
concerns at this time. 

Tomorrow Night

Cloud cover increases tomorrow night ahead of a robust low-pressure 
system that is forecast to bring significant precipitation to 
southern New England. Precipitation will begin after midnight 
tomorrow night as a surface warm front associated with the low-
pressure center over western New York begins to lift north over the 
region. Antecedent conditions ahead of the warm frontal boundary 
will be favorable to support a brief period of snowfall or perhaps 
freezing rain at the onset of precipitation, which will be during 
the very early hours of Saturday. Icing would be limited to trace 
amounts at this time and be focused over the CT River Valley and The 
Berkshires. Temperature profile only looks supportive of snow for 
the areas along and north of I-90 where a dusting to an inch of 
accumulating snow may be possible before a quick changeover to rain. 
Winds will gradually strengthen out of the south reaching speeds of 
10 to 20 mph Saturday morning. The bulk of the precipitation and 
duration of the storm will take place during the day Friday. See the 
long term section of the AFD for more details. 

&&

.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
Highlights: 

* Minor snow accum possible late Fri night into early Sat in 
  the interior

* Widespread rain, heavy at times Sat into Sat evening capable of 
  minor urban and poor drainage flooding and some river flooding

* Trending drier for Sun into early next week, but blustery with 
  below normal temps

Friday Night into Saturday Night... 

Potent northern stream trough moves into New Eng with enough 
interaction with southern branch to bring a plume of anomalous PWATs 
northward into SNE. Meanwhile southern stream low pres is forecast 
to lift northward along the mid Atlc coast Sat then track south and 
east of Nantucket Sat night. Inverted trough extending north from 
the low pres combined with coupled upper level jet structure will 
result in strong forcing for ascent, acting on anomalous moisture to 
bring heavy rainfall to SNE Sat into Sat evening. 

Initial warm advection and deepening moisture ahead of the 
approaching mid level trough will result in precip developing from 
west to east mainly after midnight Fri night. The column is cold 
enough to support a few hours of snow north and west of I-95 
corridor where a coating to one half inch is possible before snow 
changes to rain. Snow will persist longer further in the interior, 
with 1-3 inches possible north of the Route 2 corridor in far 
northern MA, especially over the higher terrain. Snow will change to 
rain here Sat morning and there could also be a period of freezing 
rain during the snow to rain transition. 

The bigger impact from this storm will be the heavy rainfall during 
Sat into Sat evening which will be focused along and to the west of 
the surface boundary/inverted trough. The heaviest rain will 
initially be focused across the interior during Sat but shift to the 
SE New Eng late Sat and especially Sat evening as low pres tracks 
south of Nantucket. Deterministic and ensemble guidance suggesting 
potential for 1.5 to 3 inches of rainfall. However, where this axis 
of heaviest rainfall sets up remains uncertain. GEFS and CMC 
ensemble probs of 2+ inches favor areas south of the MA Pike while 
ECMWF ensembles have heaviest rainfall in the interior. Still need 
to iron out these details but the heavy rainfall may lead to areas 
of minor urban and poor drainage flooding. In addition, MMEFS 
probabilistic hydrographs based on the GEFS are indicating high 
probs (70-80 percent) of minor flood for the Pawtuxet and Wood River 
basins in RI, with 30-40 percent probs of moderate flood. 

Rain will be ending from west to east Sat night as colder air begins 
to move back into the region. If cold air comes in quicker it is 
possible rain could change to a period of snow before ending, mainly 
interior where some minor accum are possible. But this is a low 
confidence forecast at this time.

Regarding potential for coastal flooding Sat, it is looking like a 
rather low risk at this time. Along the south coast, the tide in 
question is the Sat evening high tide. Providence would need a 2.5 
ft surge to reach minor flood, and we are currently forecasting a 1-
2 ft surge. No concern along the E coast for the Sat and Sat night 
high tides.

Sunday into Wednesday...

Deterministic guidance continues to trend drier for Sun into early 
next week as ocean storm remains well offshore with high pres 
building to the north. However, ensemble guidance still showing low 
probs for measurable QPF across SE New Eng Sun-Mon so we continued 
low pops in the grids. Still a chance that a piece of moisture could 
wrap around the low pres and back in across SE New Eng sometime Mon 
or Tue so will have to watch this. The shower chances increase again 
toward midweek as a shortwave approaches from the west. Persistent 
onshore flow will keep temps below normal. 

Not expecting any coastal flooding issues for the east coast Sun 
into early next week as forecast surge is much less than what is 
needed to reach minor flood.

&&

.AVIATION /20Z THURSDAY THROUGH TUESDAY/...
Forecast Confidence Levels:

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

Through 00Z...High confidence

VFR with strong W to WNW winds at 15-25 kts. Gusts of 30-40 kts
gradually ease to 25-35 kts by this evening.

Tonight...High confidence.
 
VFR with winds out of the WNW to NW at 10-20 kts, with gusts of
20-30 kts for most of the night. Anticipate that the gusty winds
cease by roughly 08-12Z. 

Friday... High confidence. 

VFR with NW winds at 5-10 kts shifting to the W by late morning.
Should continue to shift to the SW by the afternoon. Increasing
mid/high clouds during the afternoon.

Friday Night...High confidence in trends, moderate in exact
timing.

VFR to start, but will have conditions deteriorate as
precipitation spreads in. Should see MVFR to IFR after 06Z with
light snow to start for most. Will stay as snow across the
higher terrain, but transition over to all rain elsewhere fairly
quickly. 

KBOS TAF... High confidence in TAF. 

VFR with WNW winds at 20-25 kts through the day and winds
gusting 35 kts. Should ease tonight, but still will be gusty 
until the Fri AM push. Winds shift to the SW Fri afternoon.

KBDL TAF...High confidence in TAF. 

VFR with WNW/NW winds 15-20 kts and gusts 30 kts through the 
day. Winds ease tonight, but still remain gusty until the Fri AM
push. Winds shift to the W/SW Fri afternoon.

Outlook /Friday Night through Tuesday/...

Saturday: Mainly IFR, with areas MVFR possible. Windy with
gusts up to 35 kt. RA.

Saturday Night: Mainly VFR, with local IFR possible. Strong
winds with local gusts up to 40 kt. Chance RA, slight chance
SN.

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

Sunday Night: VFR. Strong winds with local gusts up to 40 kt.
Slight chance RA.

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

&&

.MARINE...
Forecaster Confidence Levels:

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

Tonight

Moderate westerly winds continue to blow from 30 to 40 mph this 
evening and tonight but gradually diminish to 20 to 30 mph by 
tomorrow morning. A period of light freezing spray will be possible 
overnight over the easter marine zones where temperatures will be 
very cool in the low to mid 20s. Significant wave heights up to 8 
feet over the outer marine zones should subside to 4 to 6 feet with 
the diminishing winds by day break. Near-shore marine zone wave 
heights subside to 1 to 3 feet. 

Tomorrow

High pressure builds over the coastal waters tomorrow and allows 
winds and seas to continue to diminish and subside to more calm 
levels.

Tomorrow Night

Relatively quiet marine conditions continue overnight, but winds 
begin to strengthen out of the south/southeast a few hours before 
sunrise as a robust low-pressure system approaches the northeast. 
Increasing winds will also be accompanied by gradually rising seas. 
Despite increasing winds and seas, SCY criteria conditions 
should persist until at least late morning/early afternoon 
Saturday.


Outlook /Friday Night through Tuesday/...

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

Friday Night: Winds less than 25 kt. Chance of rain. 

Saturday: Low risk for gale force winds with gusts up to 35 kt.
Areas of rough seas. Rain. Local visibility 1 to 3 nm.

Saturday Night: Moderate risk for gale force winds with gusts
up to 40 kt. Rough seas up to 14 ft. Rain. Areas of visibility
1 to 3 nm.

Sunday: Moderate risk for gale force winds with gusts up to
40 kt. Rough seas up to 14 ft. Slight chance of rain. 

Sunday Night through Monday: Moderate risk for gale force winds
with gusts up to 40 kt. Rough seas up to 13 ft. Slight chance
of rain.

&&

.FIRE WEATHER...
Elevated fire weather concerns today and also potentially into 
Friday. Today offers a combination of gusty NW winds between 35
and 50 mph and lowest RHs around 20-35 percent. In addition, 
rainfall received on Wednesday were less than 0.2 inches.

In collaboration with our neighboring WFOs and state partners, a 
special weather statement for Elevated Fire Weather Concerns goes 
into effect from 11am to 8pm .  

For Friday, NW to W winds are lighter but RHs project to be lower in 
the upper teens to 30 percent range. Will reassess with incoming 
guidance before coordinating with our fire weather partners over the 
coming days.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Wind Advisory until 8 PM EDT this evening for MAZ002-008-009.
RI...None.
MARINE...Gale Warning until 8 PM EDT this evening for ANZ230.
     Gale Warning until 2 AM EDT Friday for ANZ231>235-237-250-251-
     254>256.
     Small Craft Advisory until 2 AM EDT Friday for ANZ236.

&&

$$

SYNOPSIS...KJC/Dooley
NEAR TERM...RM
SHORT TERM...RM
LONG TERM...Belk
AVIATION...Belk/BL
MARINE...Belk/RM
FIRE WEATHER...
      

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