Lexington Weather

Lexington, Massachusetts, USA

46°F

4/18/2024 7:55am

Lexington Conditions: Overcast
Temperature: 45.9°F / 7.7°C
Dew Point: 36.7°F
Relative Humidity: 70%
Wind: Calm, 10-min avg: Calm, gust: None
Barometer: 30.12 in Rising Slowly
Visibility: 10 miles
Rain Today: 0.00 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 121945
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
345 PM EDT Fri Apr 12 2024

.SYNOPSIS...
An occluded front will sweep across the region late this
afternoon and evening, accompanied by a wind shift to the
southwest along with drier and cooler air. The front will be
accompanied by scattered showers, especially in CT and western-
central MA. It will remain mostly cloudy tonight and Saturday,
along with turning seasonably cool. Sunday is largely dry and  
comfortable, a quick moving system does bring showers late 
Sunday and exits before sunrise on Monday. Early next week 
features dry and above normal temperatures. Mid to late next 
week the forecast becomes unsettled with rain chances. 

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...

345 PM update:

Occluded front moving into southwest CT at 330 pm. This feature
is accompanied by a cluster of showers moving SW to NE thru CT
and into western-central MA. Showers will be much less numerous
in RI and eastern MA late this afternoon/early evening. Despite
western MA being in a marginal risk from SPC, current thinking
is the limited instability will preclude any storms from forming
and any thunderstorms confined to much farther north across VT
and upstate NY, north of Albany. 

The front will also be accompanied by a wind shift from SSE to 
the SW, ushering in drier and cooler air. In fact, the core of 
the cold air aloft (-26C at 500 mb) advects across SNE between 
06z-09z. This could trigger an isolated shower overnight, 
otherwise mainly dry weather prevails in the post frontal 
airmass. Despite the cold air aloft, lows only dip into the 40s 
overnight, about 10 degs above normal. Dew pts only drop into 
the 40s as well, also above normal for mid April, but there 
should be sufficient wind/mixing to preclude any fog. Hence, 
remaining breezy behind the front, with SW winds 15-25 mph. 

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...

345 PM update:

Saturday:

Good mixing via WSW winds 15-25 mph, gusting up to 30 mph along
the south coast including Cape Cod and the Islands. This
promotes drier air aloft to mix to the surface, with dew pts
falling into the 30s. Cyclonic flow will yield lots of clouds,
mostly cloudy the likely scenario. Best chance for sunny breaks
will be over southeast MA, including Cape Cod and Islands. Temps
begin to warm aloft during the day, this should limit
instability shower coverage to isolated, hence a mostly dry 
day. The exception will be across western MA, where upslope flow
over the Berkshires will yield more numerous showers for 
western MA. 

Temps seasonable Saturday, with highs in the mid to upper 50s.
Although, there will be a cool breeze as noted above, from the
WSW 15-25 mph, higher gusts south coast MA/RI. 

Saturday night...

Short wave ridging and warming temps aloft will promote
decreasing cloudiness. Thus, dry weather prevails. Gusty west
winds 15-25 mph during the evening, slowly slacken overnight.
Seasonably cool with lows in the upper 30s and lower 40s. 

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...

345 PM update...

Highlights: 

* Dry for much of Sunday, but a quick moving system will bring 
  showers late evening and wrapping up predawn Monday. 

* Early next week, Monday and Tuesday, features dry conditions and 
  above normal temperatures.

* Unsettled conditions return to the region by mid/late next week.  

Sunday and Sunday Night - Brief mid-level ridging and surface high 
pressure noses north, leading to an all around a nice day with 
sunshine during the first-half of the day, but increasing cloud 
cover during the afternoon ahead of a fast moving low pressure 
system coming out of the northern Great Lakes. Afternoon 
temperatures are pretty comfortable, 850mb temperatures are +2C to 
+5C, with a well mixed boundary layer, expect highs in the upper-50s 
to lower-60s. Winds do increase during the afternoon as well due to 
a quick moving 925mb LLJ, while the core is primarily over southern 
Rhode Island and southeastern Massachusetts, southwest gusts are in 
the range of 20 and 30 MPH, interior winds are generally around 15 
to 20 MPH. Most if not all of the daylight hours remain dry, it is 
not until the late afternoon/early evening we introduce POPs across 
far western zones. PWATs are fairly healthy around 0.8 and 1.1 inch, 
the best forcing does remain north across northern New England. Do 
think there will be terrain enhancement for the Berkshires, leading 
to little more in the way of rainfall overnight. With some MUCAPE 
don't be surprised if there are some rumbles of thunder - SPC does 
have areas west of Hartford and Springfield under general thunder in 
its day three outlook. Surface low pressure system is progressive 
and exits east of the coastal waters before dawn on Monday. QPF is 
less than a tenth of an inch across much of the CWA, with slightly 
higher values for the eastern slopes of the Berkshires where two 
tenths of an inch is possible. 

Monday - Low pressure system races east of the coastal waters with a 
drier air mass aloft moving into the region. Clouds to start, though 
expect morning clouds gives way to a mostly sunny Patriots Day. Made 
an adjustment to sky cover, as NBM held onto higher values of sky 
cover despite the mid-levels drying. Also lowered wind gusts due to 
the high bias NBM, had gusts 20 to 25 knots. BUFKIT showed winds at 
the top of the boundary layer generally between 12 and 17 knots, did 
blend in the CONSALL guidance to temper those gusts down. Northwest 
winds 10 mph with occasional gusts 15 to 20 mph. With the winds at 
the top of the boundary layer greater than 10 knots, the threat for 
a sea breeze at Boston remains low. Temperatures climb once again 
into the 60s, perhaps reaching the 70 degree mark due to the dry 
atmosphere and pre-greenup conditions, recipe to have over 
performing temperatures. 

Tuesday - Another stunning day thanks to surface high pressure to 
the south and mid-level ridging aloft. Do think our conditions will 
be similar to Monday, though slightly more of a WNW breeze. Mostly 
sunny conditions and highs in the 60s to near 70 degrees. As 
mentioned on Monday, this pre-greenup period and dry atmosphere 
could allow the highs to sneak up into the lower-70s.

Wednesday and Thursday - This period does look unsettled as the 
global models have a developing surface low pressure system in the 
central plains on Tuesday that races towards the Great Lakes. 
Perhaps a warm front develops with showers on Wednesday with a 
trailing cold front on Thursday. Still a lot of time between now and 
then. Have run with POPs of Chance due to the uncertainty at this 
point in time. 

&&

.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:

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

18Z TAF Update...

Thru 00z...high confidence on trends, lower on exact timing of
details.

At 18z, occluded front from NYC area northwest into NY state is
accompanied by a wind shift from SSE to SW and cigs improving
from IFR/LIFR to MVFR/VFR. This will overspread SNE between
19z-20z across western CT/MA, then arriving into eastern MA
22z-23z. Shower activity with this front should be confined to
CT and western-central MA. Mainly dry weather prevails across RI
into eastern MA. Pre and post frontal winds will gusts up to 30
kt. 

After 00z: High confidence on trends, lower on exact timing of
details.

VFR cloud bases and mainly dry, but MVFR with scattered showers
across western MA. SSW winds 15-25 KT. 

Saturday: High confidence.

VFR cloud bases with just a few isolated showers possible.
However, MVFR with scattered showers across western MA. SW winds
15-25 kt, gusts up to 30 kt south coast, including Cape Cod and
Islands. 

Saturday night: high confidence. 

VFR, except MVFR early across western MA. West winds 15-25 kt
slowly diminishing toward Sunday morning. Dry weather prevails. 

KBOS TAF...High confidence in TAF trends, but lower on exact
timing. Frontal passage/wind shift and improving to MVFR/VFR
approximately 22z-23z. Pre and post frontal winds gusting up to
30 KT at times. 

KBDL TAF...High confidence in TAF trends, but lower on exact
timing.  Frontal passage/wind shift and improving to MVFR/VFR
approximately around 20z. Pre and post frontal winds gusting up
to 30 KT at times. Showers til about 20z-21z. 

Outlook /Sunday through Wednesday/... 

Sunday: VFR. Breezy. Slight chance SHRA.

Sunday Night: Mainly VFR, with local MVFR possible. Breezy.
Chance SHRA.

Monday through Monday Night: VFR. 

Tuesday: VFR. Breezy. 

Tuesday Night: VFR. 

Wednesday: VFR. Chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

345 PM update:

Tonight...

Frontal passage this evening, shifting winds from SSE to SSW.
Similar speeds pre and post frontal, 15-25 kt, gusting up to 30
kt at times. A few showers possible this evening, the dry. Vsby
improves with the wind shift. 

Saturday...

Mainly dry weather and good vsby. WSW winds 15-25 kt, up to 30
kt across the southern MA/RI waters. 

Saturday night...

Dry weather continues with winds becoming more westerly and
slowly diminishing overnight, from 15-25 kt in the evening to
10-20 toward daybreak Sunday. 

Outlook /Sunday through Wednesday/... 

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

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

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

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

Tuesday through Tuesday Night: Winds less than 25 kt. 

Wednesday: Winds less than 25 kt. Chance of rain showers. 

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ230-
     236.
     Small Craft Advisory until 8 AM EDT Sunday for ANZ231>235-237-
     250-251-254>256.

&&

$$

SYNOPSIS...Nocera/Dooley
NEAR TERM...Nocera
SHORT TERM...Nocera
LONG TERM...Dooley
AVIATION...Nocera/Dooley
MARINE...Nocera/Dooley