Lexington Weather

Lexington, Massachusetts, USA

55°F

5/11/2024 3:59pm

Lexington Conditions: Mostly cloudy
Temperature: 54.7°F / 12.6°C
Dew Point: 42.3°F
Relative Humidity: 63%
Wind: Calm, 10-min avg: Calm, gust: 2 mph
Barometer: 29.80 in Steady
Visibility: 10 miles
Rain Today: 0.00 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 071049
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
649 AM EDT Tue May 7 2024

.SYNOPSIS...
Warm and dry conditions today with high pressure in control. A 
warm front will bring a round of showers and isolated 
thunderstorms very late tonight and Wednesday, with a low risk 
for a few strong thunderstorms in western MA/CT Wednesday 
afternoon. Unsettled pattern continues for the end of the week 
into the weekend with the risk of occasional showers and cooler
temperatures.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
High pres in control today with subsidence and low PWATs bringing 
abundant sunshine. However, fog and stratus may linger into the 
start of the day for the Cape/Islands before clearing by late 
morning. A warm day in store today as 925 mb temps 16-17C support 
highs mid-upper 70s across much of SNE away from the coast, with a 
few locations in CT valley possibly reaching 80. Light NW flow in 
the boundary layer will allow sea breezes to develop which will keep 
temps in the upper 60s along the immediate coast.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
Tonight...

Deamplifying upper ridge moves E from the Gt Lakes with weak 
shortwave energy spilling into SNE late tonight, while more potent 
trough and shortwave moves into the Gt Lakes. A warm front will 
approach SNE from the SW with low level SW flow increasing moisture 
transport into SNE as PWATs increase to 1-1.50" by 12z Wed. 
Scattered showers may spill into western MA/CT toward daybreak in 
response to the moisture increase. Lows will be mostly in the upper 
40s and lower 50s. Patchy fog and stratus will redevelop over 
Cape/Islands but should remain confined to this area.

Wednesday...

Key points...

* Showers and a few t-storms in the morning
* Low risk for a few strong to severs storms in western MA/CT during 
  the afternoon

Deep moisture plume ahead of the warm front along with increasing 
elevated instability will result in a round of showers moving across 
SNE during the morning, with a few t-storms possible as well. Looks 
like a wet morning, especially interior. Dry slot quickly moves in 
from the west during the afternoon which should yield drying 
conditions, but potent shortwave will be moving into New Eng during 
the afternoon which will result in scattered showers and a few t-
storms developing ahead of the attendant cold front. Much of the 
convection should be elevated but depending on location of warm 
front and how far north and east it gets, surface based convection 
is possible in a portion of SNE, especially western areas where 
HREF highlighting max updrafts. 

Increasing mid level winds will lead to a strongly sheared 
environment with 0-6km shear 50-70 kt, but instability will be a 
limiting factor as not expecting much sunshine. Steepening mid level 
lapse rates will help to generate marginal SB instability with CAPES 
around 500 J/kg. Best chance for a few strong to severe storms will 
be in western MA/CT near the warm front. CSU ML probs and SPC SREF 
highlight this area for a low risk for severe, and NCAR Neural 
Network also indicating low probs for severe. SPC has western half 
of SNE in a marginal risk. Severe risk will be dependent on
sufficient SB instability developing which is uncertain at this
time. 

Temp forecast will be tricky due to the uncertainty in the location 
of the warm front. Best chance of temps reaching 70+ will be in 
western CT with 60s for rest of interior, while upper 50s more 
likely across eastern MA.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Highlights...

* Several disturbances will bring periods of rain Thursday through 
  early next week.

* Timing, strength, and location of these disturbances remain highly 
  uncertain. 

After a nice start to the week weather wise, things begin to take a 
turn off the deep end for the remainder of the week into the 
weekend. An upper level trough begins to deepen on Thursday 
eventually becoming a closed trough and stalling out over the region 
through the weekend. This leaves the region under cyclonic flow 
sending multiple rounds of shortwave energy through the region. 
Deterministic and ensemble guidance remain very spread out and 
confidence in any one model remains low for much of this time 
period. The first round of precipitation looks to come through 
sometime Thursday into Friday as a low pressure center passes nearby 
the region. The GFS shows a wetter and slower moving system with a 
stronger low to the north and a secondary low forming to the south. 
The EURO is more progressive with less QPF and the primary low 
passing just offshore to the south. Meanwhile, the NAM and Canadian 
models have little to no precipitation Thursday with high pressure 
dipping south from Canada pushing the low well offshore to the 
south. Ensembles also remain very spread out which is why 24 hour 
probs for 0.5 inches of rain are less then 50% despite PWATS around 
1.1-1.3 inches and good forcing from the upper level trough. 
Confidence in the forecast drops even further into the weekend as 
guidance continues to struggle with placement and timing of a potent 
surface low ejecting out of the Carolinas before moving north. 
Latest guidance now keeps this low well offshore, however, there has 
been little run to run consistency in this time range and will need 
to be monitored closely.  

The area of the forecast that is more certain is that temperatures 
will be taking a dive off the deep end this week as the cold pool 
from the closed low get stuck over the region. Highs Thursday remain 
the most uncertain as flow becomes onshore, but timing of when 
onshore flow begins is a bit more uncertain. If winds hold off from 
turning ENE until late in the day Thursday, High temps could reach 
the low to mid 70s esspically over the CT River Valley. However, if 
winds turn ENE early in the day, highs likely remain in the mid to 
upper 60s, with mid 50s near the coast. Friday is looking like the 
coldest day of the week due to low cloud cover and onshore flow. 
Highs on Friday possibly do not top 60F region wide. Surface winds 
turn more southerly over the weekend which will allow high temps to 
moderate a bit into the mid 60s.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
Forecast Confidence Levels:

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

Today...High confidence away from the Cape/Islands. Moderate 
confidence for the Cape/Islands. 

VFR for all interior terminals today. IFR status and fog is
beginning to develop over the Cape and Islands. Fog should burn
off around 14-15z. NW wind 5-10 kt with sea breezes developing 
along the coast. 

Tonight...Moderate confidence.

Stratus and fog with IFR-LIFR redeveloping over Cape/Islands,
with mainly VFR elsewhere. Scattered showers moving into western
MA/CT 09-12z. 

Wednesday...Moderate confidence.

MVFR-IFR expanding across all SNE as showers and isolated 
t-storms move across the region through the morning. Decreasing
coverage of showers in the afternoon, but a few t-storms may 
develop in the interior mid-late afternoon. S-SE wind 5-10 kt.

KBOS TAF...High confidence in TAF. VFR. Sea breeze developing 
by 15z. 

KBDL TAF...High Confidence in TAF. VFR.

Outlook /Wednesday Night through Saturday/... 

Wednesday Night: Mainly VFR, with local IFR possible. Breezy.
Slight chance SHRA.

Thursday: Mainly VFR, with local IFR possible. Chance RA.

Thursday Night through Friday Night: MVFR/IFR conditions
possible. Breezy. Chance RA.

Saturday: Mainly VFR, with local IFR possible. Breezy. Chance
RA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Through Wednesday...High Confidence

Winds and seas below SCA thresholds through the period. Onshore 
winds developing today over the nearshore waters as sea breezes 
develop. S-SE winds 10-15 kt Wed. Fog may reduce vsbys this morning, 
then showers develop Wed morning. 

Outlook /Wednesday Night through Saturday/... 

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

Thursday: Winds less than 25 kt. Chance of rain. 

Thursday Night through Friday Night: Winds less than 25 kt.
Seas up to 5 ft. Chance of rain. 

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

&&

.TIDES/COASTAL FLOODING...
High astro tides this week and concern becomes late Thu into 
Fri with potential frontal wave tracking south of New England, 
generating onshore flow into eastern MA. Magnitude of potential 
inundation and erosion will depend on strength and timing of 
surface low. Too early for specifics with any certainty, but 
given astro tides are already over 11 ft at Boston, it will only
take a 1 ft storm surge and modest wave action to yield minor 
inundation and erosion. Stay tuned throughout the week for 
updated information.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

$$

SYNOPSIS...KJC/KP
NEAR TERM...KJC
SHORT TERM...KJC
LONG TERM...KP
AVIATION...KJC/KP
MARINE...KJC/KP
TIDES/COASTAL FLOODING...BL