Old Res Weather

Lexington, Massachusetts, USA

62°F

4/23/2024 11:33am

Lexington Conditions: Clear
Temperature: 61.5°F / 16.4°C
Dew Point: 32.9°F
Relative Humidity: 34%
Wind: Calm, 10-min avg: Calm, gust: None
Barometer: 30.17 in Falling Slowly
Visibility: 10 miles
Rain Today: 0.00 in
UV Index: $VPuv Medium

Area Forecast Discussion
for Lexington, MA

        
000
FXUS61 KBOX 231313
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
913 AM EDT Tue Apr 23 2024

.SYNOPSIS...
Chilly this morning, then turning comfortable and mostly sunny 
this afternoon. Cold front moves across southern New England on 
Wednesday with showers and perhaps isolated thunderstorms. Large
high pressure will build into the region Thursday through 
Saturday bringing dry weather with moderating temperatures 
Friday and Saturday. The next chance of showers will be Saturday
night into Sunday as a frontal system approaches. Much warmer 
temperatures are possible by Sunday/Monday but a backdoor front 
may keep much of the region cooler after all.

&&

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

9AM Update...

Pesky, but impactful, area of fog that draped over the southern
I-95 corridor from Providence to Boston this morning has fully
dissipated as of this writing thanks to daytime heating. This
area of fog formed along a well defined dewpoint boundary, where
dews were as much as 10F lower just north and west of the fog
compared to right along the boundary, where dews were observed
in the mid 30s to low 40s. 

For the rest of the day, expecting abundant sunshine with
temperatures warming to near and above normal. 

Previous update...

Highlights: 

* Clear and chilly to start. Sunny and comfortable this afternoon.

Brr, a chilly start to the day thanks to clear sky cover overnight 
and calm winds. Frost Advisory remains in effect until 7am due to 
morning temperatures across portions of Connecticut and southeast 
Massachusetts, as well as Rhode Island. Temperatures will quickly 
climb into the low and middle 60s this afternoon, while the 
immediate coast remains in the upper 50s. Plenty of sunshine this 
afternoon due to a broad area of high pressure stretching across 
much of the eastern seaboard. 

Due to the dry profile of the lower atmosphere could have issues 
with our dewpoint forecast today, did opt to use the the 
percentile of the NBM, but this might not be low enough - 
something the day shift will need to monitor. As it stands, the 
minimum value of relative humidity this afternoon is 20 to 30 
percent. Winds are from the south this afternoon at 10 to 15 mph
and gusts to 25 mph.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
Highlights: 

* Less cold Tuesday night, showers return for Wednesday and perhaps 
  an isolated thunderstorm during the afternoon. 

Overnight into Wednesday morning is less cold, due to the increasing 
cloud cover and steady southerly wind, temperatures only drop back 
into the upper 30s and low 40s. No threat for frost, but that does 
return Wednesday night - likely to result in a new frost headline. 

Our next chance for rain and perhaps an isolated thunderstorm is 
Wednesday with the passage of a cold front and its associated robust 
mid-level shortwave/trough. There is adequate moisture, PWATs are 
between 0.7 and 1.0 inches, and lift to support numerous showers 
during Wednesday morning. Do think the better chance for any rumbles 
of thunder would be during the afternoon do the the steep mid-level 
lapse rates - in addition to a couple hundred units of surface based 
CAPE. QPF is in the neighborhood of 0.10 to 0.15 inch, but isolated 
areas of higher amounts are possible within these isolated 
thunderstorms. 

Afternoon highs will depend a bit on the amount of clearing we have 
during the afternoon, but generally a seasonable temperatures in the 
upper 50s to low 60s. Behind the front, the wind becomes northwest 
and sets the stage for a much colder night ahead.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Key Points...

* Widespread showers Wed and possibly an isolated t-storm, then 
  drying and cold Wed night with freezing temps.

* Dry Thu through Sat. Cool Thu then milder Fri-Sat

* Chance of showers Sat night and Sun

Details...

Dry, post frontal NW flow kicks in late Wednesday and persists into 
Thursday as high pressure expands from the Great Lakes into New 
England. This will lead to a colder airmass once again overspreading 
the region and lows in the upper 20s/low 30s Thursday morning. 
Frost/Freeze headlines will likely be needed on Thursday and 
potentially Friday mornings. The surface high remains in control 
through Saturday, becoming centered over New England on Friday and 
sinking to our southeast by Saturday night. This pattern offers 
plenty of sun and light winds each day, so while relative humidities 
will be quite dry on Thursday (20-30%) fire conditions shouldn't be 
too elevated unless the high is slower to advance east (and breezy 
winds were to then linger into Thursday afternoon). 

Our next chance of rain comes in the second half of the weekend as 
the high pressure is shunted southward by our next shortwave 
rounding the ridge. However, confidence is low for this portion of 
the forecast given the wide range of possible scenarios. For what 
it's worth, both the EPS and GEFS ensemble guidance have at least a 
30% chance of measurable rain by Sunday afternoon, so odds of 
unsettled weather will be on the rise regardless. The biggest 
forecast challenge will be for high temperatures Sunday and Monday. 
Guidance continues to advertise the chance for the warmest temps of 
the season so far (well into the 70s). However, the possibility of a 
backdoor cold front to keep much of our region colder looms large; 
this would result in a large gradient from eastern MA to southwest 
CT. GEFS ensemble guidance is less enthused with the widespread 
warmth than the EPS at this point. Stay tuned.

&&

.AVIATION /13Z TUESDAY THROUGH SATURDAY/...
Forecast Confidence Levels:

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

Today...High confidence.

VFR. Southeast wind, 10 to 15 knots, isolated gusts this 
afternoon to 20 knots. Eastern Massachusetts, Cape Cod, and 
Islands have more or an south/southeast wind direction. 

Tonight...High confidence. 

VFR. Increasing high clouds early, then mid-level clouds late in the 
night. South/southwest winds 8 to 12 knots. 

Wednesday...High confidence. 

MVFR, but IFR is possible in areas of RA or TSRA. RA arrives after 
12z from west to east, TSRA possible mid to late afternoon with the 
passage of a cold front. Southwest winds early around 10 knots, then 
becoming northwest 10 to 15 knots late afternoon. 

KBOS TAF...High Confidence in TAF. Winds shift to the southeast
this morning before becoming southerly late this afternoon as
gusts pick up to as high as 20kt. Morning fog has dissipated and
will cause no further concern to the terminal. 

KBDL TAF...High Confidence in TAF. 

Outlook /Wednesday Night through Saturday/... 

Wednesday Night: VFR. Windy with local gusts up to 30 kt. 

Thursday through Friday Night: VFR. 

Saturday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels:

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

Today through Wednesday...High confidence.

Tranquil early season boating conditions due to a broad area of high 
pressure across the eastern seaboard. A cold front moves across the 
waters Wednesday, bringing showers and the potential for isolated 
thunderstorms during the second-half of the day. This period 
features seas and winds below advisory criteria, but behind the cold 
front Wednesday night, gusty northwest winds may result in marginal 
small craft conditions. 

Outlook /Wednesday Night through Saturday/... 

Wednesday Night: Low risk for Small Craft Advisory winds with
gusts up to 30 kt. Areas of rough seas. 

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

Thursday Night through Saturday: Winds less than 25 kt.

&&

.FIRE WEATHER...
Today...Elevated Fire Weather Concerns. 

Minimum values of relative humidity this afternoon are forecast
between 20 and 30 percent this afternoon along with gusts up to
20 MPH. Due to pre-greenup conditions and a dry atmosphere there
are elevated fire weather concerns this afternoon.

&&

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

&&

$$

SYNOPSIS...BW/Dooley
NEAR TERM...Dooley/KS
SHORT TERM...Dooley
LONG TERM...BW
AVIATION...BW/Dooley
MARINE...BW/Dooley
FIRE WEATHER...Dooley