Lexington Weather

Lexington, Massachusetts, USA

55°F

4/19/2024 11:30am

Lexington Conditions: Clear
Temperature: 55.2°F / 12.9°C
Dew Point: 41.2°F
Relative Humidity: 59%
Wind: Calm, 10-min avg: Calm, gust: 5 mph
Barometer: 30.13 in Steady
Visibility: 10 miles
Rain Today: 0.00 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 191051
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
651 AM EDT Fri Apr 19 2024

.SYNOPSIS...

Partial sunshine and seasonable temperatures return to the region 
today...but it will be cooler on the immediate coast. An approaching 
cold front will bring a period of showers and a few downpours very 
late tonight into Saturday morning. Gradual partial clearing and 
pleasant temperatures are in store for later Saturday. Elevated fire 
weather potential possible Sunday through Tuesday due dry and 
gusty winds. Our next opportunity for unsettled wet weather 
returns mid week with colder temperatures.

&&

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

650 AM Update...

Forecast remains on track. No changes in the latest update.

305 AM Update...

* Partly sunny today with highs near 60...but 50-55 on the coast

Considerable mid-level cloudiness covered the region very early this 
morning with even a left over spot shower. Brief upper level ridging 
does build into the region today. This should probably result in 
enough subsidence for a period of partial sunshine later this 
morning and afternoon. Confidence on sky conditions today is a lower 
than normal for a near term forecast...so later shifts may need to 
make adjustments. Given the mild start...this should be enough to 
push high temps to near 60 in most locations. However...onshore
surface winds will keep high temperatures generally in the 50 to 55 
degree range along much of the immediate coast.

&&

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

Key Points...

* Period of showers late tonight into Saturday am with some downpours
* Partial sunshine returns later Sat with highs well into the 60s

Details...

Tonight and Saturday...

A cold front/shortwave will be approaching the region late tonight 
into Saturday morning. The guidance has increased the low level 
moisture return & forcing associated with this front over its last 
few cycles. A modest southwest LLJ coupled with Pwats increasing to 
over 1 inch support a period of widespread showers late tonight 
into Sat morning. We also expect some downpours given this 
combination. There is even a low risk for a rumble of thunder...but 
did not feel it was worth inserting into the forecast at this point.

Most of the showers will have exited the coast by Saturday 
afternoon. In fact...we expect some partial sunshine to develop 
from west to east as drier air works into the region. Despite 
cooling temps aloft...a mild start and the increasing April sun 
angle should push afternoon highs well into the 60s across most 
locations. While generally dry weather is expected Saturday 
afternoon...enough heating coupled with a cold pool aloft may 
trigger a few brief spot showers.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...

Highlights

* Dry and breezy Sun through Tue. Elevated fire weather concerns 
  possible.

* Shower chances return late Tue through Wed. Temps trending cooler.

* Turning drier on Thu with much colder temps.

Saturday Night through Tuesday...

Cyclonic flow in place through this timeframe. Will have a shortwave 
skirt through New England on Sun. A southern stream trough will 
remain shunted well to our south of Mon. Another trough slides 
into/across the Great Lakes on Tue. A mid level ridge builds from 
the Northern Plains late Sat into the Great Lakes/Mississippi River 
Valley by early Mon and into/offshore of New England by late Tue. 
High pressure begins nudging into our region from the center of the 
country late Sat/Sun. The high builds into the Lower Mississippi 
River Valley to OH Valley by late Mon and offshore on Tue. 

Dry and quiet weather expected through this timeframe. Though there 
could be a few lingering showers tapering off late Sat. Main concern 
during this timeframe is elevated fire weather concerns. Despite the 
high nudging in we remain gusty Sun/Mon due to a tightened pressure 
gradient between the high and the lows well off to our north and 
east. The GFS and NAM both show we should be able to mix to roughly 
800 hPa per Bufkit soundings. The GFS also shows us being this well 
mixed on Tue as well. This should allow drier air to mix down fairly 
easily aloft. With this in mind and given the pre-greenup have 
increased temps and lowered dew points/RH values during this 
timeframe from the default NBM. As we saw earlier in the week we 
tend to overachieve in these set ups, so am anticipating the same. 
At this point though am more confident for the Sun/Mon timeframe 
given upper flow will be out of the W/WNW, which will aid in 
downsloping. Could be a bit tougher on Tue as winds turn southerly 
ahead of our next incoming system. Increased temps to the 75th 
percentile of guidance for now and results in temps ranging from the 
upper 50s to mid 60s. Lowered RH/dew points to the 10th percentile 
of guidance for Sun/Mon and the 25th for Tue. Min RH values 
bottoming out in the mid 20s to the low 40s. Given the 20-30 mph 
gusts there could be elevated fire weather concerns.

Tuesday Night through Thursday...

Another period where we are caught in cyclonic flow. A trough will 
dig into the Great Lakes region Tue Night into early Wed. The 
trough/cutoff digs into New England on Wed. The trough/cutoff may 
still be overhead or kicked out of the region on Thu. Our next 
opportunity for unsettled/wet weather late Tue into Wed as a system 
slides in and perhaps through. The system may still be nearby on Thu.

A cold frontal system swings through New England late Tue through 
Wed. At this point appears that the be opportunity for widespread 
rain showers comes during the Wed timeframe. The PWAT plume not 
appearing overly impressive with only low probs (10-20 percent) of 
PWATs AOA 1 inch per the EPS/GEFS and GEPS. Do have a deeper S/SWly 
low level jet at 850 hPa, which could really help squeeze out the 
moisture available. At this point deterministic guidance show 
roughly 30-50+ kt jet in place. Should remain mild as the system is 
swinging through, so precip will be all rain. However, as things are 
winding down much colder air filters in late Wed into early Thu. 
Would not be surprised if there are some snowflakes mixing in. At 
this point total precip appearing to be generally between 0.1 and 
0.5 inches. We've got mod to high (30-80+ percent) probs of totals 
AOA 0.1 inches and low probs (10-30 percent) of 0.5 inches. For now 
have just stuck with WPC. 

Will be seeing temperatures trending downward through this 
timeframe. Much cooler on Thu with highs in the 50s.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...

Forecast Confidence Levels:

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

06z TAF Update...

Today...High confidence.

VFR across the region. Will have light E/ESE winds to start.
Winds gradually shift to the SE/S by this afternoon and
increase. Could see some 15-20 kt gusts across the higher
terrain. 

Tonight and Saturday...High Confidence.

An approaching cold front will bring a period of MVFR-IFR
conditions late tonight into Sat morning. This will also be 
accompanied by several hours of showers with a few downpours 
too. Most locations should see conditions improve to VFR by 
early Saturday afternoon, but this process may take a few hours
longer towards the Cape and Islands. Low probability for a
rumble of thunder or two as these showers move through. S winds
5 to 10 knots tonight becoming W at 10 to 15 knots by Sat 
afternoon. A few gusts in the 20 to 25 knot range may also 
develop across the interior by mid to late afternoon. 

KBOS TAF...High Confidence in TAF.

KBDL TAF...High Confidence in TAF. 

Outlook /Saturday Night through Tuesday/... 

Saturday Night through Monday: VFR. Breezy. 

Monday Night: VFR. 

Tuesday: VFR. Breezy. 

&&

.MARINE...

Forecaster Confidence Levels:

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

Today through Saturday...High Confidence.

Continued small craft headlines this morning for our far southwest 
waters from leftover lingering marginal 5 foot swell...but these 
should diminish by early afternoon. Otherwise...a relatively weak 
pressure gradient should keeps winds & seas below small craft 
advisory thresholds into Saturday. 

Outlook /Saturday Night through Tuesday/... 

Saturday Night: Winds less than 25 kt. 

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

Monday through Monday Night: Winds less than 25 kt. 

Tuesday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas locally approaching 5 ft. 

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 1 PM EDT this afternoon for ANZ255-
     256.

&&

$$

SYNOPSIS...Frank/BL
NEAR TERM...Frank/BL
SHORT TERM...Frank
LONG TERM...BL
AVIATION...Frank/BL
MARINE...Frank/BL