Lexington Weather

Lexington, Massachusetts, USA

65°F

5/20/2024 5:06pm

Lexington Conditions: Clear
Temperature: 64.9°F / 18.3°C
Dew Point: 56.8°F
Relative Humidity: 75%
Wind: Calm, 10-min avg: Calm, gust: 3 mph
Barometer: 29.96 in Steady
Visibility: 10 miles
Rain Today: 0.00 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 181428
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1028 AM EDT Sat May 18 2024

.SYNOPSIS...
Unsettled and cool today with scattered showers. Trending drier
with breaks of sunshine developing Sunday afternoon from
northwest to southeast, as high pressure begins to nudge in 
from the southwest. Early summerlike temperatures expected 
Monday through Wednesday, with the warmest days expected to be 
Tuesday and Wednesday. A cold front around Thursday offers the 
next chance at showers or thunderstorms, with temperatures then 
cooling to more seasonable levels by late in the week.

&&

.NEAR TERM /UNTIL 8 PM THIS EVENING/...

1015 AM Update: 

Not much change from previous forecast, cloudy with periods of
light rain and drizzle. Not a washout, but more nuisance rain.
Currently some enhancement to the rainfall taking place across
the Worcester Hills. This is in response to NE flow up to 19 kt
at KORH, providing upslope component. Otherwise, it's periods of
light rain/drizzle. Rain shield struggling to reach western
MA/CT, as low level jet weakens westward. In fact, across this
region there are some breaks in the overcast and dry weather 
yielding temps in the low 60s. Meanwhile, the remainder of the 
region is stuck in the 50s. Normal high for May 18th is 67-72. 
Thus, much cooler than normal especially across eastern MA and 
RI. Previous discussion below. 

----------------------------------------------------------------

Forecast still looks on track as vertically stacked circulation
to our south draws maritime moisture back westward. Unfortunately
that will translate to a cool, raw overcast, with 
intermittent/periodic light rain showers mainly in eastern MA
and RI. The showers won't necessarily be present all the time or
be a washout, but there will be some to dodge. There is some 
guarded optimism that western MA could see more of a partly to 
mostly cloudy look but most everywhere should be socked in with 
lower clouds. A good day for a bowl of clam chowdah! Temps not 
likely to go very far from existing values, in the mid 50s to 
lower-mid 60s.

&&

.SHORT TERM /8 PM THIS EVENING THROUGH 6 PM SUNDAY/...

Pattern of persistence carries through this evening with little 
change in the synoptic setup through early tomorrow morning. 
Shortwave passing to our Northwest may renew shower activity 
between 00-06Z tonight. Widely scattered shower activity across 
the eastern half of the CWA will become increasingly sparse 
after the midnight hour, giving way to a more drizzle-stratus 
dominated environment by early morning. Temps will pretty much 
remain stagnant overnight given no change in the pattern with 
low sin the 50s.

While Sunday previously looked to be a much nicer day for southern 
New England, there are indications that the influence of onshore 
flow will persist through the better part of the day across eastern 
MA and RI, though conditions should improve across CT and western MA 
as weak high pressure is able to take better hold over the region. 
Fortunately, pesky mid level low tracks seaward, which will allow 
rain chances to decrease significantly by sunrise. As has been the 
case with many days this Spring, it's likely Sunday is another case 
of the "haves and have nots", as the CT River Valley breaks out into 
sunshine and temperatures warm into the low 70s while strong onshore 
flow pins stratus across eastern MA and much of RI where temps 
struggle to climb out of the 50s along the immediate coast. It's 
probably safe to say those in the Boston to Providence corridor are 
ready to shake this gloomy pattern, but fear not, the long term AFD 
highlights a significant pattern chance by mid week!

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...

Highlights: 

* Warming temperatures under partly to mostly sunny weather through 
  midweek, with the warmest days likely on Tuesday and Wednesday. 
  Could have our first 80 degree day in Boston Tuesday and/or 
  Wednesday, with 3 days of lower-mid 80s in Hartford.

* Our next chance for rains is around later Wednesday night or 
  Thursday with showers or thundershowers associated with a cold 
  front. 

* Cooling to more seasonable levels for late-week.

Details: 

While the general theme of a substantial warming trend to 
temperatures for the early to midweek period is still valid, today's 
00z guidance indicated more potential for continued cloud cover on 
Monday with higher RH in the 1000-850 mb layer, especially for 
eastern and southeast New England. Ended up bringing highs down from 
NBM by a couple degrees for Monday on the basis of this cloud cover, 
though the temperature forecast has obvious sensitivities to how 
long clouds linger/scatter out, and that is still a bit unclear. 
Kept highs in the mid 50s to mid 60s for the coasts and the coastal 
plain, but still think highs soar into the mid to upper 70s from 
central MA/eastern CT westward with less cloud cover. 

Warmest days look to be on Tuesday and Wednesday, with full 
sunshine, southwest breezes and continue dry weather. Relatively 
strong SW flow should keep sea breezes from making much of any 
intrusion landwards, so even sites such as Boston and the North and 
South Shore have a solid chance at reaching 80 degrees, having last 
occurred at Boston on October 28th of last year. Mid 80s inland seem 
reasonable on both days. Despite the breezes, both days should feel 
more reminiscent of early summer with dewpoint temps in the mid to 
upper 50s.  

Dry weather to prevail through Wednesday. Our next chance for 
showers or thundershowers isn't until a cold front arrives around 
Wednesday night or Thursday, but the timing and the strength of any 
thunderstorms are both uncertain. Latest guidance favors 
Thursday for frontal passage so favored the highest PoP around 
Thursday but only around 20-30 percent given the uncertainties 
in timing. Friday appears to be more entrenched in post-frontal 
colder air, with temps seemingly poised to return closer to 
late-May climatological levels.

&&

.AVIATION /14Z SATURDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:

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

15z TAF Update: not much change from previous TAFs. Only
consideration is adding a PROB30 of LIFR conditions overnight,
as all guidance sources suggest these conditions across eastern
MA, including KBOS. Earlier discussion below. 

---------------------------------------------------------------

Today: High confidence in trends, though moderate on timing. 

IFR bases were already common over south coastal MA and were 
starting to lower into MVFR range the PVD/BOS corridor, with VFR
in the interior. Continued deterioration anticipated in all
areas with MVFR becoming common, and IFR/at times LIFR for
central/eastern MA and RI. Scattered hit-or-miss showers for
the eastern which was messaged in TAFs as P6SM -RA, although 
could be a round of steadier rains developing later today. NE 
Winds 5-15kt with a few gusts to 20kt possible along the 
immediate eastern coastline. 

Saturday Night...Moderate confidence.

Conditions remain consistently MVFR to LIFR from West to
Southeast, lowest on the Cape and Islands. Light showers and
drizzle continue through the first half of the evening. MVFR to
IFR conditions persist due to pesky onshore flow. Winds continue
to blow from the E/ENE gusting to around 10-15kt overnight. 

Sunday... Moderate Confidence

Conditions improve from west to east after sunrise from 
MVFR/IFR to VFR/MVFR. VFR possible for BOS-PVD line, SE after 
18Z, though MVFR to hang on across the Cape for the duration of 
the day. NE winds gusting 15 to perhaps 20kt once again. 


KBOS TAF...High confidence in TAF through 00Z. Moderate after
this time.

MVFR to deteriorate to IFR late morning/early afternoon, with
periodic -SHRA, though may trend towards a steady light rain
after 00z. NE flow 10-15kt with the occasional gust to 20kt 
possible. 

KBDL TAF...High confidence in TAF. 

Generally VFR but will become borderline VFR/MVFR this
afternoon. Showers most likely stay east of the terminal but a 
stray shower may impact the terminal this afternoon or early 
evening. Winds NE 5-10kt with gusts to 15kt. 

Outlook /Sunday Night through Wednesday/...

Sunday Night through Monday: Mainly VFR, with local MVFR
possible. 

Monday Night through Tuesday Night: VFR. 

Wednesday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels:

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

Extended the SCA for the eastern outer waters through early
Monday morning for persistent seas. 

Saturday... High confidence.

Scattered light rain and drizzle across the waters. Will have
visibilities of 3-5 SM. Persistent 15-20 kts out of the NE with
gusts up to 20 kts. Seas 1-4 ft across the interior waters and
4-6 ft for the outer.

Saturday Night...Moderate confidence.

Scattered light rain and drizzle anticipated to persist. Will 
continue to see NE winds at 10-15 kts and gusts around 20 kts. 
Visibilities of 3-5 SM and seas 3-6 ft for the outer waters.

Sunday... High Confidence. 

Continued NE winds 10-15kt. Seas across the eastern outer
waters will remain above 5 feet through the period, but will 
fall below 5 ft elsewhere. Vsby reductions early Sunday morning 
should improve through the day. 

Outlook /Sunday Night through Wednesday/...

Sunday Night: Winds less than 25 kt. Seas up to 5 ft. 

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

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

Tuesday Night through Wednesday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 2 AM EDT Monday for ANZ250-254.
     Small Craft Advisory until 8 PM EDT this evening for ANZ255-
     256.

&&

$$

SYNOPSIS...Loconto/KS
NEAR TERM...Loconto/Nocera/KS
SHORT TERM...KS
LONG TERM...Loconto
AVIATION...Loconto/Nocera/KS
MARINE...Loconto/KS