Lexington Weather

Lexington, Massachusetts, USA

66°F

5/20/2024 3:06pm

Lexington Conditions: Clear
Temperature: 65.8°F / 18.8°C
Dew Point: 56.5°F
Relative Humidity: 72%
Wind: Calm, 10-min avg: Calm, gust: 3 mph
Barometer: 29.99 in Steady
Visibility: 10 miles
Rain Today: 0.00 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 161108
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
708 AM EDT Thu May 16 2024

.SYNOPSIS...
Moderate to heavy rainfall gradually wanes through the afternoon
giving way to a dry end to the week. Onshore flow will keep
temperatures in check along the coast. The weekend features 
generally dry weather and onshore breezes, but still a good 
amount of cloud cover. Warming trend then develops Monday 
through Wednesday, and we could see a couple days of high 
temperatures in the low 80s over interior sections of Southern 
New England. After today, our next chance for rains may not 
develop until later next week.

&&

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

Low pressure south of southern New England will continue to bring 
widespread moderate, to at times heavy, rain to the region this 
morning. Even in the immediate term, guidance remains quite jumpy in 
the placement of the axis of heaviest precipitation as well as how 
much additional rain can be expected to fall, with the hourly HRRR 
forecast continuing to shift eastward with each subsequent run. 
Overnight, the heaviest rain blossomed across Connecticut where, as 
of 7Z, 6 hour QPF approached 1.5". Hi-res guidance continues to
depict a developing line of moderate to heavy rainfall that 
will pivot from the south coast into southeast MA and RI through
the morning commute, with the beginning stages of this line, 
capable of 1 inch per hour rainfall rates, already present on 
radar, moving north from the Westerly/south Coast area early 
this morning. The greatest period of concern for inch per hour 
rainfall rates is from now through about 14Z, which, if located
over highly urbanized locations, could continue to heighten 
concerns over minor urban and poor drainage flooding. 
Fortunately, the heaviest rain overnight fell across more rural 
parts of the region which combined with a lull in precip 
intensity over much of RI and SE MA has mitigated flooding 
threats thusfar. Some modest river rises have been observed on 
small rivers and streams across far southern New England, but 
all forecast points remain below action stage as of this 
writing.

In terms of additional precipitation, additional QPF amounts will be 
highly dependent convective elements making their way onshore,
with just isolated lightning pulses currently offshore, and 
moisture enhancement along the the LLJ, generally draped south 
of the I-90 corridor; with bets hedged towards the influence of 
the latter being greater. Given higher than average uncertainty 
in the hi- resolution guidance, heavily relied on ensemble 
probabilities and mean HREF QPF to derive this morning's 
expected rainfall, with both pointing to an max of around 1-2", 
locally higher pockets, of additional rainfall across SE MA/RI. 
Much lower amounts will fall, to as little as a tenth of an inch
of additional QPF, across far northern MA. 

Low pressure peaks in proximity to the region this morning before 
gradually drawing southward through the afternoon, pulling the 
precipitation shield along with it. Rain will become more showery in 
nature after the lunch hour before coming to an end, from north to 
south, through sunset this evening.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
Low pressure continues to work south and east of the region 
overnight, which will yield clearing skies and dry conditions. Given 
residual moisture and slackening winds, as LLJ accompanies the 
departing low, some patchy fog is possible. We wont see much of an 
airmass change, so dewpoints will remain the driving force in 
keeping low temperatures seasonable for mid-May, in the low 50s 
region wide. 

Friday is shaping up to be a dry and pleasant day as mid level 
ridging builds into southern New England. Any low cloud/stratus that 
forms overnight will burn off, yielding a mix of clouds and sun. 
High temperatures have a "boom or bust potential" given persistent 
onshore flow and lackluster temps aloft, around 10-11C at 925mb. 
There remains uncertainty in how far inland the "sea breeze", or 
rather, synoptic E/ENE flow will influence afternoon temperatures, 
but it will certainly be another significant temperature gradient 
day with highs warming into the 70s across the CT River Valley and 
struggling to warm into the 60s along the eastern coastline.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Highlights: 

* Other than a spot shower, mainly dry weather prevails with partly 
  to mostly cloudy conditions, along with onshore breezes this 
  weekend.

* Warming trend Mon through Wed, with less cloud cover. Could see a 
  couple days of highs in the lower 80s inland.

Details:

Today's global model ensembles from the 00z cycle have trended the 
forecast in a more optimistic direction, as a closed upper level 
circulation initially over the western Appalachians becomes parked 
over the mid-Atlantic/Chesapeake Bay vicinity this weekend. 
Surface ridge stretching from Nova Scotia southwestward through 
Southern New England is progged to remain in place for several 
days, at least into the early to midweek timeframe. In addition,
there continues to be indications of a warming trend to 
temperatures by the early to mid next week period as 500 mb 
shortwave ridge extends into Southern New England. These were 
trends noted over the last day or two and there is now a greater
degree of agreement on this anticipated warming trend Monday 
thru Wednesday. Other than a couple hit or miss showers, drier 
weather looks to predominate; we may not see widespread rains 
develop until late next week. 

The Weekend: 

Surface ridge of high pressure extending in from Atlantic Canada 
will maintain onshore breezes. While generally dry, there should be 
still a good amt of cloud cover around with partly to mostly cloudy 
sky conditions. Expect high temperatures to be coolest near the 
coast given the cooler onshore flow, in the upper 50s to lower 60s. 
High temperatures further inland still project considerably warmer, 
but how warm they get will depend on if we can see any cloudy 
breaks/stronger heating; offered highs well into the 60s to the 
lower 70s, but there is room for warmer temperatures if we see less 
cloud cover than anticipated. 

Monday through Wednesday: 

High pressure still governs at the surface, but we'll be adding 500 
mb height rises. 850 mb temps warm to the +10 to +12C neighborhood 
and with less cloud cover, highs inland could be pushing into the 
lower 80s, with mid 60s to mid 70s in the coasts and the immediate 
coastal plain with potential for seabreezes to develop.

&&

.AVIATION /11Z THURSDAY THROUGH MONDAY/...
Forecast Confidence Levels:

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

00z TAF Update...

Tonight...Moderate confidence.

Conditions deteriorate to MVFR/IFR from south to north and 
perhaps even some localized LIFR possible after 06Z as steadier 
rains push in from the south. Could see an embedded t-storm or
two overnight into Thu am push for portions of the south coast,
but given the limited instability the risk was too low to 
include in the TAF forecast. Heavier rains possible across CT, 
RI and perhaps into SE MA. Winds shift to the E and increase to 
around 10-15 kts. Will have some 20-25 kt gusts along the 
immediate south coast late.

Through Today ...Moderate confidence.

Widespread rain, heavy at times south of the MA Turnpike through
at least the lunch hour with lingering showers through 00Z this
evening. Generally IFR with pockets of MVFR improving to MVFR
and VFR by late this afternoon and evening as rain comes to an
end; improvement occurring from north to south as low pressure
pulls south. Breezy conditions, especially for terminals in RI
and SE MA, with E/ENE winds gusting to as high as 25kt. LLWS
may be an issue for the Cape and Islands. 


Thursday Night...Moderate confidence.

Conditions improve to VFR for most but lingering MVFR/IFR
possible early this evening for the south coast. Pockets of IFR
stratus/fog possible by 12Z Friday. Winds ENE around 5 to 10kt. 

Friday...

Widespread VFR after any AM fog burns off. Dry, E/NE winds
gusting to around 15kt. 

KBOS TAF...Moderate confidence in TAF.

Generally IFR with brief periods of MVFR this morning improving
to MVFR/VFR this afternoon. VFR to persist through the period
once it develops this evening. Rain, moderate at times, 
persists through lunchtime before becoming more scattered in 
nature. E/ENE winds gusting to 20kt.


KBDL TAF...Moderate confidence in TAF.

IFR with fleeting periods of MVFR this morning gradually
improving to MVFR and VFR this evening. VFR persists through
Friday once it develops with the exception of perhaps some early
am IFR due to Fog on Friday. Rain, moderate to heavy at times, 
becoming more scattered after 16Z. E/ENE winds 15-20kt 
diminishing to around 5kt overnight.

Outlook /Friday Night through Monday/...

Friday Night through Sunday: VFR. 

Sunday Night: Mainly VFR, with local IFR possible. 

Monday: VFR.

&&

.MARINE...
Forecaster Confidence Levels:

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

2 AM Update...

Today...High confidence. 

E/ENE winds 15-25 kts, gusts 20-30 kts possible. Areas of rough
seas with rain. Could still see some embedded thunderstorms
across the southern waters through the first half of the day.
Rain tapering off from north to south across the eastern waters
during the afternoon.

Tonight...High confidence. Rain tapering off across the 
southern waters north to south as the night progresses. Winds 
ENE to NE at 10-20 kts with gusts 15-20 kts gradually easing
through Friday morning. Winds should preclude widespread
fog/stratus formation but some pockets of fog may form by
sunrise. 

Friday... High Confidence.

Any pockets of fog will burn off quickly Friday morning. Dry
with E/ENE winds gusting 15-20kt. Residual high seas resulted in
the extension of outer water small craft advisories through the
period. 

Outlook /Friday Night through Monday/...

Winds less than 25 kt. Seas up to 5 ft.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ231-
     233-234.
     Small Craft Advisory until 11 PM EDT this evening for ANZ232-
     235>237.
     Small Craft Advisory until 8 PM EDT Friday for ANZ254>256.

&&

$$

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