Lexington Weather

Lexington, Massachusetts, USA

41°F

5/11/2024 3:44am

Lexington Conditions: Clear
Temperature: 40.8°F / 4.9°C
Dew Point: 37.0°F
Relative Humidity: 86%
Wind: Calm, 10-min avg: Calm, gust: None
Barometer: 29.82 in Steady
Visibility: 10 miles
Rain Today: 0.00 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 041300
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
900 AM EDT Sat May 4 2024

.SYNOPSIS...
High pressure brings dry weather with cooler onshore breezes 
Saturday. A slow-moving frontal boundary brings widespread showers 
Sunday into early Monday. Then gradual clearing Monday afternoon 
along with warming temperatures. Tuesday looks to be the pick of the 
week, with abundant sunshine and highs in the 70s to near 80, 
although significantly cooler near the coast with afternoon 
seabreezes. Then lots of clouds Wed, Thu and Fri along with periodic 
showers possible.

&&

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

9 AM Update

* Partly Sunny with some increasing clouds into the afternoon
* Highs lower 50s coast, 60+ inland and near 70 lower CT Rvr

Previous forecast is on track. High pressure across the Canadian
Maritimes will continue to generate a low level easterly flow of
air across southern New England. Therefore...we will have a
large range in temperatures across the region. Highs should
range from the lower 50s along the immediate coast...but 60+ not
too far inland and near 70 in the lower CT River Valley.

Dry weather with partly sunny skies are anticipated through the
afternoon with upper level ridging in control. We do expect 
some lower clouds to invade areas near the coast and some higher
clouds to overspread the region from the west through the 
afternoon. 

&&

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

Overcast skies fill back in overnight as the boundary layer cools. 
This will limit temperatures from falling to far, so expect 
seasonable low temps in the low to mid 40s across much of the 
region. High pressure drops to the southeast which will result in 
easterly winds gradually shifting to the southeast as we approach 
the dawn hours. 

Tomorrow

Winds shift from southeast to south during the day tomorrow allowing 
for a surge of moisture across the region. This will support 
increasing moisture with PWATs rising close to an inch across the 
region. Precip chances increase gradually from west to east across 
the region as northern stream short wave energy traverses over The 
Northeast. Latest suite of model guidance suggests shower chances 
will peak during the mid-afternoon hours with the steadiest 
precipitation taking place tomorrow night (see long-term AFD). Skies 
will be overcast for much of the day tomorrow which will support 
cooler temperature sin the mid to upper 50s across the region.

&&

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

* Cool with rain Sunday into early Mon, then gradual clearing Monday 
  afternoon, although clouds may linger over southeast MA 

* Tue looks to be the pick of the week, with abundant sunshine and 
  highs in the 70s to near 80, although much cooler at the coast 

* Lots of clouds Wed, Thu & Fri along with the risk of periodic 
  showers and cooler

Temperatures...

Warm westerly flow aloft Monday with 850 mb temps well above normal, 
about +11C at 18z. Timing of clearing will be crucial to temp 
forecast. Ensembles supporting 80-100% probability of 70+ highs 
Monday in the CT River Valley and Merrimack River Valley. More 
uncertainty southeast across RI and southeast MA given departure 
timing of clouds. Not quite as warm aloft Tue, but still above 
normal with +8C to +9C at 850 mb, but warmer blyr temps of +16 to 
+17C at 925 mb, along with NW winds providing downslope flow. This 
results in ensembles offering 90-100% probabilities of 70+ highs 
away from the coastline, where afternoon seabreezes will yield 
cooler temps. Farther inland, not out of the question a few towns 
make a run at 80 degs! This combined with abundant sunshine, low dew 
pts/low RH likely results in Tue being the pick of the week. 

Not as warm Wed, Thu and Fri with frontal boundary getting hung up 
over or near SNE, along with possible waves of low pressure tracking 
south of the region. Highs likely in the 60s, except 50s along the 
coast, including Cape Cod and the Islands.  

Precipitation...

Height falls and associated cold front will combine with good 
moisture advection (PWATs +2 sigma) to yield widespread showers 
Sunday afternoon thru Monday morning across southeast MA. High 
probability for 0.10 to 0.25 inches of rainfall during this time, 
with low probs up to 0.50 inches. Clearing develops NW to SE during 
Monday afternoon (last across SE MA) as the dry slot overspreads the 
region. With diurnal heating, weak cyclonic flow aloft and surface 
front lingering over the region, low probability of a few showers 
and/or an isolated thunderstorm late in the day across the interior, 
where duration of heating/sunshine will be greatest. 

Dry weather Tuesday with PWATs only about 60% of normal. Then 
becoming unsettled Wed, Thu and possibly Fri, along with a low 
confidence forecast. Negative height anomaly downstream over 
Newfoundland keeps a ridge axis with above normal heights from the 
Mid Atlantic into New England. Meanwhile, a positive tilt trough over 
the high plains ejects multiple plumes of moisture towards New 
England. Models struggling with the large scale flow, specifically 
how much of this moisture advects east into SNE, or dampens out 
running into the ridge or is shunted southeast of New England? 
Nonetheless, chance of showers both Wed, Thu and Fri. Although, 
there will also be periods of dry weather during this time period.

&&

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

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

12z TAF Update: 

Through 12Z: High confidence, only low confidence for the
immediate eastern MA coast, as low clouds come onshore this
morning. Thining marginal IFR/MVFR clouds will be confined to
the immediate coast, then lift to VFR cloud bases farther inland
away from the coast. Earlier discussion below. 

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

VFR conditions persist through 12Z with light and variable winds
becoming more steady out of the east/northeast by sunrise.

Today...Moderate confidence

MVFR level cloud bases move onshore this morning from the east,
but there is a bit of uncertainty with respect to sky cover.
Humidity in the low levels is choppy, so coverage may range from
SCT to BKN at times. So expect intermittent periods of MVFR
ceilings for the first half of the day until the skies fill into
BKN/OVC buy mid-afternoon/evening. Steady east/northeast winds
from 5 to 10 knots.

Tonight...High Confidence

MVFR/IFR ceilings return overnight with continued light easterly
winds. Winds becoming more east/southeasterly by 12Z Sunday.

Tomorrow...High Confidence

MVFR borderline IFR ceilings for most of the day tomorrow with
-RA spreading from west to east during the day. Southeast winds
 becoming more southerly by the afternoon.

KBOS TAF...Moderate Confidence

High confidence in MVFR cloud bases, but less confidence in
coverage. There may be intermittent periods of SCT/BKN VFR/MVFR
ceilings. 

KBDL TAF...High confidence in TAF. 

Outlook /Sunday Night through Wednesday/... 

Sunday Night: MVFR/IFR conditions possible. SHRA likely.

Monday: Mainly VFR, with local IFR possible. Chance SHRA.

Monday Night through Tuesday: VFR. Slight chance SHRA.

Tuesday Night: VFR. Chance SHRA.

Wednesday: Mainly VFR, with areas MVFR possible. Breezy. Chance
SHRA, isolated TSRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Marine


Today through Tomorrow

Conditions remain on the calm and quiet side across the coastal 
waters through the weekend with high pressure largely in control. 
Easterly winds today become more southeasterly overnight and 
eventually southerly by Sunday. Seas generally in the 1 to 3 foot 
range. 

Outlook /Sunday Night through Wednesday/... 

Sunday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Rain showers likely. 

Monday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain showers. 

Monday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain showers. 

Tuesday: Winds less than 25 kt. Slight chance of rain showers. 

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

&&

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

&&

$$

SYNOPSIS...Nocera/RM
NEAR TERM...Frank
SHORT TERM...RM
LONG TERM...Nocera
AVIATION...Nocera/RM
MARINE...Nocera/RM