Lexington Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 270209
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1009 PM EDT Fri Apr 26 2024

.SYNOPSIS...
High pressure over New England moves offshore tonight and
remains offshore on Saturday. Another chilly night tonight but
not as chilly as last night. Mostly sunny on Saturday, though
increasing clouds with chances for light showers arrive early
Sunday. Unsettled pattern sets up for Sunday into early next 
week, though the best chance for showers is around Tuesday or 
Wednesday. Temperatures turn quite mild for interior western New
England Monday, but a backdoor cold front brings much cooler air
to coastal areas.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Update: 10pm

Forecast remains on track with no notable updates to the 
forecast. See prior discussion below. 

High pressure will continue to gradually shift ESE 
into the southern offshore waters tonight. Seabreezes should 
diminish around or shortly before sundown, setting the stage for
another night of clear skies and light to calm winds. We should
see good radiational cooling conditions develop again. Frost 
Advisories have been hoisted for several counties in CT, RI and 
eastern MA where the frost/freeze program is active; that being 
said, with temperatures running about 3-5 degrees warmer than 
yesterday, prospects for frost are a little more borderline than
was the case last night. This was enough to hold Suffolk and 
eastern Norfolk Counties out of the Advisory, and it also could 
be more borderline in Hartford County and those counties around 
the Providence area but will be close enough to hoist for these 
locations. If you had planted early, even in areas outside where
the Frost Advisory is in effect, take the necessary actions to 
protect your plants and crops from damage related to frost. 
Following MOS based approaches to lows, lows range from the 
upper 20s/around 30 in northwest MA, and around 33-36 for most 
everywhere, though upper 30s/around 40 in the Boston area.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
355 PM Update:

Saturday: 

High pressure continues to be anchored offshore on Sat, with a 
highly amplified upper level ridge begins to build into western New 
England. Expecting a good deal of sunshine again, with sea breezes 
again developing near the southern and eastern coasts as has been 
the case the last couple days. However will be seeing an increasing 
canopy of high clouds spreading in later in the day into western 
sections of SNE. 

With temps gradually warming each day, continued strong heating 
combined with an increased WSW wind away from the immediate coast, 
it has the look of one of those pre-greenup spring days where temps 
overachieve available guidance by a significant margin. Highs 
Saturday away from the coasts should punch well into the 60s and 
wouldn't rule out some locations in the CT and Merrimack Valleys 
reaching 70 degrees. Noticeably cooler near shore with highs only in 
the 50s where seabreezes will govern. 

Saturday Night: 

Clouds that had been moving in later Sat aftn continue to lower, 
thicken and spread eastward through much of the night. This is in 
response to a burst of pretty strong warm and moist advection as 
upper ridge axis crests offshore. Some indication in guidance that 
lighter showers could develop in western MA/CT during the late-
overnight to pre-dawn period, but think modeled QPF is overdone as 
low levels initially struggle to saturate up with several days of 
preceding dry weather. In fact there's quite a reservoir of dry 
subcloud air shown on model soundings which even in western areas 
only saturates enough to support light showers around 09-12z Sun. 
Carried a 15-45% PoP mention for showers west of Providence, with 
highest chances near the Berkshires. This would be a relatively 
higher PoP but very low QPF scenario though. 

With increasing overcast and warming temps aloft, lows project to be 
considerably warmer than prior nights with no chance for frost. Lows 
should only dip into the low to mid 40s, and a few of the urban 
centers may stay around the mid/upper 40s.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Key Points...

* Low chance for isolated showers Sunday and Monday. More widespread 
  rain possible mid week

* Warming trend through much of next week, but a back door cold 
  front will keep eastern SNE cooler then western SNE.

Sunday and Monday

The center of the high pressure drops south to the Carolinas, but 
the upper level ridge axis continues to stretch north in SNE. Being 
at the top of the ridge axis, weak vorticity impulses, along with 
weak mid level warm air advection will bring mid to high clouds and 
low chances for isolated showers both Sunday and Monday. High 
temperatures Sunday and Monday will be very dependent on a back door 
cold front working in. Guidance continues to struggle with how far 
inland the back door cold front will penetrate Sunday, and again on 
Monday. What will likely occur is that eastern SNE will see high 
temperatures in the low to mid 60s, while western SNE will see mid 
to upper 70s, with a chance at low 80s.

Tuesday through Friday

Upper level ridge axis begins to break down Tuesday into Wednesday 
as a weakening shortwave trough moves through the region. Details on 
exact timing and coverage of precip remains very uncertain with weak 
upper level forcing and large spread in the guidance. LREF probs for 
0.25 inches of rain remain low, less then 30% each day through 
Friday. The temperature forecast remains very uncertain during this 
time period as another upper level ridge builds in to our west 
allowing another surface high pressure to build over the Gulf of 
Maine. This could bring continued onshore flow to the region along 
with continued back door cold fronts. Ensembles are still showing 
significant amount of spread with the 25th to 75th percentile for 
high temperatures ranging from the upper 50s to upper 70s across the 
region.

&&

.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:

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

00z TAF Update:

Tonight: High confidence. 

VFR SKC. For this afternoon, Light S winds for all areas 
overnight. 

Saturday: High confidence. 

VFR, although with an increasing canopy of high clouds late-
day. Light SW winds increase thru the day to around 7-10 kt;
though sea-breezes again develop near the coasts between 14-16z
Sat. 

Saturday Night: High confidence in trends though moderate on
exact timing. 

Cigs start VFR but will be steadily lowering. Best chance at
sub-VFR ceilings and light rain showers is after 06z and mainly
from ORH westward; cigs could be as low as IFR but think MVFR 
predominate for those interior western terminals. Still think 
we're looking at OVC VFR for eastern terminals. SW winds around 
8-12 kt to start, but decrease to around 5-8 kt late. Low prob 
of low level wind shear south of I-90. 

KBOS TAF...High confidence in TAF. VFR. Winds become light 
southerly tonight. Seabreezes again likely for Sat, following 
similar 14-16z timeframe as prior days.

KBDL TAF...High confidence in TAF. VFR. Light north winds most
of today, but will trend southerly around 4-7 kt late today into
tonight.

Outlook /Sunday through Wednesday/... 

Sunday: Mainly VFR, with local IFR possible. Slight chance
SHRA.

Sunday Night: VFR. Slight chance SHRA.

Monday: Mainly VFR, with local MVFR possible. Slight chance
SHRA.

Monday Night: Mainly VFR, with local IFR possible. Slight
chance SHRA.

Tuesday: Mainly VFR, with areas MVFR possible. Chance SHRA.

Tuesday Night: Mainly VFR, with areas IFR possible. Chance RA.

Wednesday: Mainly VFR, with areas IFR possible.

&&

.MARINE...
Forecaster Confidence Levels:

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

Tonight through Saturday Night: High confidence.

Pleasant boating weather conditions for mariners through most of
Saturday, and while that should generally be the case into
Saturday evening as well, there is a low chance for showers on
the southern waters late Sat night into pre-dawn Sunday.

Light southerly winds tonight and into early on Sat. SW winds
increase a bit to around 10-15 kt on Sat on all waters, though 
will become ESE on the eastern nearshore waters Sat late-morning
to early evening. Seas mainly 3ft or less all waters.

Outlook /Sunday through Wednesday/... 

Sunday through Sunday Night: Winds less than 25 kt. Slight
chance of rain showers. 

Monday: Winds less than 25 kt. 

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

Tuesday Night through Wednesday: Winds less than 25 kt. Seas
locally approaching 5 ft. Slight chance of rain.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Frost Advisory from 2 AM to 8 AM EDT Saturday for CTZ002>004.
MA...Frost Advisory from 2 AM to 8 AM EDT Saturday for MAZ007-014-
     017>024.
RI...Frost Advisory from 2 AM to 8 AM EDT Saturday for RIZ001>007.
MARINE...None.

&&

$$

SYNOPSIS...Loconto/KP
NEAR TERM...Loconto/Dooley/KP
SHORT TERM...Loconto/KP
LONG TERM...KP
AVIATION...Loconto/KP
MARINE...Loconto/KP