Lexington Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 200154
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
954 PM EDT Fri Apr 19 2024

.SYNOPSIS...
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. Mostly clear skies and dry weather prevails 
Sunday and Monday, although both days could feature low relative
humidities. Increasing clouds on Tuesday and Tuesday night 
heralds a frontal passage and rain chances for Wednesday. 
Conditions trend drier for late next week. Temperatures should 
be around seasonable much of next week.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...

955 PM Update...

* Widespread Showers overspread the region between 2 and 8 AM

Previous forecast is pretty much on track. A fair amount of mid
level cloudiness have overspread the region this evening...but 
dry weather prevailed. The shortwave/cold front was still back 
across western NY into central PA and there was not a ton of 
showers with it currently. That being said...we do expect 
forcing/deeper moisture to advect into the region ahead of the 
front. Therefore...showers will blossom across the region. Most 
of this activity will not overspread western MA/CT until after
2-3 am and will wait until near or after daybreak to impact 
much of the I-95 corridor. While there might be a spot shower or
two a bit earlier...the main widespread showers will not 
overspread the region until between 2 and 8 am Saturday morning
and perhaps a bit later across the Cape and Islands. Enough 
forcing and low level moisture are available to support a few 
brief downpours too. The clouds and increasing low level 
moisture will hold overnight low temps in the 40s.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...

Should have improving conditions from northwest to southeast 
from mid-morning to early-afternoon. QPF is in the neighborhood 
of a quarter and third of an inch, enough to provide the region 
with a wetting rain. The second-half of the day features mid-
level dry air mass, should reduce the cloud cover, giving us a 
mix of sun and clouds. This should lead to a nice afternoon with
highs in the low and middle 60s. Low clouds will be stubborn 
for the Cape and Island, but should clear our late afternoon, 
perhaps in time for sunset. Here the highs are slightly cooler 
in the middle and upper 50s.

Guidance this afternoon does show the a trailing mid-level shortwave 
that reaches southern New England mid to later afternoon. With this 
passage, a couple of rouge showers are possible, but should come to 
an end by sunset. 

Overnight skies area clearing and despite s northwest wind at 10 to 
15 mph, temperatures fall into the 30s. While much of the area 
remains above freezing, northern Worcester County and the east 
slopes of the Berkshires could see morning lows 30-34 degrees. May 
want to keep that in mind if you bought any potted outdoor
plants.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
330PM UPDATE:

Highlights: 

* Clear and dry weather Sun and Mon with seasonable temps. Possible 
  elevated fire weather concerns for both days, but especially Mon 
  as NW winds increase. 

* Continued dry, but with SW breezes along with more cloud cover. 

* Although not a soaking rain, a frontal system around Wed or Wed 
  night brings our next chance for rains. 

* More uncertainty in the late-week pattern, but favoring dry 
  weather.

Details:

Sunday through Tuesday: 

Cyclonic flow aloft begins this period, associated with a potent 
shortwave disturbance which passes over northern New England into 
Mon. System's passing cold front moves through Mon too, but it will 
be a dry frontal passage with a windshift to NW and cooler 
temperatures being the only things really noticeable about the 
frontal passage. Pattern starts to flatten Mon night into Tue with a 
broad 1020+ mb high pressure cell ridging into Southern New England. 

Dry weather to prevail in this period, even with the frontal passage 
passing to the north on Mon. Much of this period features mostly 
clear skies and though it will be a bit breezy from the northwest on 
Monday, it should be a stretch of pretty nice weather on the whole. 
But as is typically the case in the early-spring/pre-greenup period 
with clear skies and good mixing leading to lower dewpoints, both 
Sun and Mon could feature elevated fire weather concerns. Of the two 
days, Mon looks to feature the lowest relative humidities and period 
of stronger NW winds (gusts 25-30 mph). Highs Sun and Mon look 
similar each day, in the 50s (upper 50s/near 60 in eastern MA). Lows 
in the mid/upper 30s Sunday night and in the low to mid 30s Mon 
night. 

For Tue, high pressure shifts offshore early in the day, allowing 
for returning SW flow bringing modest SW breezes, but also 
increasing cloud cover (greatest late-day). RHs are a touch higher 
(35-50 percent) Tuesday so not thinking period of fire weather for 
Tue. Highs Tue should get to around 60 degrees. Turning mostly 
cloudy on Tue night ahead of a frontal system for Wed, and the 
increase in clouds brings milder nighttime lows in the 40s.  

Wednesday: 

12z ensembles and most deterministic models show a progressive 
frontal system moving across Southern New England in this period. 
There is some timing differences that still need to be sorted out, 
with the ECMWF camp being slower with the progression (Wed late day 
into early-overnight Thurs); those differences led to PoP being no 
higher than Likely. A few days of dry weather preceding this frontal 
passage could favor a slower timing (e.g. some of the modeled QPF 
lost to evaporation through dry air layers) but won't deviate 
farther from NBM output to let the timing uncertainties iron 
themselves out. This doesn't look to be anything close to the 
soaking rains that plagued us in March but we should be able to see 
a period of wetting rains over a quarter-inch or so but not much 
more. 

Late Week: 

A bit of uncertainty here with differences in mass field evolution 
between the drier ECMWF/Canadian GEM and the GFS, which deepens an 
upper trough which closes off into a closed low near or west of 
Southern New England. That would bring unsettled weather and 
cloudier conditions to the area. This solution doesn't seem to have 
much support from its ensemble; official forecast will keep close to 
NBM for this period, but with a tilt towards the international 
guidance favoring drier conditions.

&&

.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 in trends, though moderate to high on 
timing. 

VFR through at least 04z (and 07-09z for eastern terminals),
though with lowering cloud bases. MVFR ceilings around 06-08z 
for western terminals and after 09z for eastern airports as
showers begin to overspread, then period of MVFR/IFR ceilings
with steadier rains through 12z. S to SW winds around 10-12 kt
to start, but will decrease to around 6-10 kt by daybreak.

Saturday...High confidence in trends, moderate confidence in the
exact timing. 

IFR/MVFR to start, -SHRA continues for terminals in Rhode 
Island and eastern Massachusetts through 15z/17z. May linger a
bit longer for the outer Cape and Islands. Winds are 8 to 12
knots and are generally from the west, though eastern 
Massachusetts winds may remain out of the west/southwest. 

Lastly, there is a low chance of a late afternoon pop-up shower
due to a trailing shortwave, this could produce widely 
scattered rain.

Saturday Night...High confidence. 

VFR, any lingering MVFR over the Cape and Islands become VFR
between 02z and 04z. Otherwise a dry night. Winds are 10 to 15
knots from the west/northwest. Perhaps some gusts for the Cape
and Island to 20 to 25 knots. 

KBOS TAF...High Confidence in TAF.

KBDL TAF...High Confidence in TAF. 

Outlook /Sunday through Wednesday/... 

Sunday through Tuesday: VFR. Breezy. 

Tuesday Night: VFR. Breezy. Slight chance SHRA.

Wednesday: Mainly VFR, with local IFR possible. Breezy. Chance
RA.

&&

.MARINE...
Forecaster Confidence Levels:

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

330PM UPDATE:

Today through Saturday Night...High Confidence.

Quiet conditions for the rest of Friday and tonight with seas
and winds below advisory criteria. An approaching front does
bring showers and perhaps a rumble of thunder Saturday morning
with a wind shift from ESE/WSW. Showers linger into late
Saturday morning/early afternoon. Drying out Saturday evening
into the overnight hours. Winds may briefly reach advisory
criteria late Saturday night 25 to 28 knots over the waters
south of Rhode Island and Block Island. Given how marginal this
is, held off on issuing a Small Craft Advisory. Later forecast
may want to include if confidence increases. 

Outlook /Sunday through Wednesday/... 

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

Monday through Tuesday: Winds less than 25 kt. 

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

Wednesday: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of seas approaching 5 ft. Chance of
rain.

&&

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

&&

$$

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