Lexington Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 140612
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
212 AM EDT Sun Apr 14 2024

.SYNOPSIS...
Clouds briefly decrease tonight, but increase again on Sunday as
a fast-moving frontal system moves through. This should bring 
another round of light rain showers, but there is a chance for 
isolated thunderstorms across portions of CT, RI and south of 
the Mass Pike in MA Sunday afternoon and night. Showers diminish
Sunday night, setting the stage for a mild and dry start to the
work week. More unsettled by mid week, with a large degree of 
uncertainty revolving around temperatures and precipitation 
timing.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
1005 PM Update: 

Earlier scattered showers have continued to dissipate, but still
dealing with a good deal of cloud cover and westerly winds
around 10-15 mph (around 20 mph Cape and Islands) with gusts
20-30 mph. Brought hourly temps up by 3-5 degrees over inherited
forecast thru early overnight to account for slow cooling under
clouds and the breezes with this update, but cloud cover should
begin to decrease more significantly after midnight coinciding 
with eastward passage of 500 mb trough axis into the Canadian 
Maritimes. That also should bring easing gust speeds too,
although sustained winds still will run around 10 mph for most
of the night. Forecast for second half of the night seems to 
reflect these expectations well and made no changes there with 
this update.

Previous Discussion...

A smattering of diurnal showers continues across much of
southern New England this afternoon driven largely by the broad 
trough passing overhead. The axis of said trough (now just east 
of the region) will continue to march east through the evening 
as the shortwave lifts out. This loss of synoptic forcing
together with loss of daytime heating will mean diminishing
showers and cloud coverage toward sunset, with skies really
clearing after 2-3AM. As mid level heights briefly rise we'll
end the night and start Sunday with mostly clear skies. While
winds will remain breezy overnight, temps should drop several
degrees compared to lows last night under the cooler air mass,
into the upper 30s/low 40s.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/...
If you get outside during the morning hours tomorrow you should
be able to get enjoy party sunny skies, though an approaching
warm front and associated mid level trough will mean skies
quickly cloud over after noon. It will be followed quickly by a 
cold front as the weak surface low passes overhead or just to
our north Sunday afternoon and evening. Given the 30-60 kt LLJ
passing just offshore and a modest PWAT plume of ~1 inch this
frontal system should bring anywhere from a few hundredths of 
an inch to a half inch of rain. Hi- resolution guidance is in 
general agreement that we'll see two distinct rounds of rain:
first some light warm advection showers in the late
morning/early afternoon followed by a lull and then a round of
heavier rain accompanying the cold front Sunday evening. Where 
confidence is lower is how much drying we'll have between these 
rounds or if showers hang around much of the day. There remains 
potential for some rumbles of thunder ahead of the cold front as
well, depending on how far the warm sector extends east into 
southern New England. Currently decent mid-level lapse rates 
(6.5- 7.5C/km) and a few hundred J/kg of CAPE extend into 
western CT/MA where the best chance of thunder will be in the 
afternoon, and the SPC has these locations under a Marginal Risk
(level 1 of 5) of severe storms. Can't rule out a rumble of 
thunder along the immediate south coast later in the evening as 
the low passes. The cold front and line of rain/thunderstorms 
should move off of Cape Cod by midnight leaving rapidly clearing
skies under drying NW flow.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Highlights:

* Drying trend develops Monday and Tuesday

* Mild start to the week, uncertainty in temperatures the second  
  half of the work week

* Unsettled conditions should return late Wednesday into next
  weekend 

Much of this portion of the forecast should feature a broad mid  
level over southern New England through early next week. A
stronger mid level cutoff should move from Hudson Bay to the
Saint Lawrence Valley during this time as well. We should catch 
a brief break beneath a ridge towards Wednesday. After then
though, there is quite a bit of uncertainty in the synoptic
details within the latest guidance suite. Have sketched out a
general period of unsettled weather from late Wednesday into
next Saturday, but fully expecting the timing details to change 
with later forecasts. 

Not much different at the surface. High pressure starts to build  
across southern New England for Monday, but is more in place for
Tuesday. Thus, despite the trough aloft, thinking we will see 
dry weather with at least some sunshine. Will have to monitor 
the humidity, as this could be a setup for more diurnal clouds, 
at least for Monday.

Then the aforementioned timing issues become more of a factor.
High pressure should move off to the east, opening a path for a
low pressure to impact our region sometime from late Wednesday
into Thursday morning. This low pressure is currently projected 
to move offshore for Friday, but a warm front should be
lingering nearby. A cold front should sweep most of the
unsettled weather out over the North Atlantic for Saturday,
assuming the current timing holds. 

Temperatures expected to be near to above normal through this 
portion of the forecast.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
Forecast Confidence Levels:

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

06z TAF Update: 

Through 12z Sunday: High confidence. 

SCT-OVC VFR cloudiness, bases 035-060, but decreasing by
daybreak from west to east. W to WSW winds around 10-12 kt, with
occasional 20-kt gusts eastern TAFs.

Today and Tonight: High confidence in TAF/trends, moderate on 
t-storm coverage and timing. 

Categories should be primarily VFR. Increasing mid to high 
clouds thru the morning hrs from W to E. By afternoon, a frontal
system arrives from the WNW spreading at least light showers
after 18z. Potential exists for thunder late in the day (after 
22z) but the best chance is at BAF and BDL where PROB30 -TSRA 
was indicated. It is possible that PVD could see -TSRA too, but 
think the best chance is southwest of there. Winds to back from 
W to SW/S and increase in speed to around 10-15 kt; gusts to 
20-25 kt over southeast MA.

Likely ongoing SHRA (possible TS for southern/southwestern 
airports) to then shift SE into the waters by 02-04z. SCT-BKN 
VFR ceilings to then predominate for the evening/overnight. SW 
winds shift to W/WNW and decrease to around 5-10 kt by daybreak.

Monday: High confidence. 

VFR. NW winds increase to around 8-12 kt with gusts 18-22 kt,
with strongest gusts over the terrain.

KBOS TAF...High confidence in TAF. Mainly VFR through the
period. That said, risk of -SHRA could start as soon as 18z but
thinking best chance is after 22z. Showers end after 02z. W
winds around 10-13 kt this morning shift to SW at similar
speeds, with occasional gusts to 20 kt. Winds shift to W/WNW
tonight.

KBDL TAF...Moderate to high confidence in TAF. VFR most of
today, although could see temporary/brief MVFR/IFR visby if 
TSRA can develop around 22-02z. W winds become S today around
10-12 kt, then shifting to SW-W-WNW tonight.

Outlook /Monday Night through Thursday/... 

Monday: VFR. Breezy. 

Monday Night: VFR. 

Tuesday: VFR. Breezy. 

Tuesday Night: VFR. 

Wednesday: VFR. Chance SHRA.

Wednesday Night: MVFR/IFR conditions possible. Breezy. SHRA
likely.

Thursday: MVFR/IFR conditions possible. Breezy. Chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

High confidence...

Gusty SW to W wind gusts 25-30 kt on the eastern waters, and up 
to 35 kt on the southern nearshore and offshore waters. Winds
subside later tonight. Seas will remain elevated and rough,
around 7-10 ft on the outer waters. 

Sunday morning SW gusts ramp up again to around 15-20 kt with  
seas around 4-6 ft on Sunday. Winds gust to 20-30 kts during the 
early overnight hours, diminishing after midnight. Chance for a
few t-storms on the far southern outer waters very late Sunday
afternoon, but at least scattered showers develop during the
afternoon on all waters. 

Outlook /Monday Night through Thursday/... 

Monday: Winds less than 25 kt. Local rough seas. 

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

Tuesday through Tuesday Night: Winds less than 25 kt. 

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

Wednesday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas locally approaching 5 ft. Chance of
rain showers. 

Thursday: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 AM EDT this morning for ANZ230.
     Small Craft Advisory until 2 PM EDT this afternoon for ANZ231-
     251.
     Small Craft Advisory until 2 PM EDT Monday for ANZ232>235-237-
     250.
     Small Craft Advisory until 8 PM EDT Monday for ANZ254>256.

&&

$$

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