LexMAWeather

Area Forecast Discussion
for Boston, MA

        
706 
FXUS61 KBOX 240214
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1014 PM EDT Mon Apr 23 2018

.SYNOPSIS...
High pressure remains in control through Tuesday bringing dry
weather with mild daytime temperatures. Low pressure approaches
and then passes through New England Tuesday night into 
Wednesday night, bringing rain to the area. Another weak low 
pressure center may bring another round of showers to the area 
Friday night.

&&

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

955 PM Update...

Temps at 01Z ranged from the lower-mid 40s across RI/SE Mass to
the mid-upper 50s across the Route 2 region of N Mass. Skies
were mainly clear, though noting leading band of thin cirrus
clouds across SE NY into SW CT that were moving slowly but
steadily NE as seen on latest GOES-East Night fog channel. 

Winds had shifted to mainly light southerly, which has allowed 
dewpts to rise to the 20s across most areas, except up to the 
30s to near 40 across S coastal RI/MA, and up to 40 at KACK.
Will need to monitor for possible patchy fog along the immediate
S coast as T/Td spreads lower especially across the outer Cape
and Nantucket.

As nose of high pressure continues to slowly shift E tonight,
will see the high clouds continue to move across and thicken.
This should tend to cap temps especially across central and
western areas around or after 04Z-05Z. Will also have to monitor
temp trends across SE Mass with the onshore winds off the milder
ocean waters. 

Previous discussion...

Clear skies continue. With winds expected to be light, expect 
good radiational cooling. Forecasting lows in the 30s for much 
of the area, except for low 40s in some urban centers and 
portions of the Cape and Islands. 

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
Tuesday...

As the surface high moves further offshore, Tuesday will bring 
developing S to SW wind. A sea breeze is possible along east coastal 
MA for part of the day, however as the SW flow increases some during 
the afternoon, the east coastal sea breeze should come to an end. 
Mostly sunny skies expected for much of the day, with increasing 
clouds during the afternoon. A slightly warmer day with highs in the 
60s across much of the area, some locales may reach 70 degrees. The 
cooler area will be the immediate south coast of MA/RI, where the 
persistent S wind will keep highs in the upper 50s to near 60. 

Tuesday night...

Models show mid level ridging moving east of our area while deep 
trough currently over the lower Ohio/Mississippi Valleys works 
its way eastward. This pattern shift prompts a moisture-rich 
low pressure system to track eastward towards the Delmarva 
coastline. Moisture well ahead of this system will result in 
skies becoming cloudy during the evening, but it will take some 
time to moisten the column with respect to any precipitation. 
Expecting rain to become likely after midnight. PWATs during the
overnight increase to 1 to 1.3 inches, so some moderate 
rainfall possible but generally thinking rainfall of a tenth to 
half inch prior to 12Z Wed. 

Cloud cover and increasing dew points will keep overnight lows 
somewhat milder, lows in the low to mid 40s for much of the area.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Highlights...

* Wet weather Wednesday, diminishing Wednesday night
* Another round of showers possible Friday night and late Saturday

Discussion...

The 23/12Z operational guidance has come into better agreement
with the details into Thursday. Fairly good overall agreement
thereafter, although the Canadian model really goes off on its
own later this weekend. Preferred a solution more like the GFS
and ECMWF camp. Further prefer an ensemble mean approach,
especially after Thursday.

Wednesday and Wednesday night...

Essentially the same story from the past few days. Multiple
waves phase in the vicinity of the central Appalachians, or
perhaps into the Mid Atlantic. Coastal low develops and tracks 
north through southern New England Tuesday night into Wednesday
night. This will mean a period of wet weather for our region. 
Modest elevated instability still present, so cannot dismiss the
possibility of isolated thunderstorms.

Still looking like a general one half to one inch of rainfall
when all is done. Locally heavier amounts possible in any
persistent/slow-moving thunderstorms. 

Thursday through Friday...

Except for possibly widely scattered late Thursday afternoon or 
early evening instability showers over the NW higher terrain, it 
looks dry Thursday afternoon through at least most of Friday. 
Confidence has increased of at least most of daytime Friday 
remaining dry.

Friday night...

A weak coastal low pressure may pass by just close enough for a
risk of showers late Friday into Friday night, mainly across
southeast MA and RI. Also will have to monitor the progress of a
cold front associated with a low pressure in the St. Lawrence
valley, which could also bring a chance for showers across the
western half of southern New England late Friday night. Confidence
remains rather low on these details, so later forecasts may
change.

Rest of this weekend...

A cold front associated with a northern stream trough may 
result in scattered showers Saturday, but confidence in details
remains low.

Monday...High pressure expected to build in with drier weather.

&&

.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
Forecaster Confidence Levels...

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

Short Term /through Tuesday Night/...High confidence.

Overnight...VFR with clear skies and excellent visibility. 
Light S-SW winds. Low risk of MVFR VSBYS in patchy fog across 
outer Cape Cod and KACK after 04Z-05Z. 

Tuesday...VFR. Prevailing wind out of the S-SW, initially light
enough where a sea breeze may develop along east coastal MA for
a time. Then as winds aloft strengthen somewhat during the 
afternoon, the winds along east coastal MA should shift back to 
the S-SW. 

Tuesday night...VFR to start. Becoming mainly MVFR after 
midnight, with local IFR possible towards daybreak. SHRA 
spreading into the area mainly after midnight. 

KBOS Terminal...High confidence in TAF. Sea breeze this afternoon, 
with a sea breeze probable for late morning into early afternoon 
Tue. 

KBDL Terminal...High confidence in TAF.

Outlook /Wednesday through Saturday/...High confidence.

Wednesday: Mainly IFR, with local MVFR possible. Windy with
local gusts to 30 kt. RA with isolated TSRA. Patchy FG.

Wednesday Night: Mainly IFR, with local MVFR possible. Breezy.
RA likely, tapering off to SHRA. Isolated TSRA possible. Patchy
FG.

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

Thursday Night through Friday: VFR. 

Friday Night through Saturday: VFR. Slight chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Tuesday Night/...High confidence. 

Overnight...
High pressure across the waters with southerly winds 10 kt or 
less, seas 1 to 2 feet on the outer coastal waters. Good 
visibility. 

Tuesday...
S-SW wind increasing over the course of the day to 10-20 kts. 
Sea breeze along east coastal MA possible late morning or 
midday, then S winds should prevail as they strengthen. Seas 1 
to 3 feet. 

Tuesday Night...SE winds less than 25 kt. Seas locally 
approaching 5 ft, especially on the southern outer coastal 
waters. SCA headlines may be needed. Rain showers becoming 
likely towards daybreak. 

Outlook /Wednesday through Saturday/...High confidence.

Wednesday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Areas of rough seas. Rain, isolated
thunderstorms, patchy fog. Areas of visibility 1 nm or less.

Wednesday Night: Low risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 13 ft. Rain likely, chance
of rain showers, isolated thunderstorms, patchy fog. Local
visibility 1 nm or less.

Thursday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Rough seas up to 10 ft. Slight chance of rain
showers. 

Thursday Night: Winds less than 25 kt. Areas of rough seas. 

Friday: Winds less than 25 kt. Seas up to 5 ft. Slight chance
of rain showers. 

Friday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain showers. 

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

&&

.EQUIPMENT...
The NOAA Weather Radio transmitter serving Providence is out of
service due to phone line problems. The phone company has 
prioritized the issues and is working to get the weather 
broadcast back on the air as soon as possible. The transmitter
serving Hyannis is back in service.

&&

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

&&

$$
SYNOPSIS...Belk/NMB
NEAR TERM...Belk/EVT
SHORT TERM...NMB
LONG TERM...Belk
AVIATION...Belk/EVT/NMB
MARINE...Belk/EVT/NMB
EQUIPMENT...Staff