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Area Forecast Discussion (AFD)

Issued by Boston / Norton, MA (BOX)

                            
917 
FXUS61 KBOX 230534
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
134 AM EDT Mon Apr 23 2018

.SYNOPSIS...
High pressure remains in control through Tuesday bringing dry
weather with moderating temperatures. Wet weather returns
Wednesday into Thursday as low pressure moves through our 
region. Unsettled weather continues into the weekend, but not a
washout.

&&

.NEAR TERM /THROUGH TODAY/...

Early morning...

High pressure over the Northeast USA with a light pressure 
gradient over New England. High pressure continues to show 
clear skies over New England as well as much of NY/NJ/PA. 

With clear skies/light wind/dry air, expect radiational cooling
with temperatures falling to the upper 20s and 30s. The air is 
dry enough to allow some of the normal cold spots to reach as 
low as the mid 20s. 

Today...

High pressure remains in place over Southern New England. Expect
lots of sunshine and light wind. Mixing again should reach to at
least 850 mb and possibly higher than 800 mb. Note that inland
mixing yesterday reached above 750 mb. Temps at 850 mb support
max sfc temps of 62-64F, while 800 mb temps support 65-68F. We
tend toward the higher values inland, especially in the
traditional hot spots... Hartford-Springfield and parts of the
Boston Metrowest. 

The light flow will support sea breezes along the coast, which
will keep temps cooler along the coast. Will maintain max temps
in the 60s inland and 50s coast.

&&

.SHORT TERM /TONIGHT THROUGH 6 PM TUESDAY/...

The high pressure remains overhead tonight, then shifts off to
the east Tuesday. This should maintain clear skies tonight, and
sunshine through high clouds Tuesday. 

Radiational cooling tonight should again allow temperatures to 
fall into the 30s, with the usual cold spots around freezing or 
a little below. 

With the surface high moving offshore, Tuesday will feature a
developing south to southwest wind which will allow a sea breeze
only along the south-facing coasts. The ridge will maintain dry
air through the day. High level moisture fields do indicate
increasing clouds during the mid to late afternoon, but late
enough to allow sunshine through the day. Mixing will be a
little shallower, but temps at all levels will be increasing. So
temperatures Tuesday should again climb into the 60s except 50s
along the South Coast.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
*/ Highlights...

 - Wet and breezy midweek
 - Perhaps a reprieve Friday
 - More showers possible Saturday

Overview and model preferences...
22/12Z guidance remains in decent overall agreement through 
this portion of the forecast, although more detail differences 
arise after Wednesday. 

Generally expecting two mid level waves to phase over the Ohio
valley/central Appalachians towards Wednesday. This amplify the
resulting trough, and steer a low pressure closer to southern
New England Wednesday into Thursday. Near normal temperatures
much of this period, except for Wednesday.

Continue to favor an ensemble approach for this portion of the
forecast, especially after Wednesday.

Details...

Dry weather through Tuesday, with a large high pressure over the
Maritimes. Some question as to how quickly this high pressure
will move offshore. Latest guidance has sped up the arrival of
rainfall into late Tuesday night. Some surface ridging noted 
over southern New England Wednesday morning, so this might be
too fast. Preferred a slower arrival to rainfall than the 
latest guidance for this reason.

Good setup for a soaking rain Wednesday into Wednesday night.
This looks to be our most likely period of wet weather during
the next 7 days. Southern New England should be in the dry slot
of this system Thursday, although there could be some lingering
showers north of the Mass Pike Thursday morning.

A brief dry period possible Thursday night into early Friday, 
before another low pressure moves into the Great Lakes. This
system should be close enough where there would at least be a
chance for some showers. Not looking like a washout, though.

High pressure may start to arrive Sunday, leading to drier
weather.

&&

.AVIATION /05Z MONDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...

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

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

VFR. Light W/NW winds today with sea breezes developing along
the coasts toward midday/afternoon, then dissipating in the
evening. Light south winds tonight and Tuesday. 

KBOS Terminal...High confidence in TAF. 

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday Night through Friday/...High confidence.

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

Wednesday: MVFR/IFR conditions possible. Breezy. RA.

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

Thursday: VFR. Breezy. Slight chance SHRA.

Thursday Night: VFR. Breezy. 

Friday: VFR. Breezy. 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/...High confidence. 

High pressure over the waters today with light winds, flat 
seas, and good visibility. The high moves off to the east
tonight and Tuesday, with winds turning from the south by
Tuesday, but remaining light.

Only concern for recreational boaters is for sea breezes along 
the coastline today with 15-20kt gusts and choppy seas near 
shore, especially when opposing outgoing tide. 

Outlook /Tuesday Night through Friday/...High confidence.

Tuesday Night: Winds less than 25 kt. Seas locally approaching 
5 ft. Chance of rain. 

Wednesday: Low risk for Small Craft Advisory winds with gusts
up to 25 kt. Areas of rough seas. Rain. 

Wednesday Night: Winds less than 25 kt. Rough seas up to 12 ft.
Chance of rain, slight chance of rain showers. 

Thursday: Winds less than 25 kt. Rough seas up to 9 ft. 

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

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

&&

.EQUIPMENT...
NOAA Weather Radio transmitters serving Providence and Hyannis
are 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.

&&

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

&&

$$
SYNOPSIS...WTB/Belk
NEAR TERM...WTB
SHORT TERM...WTB
LONG TERM...Belk
AVIATION...WTB/Belk
MARINE...WTB/Belk
EQUIPMENT...