Area Forecast Discussion
National Weather Service Boston/Norton MA
213 PM EDT Thu May 6 2021

.SYNOPSIS...
High pressure will maintain dry and seasonable weather tonight
and Friday as it becomes centered over the Gulf of Maine. A few
showers are possible Saturday, but most of the day should be
dry, as a coastal low passes offshore. Dry weather briefly 
returns Sunday, before rain possibly impacts the region Sunday 
night into Monday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
215 PM Update:

Subsidence and drying in wake of mid level short wave has
resulted in diminishing cloud cover across SNE this afternoon.
Gusty NW winds will subside late this afternoon, leading to
clear skies and light winds tonight with a dry airmass in place.
Although we will see some high clouds stream into region later 
tonight, they should do little against radiational cooling, so
sided toward colder MOS temperatures for lows tonight - ranging
from some mid 30s in NW MA to mid 40s along coast. 

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
215 PM Update:

High pressure builds to Gulf of Maine Friday and Friday night.
This sets up an onshore flow but forecast soundings show fairly
dry air through column. Consensus of short range models and 
ensembles keep any showers to west of New England through Friday
night, which makes sense given amplifying upper flow and 
surface ridge remaining in place. Planning on a dry forecast,
although will begin to increase PoPs around daybreak Saturday to
lead into extended forecast.

Onshore flow Friday means cooler temps along coast (50s Boston)
with warmer temps inland (low to mid 60s Hartford/Springfield. 

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Highlights...

* Cooler than normal temperatures through midweek

* Periodic chances of rain, first on Saturday, then more 
  substantial rain Sunday night and Monday

Details...

Friday night and Saturday...

Clouds will be on the increase overnight Friday into Saturday 
morning as northern stream energy rounds the base of the broad 
mid level trough, with a weak low center to the northwest. Not 
expecting any precipitation overnight. Lows dip into the low 
40s. 

By Saturday that lobe of mid/upper level energy crosses the 
region as downstream the coastal low continues to deepen as it 
moves into the maritimes. An inverted trough extending west from
that low center will provide enough of a focus for some widely 
scattered rain showers Saturday into Saturday night, but not a 
washout by any means. Many places will be dry at any given time.
Overall we are seeing a downward trend in the rain expected for
the first half of this weekend compared to what we were looking
at the last few nights. 

Sunday...

A break in the unsettled weather comes Sunday thanks to a 
transient mid level ridge and building high pressure at the 
surface. This means a good deal of sun, with seasonable 
temperatures, in the mid to upper 60s, even for coastal regions 
thanks to westerly flow. 

Next week...

No big change in the weather pattern is expected through the 7 
day forecast. The broad troughing over the east coast continues 
through at least Wednesday, with periodic shortwaves bringing 
rain chances to southern New England. The best shot at
widespread rain is Sunday night and Monday as a surface low 
moves from the Ohio Valley into southern New England bringing a 
deep plume of moisture with it (PWATs greater than 1 inch). 
Perhaps a drying trend for Tuesday into mid week under a weak 
ridge, but confidence is low at this point. Temperatures will 
not see a big warm up through at least mid week either, 
remaining in the mid 60s each day.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
Forecaster Confidence Levels.

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

18Z Update: High confidence.

VFR. NW winds gusting to 20-25kt subside during afternoon and
become light E/SE Fri. Should see VFR ceilings aoa 080 develop
Fri night with P6SM -SHRA possible in western MA toward 12Z Sat.

KBOS TAF...High confidence. NW flow thru tonight. E flow Fri.

KBDL TAF...High confidence.

Outlook /Saturday through Monday/...

Saturday: Mainly VFR, with local MVFR possible. Chance SHRA.

Saturday Night: VFR. 

Sunday: VFR. Breezy. 

Sunday Night through Monday: VFR. Breezy. Chance SHRA.

&&

.MARINE...
215 PM Update:

Based upon latest buoy observations and wave guidance, plan to
expire Small Craft Advisories through this evening as winds and
seas subside. Otherwise lighter E/SE winds expected Fri and Fri
night as weak high pressure remains over New England waters.

Outlook /Saturday through Monday/...

Saturday: Winds less than 25 kt. Areas of seas approaching 5 
ft. Slight chance of rain showers. 

Saturday Night: Winds less than 25 kt. Seas up to 5 ft. 

Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Slight chance of rain showers. 

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

Monday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain showers. 

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 4 PM EDT this afternoon for
	 ANZ250.
		 Small Craft Advisory until 8 PM EDT this evening for
	 ANZ254>256.
	 Small Craft Advisory from 3 AM to 6 PM EDT Friday for ANZ255.

&&