LexMAWeather

Area Forecast Discussion
for Boston, MA

        
000
FXUS61 KBOX 192357
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
757 PM EDT Wed Sep 19 2018

.SYNOPSIS...
A mix of clouds to the east and sun to the west today. High 
pressure builds into New England tonight and Thursday yielding 
dry cool weather. Warmer Friday ahead of an approaching cold 
front then turning cooler over the weekend as high pressure 
builds into the area from the Great Lakes.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Still expecting lower clouds to return overnight in persistent
NE flow. Based upon some of the high resolution mesoscale 
guidance, also starting to think we might see a few sprinkles 
after midnight, too. Any sprinkles would be mainly across SE MA,
and perhaps along the east slopes of the Worcester hills and 
the Berkshires. Minor tweaks to the forecast to reflect these 
ideas.

Also adjusted temperatures and dew points based on observed
trends.

Previous Discussion...

Satellite imagery this afternoon shows the directional shear in
the atmosphere through the moist lower levels and drier upper
levels, evident by the low clouds streaming in from the
northeast and the scattered high clouds moving west. Partly sunny
skies will continue for western MA and CT while along the coast
the clouds will likely hang around through the night. This means
warmer highs in the CT valley (mid 70s) than along the coast
(60s). The moist northeast flow in response to the surface high
pressure over the Canadian maritimes will continue through the 
overnight and early morning hours as the high pressure begins to
build south. This means likely continuation of stratus Thursday
morning and along with some patchy fog. As far as winds go, 
today the pressure gradient tightens over the Atlantic 
associated with the low to our southeast. This means gusty winds
over the waters, Cape, and islands up to 30 mph. The gradient 
relaxes early Thursday morning and winds will be on the 
decrease. Light winds and partial clearing over the western 
zones overnight will allow for some good radiational cooling in 
western MA/CT along with potential for patchy fog inland 
overnight. Lows dip into the low to mid 50s.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
Heights will again be on the rise through the day Thursday as
the upper ridge builds over the east coast and our surface high
center builds further south. The light winds and subsidence
associated with the high pressure will keep a lid on our low
level moisture and at least partly cloudy skies with some sun
mixed in are likely to persist though the day, with the clearest
skies to the west. There is some uncertainty as to how long 
the clouds will hang on. We could even see some drizzle early, 
especially nearer to the coast. Highs are expected to be 
similar to today in eastern MA/RI, but a few degrees cooler in 
the CT valley, around 70. 

Thursday night a surface low moving up through the Great Lakes
region will drag a warm front up through our region. Most of the
synoptic guidance keeps the majority of the rainfall to our
north but we'll see rain chances increase for northwestern MA
late Friday night/early Friday morning. WAA associated with this
front will potentially work to offset any radiational cooling we
can get if skies clear out enough, but right now temps look to
bottom out in the low to mid 50s.

&&

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

* A warm front will bring a few showers across north central 
  and western areas early Fri
* A cold front approaches late Fri, bringing scattered showers 
  and isolated thunderstorms especially across the interior
* Large high pressure builds in from central and eastern Canada
  Saturday afternoon into Monday, bringing cool, dry conditions
  
Overview...

19/12Z guidance suite remains in rather good agreement with their 
synoptic patterns through much of this weekend. The differences in 
timing and amplitude of a potent mid level shortwave start to creep 
into the forecast early next week. Main forecast theme for the 
overall pattern continues. Nearly zonal flow transitions to weak 
ridging Friday, then back to a more zonal flow this weekend. We may 
see another brief warmup early next week as an upstream trough 
amplifies a ridge over the Northeast USA. Should this occur as 
currently expected, we could be looking at widespread low 
temperatures in the 40s Sunday night.

A low pressure moving across eastern Canada should push its warm 
front through our region Friday, with its cold front crossing our 
region Friday night into Saturday morning. This has been a 
consistent timing for these features. High pressure over northern 
New England dominates this weekend. A pair of weak fronts could be 
near our region early next week, but its a low confidence forecast.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
Forecaster Confidence Levels...

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

Short Term /through Thursday Night/...

Tonight...Moderate confidence.
Areas of MVFR/IFR cigs likely redeveloping across the region.
Patchy fog possible, most likely across interior MA. 

Thursday...Moderate confidence. 
Improving to VFR, but areas of MVFR cigs persisting over
Cape/Islands. 

KBOS Terminal...Moderate confidence in MVFR cigs lifting to VFR
this evening before coming down to IFR overnight.

KBDL Terminal...Moderate confidence. Mainly VFR conditions, but
MVFR cigs possible for a few hours overnight. 

Outlook /Friday through Monday/...

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

Friday Night: Mainly VFR, with areas MVFR possible. Windy with
gusts to 30 kt. Chance SHRA, isolated TSRA.

Saturday: VFR. Breezy. Slight chance SHRA.

Saturday Night through Sunday Night: VFR. 

Monday:

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Thursday Night/...

Decided to post a Small Craft Advisory into Cape Cod Bay tonight
for 5 ft seas across the northern half of the Bay. Also 
extended a Small Craft Advisory for the south coastal MA bays 
and sounds.

Previous Discussion...

Through Tonight...High confidence. 
Northeast winds will increase through the day, gusting to 30 mph
in the south and eastern waters, higher to the southeast closer
to the low pressure center. Seas building to 5-6 ft. Waters 
will be more tranquil further to the north. Wind gusts slowly 
diminish Thursday morning. 

Thursday...High confidence.
NE winds decreasing through the day as high pressure builds
south. Seas will remain up to 5 ft over the eastern waters
through the day. 

Outlook /Friday through Monday/...

Friday: Low risk for Small Craft Advisory winds with areas of
gusts up to 30 kt. Seas up to 5 ft. 

Friday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Local rough seas. Slight chance of rain
showers, isolated thunderstorms. 

Saturday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Local rough seas. Slight chance of rain showers. 

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

Sunday: Winds less than 25 kt. 

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

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 5 AM EDT Thursday for ANZ231>235.
     Small Craft Advisory until 8 PM EDT Thursday for ANZ250-254.
     Small Craft Advisory until 8 AM EDT Thursday for ANZ251-255-
     256.

&&

$$
SYNOPSIS...Belk/BW
NEAR TERM...Belk/BW
SHORT TERM...BW
LONG TERM...Belk
AVIATION...Belk/BW
MARINE...Belk/Nocera/BW