Lexington Weather

Area Forecast Discussion
for Boston, MA

        
000
FXUS61 KBOX 202250
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
650 PM EDT Sun Oct 20 2019

.SYNOPSIS...
South coastal skirting rain overnight associated with the 
remnants of Nestor. Majority clearing out Monday however clouds
lingering across the Cape and Islands. Dreary conditions 
returning out ahead of an approaching cold front Tuesday, with 
a period of showers Tuesday night into early Wednesday. Dry and 
seasonably mild conditions follow Wednesday afternoon into 
Friday although a cold front may bring a few showers Friday 
afternoon and night. High pressure builds in for next weekend.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
645 PM update...

Remnant moisture from Nestor getting drawn northward ahead of 
weak mid level shortwave with area of light rain across central
MA and northern CT. Drier air is beginning to move in from the 
west with rain eroding across western MA. Meanwhile, low levels
across eastern MA remain dry and this rain will struggle to get
into NE MA where low levels don't really moisten up. So expect
the light rain to gradually dissipate across interior MA and CT
through the evening with focus shifting to the south coast 
overnight. Blended previous forecast with hi-res guidance for
PoPs/QPF. Rainfall 0.10-0.20" confined to immediate south coast
increasing to around 0.50" for ACK. 

Breezy E/NE winds developing Cape/Islands late tonight not only
with isallobaric wind but also the gradient wind subsequent of 
Nestor's close approach. Gusts up to 30 mph are possible towards
Monday morning across the Islands.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
2 pm update...

Monday into Monday night...

Nestor remnants not going far. N-Plains cyclone occludes, tightens 
towards 990 mb, the mid-upper level ridge downstream builds across 
the NE CONUS pushing the mid-latitude flow northward resulting in a 
wobbling, cut-off Nestor lingering S/E of the 40N/70W benchmark. An 
E-fetch drawn from the wrapping tropical low-level moisture round 
Nestor back towards the approaching midweek occluded front, riding 
beneath a dry-inversion settling down around H8-9. Moisture pooling, 
saturating, while partial clearing is expected on Monday, going into 
Monday night forecasting lowering conditions with nocturnal cooling, 
brought inland by a stout E low-level jet, upsloping, can't rule out 
some drizzle as well for E/SE-coastal MA. So dry and seasonable for 
Monday with highs getting into the low 60s for most of New England 
but E/SE-coastal MA with onshore flow and lingering clouds. Then 
overnight it turns dreary with lows in the 40s.

&&

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

* Low clouds Tue with light rain or patchy drizzle at times
* Period of showers Tue night into early Wed then improving 
  conditions
* Dry and mild weather Thu/Fri
* Continued mainly dry and cooler for next weekend

Tuesday into Wednesday...

Easterly flow Tue with considerable low level moisture 
developing will result in low clouds overspreading much of the 
region. Models generating light QPF moving in from the east.
This is likely a signal for some light rain or patchy drizzle 
developing within moist easterly flow beneath dry air through 
the mid levels. Then approaching shortwave and attending cold 
front moves into the region Tue night. Deep moisture plume and 
low level convergence will result in a period of showers moving 
west to east across SNE. The low level jet is somewhat fractured
and not particularly strong so not expecting an organized area 
of heavy rainfall. But some locally heavier rain is possible Tue
night as a wave develops on the front which enhances low level 
convergence. However, better chance likely across Maine on Wed 
north of the developing surface wave where decent E/SE low level
jet develops. Much of the shower activity should be east of New
Eng by Wed morning, but can't rule out a few lingering showers 
into Wed morning, mainly across eastern MA. Otherwise, expect 
increasing sunshine Wed as good mid level drying moves in with 
mild temps well into the 60s. 

Thursday through Sunday...

High pres moves off the mid Atlc coast Thu with return flow 
developing. Sunshine and seasonable temps for Thu. Models differ on 
the pattern for the end of the week into the weekend. ECMWF showing 
a split flow pattern with dominant northern stream into the weekend 
with southern stream low pres approaching late in the weekend. GFS 
has more of phased system with rain impacting SNE on Sat. Leaning 
toward ECMWF solution which has support of other global guidance 
including UKMET/GGEM. This supports a frontal passage late Fri/Fri 
night which may be accompanied by some showers then high pres 
building in for the weekend with dry and cooler conditions. Will 
have to watch possible southern stream system approaching late in 
the weekend. If timing speeds up then some rain may begin to impact 
the region sometime Sunday, but going with a dry forecast for now.

&&

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

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

Short Term /through Monday Night/...

00z update...

Tonight...Moderate confidence. 
BKN-OVC VFR cigs with MVFR developing along the south coast, 
with risk of IFR across the Cape and Islands late tonight.
Clearing western MA and CT valley toward daybreak. Increasing 
E/NE wind 10 to 15 kts along the S coast, as high as 20 kts 
across the Cape and Islands with gusts as high as 30 kts that 
heighten early morning Monday.

Monday...Moderate confidence.
Low-end VFR - MVFR CIGs eroding S/E through morning except out
across southeast MA. A NE wind persisting, MVFR BKN-OVC CIGs 
linger across the Cape and Islands much of the day. Breezy E/NE
winds throughout especially along the coast, 10 to 15 kts, gusts
to 25 kts. 

Monday night...Moderate confidence.
BKN-OVC lowering CIGs over all of S New England. Confident MVFR
however could see IFR issues. Winds becoming E, remaining 10 to
15 kts, strongest along the coast with gusts up to 25 kts.

KBOS Terminal...
High confidence in TAF.

KBDL Terminal...
High confidence in TAF.
  
Outlook /Tuesday through Friday/...Moderate confidence.

Tuesday: Mainly MVFR, with local IFR possible. Breezy. Chance
RA, chance DZ.

Tuesday Night: Mainly MVFR, with areas IFR possible. SHRA
likely.

Wednesday: Mainly VFR, with local MVFR possible. Breezy. 

Wednesday Night: VFR. Breezy. 

Thursday through Thursday Night: VFR. 

Friday: Mainly VFR, with local MVFR possible. Breezy. 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 Monday Night/...

2 pm update...

Nestor remnants sweep N/E near and SE of the 40N/70W benchmark
overnight, stalling and wobbling Monday into Monday night. With
high pressure settled N across New England into the SE Canadian
maritimes, the neighboring airmasses yield a stout E/NE gradient
wind into S New England. Generally 10 to 15 kts with gusts up as
high as 30 kts Monday morning. Seas potentially building 6 to 8
feet over the S/SE waters. SMALL CRAFT HEADLINES posted for those
outer waters up against the S-coast, Cape Cod and Islands. 

Rain overnight tonight, lower visibility with rain especially on
the S-waters. Partial clearing Monday, but lower conditions return
Monday night along with forecast drizzle. 

Outlook /Tuesday through Friday/...Moderate confidence. 

Tuesday: Winds less than 25 kt. Areas of rough seas. Chance of
rain, chance of drizzle. 

Tuesday Night: Winds less than 25 kt. Areas of rough seas. Rain
showers likely. 

Wednesday: Low risk for Small Craft Advisory winds with gusts
up to 30 kt. Seas up to 5 ft. Chance of rain showers. 

Wednesday Night through Thursday: Winds less than 25 kt. Seas
up to 5 ft. 

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

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 6 AM to 8 PM EDT Monday for 
     ANZ232>234.
     Small Craft Advisory from 4 AM Monday to 6 AM EDT Tuesday for 
     ANZ235-237.
     Small Craft Advisory from 2 PM Monday to 6 AM EDT Tuesday for 
     ANZ250.
     Small Craft Advisory from 2 AM Monday to 6 AM EDT Tuesday for 
     ANZ254-255.
     Small Craft Advisory from midnight tonight to 6 AM EDT Tuesday 
     for ANZ256.

&&

$$
SYNOPSIS...KJC/Sipprell
NEAR TERM...KJC/Sipprell
SHORT TERM...Sipprell
LONG TERM...KJC
AVIATION...KJC/Sipprell
MARINE...KJC/Sipprell