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Area Forecast Discussion (AFD)

Issued by Boston / Norton, MA (BOX)

FXUS61 KBOX 210838

Area Forecast Discussion
National Weather Service Boston/Norton MA
438 AM EDT Sat Sep 21 2019

High pressure remains in control into Monday with summer-like 
temperatures and dry weather. A cold front will bring a period
of showers late Monday and Monday night followed by cooler, but
seasonably warm, weather through the rest of next week.


Dry weather continues with high pressure centered to our south.
Light westerly winds will become light south to southwest 
across the interior. A different story towards the coast, where 
the combination of above normal temperatures and light winds 
will lead to seabreezes. Max temperatures today should be a few 
degrees higher than Friday, even towards the coast.

While the swell from Hurricane Humberto will be subsiding, it 
will not be entirely gone. Still an elevated risk for rip 
currents Saturday. If going to the beach this weekend, be 
especially cautious if there are no lifeguards present.


Dry weather tonight into Sunday. The warming trend continues
with a high pressure off to our southeast producing an
increasing southwest wind. Above normal temperatures through 
this period.


*/ Highlights...

 - Rain anticipated late Monday into Monday night  
 - Thereafter mild days, cool nights, dry the remainder of the
 - Temperatures running above average throughout

*/ Overview... 

Amplifying pattern. Impressive N Pacific jet signaled by a 
+WPO/+EPO that cascades energy and mild air over the CONUS 
initially. Kicking downsheared energy across the 4-corners 
region, a closing mid-level low latched onto continental 
moisture, there's a chance for rainfall around Monday night 
discussed in more detail below. However by late September a 
pattern-amplification emerges. One-two punch, NW Pacific Tapah 
becoming post-tropical, ingested into the Bering straight low, 
subsequent latent heat release amplifies the longwave trof that 
re- captures earlier cut-off N Pacific energy. Heightened AK 
ridge that ultimately downshears a deep trof across the W CONUS 
into the end of September, PNA becomes largely negative as does 
the EPO/WPO. With a continued active N Atlantic tropics 
emphasized by the phase 1 MJO, an impressive heat pump and 
anomalously higher heights emerge over the E CONUS. No surprise 
to see above average temperature trends and below average 
precipitation per CPC. However along the NE-periphery of the 
heat-bubble no-trouble, there are opportunities for cooler air 
and rainfall chances along SE-sweeping cold front boundaries. So
not entirely convinced we'll see the brunt of the heat expected
for the SE CONUS N into the mid-Atlantic. Perhaps just on the 
cusp yet however for late September is still above average when 
highs are normally around 70 and lows normally around 50. A 
pattern of mild days and cool nights, some shots of wet-weather 
in-between. Break down the details below. 

*/ Discussion...

Monday into Monday night...

Widespread showers and appreciable rainfall remains possible. 
Lean towards wetter solutions given consensus forecast mid-level
closed- low solution acting on a narrow-ribbon of continental 
moisture. Much of the same, precipitable waters up around 
1.75-inches, warm-cloud layer up around 12 kft preceding the 
sweeping cold front. A moist- adiabatic, conditionally-unstable 
profile, albeit brief and right along the front, expected lift, 
low-level convergent forcing, and synoptic ascent beneath 
cyclonic flow and diffluence aloft makes a case of decent upward
motions that should promote collision as well as coalescence 
such that decent rains should develop. Positive to a neutral 
tilt trof with modest W/SW shear preceding, instability is in 
question given marginal, moist-adiabatic lapse rates. Rumbles of
thunder not ruled out, nor heavier downpours. Chance to likely 
PoPs. There's increasing signal of the possibility of 
significant rainfall with amounts around 0.50 inches. 

Rest of the week...

Rain chances around Thursday night appear suppressed by the 
weight of increasing heights across the E CONUS. However with 
the prior mentioned amplified pattern tightening over the W and 
central CONUS that New England finds itself beneath NW flow 
aloft, the opportunity for some slightly cooler air and rainfall
chances along SE sweeping cold fronts over the weekend into 
early next week. However overall temperatures still look to run 
above average.


Forecaster Confidence Levels...

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

Short Term /through Sunday/...High confidence.

VFR to continue though Sunday. Generally light west winds today
across the interior. Seabreezes developing by midday along the 
coasts, impacting coastal terminals. Isolated IFR in low clouds
and fog for portions of the CT River valley around KORE this 

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF. 

Outlook /Sunday Night through Wednesday/...

Sunday Night: VFR. Breezy. 

Monday: VFR. Breezy. Chance SHRA.

Monday Night: VFR. Breezy. SHRA likely, slight chance TSRA.

Tuesday: VFR. Slight chance SHRA.

Tuesday Night through Wednesday: VFR. 


Forecaster Confidence Levels...

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

Short Term /through Sunday/...High confidence.

Adjusted the timing of Small Craft Advisories for today. Based
on latest buoy reports, swell is diminishing slower than
previously thought. Rough seas continuing up to 8 feet across 
portions of the outer coastal waters. 

Swell from Hurricane Humberto will continue to diminish through
the day. Relatively light winds will mean smaller wind waves. 
Local seabreezes near the coast today. Relatively tranquil winds
and seas expected tonight into Sunday, with light S to SW 

Outlook /Sunday Night through Wednesday/...Moderate confidence.

Sunday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of seas approaching 5 ft. 

Monday: Moderate risk for Small Craft Advisory winds with gusts
up to 25 kt. Areas of rough seas. Chance of rain showers. 

Monday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of rough seas. Rain showers likely,
slight chance of thunderstorms. 

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

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

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


MA...High Rip Current Risk through this afternoon for MAZ022-024.
MARINE...Small Craft Advisory until 11 AM EDT this morning for ANZ250-
     Small Craft Advisory until 7 AM EDT this morning for ANZ251-


LONG TERM...Sipprell