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Area Forecast Discussion (AFD)

Issued by Boston / Norton, MA (BOX)

FXUS61 KBOX 161747

Area Forecast Discussion
National Weather Service Boston/Norton MA
147 PM EDT Mon Sep 16 2019

High pressure will bring an extended period of dry weather 
into next weekend. The high will initially be accompanied by 
unseasonably cool weather Tuesday into Thursday morning. A 
gradual warmup is expected, as temperatures possibly rebound 
into the 80s this weekend.


130 PM Update...

Satellite shows not much movement in the deck of mid-high clouds
over CT/coastal RI early this afternoon. Short wave energy 
continues to move through yielding a few scattered light rain 
showers across CT. This is where deepest moisture resides, with
PWATs >1.25" in southern CT and <1" in northern CT. Dry and
sunny elsewhere with seasonable temperatures topping out in the  
70-75 range.


Tonight and Tuesday...

The large high will dominate through this timeframe, with dry
conditions in place. N winds will continue tonight into Tuesday
morning, then shift to NE by midday or early afternoon. Will see
wind gusts up to around 20 kt along the coast late tonight and

With lighter winds inland tonight, temps will drop with the
mainly clear skies in place. Temps will bottom out in the 40s,
lowest in the normally colder valley locations, ranging to the
mid-upper 50s along the immediate E coast. 

Readings will tend to rebound, but will remain cooler along the
coast with highs only in the mid to upper 60s and the higher
inland terrain, ranging to around 70 across the coastal plain
and the CT valley.


Updated 330 AM ...


* Very pleasant dry stretch of weather this period
* Fall-like temps mid week then summer warmth for the weekend


Amplifying upper air pattern this period marked by an anomalous
northwest Atlantic trough and building MS Valley/Great Lakes 
ridge. This places New England in dry anticyclonic/NW mid level 
flow. Thus not expecting any precipitation during this period 
(Tue night thru Sunday) 


Given the high amplitude upper air pattern large temperature 
fluctuations expected this period. Keep in mind normal temps 
this time of year are are highs 70-75 and average lows 53-58.

Anomalous northwest Atlantic trough delivers subzero 850 mb 
temps across the Maritimes Tue night with 850 temps down to +3C 
over eastern MA Wed morning! Thus cooler than normal temps here 
with lows in the 40s (30s & frost possible!)and highs only in 
the 60s mid week despite plenty of sunshine. Given the dry 
airmass, light winds and mainly clear skies derived min temps 
from the colder MOS guidance. After another chilly start Thu 
morning airmass slowly begins to modify with height rises in 
response to mid level ridge building into New England from the 
OH Valley. Highs will rebound into the low 70s Thu, near 80 
Friday, low 80s Saturday and possibly mid 80s Sunday. Given 
Euro ensembles have +17C air at 850 mb streaming across 
southern New England Sunday, leaned toward the warmest guidance 
(WPC) here. 

Hurricane Humberto...

No senSible weather impacts for southern New England as 
Humberto tracks out to sea passing very close to Bermuda 
Thursday morning. By Fri anomalous northwest Atlantic trough is 
expected to capture Humberto and shift its track northward, 
still passing well east of New England. However this northward 
trajectory will likely bring large swells into the New England 
waters. So a concern this weekend is as temperatures warm into 
the 80s especially Sunday, beachgoers may have to contend with 
large/rough surf and strong rip currents at ocean exposed 
beaches of RI/MA. Unfortunately now that it's mid to late Sep 
most if not all beaches no longer have lifeguards on duty.


Forecaster Confidence Levels...

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

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

18Z update...

This afternoon...VFR conditions. Mid and high clouds mainly
across CT, western MA, coastal RI this afternoon, diminishing
with time. Low chance for VCSH across N central/NE CT through 
mid afternoon. N-NW winds at 5-10 kt.

Tonight...VFR. Light N/NW winds. 

Tuesday and Tuesday night...VFR. Light N winds becoming NE.
Tuesday night toward early Wed may see some low end VFR CIGs
from ocean effect clouds. 

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF. 

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

Tuesday Night: VFR. 

Wednesday through Wednesday Night: VFR. Breezy. 

Thursday through Friday: VFR.


Forecaster Confidence Levels...

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

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

Overnight and Monday...Weak pressure gradient will allow winds 
and seas to remain well below small craft advisory thresholds.

Monday night...A cold front will cross the waters Monday
evening. Decent mixing in the cool air advection pattern should
yield a period of northerly lower 20 knot wind gusts and 2 to 4
foot seas. We can not rule out brief SCA conditions, but threat
is too marginal to hoist any headlines at this point.

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

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

Wednesday Night: Winds less than 25 kt. Local rough seas. 

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

Friday: Winds less than 25 kt. Local rough seas.




LONG TERM...Nocera