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Area Forecast Discussion (AFD)

Issued by Boston / Norton, MA (BOX)

FXUS61 KBOX 170218

Area Forecast Discussion
National Weather Service Boston/Norton MA
1018 PM EDT Mon Sep 16 2019

High pressure will continue to bring an extended period of dry 
weather right through the weekend. The high will initially be 
accompanied by rather cool temperatures Tuesday night into Thursday 
morning. A warmup occurs thereafter with unseasonably warm 
afternoons expected by the weekend as highs may reach into the 80s.


No major changes to the forecast this evening. Brought the
forecast back in line with observed trends.

A ridge of high pressure in control will result in mainly clear
skies, light winds and a good night of radiational cooling
across the region. Low temperatures by daybreak should be down 
into the 40s to the lower 50s in most locations.


Pleasant, Fall-like day on tap for Tuesday. Under the influence of a 
building surface high pressure, with dry northwest flow at the mid 
levels downstream of an amplified ridge over the Great Lakes region 
we will be dry will plenty of sun. The cooling temperature 
trend also continues, dropping below normal for mid September as
low/mid level flow becomes N then NE around the high. This 
ushers in cold Canadian air...2-5C at 850mb by early Wednesday! 
At the surface we can expect low temps in the mid to upper 40s. 

One thing to watch given the anomolously cold NE flow over our 
still relatively warm ocean waters will be the introduction of some 
ocean affect clouds late Tues and overnight, maybe even some
light rain/drizzle. The column is very dry above 800mb but given
the substantial temp differential and low level moisture we may
squeeze out some light precip over northern and eastern MA
overnight; certainly nothing substantial or widespread



* Extended period of dry weather continues through the weekend
* Cool Wed/Wed night with moderating temps Thu and especially Fri
* Unseasonably warm afternoon temps this weekend through Mon 
* High Surf/Dangerous Rip Currents possible by Fri and Sat


Amplifying trough over the Canadian Maritimes will allow for a shot 
of cool air Wed into early Thu am.  North to northeast low level 
flow will probably generate a period of clouds and perhaps even a 
brief sprinkle or two Wed am.  The main story though will be the 
cool temperatures with highs mainly in the 60s Wed, perhaps 
approaching 70 in the lower CT River Valley.  The coolest highs on 
Thu will be found on the eastern MA coast, where highs will struggle 
to get past the lower 60s with the onshore flow.

Large high pressure in control will allow for rather cool temps Wed 
night into early Thu am.  Lows should be well down into the 40s with 
perhaps some middle to upper 30s in the normally coolest outlying 
locations.  This may lead to some patchy frost in a few of these 
spots, but even if that occurs it should not be widespread.

Upper level ridging over the southern plains begins to push 
northeastward Thu into Fri allowing for moderating temperatures 
especially by Fri. The ridge will then flatten a bit by the weekend 
into Mon. This will allow more of a west southwest flow aloft and 
even warmer temperatures to overspread the region by the weekend 
into next Monday.  A good shot we see high temperatures reach into 
the 80s for at least a couple of those days.  These readings are 
generally 10 to 15 degrees above normal.

The extended period of dry weather will continue through the weekend 
with nothing more than perhaps a sprinkle or two Wed am with large 
surface high pressure in control.

Meanwhile, Hurricane Humberto currently well east of the Florida 
coast will lift northeast, passing well east of our region by
late in the week. The only impact will be from swell resulting 
in high surf/dangerous rip currents by Fri and into the weekend.
This is a concern though for beachgoers especially given it 
will be occurring with unseasonably warm temperatures.


Forecaster Confidence Levels...

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

Short Term /through Tuesday Night/...

Tonight...High confidence. VFR conditions with light winds. 

Tuesday...High confidence. VFR. N wind becoming NE at 5 to 15 
knots. Gusts into the lower 20 knots may occur across the Cape 
and Islands by mid to late afternoon.

Tuesday night...Moderate confidence. A period of MVFR ceilings
may develop along with a passing sprinkle or two possible. 

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF. 

Outlook /Wednesday through Saturday/...Moderate to high 

Wednesday: A period of MVFR ceilings are possible Wed morning 
before VFR conditions return. MVFR ceilings may linger a bit 
longer across the Cape and Islands before improvement to VFR. 
Breezy too especially along the coast.

Thursday and Thursday Night: VFR. 

Friday: VFR. Breezy. 

Friday Night: VFR. 

Saturday: VFR. Breezy.


Forecaster Confidence Levels...

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

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

Tonight...A cold front will cross the waters this 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 

Tuesday...N/NE wind gusts into the lower 20 knots. May see a few
gusts approaching 25 knots across some of our southeast waters.
Seas 2-4 ft.

Tuesday Night...NE wind gusts around 20 knots at times in the 
cool air advection pattern. Seas increasing 3-5 ft by early 
Wednesday morning across the open waters.

Outlook /Wednesday through Saturday/...Moderate confidence.

Wednesday through Wednesday Night: Small Craft Advisory winds 
with gusts up to 25 kt. Areas of rough seas. 

Thursday through Thursday Night: Winds less than 25 kt. Local
rough seas. 

Friday through Friday Night: Winds less than 25 kt. Rough seas
up to 10 ft. 

Saturday: Winds less than 25 kt. Rough seas up to 8 ft.