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Area Forecast Discussion (AFD)

Issued by Boston / Norton, MA (BOX)

FXUS61 KBOX 151817

Area Forecast Discussion
National Weather Service Boston/Norton MA
217 PM EDT Sun Sep 15 2019


High pressure will bring an extended period of dry weather into
next weekend, other than perhaps a brief spot shower or two on 
Monday. The high will initially be accompanied by unseasonably 
cool weather Tuesday into Thursday morning. A gradual warmup is 
expected with temperatures possibly rebounding into the 80s 
Friday and Saturday.



West to northwest flow aloft will allow for mid and high level
cloudiness to increase tonight ahead of a weak wave of low
pressure. Nonetheless, expect dry weather to continue tonight
with low temperatures mainly in the 50s by daybreak Monday. 
Winds will be rather light too, so a pleasant night of weather 
is on tap for the region.




A weak wave of low pressure across the southern Great Lakes
early Mon morning will slide southeastward through the day. 
This will take the better forcing/moisture to the southwest of 
our region. So while we probably will see a period of some
cloudiness, at least across our CT/RI and SE MA expect little if
any rain other than a few spot showers. Greatest risk will be 
across northern CT and near the south coast, but regardless dry
weather should dominate in this region too.

High temperatures on Monday will probably still reach the lower
to middle 70s in many locales given at least some partial 

Monday night...

High pressure in Quebec will force a cold front south of the
region Monday evening. While dry weather should continue Monday
night it will turn cooler on northerly winds. Low temperatures 
by daybreak Tuesday should mainly be in the middle 40s to the 
lower 50s.


Updated 340 AM ...


* An extended period of dry weather is likely Tuesday thru Saturday
* Fall-like Tue/Wed with highs only in the 60s and lows in the 40s 
* Summer-like warmth possible Fri and Sat with highs in the 80s

Precipitation ...

Looks like an extended period of dry weather as high amplitude 
pattern evolves with deep closed mid level low over the northwest 
Atlantic along with upstream 588 dam ridge from the MS Valley into 
the Great Lakes. This setup supports dry northwest flow into New 
England. Thus dry weather should prevail Tue thru Sat per ensembles 
and deterministic guidance. Definitely a pleasant stretch of weather. 

Temperatures ...

Very pleasant fall-like weather this period featuring mild days and 
cool nights. Cooler air begins to advect into the region Monday 
night into Tue as trailing short wave energy dives into the base of 
Maritime trough. EC ensembles have core of cool air centered over 
eastern MA Wed into Thu morning with 850 mb temps down to only +3C! 
This will translate to highs only in the 60s Tue and Wed despite 
plenty of sunshine. Normal high this time of year is 70-75. Lows 
will be mainly in the 40s, low 50s in the urban areas. As 588 dam 
ridge over the OH Valley builds eastward into New England expect a 
noticeable warmup with summer-like warmth possible Fri and Sat as 
highs likely climb into the 80s with EC ensembles offering +15C at 
850 mb. Given 1025+ mb Canadian high pressure over the region much 
of next week, weak pgradient/light winds and dry airmass will 
support radiational cooling. Thus will lean toward the cooler MOS 
nighttime temps. Light pgradient will also support afternoon 

Tropical Storm Humberto ...

Good model agreement that Humberto will track away from the east 
coast next week and then possibly impact Bermuda around Thursday. 
Thereafter the ECMWF continues its theme of anomalous western 
Atlantic trough capturing Humberto and lifting the tropical cyclone 
northward across eastern Georges Bank and towards Nova Scotia 
Fri/Sat. While this track is still southeast of New England it's 
close enough to watch closely. At the very least this track would 
yield large swells for MA/RI waters and with temps likely warming 
into the 80s Fri/Sat, rough surf and strong rip currents could be a 
concern for ocean exposed beaches. The ECMWF solution is a low 
probability but will have to be watched given other EC ensemble 
members support the operational run.


Forecaster Confidence Levels...

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

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

Tonight...VFR conditions continue despite an increase in some
mid and high level cloudiness.  Rather light winds.

Monday...VFR conditions dominate despite some mid level
cloudiness. Low risk of brief MVFR conditions south of the MA 
Turnpike and perhaps a spot shower or two. Rather light winds.

Monday night...VFR.  North winds of 5 to 10 knots.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF. 

Outlook /Tuesday through Thursday/...High confidence.



Forecaster Confidence Levels...

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

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

Tonight and Monday...Weak pressure gradient will keep winds and
seas 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 through Thursday/...Moderate confidence.

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




LONG TERM...Nocera