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Area forecast discussion
National Weather Service Boston/Norton Massachusetts
938 am EDT sun Sep 15 2019

Synopsis...

A very nice warm day with comfortable humidity levels to close
out the weekend. A secondary trailing cold front may result in
a few showers tonight into Monday. Otherwise, an extended period
of dry weather is expected beginning Tuesday and likely
continuing into next weekend as Canadian high pressure crests
across the region. 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.

&&

Near term /until 7 PM this evening/...

935 am update...

The fog has burned off with plenty of sunshine across the
region at mid morning, except for Nantucket where it remained
cloudy. We should see sun emerge across Nantucket by the
afternoon.

The weak cold front has pushed south of the region as of mid
morning too, but will begin to washout this afternoon. Main
impact will be drier low level air working into the region with
dewpoints falling into the 50s in most locations, except
portions of the cape/islands where they will remain a bit
higher.

Overall, a beautiful day to close out the weekend. Highs should
top out mainly in the upper 70s to the lower 80s with
comfortable humidity levels. Plenty of sunshine expected too,
although we will see some scattered diurnal cumulus this afternoon
especially across the interior. Dry weather should prevail with
lack of much instability/forcing.

&&

Short term /7 PM this evening through 6 PM Monday/...
tonight and Sunday...

The nearly zonal 500 mb flow across the region will allow moisture
from approaching low pres out of New York state to move in. 00z
guidance giving a strong signal of this low as it shifts east-southeast
overnight into Sunday. With this system coming from moisture
starved inland areas, may not see much precip. Pwats may rise up
to 1.3 to 1.4 inches by Monday afternoon across southern areas,
but not expecting much in the way of quantitative precipitation forecast. May see around 0.1
inches, maybe a bit higher across western areas closer to the
passing low. Expect the precip to push S of the Mass Pike during
the afternoon, but should weaken as it shifts toward the S
coast late in the day.

Temps should fall back to the 50s to around 60 tonight, mildest
along the S coast, with highs on Monday in the upper 60s to
around 70.

&&

Long term /Monday night through Saturday/...
updated 340 am ...

Highlights...

* 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 Massachusetts 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 Ohio 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
seabreezes.

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 European model (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 Massachusetts/Rhode Island 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 European model (ecmwf) solution is a low
probability but will have to be watched given other ec ensemble
members support the operational run.

&&

Aviation /14z Sunday through Thursday/...
forecaster confidence levels...

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

Short term /through Monday/...high confidence.

Today...
VFR with lingering IFR ceilings across ack lifting by afternoon.
West-southwest winds generally 5 to 10 knots by afternoon.

Tonight...
clouds increase from northwest-southeast during the night as another weak
system approaches. Mainly VFR conditions, but may see local MVFR
in any showers or patchy fog. MVFR-IFR visibilities through around 05z
in patchy fog across Cape Cod and the islands. Scattered
showers may push into into north central and northwest mass after 06z with
the next system. Light west-northwest or calm winds.

Monday...
mainly VFR conditions. May see brief, local MVFR in any
showers, but should weaken as they move S during the
afternoon. Light northerly winds early, becoming northwest 5-10 kt
during the afternoon.

Kbos terminal...high confidence in taf trends.

Kbdl terminal...high confidence in taf trends.

Outlook /Monday night through Thursday/...high confidence.

VFR.

&&

Marine...
forecaster confidence levels...

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

Short term /through Monday/...high confidence.

Winds to diminish after frontal passage this morning, though
will stall along the S coast or across the coastal waters by
this evening. Expect west winds up to about 10 kt on the eastern
waters, but light west-SW winds on the southern waters. Mainly good
visibility, but low clouds/fog may linger across the waters
near the mid and Outer Cape with visibility restrictions. Seas 4
ft or less.

Dry conditions across the waters tonight. West wind 10 kt or less
shift to north toward daybreak. Visibility restrictions linger
early tonight across the southern waters to the waters east of Cape
Cod, but should improve by 05z-06z. May see local visibility
restrictions as scattered showers move into the eastern waters
by daybreak. Seas 3 ft or less.

On Monday, area of showers moves across the region rather
quickly, weakening as they push off the S coast late in the day.
May see local visibility restrictions in the showers. North winds at
10 kt or less become light/variable during the afternoon. Seas 3
ft or less.

Outlook /Monday night through Thursday/...moderate confidence.

Monday night: winds less than 25 kt.

Tuesday through thursday: winds less than 25 kt. Areas of seas
approaching 5 ft.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...none.

&&

$$
Synopsis...nocera/evt
near term...Frank

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