Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus61 kbox 180206 
afdbox

Area forecast discussion
National Weather Service Boston/Norton Massachusetts
1006 PM EDT Tue Sep 17 2019

Synopsis...
high pressure will maintain an extended period of dry weather
into the weekend other than perhaps a brief spot
shower/sprinkle tonight into Wednesday morning. Cool
temperatures into Thursday will moderate by Friday with
unseasonably warm afternoons this weekend into Monday. Distant
Hurricane Humberto will bring high surf and dangerous rip
currents late this week, which should peak on Friday. A cold
front may finally bring a few brief showers sometime Monday
and/or Monday night, but if any rain occurs amounts will be
light.

&&

Near term /until 6 am Wednesday morning/...

Only minor tweaks to the forecast this evening to bring it back
in line with observed trends.

Previous discussion...

Upper trough over the Maritimes with upper jet flow crossing
New England as it circles the trough. One shortwave moved
through the flow and across our area this morning and midday,
bringing cold advection aloft and helping trigger the clouds
that formed across eastern and central Massachusetts/RI/NE CT.

That shortwave has moved off, but a second will move through the
flow tonight, generating another period of clouds. But the air
is dry beneath the clouds, and so we expect only isolated
sprinkles/light showers during the overnight.

Temperatures upstream last night were in the 40s. We will
forecast min temps of 40s to low 50s.

&&

Short term /6 am Wednesday morning through Wednesday night/...
upper shortwave overhead first thing Wednesday morning, but
moves off to the southeast during the day. So we may start the
day with a period of clouds until the shortwave moves offshore.
Could also be an isolated shower.

High pressure will build over New England and the Maritimes,
bringing clearing skies and northeast wind. The strongest winds
will be along the South Coast and islands with sustained 10-20
kt and gusts 20-25 kt.

Temps aloft will be 4-6c, which suggest high temps in the 60s.

High pressure brings clear skies and light wind Wednesday night.
Min temperatures upstream under the high were mostly in the 40s
but with a report of 38 in northern Ontario. We will go with
upper 30s to mid 40s inland and 45-50 along the coast.

&&

Long term /Thursday through Tuesday/...
highlights...

* extended period of dry weather continues through the weekend
* above normal temps return Fri with 80s likely Sat/sun/Mon
* high surf/dangerous rip current late this week peaking on Fri

Details...

Thursday and Friday...

Upper level ridging over the south central states will expand
northeastward Thu and Fri. This warming process will be a bit
delayed at the surface on Thu given high pressure overhead and a
rather chilly start. Nonetheless, plenty of sunshine should allow
highs Thu afternoon to recover into the 60s to around 70. Light
winds and a dry airmass in place should allow for good radiational
cooling Thu night/early Fri morning. Low temps by daybreak Fri will
be well down into the 40s with a few upper 30s possible in the
normally coolest outlying locations. Plenty of sunshine Fri and
higher heights/better mixing should allow for afternoon highs to
recover well into the 70s to near 80.

Saturday/Sunday/Monday...

The upper level ridge of high pressure over the southeast states
will push a bit further southwest. This will allow a better
southwest flow of air aloft and even warmer temperatures this
weekend into Mon. We expect high temperatures reaching into the 80s
this weekend and Mon across many locations. These highs will be
close to 15 degrees above normal for this time of year.

As for precipitation chances, surface high pressure will remain in
control this weekend allowing the prolonged period of dry weather to
continue. An approaching cold front may bring a few brief showers
sometime Mon and/or Mon night, but deeper moisture/instability will
be lacking so any rainfall that occurs should be light and short-
lived.

Tuesday...

Somewhat cooler air should move into the region behind monday's cold
front. Still probably will have highs reach into the 70s across
much of the region with mainly dry weather.

High surf & dangerous rip currents from distant Humberto...

Hurricane Humberto well east of the Carolina coast will continue to
lift northeast. It will pass well east of our latitude by Friday
with no impacts other than swell resulting in high surf/dangerous
rip currents to some of our ocean exposed beaches late this
week. The main time frame of concern is Thu through Sat with the
worst of it peaking on Friday. Given the above normal
temperatures by Fri/Sat and ideal late season beach weather,
there is concern for beachgoers. A high surf advisory may
eventually be needed by Fri and perhaps lingering into Sat.
Conditions on the beaches should improve by sun.

&&

Aviation /02z Wednesday through Sunday/...
forecaster confidence levels...

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

Short term /through Wednesday night/...

Tonight and Wednesday...
mainly VFR with scattered to broken mid level cloudiness at
times tonight into Wed. Some brief marginal MVFR cigs are also
possible at times, especially across southeast New England. NE
wind gusts of 20 to 25 knots will develop on Wed across eastern
New England, with perhaps some gusts up to 30 knots across
Nantucket.

Wednesday night...
VFR.

Kbos terminal...high confidence in taf.

Kbdl terminal...high confidence in taf.

Outlook /Thursday through Sunday/...

Thursday through sunday: VFR.

&&

Marine...
forecaster confidence levels...

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

Short term /through Wednesday night/...high confidence.

Tonight...

High pressure to our north will bring northeast winds and 10-20
kt speeds with a few gusts near 25 knots across our southern
waters towards daybreak. This will build seas slowly, with the
southern outer waters reaching 5 feet toward morning. A Small
Craft Advisory has been issued for the outer waters for tonight.

Wednesday...

Expanded Small Craft Advisory headlines to include all waters except Boston
Harbor. Decent cool advection over the relatively mild ocean
should yield NE wind gusts of 20 to 25 knots across most open
waters and 25 to 30 knots across our southern waters. Seas build
to between 4 and 7 feet across the open waters.

Wednesday night...

High pressure builds over the waters at night. Winds and seas
will linger on the outer waters but diminish nearshore. Small
Craft Advisory continues on the outer waters.

Outlook /Thursday through Sunday/...moderate confidence.

Thursday through Thursday night: winds less than 25 kt. Areas
of rough seas.

Friday: winds less than 25 kt. Rough seas up to 12 ft.

Friday night: winds less than 25 kt. Rough seas up to 10 ft.

Saturday: winds less than 25 kt. Seas up to 5 ft.

Saturday night: winds less than 25 kt. Seas locally approaching
5 ft.

Sunday: winds less than 25 kt.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...Small Craft Advisory from 8 am Wednesday to 2 am EDT Thursday
for anz231>234.
Small Craft Advisory from 10 am to 8 PM EDT Wednesday for
anz236.
Small Craft Advisory from 8 am Wednesday to 8 am EDT Thursday
for anz235-237.
Small Craft Advisory from 2 am Wednesday to 8 PM EDT Thursday
for anz250-254>256.
Small Craft Advisory from 8 am to 8 PM EDT Wednesday for
anz251.

&&

$$
Synopsis...wtb/Frank
near term...wtb/Belk/Frank

National Weather Service Glossary of Abbreviations