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Area forecast discussion
National Weather Service Boston/Norton Massachusetts
122 PM EDT Mon Jul 15 2019

Synopsis...
warm and comfortable weather today, then the heat and humidity
starts to build again Tuesday. Hot and humid for Wednesday. The
remnants of Barry may bring tropical downpours as early as
Thursday, possibly lingering into Friday morning. A drying trend
develops later Friday. Hot weather likely returns Friday
afternoon with a drier heat possible next weekend.

&&

Near term /until 6 PM this evening/...
1030 am update...

No major changes to the current forecast. High pressure
centered over the Appalachians builds over southern New England
today. Not expecting a sea breeze to develop today with just
enough wind to hold it off, but its a non-zero possibility.
Should temperatures become higher than current expectations,
seabreezes would be more likely.

Dewpoints will be the lowest they have been in a few days. Add
in the drier air aloft, and we're looking at abundant sunshine
and no rainfall. Expecting temperatures to be closer to normal
than Sunday.

&&

Short term /6 PM this evening through 6 PM Tuesday/...
high pressure dominates our weather as it moves overhead tonight
and Tuesday morning. More comfortable humidity is expected to
last through tonight, then start to increase once more Tuesday
afternoon as a southwest wind develops. Near to slightly above
normal temperatures expected.

While more humid air moves in aloft, still thinking we remain
rain-free through Tuesday. The timing of this moisture, a mid
level shortwave and a warm front may change relative to each
other. This could lead to an increased risk for at least a few
showers Tuesday.

&&

Long term /Tuesday night through Sunday/...
big picture...

Zonal flow across the northern half of the nation Tuesday night,
while subtropical high pressure controls most of the southern
half. Remnants of Barry will be moving into the Midwest Tuesday
night and merging into the zonal flow, then moving east with
that flow and crossing southern New England late Wednesday
through Thursday.

GFS and ggem show an upper ridge building over New England for
the weekend with contour heights well above normal. The European model (ecmwf)
is less beefy, digging a maritime trough while maintaining the
ridge to our west and south with the jet flow over New England.
Favor the GFS/ggem scenario.

Normal 500-mb heights for mid July are 580 to 582 dm. Forecast
heights are 585 to 591 dm. Expect warmer than normal temperatures.

Mass fields are similar through Thursday, but with the GFS showing
a fast-bias in handling the remnants of Barry. Forecast confidence
is moderate.

Concerns...

Tuesday night-Wednesday morning...

GFS and sref show a few showers moving across the region
Tuesday night, possibly as a response to increasing dew points
as the tropical air moves north. The remaining models stay
rain-free although indicate increasing sky cover. We will indicate
a period of slight chance pops Tuesday night, then rain-free
late night through Wednesday morning. With increasing clouds
along with dew points climbing through the 60s, expect min temps
in the upper 60s and 70s.

Wednesday afternoon-Thursday...

A fore-taste of the subtropical ridge moves in for Wednesday
afternoon. The GFS shows mixing only to 925 mb, which seems
too conservative for mid-July unless skies are mostly cloudy.
GFS temps at 850 mb are 16-17c, while the European model (ecmwf) is 17-18c.
Ec temps at 925 mb are comparable to the 850 mb temps of both models.
Will follow along with the higher mixing and forecast Wed aftn
Max temps around 90 or the lower 90s. Dew points will be near
70, so expect it to be an uncomfortable afternoon.

The remnants of Barry then move in late Wednesday with precipitable water values
rising to 2-2.5 and favorable convective parameters... Li -2 to
-3, k index mid 30s, cape around 1000 j/kg...Wednesday night
through Thursday night. Expect showers and some thunder, along
with local downpours with potential for street and poor drainage
flooding.

Friday through Sunday...

The remnants move off to the east Friday, but there may be leftover
showers for part of the day. As noted above, the subtropical
ridge then builds into New England bringing subsidence and
heating. Along with the ridge, there are signs of a cold front
working through New England during the weekend. This would bring
a wind shift from the west-northwest as well as some drying of
the humidity with dew points in the 60s rather than the 70s.

Mixing should reach at least 850 mb and possibly 800 mb. Temps at
these levels would support Max temps into the 90s.

&&

Aviation /17z Monday through Friday/...
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.

18z update...

VFR through Tuesday night. Light northwest winds becoming SW and
picking up a bit on Tuesday.

Kbos terminal...high confidence in taf.

Kbdl terminal...high confidence in taf.

Outlook /Tuesday night through Friday/...high confidence.

Tuesday night: mainly VFR, with local MVFR possible. Slight
chance shra, isolated thunderstorms and rain.

Wednesday: mainly VFR, with areas MVFR possible. Chance shra,
slight chance thunderstorms and rain.

Wednesday night: MVFR/IFR conditions possible. Rain showers likely,
chance tsra, patchy br.

Thursday: mainly MVFR, with areas VFR possible. Rain showers likely,
chance thunderstorms and rain.

Thursday night: MVFR/IFR conditions possible. Chance shra,
slight chance tsra, patchy br.

Friday: mainly VFR, with local MVFR possible. Slight chance
shra, isolated thunderstorms and rain.

&&

Marine...
forecaster confidence levels...

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

Short term /through Tuesday/...high confidence.

Relatively tranquil boating weather across the coastal waters
through Tuesday. Seas generally 4 feet or less with winds 20 kt
or less.

Outlook /Tuesday night through Friday/...high confidence.

Tuesday night: winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain showers, isolated thunderstorms.

Wednesday: winds less than 25 kt. Seas less than 5 ft. Slight
chance of rain showers, isolated thunderstorms.

Wednesday night: winds less than 25 kt. Seas less than 5 ft.
Chance of rain showers, slight chance of thunderstorms.

Thursday: winds less than 25 kt. Seas less than 5 ft. Rain
showers likely, chance of thunderstorms.

Thursday night: winds less than 25 kt. Seas less than 5 ft.
Chance of rain showers, slight chance of thunderstorms.

Friday: winds less than 25 kt. Seas locally approaching 5 ft.
Slight chance of rain showers, isolated thunderstorms.

&&

Climate...
record highs for Wednesday July 17th are as follows:

Bos: 98f in 1999
bdl: 97f in 1999
pvd: 97f in 1999
orh: 93f in 1900

&&

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

&&

$$
Synopsis...wtb/Belk
near term...wtb/bw
short term...Belk

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