SEPTEMBER/OCTOBER 2019
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DISCOVER 53
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and warnings allows meteorologists to pro-
vide information in the most useful way.
One of the biggest challenges for
meteorologists is condensing a forecast,
which represents a spread of possible
weather conditions to expect, into a
single icon or a few sentences that appear
in your weather app.
Take, for instance, today’s chance
of rain in your area. This could mean
slightly different things coming from dif-
ferent meteorologists, but in general, it’s
not simply the odds that you, personally,
will witness rain that day. Most forecast-
ers calculate this number by multiplying
their confidence that rain will occur by
the area in which the rain might happen.
So a 40 percent chance of rain might be a
100 percent chance in 40 percent of your
county, or, a 60 percent chance across 70
percent of your county.
In addition, what this number doesn’t
tell you is how much it will rain, how
hard, when or for how long. So the next
time you see a low chance of rain in your
forecast, check the full weather report
before you leave the umbrella at home.
“The science has outrun our com-
munications skills and knowledge, to a
certain extent. So a lot of the challenge
now is, how do we get people what they
need?” says Henson. That’s because more
information isn’t always the best way to
communicate. “If people don’t under-
stand it, then it doesn’t help,” he says.
NOAA is working with social scientists
to develop forecasts that are more relevant
and better targeted. This is especially
important because of how the internet
has changed the way people obtain and
share information, Kelsch says.
For instance, when creating the official
forecast, meteorologists account for uncer-
tainties by running a model several times.
Each time, the model will give a slightly
different result, but most results will be
very similar. This ensemble of predictions
is what becomes the official forecast.
But outlying, low-probability results
occur in the ensemble, too. Since these
data are accessible to the public, there’s
always a risk the data will be shared out
of context on social media. “That’s not a
challenge that’s going away,” says Kelsch.
And though forecasts have improved
dramatically, meteorologists are still
blamed when they are wrong. “We
always need to remember that there
never will be perfect forecasts, but we’re
still improving them,” Judt says.
Because for all of us, “the most salient
weather forecast is the one that was
wrong — when you expected some-
thing and you were surprised, those
are the ones you remember. You don’t
Where the Magic (Forecast) Happens
In many countries, a single
public weather service is
typically the only source
available for forecasts,
warnings and alerts. These
meteorologists work for
public (government) orga-
nizations or universities.
By contrast, the United
States has strong public,
private (commercial) and
university-based weather
observation and forecast-
ing programs.
“We also are a large
country and a populous
country, and one with
a great deal of weather
variation. I think all those
things have strengthened
our interest in weather
and our support for
weather research and
forecasting,” says Weather
Underground’s Bob
Henson.
In other words, the U.S.
is a bit of a weather power-
house. Here, most forecasts
originate at the National
Centers for Environmental
Prediction (NCEP). These
centers are part of the
National Weather Service
(NWS), which itself is
a part of the National
Oceanic and Atmospheric
Administration (NOAA).
The NCEP runs weather
models, then disseminates
the results — as well
as forecasts — to NWS
offices, which may custom-
ize the forecasts for their
region.
For long-term, large-
area predictions, the most
popular U.S. model is the
Global Forecast System,
or GFS. On June 12, NOAA
announced its first major
upgrade for GFS in nearly
40 years. The upgrade
incorporates a new dy-
namical core, which is the
model’s description of how
the atmosphere behaves.
The new system, called
GFS-FV3, is better at mod-
eling moisture and clouds,
allowing meteorologists
to forecast storms with
greater accuracy than
ever before.
Commercial weather
providers typically have
some weather modeling
capabilities of their own.
For example, Weather
Underground refines
the official forecast to a
neighborhood scale by
adding information from
its network of over a
quarter-million personal
weather stations. This
gives you accurate
weather information for
your exact location when
you open the service’s
app, rather than what the
weather is doing across
town.
Each company fills a dif-
ferent niche, providing dif-
ferent forecasts that focus
on, say, surfing conditions,
fire conditions or trans-
portation concerns, based
on specific observations
and models that refine the
broad public-sector data.
These differences are also
why you might prefer using
one app or service over
another.
— A.K.remember all the times that it was just
as we expected because that’s not news,”
Henson says.
For meteorologists, then, the end goal
is to make almost every day’s forecast an
utterly forgettable one.
D
Alison Klesman is an associate editor
at Astronomy magazine.
Forecasters at the National Weather Service are all hands on deck during a major storm. Here,
meteorologists monitor Hurricane Irma in September 2017 at the hurricane center in Miami.