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Forecasting atmospheric weather is tricky enough; predicting Northern Lights is that much harder

Why is forecasting the Northern Lights so hard?
Why is forecasting the Northern Lights so hard? 01:58

MINNEAPOLIS — The Northern Lights put on a show last night, but it got started a few hours later than expected, leaving some local observers disappointed.

While WCCO's Mike Augustyniak was one of those people, he urges, "Be patient, because space-weather forecasting is hard."

The sun is constantly spewing energy at us — light we can see, and other particles we can't.  Those particles make up what's called the "solar wind," which travels at speeds of about 250 to 500 miles per second. The fastest and most energetic solar winds are produced by holes in the sun's outermost atmosphere, called the "corona." When that wind is aimed at Earth's, it can generate auroras.

NOAA space-weather forecasters track coronal holes in an effort to forecast the solar wind, but those holes can interact in unpredictable ways.

To make things even more complicated, the sun rotates every 27 days, turning the solar wind into a complex spiral of high and low speeds that looks like the twirling skirt of a dancer.

Computer models help with forecasting, and several satellites in deep space take observations of the solar wind as it passes by. The real-time measurements taken by those satellites help to refine forecasts. But, even a million miles away, it only takes about an hour for the solar wind to pass those satellites and reach Earth.

The sun is 91 million miles from Earth, which means a fast solar wind reaches us in about 80 to 90 hours; that's why accurate aurora forecasts are hard to make beyond two to three days.

It also means that, if the forecasted solar wind speed is off by only 1% to 2%, the time of arrival at Earth will be 1 to 2 hours different. That's a big impact for such a slim margin of error.

Strong solar storms can impact life in space, but also here on Earth. GPS and communications satellites, and even the power grid can be interrupted. Commercial flights that would normally take a time-saving route over the north or south poles — where auroras are more common — are often rerouted to avoid radio blackouts.

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