A Simple Guide to Aurora Forecasting in the U.S.

Once you get a sense of what it’s like to chase the Northern Lights in the mid-latitudes, you may find you need more information to make a sighting happen! That may leave you wanting an in-depth explanation of the Aurora forecasts. So, let’s break it down.

What causes the Northern Lights and why is it so difficult to predict? In simple terms, our planet’s Aurora are created by the solar wind that is emitted from the sun’s surface. A solar flare (or other activity on the sun) sends solar plasma speeding into space, and scientists work to predict the resulting impacts on our atmosphere.

If the solar wind penetrates Earth’s atmosphere, it interacts with air molecules to emit light — creating the Northern Lights!

Why doesn’t it always work out?

💥 Sometimes, the solar wind blows right past our planet, and what could have been a hit becomes a miss.
💥 Sometimes, the solar wind flows effortlessly into the atmosphere, helped by magnetic field conditions. (This happens when we have negative/southward Bz.)
💥 Sometimes, the solar wind moves slower or faster than anticipated, making the forecast irrelevant and causing us to miss the display.
💥 Sometimes, the solar wind makes a direct hit, but Earth’s magnetic field flips like a polarized magnet and blocks any solar matter from entering the atmosphere. (This happens when we have sustained positive/northward Bz.) In this case, any predicted activity usually becomes a dud.

For a good Northern Lights display in the mid-latitudes, we need solar wind that is fast (high speed), substantial (high density), able to enter our atmosphere (low Bz), and packs a lot of power (measured by gigawatts of hemispheric power, or by the K-index). In the Midwest, we also need clear skies for good viewing, which can be rare because of lake effect weather.

The strongest Aurora events reach storm levels, causing geomagnetic storms ranked at G1 (same as K5), G2 (K6), G3 (K7), G4 (K8) or G5 (same as K9, which could probably take out the planet’s electrical grid!)

Unless you are very experienced and know what to look for, you are probably not going to see Northern Lights above the 45th parallel until it reaches at least K4 on the K-index (a scale of 0-9). At K4, the northernmost parts of the continental U.S. might get lucky. More likely, we need a G1 Storm (K5) to provide good viewing for anyone above the 45th parallel. Below the 45th parallel, you would need a G2 Storm (K6) or stronger to view Northern Lights. Other factors considered, a G2 Storm should be strong enough to send Aurora dancing above the 42nd parallel across the U.S.

Keep in mind, apps and other websites often give you the “Kp,” with the “p” making the stat a “planetary average” of what happened over the last 3 hours and not necessarily an indication of future conditions. That said, many maps are available that show you what K or Kp you would need to view Aurora at your latitude. This value will always remain the same. It’s just a question of whether the Northern Lights on any given night will achieve that kind of power, radiating southward from the North Pole, where Aurora Borealis enters our atmosphere. (Aurora Australis also radiate northward from the South Pole.)

Regardless, when speed, density, Bz and other factors cooperate, the Aurora can surprise us. Those who are truly devoted to staying up all night to monitor the skies can capture Aurora for short intervals pretty frequently in northern U.S. states — when the conditions align. Obviously, Alaska tends to have much better viewing.

The science behind aurora forecasts

It’s a science!

Auroral activity is monitored in order to protect our resources on Earth from the side effects, such as impacts on GPS, electrical surges, and drag on satellites that orbit the Earth. So, the forecasts are always given in Universal Coordinated Time (UTC), as a scientific standard. The forecasts are also designed to over-predict potential activity, to help government agencies manage the potential risks.

The best data we have appears in real time. The short-term forecasts, which will almost always be greater than actual activity, come from NOAA’s Space Weather Prediction Center 2-3 days in advance, which is how much time it takes solar plasma to travel from the sun’s surface to Earth’s atmosphere.

My advice? Use the forecasts more as a guide for when to be alert, not an exact schedule. Know what K/Kp you need to view Aurora at your latitude. Find a mapped visual or real-time resource that works for you. Use social media to help you on your chase. Watch for real-time alerts and live sightings, if you want reliable info. Before you go out, check local forecasts for cloud cover and clear skies.

Most of all, make plans that will lead you to enjoy the night, no matter what the conditions bring!

We call it “Aurora Chasing,” not “Aurora Viewing,” for a reason. That’s because the Aurora is so extremely difficult to predict, even for the most experienced scientists. A huge part of this passion is enjoying the chase! Good luck, Aurora Chasers!

Have another question? Join one of many area groups devoted to Aurora Chasing: KaelinArt.com/links

Author’s Note: The goal of this blog is to give practical advice for viewing the Northern Lights to beginners and amateur space weather enthusiasts, using the simplest terms, common topics, and popular sources. I draw upon my experience as a journalist and an Aurora Chaser, though I do not have formal training in the field. Feature photo by Jonatan Pie/Unsplash. Graphic courtesy of NASA.

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