The northern lights typically form about 80 to 500 kilometers (roughly 50 to 310 miles) above Earth’s surface, according to NOAA’s Space Weather Prediction Center. That puts them far above where airplanes fly and clouds form.
Earth’s magnetic field steers incoming electrons into two oval-shaped zones centered near the magnetic poles, which is why the aurora is seen most often between about 60 and 75 degrees latitude. During strong geomagnetic storms these ovals expand, and the aurora can be visible across much of the United States.
Source: NOAA Space Weather Prediction Center: Aurora.
Image: Aurora borealis; U.S. Air Force photo by Senior Airman Joshua Strang, public domain, via Wikimedia Commons.