Sporadic E propagation. Its when dense ionization in the ionosphere 56 to 93 miles above the earth can reflect radio waves thousands of miles from their original source. Usually you need sensitive equipment to pick it up but occasionally it's strong enough that typical radios can pick them up.
I remember when I was a kid in the 80s picking up a station from El Paso, Texas occasionally during this time of year. That was with a mono magnavox boombox. It's kind of cool how weather and heat can affect radio waves.