Current science has no known explanation.
Footprints of Thunder postulates such a theory, and shows what happens when the rate of occurrence begins to drastically accelerate. In the skies flocks of seagulls in flight disappeared, as did the military and civilian aircraft in the affected regions. As the effect reached the East Coast it continued on land. The effect was systemic, but not thorough. As the effect washed across the planet's surface, it rippled, leaving some regions untouched.