A ‘fire rainbow’ is spotted over coastal South Carolina. What caused the phenomenon?

A strange weather event that resembled a horizontal rainbow hovered over North Myrtle Beach this week, prompting an explanation from the National Weather Service.

Multiple images of the oddity were shared on Facebook and Twitter, showing a streak of rainbow colors wedged between more ordinary clouds.

It’s called a circumhorizontal arc, or “fire rainbow,” according to the National Weather Service office in Wilmington.

The photos, taken Tuesday, were credited to Frank DiPalma and mark at least the second time this summer a “fire rainbow” has been photographed in the Southeast.

In June, one shaped like a dragon was seen over Atlanta, Georgia, according to a post on a Neil deGrasse Tyson Facebook group.

The origin of the term “fire rainbow“ appears to be up for debate, with some saying it describes a “rainbow that has spontaneously combusted” and others preferring a more romantic explanation that it resembles a mythical dragon’s fiery breath.

Multiple atmospheric conditions must be aligned for the arcs appear, including ice crystals, according to NASA.

“Why would clouds appear to be different colors? The reason here is that ice crystals in distant cirrus clouds are acting like little floating prisms,” NASA reported in 2019.

“For a circumhorizontal arc to be visible, the Sun must be at least 58 degrees high in a sky where cirrus clouds are present. Furthermore, the numerous, flat, hexagonal ice-crystals that compose the cirrus cloud must be aligned horizontally to properly refract sunlight in a collectively similar manner.”

Considering all that is required, “circumhorizontal arcs are quite unusual to see,” NASA concludes.

This story was originally published July 28, 2021 at 3:04 PM with the headline "A ‘fire rainbow’ is spotted over coastal South Carolina. What caused the phenomenon?."