DES MOINES, Iowa – A round of showers and storms Friday morning caused dramatic cloud formations caused by a phenomenon known as gravity waves.

The above photos were captured by Callista Wilkey in Afton. These arcus clouds are especially wispy and dramatic, even appearing to take a waterfall shape.

These arcus clouds were seen by Cindy Hacker near Osceola. She experienced a cool blast as the clouds passed through.

This is to be expected, as this morning’s gravity waves were caused by storms in northern Iowa. Gravity waves are, as the name implies, waves in the atmosphere. They’re caused by air that is forced upward by something like mountains or a storm updraft. When air is forced up in a stable environment, it is forced back down. Think of the pattern that develops like ripples from a stone thrown into a pond.

These ripples can be seen on radar, such as WHO 13’s MegaDoppler-S.

MegaDoppler-S at 5:30 AM on Friday, August 25, 2023

At around 5:30 AM, a storm can be seen moving into Hamilton County.

MegaDoppler-S at 6:17 AM on Friday, August 25, 2023

Roughly 45 minutes later, an outflow boundary can be seen on radar. These are common in thunderstorms and form when the rain-cooled air from the storm rushes out ahead, pushing up the warm, moist air and causing clouds to form. Shelf and roll clouds (which fall into the arcus cloud family) can form along with outflow boundaries.

MegaDoppler-S at 6:44 AM on Friday, August 25, 2023

Roughly half an hour later, what appears to be several outflow boundaries can be seen. This is how gravity waves appear on radar. The rising motion of the wave causes clouds to form, while the subsequent sinking air results in clear skies. This appears as “lines” on radar and to the eye can form as rolls of clouds with clear skies between them.

Radar at 7:53 AM on Friday, August 25, 2023

The gravity waves can be seen rippling farther south into southern Iowa.

A relatively stable environment south of the storms in northern Iowa allowed these waves to form as the outflow encountered the sinking air to the south. This resulted in quite a few dramatic images this morning!

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