Clouds take on some stunning forms—an indication of unseen processes at work in the atmosphere. The wave clouds visible in this image over Bristol Bay in southwest Alaska are the result of two air masses colliding.

The natural-color image was acquired on May 14, 2017, with the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite. The clouds are likely stratocumulus—a low-level cloud similar to cumulus, but larger.

According to Sam Albanese, a meteorologist at the National Weather Service in Anchorage, Alaska, the local weather that day was influenced by a weak area of high pressure. West-northwesterly winds pushed clouds toward the Alaska Peninsula and along the coast. “What is notable is the slightly convective nature of those clouds and that they hug the coast of Bristol Bay, while skies over land are clear,” Albanese said.

At the same time, a warm front moving into the region gave rise to the band of whiter clouds in the bottom-left corner. Where this mass of warm, moist air meets the cooler, dry air from over land, an area of “wave clouds” is visible. This cloud type forms on the waves of colliding air masses, condensing on the upward part of the wave and evaporating on the downward region.

Other striking examples of wave clouds were visible in recent satellite images acquired off of western Africa and Western Australia.

NASA Earth Observatory image by Joshua Stevens, using MODIS data from LANCE/EOSDIS Rapid Response. Story by Kathryn Hansen.