Thunderstorm at sunset, northwest Kansas.

High-based thunderstorm near Artesia, New Mexico.

Thunderstorm, Grand Canyon, Arizona.

Thunderstorm anvils and mammatus at sunset, Colorado.

Thunderstorm, Grand Canyon, Arizona.

Thunderstorm, northwestern South Dakota.

Cumulus congestus, Painted Desert, Arizona.

Cumulus congestus, Grand Canyon, Arizona.

Thunderstorm and arcus, Wupatki National Monument, Arizona.

Thunderstorm at sunset, Sedona, Arizona.

Towering cumulus, Florida Keys.

Thunderstorm with a circular anvil near Brighton, Colorado.

Cumulonimbus mammatus, western Nebraska.

Cumlonimbus mammatus, western Kansas.

Cumulonimbus mammatus, northern Arizona.

Cumulus towers, eastern New Mexico.

Towering cumulus, San Fransciso Peaks, northern Arizona.

Cumulonimbus with ranch house and windmill, western Kansas.

Cumulonimbus with horizontal vortex in anvil, eastern Colorado.

Thunderstorm with pileus, northern Arizona.

Thunderstorm anvils and mammatus at sunset, Arizona.

Thunderstorm anvils and mammatus at sunset, Colorado.

Thunderstorm at sunset, eastern Colorado.

Thunderstorm anvil, northeastern Wyoming.