Jim Brandenburg / Thickspike Gayfeather (Liatris pycnostachya) flowers with eagle-shaped cloud, Touch the Sky Northern Tallgrass Prairie National Wildlife Refuge, Minnesota

Tim Fitzharris / Stand of conifers in the Elk Mountains near Crested Butte, Colorado

Tim Fitzharris / Clouds and sunset reflected in stream, Hellroaring Plateau, Montana

Jim Brandenburg / Prairie under threatening thunder clouds, South Dakota

Thomas Mangelsen / Clouds over Yellowstone River, Hayden Valley, Yellowstone National Park, Wyoming

Tim Fitzharris / Lily pads and cloud reflection, Granadier Range, Molas Pass, Weminuche Wilderness, Colorado

Jim Brandenburg / Ponderosa Pine (Pinus ponderosa) tree on prairie, Wind Cave National Park, South Dakota

Jim Brandenburg / Rainbow over prairie with storm clouds, South Dakota

Jim Brandenburg / Nimbus storm clouds over prairie, Minnesota

Jim Brandenburg / Cloudy sky over tallgrass prairie, Wind Cave National Park, South Dakota

Tim Fitzharris / Storm clouds over grasslands, Medicine Bow-Routt National Forest, Wyoming

Jim Brandenburg / Storm over Touch the Sky Northern Tallgrass Prairie National Wildlife Refuge, Minnesota