Wave Arch Over Helena (panorama)

An Easter Day mountain wave cloud stretches over the city of Helena, MT. These peculiar clouds are some of my favorite to photograph.
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Mountain wave clouds are formed when moist & fast-moving air flows perpendicular to a mountain range and is forced up and over the terrain forming these fascinating clouds. The same phenomena is no different than water flowing over a large rock in a river and forming a wave in a rapid. In this case, the rock in the ‘river’ are the Rocky Mountains.
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The result of these events for folks living on the east or ‘lee’ side of large mountain ranges are warmer than average temperatures and as you may have imaged, breezy conditions. As the air races downhill, the atmosphere is literally compressed and by the rules of physics is warmed. The Blackfoot people call these winds the "snow eater" however, the more commonly used term “Chinook winds” originates from the name of the Chinook people, who lived along the lower Columbia River.