Foehn winds are warm, dry winds that occur on the leeward side of mountain ranges. They form when moist air rises over the mountains, cools, and loses moisture as precipitation. As the air descends on the other side, it warms up, leading to a significant temperature increase. These winds can cause rapid changes in weather, often resulting in clear skies and higher temperatures in valleys. Foehn winds are commonly observed in regions like the Alps in Europe and the Rocky Mountains in North America, where they can impact local climates and ecosystems.