AY Honors/Weather/Answer Key
Orographic lift occurs when an air mass is forced from a low elevation to a higher elevation as it moves over rising terrain. As the air mass gains altitude it expands and cools adiabatically. This cooler air cannot hold the moisture as well as warm air and this effectively raises the relative humidity to 100%, creating precipitation.
Orographic Lift is demonstrated in many places in the world, but few examples are as clear as those in the United States. In the U.S. states of Washington and Oregon, places on the sea-facing side of the mountains see over 100 inches (over 2.5 m) of precipitation per year. These places are on the side of the mountains which is in the way of storm systems, and therefore receives the moisture which is effectively squeezed from the clouds. However, on the other side of the mountains, sometimes as little as 15 miles (25 km) away, annual precipitation can be as low as 8 inches (200 mm) per year.
