Boulder and its neighbors just east of the Front Range are prone to damaging downslope winds, especially in the winter. They occur when the upper-level jet stream flows from west to east atop the Front Range, which serves as a north-south barrier. The winds are forced up and over the mountains. If conditions are right, they can be pushed "downslope" with gusts well over 100 miles (161 kilometers) per hour. A gust of 137 mph (220 kph) was recorded on the NCAR mesa on January 17, 1982.
Because downslope winds occur so frequently, native trees and wildlife are well adapted, but the fierce winds may break car windows and unroof homes. Some trees on this mesa bend toward the east, away from the mountains. When a downslope wind brings warmer air, it is called a chinook; if it is a cold wind, it is labeled a bora. A wind-measuring device called an anemometer sits atop the Mesa Lab's northernmost tower. The spinning arms of the instrument measure the wind speed. The vane points into the wind, giving its direction.
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