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Why 'Mountain Breeze' Creates Poor Air Quality In Colorado's Central Mountains

By Chris Spears

SUMMIT COUNTY, Colo. (CBS4)- Alerts for air quality continue in Colorado's central mountains, including the counties of Eagle, Summit, Grand and Lake.

For places like Breckenridge, which sits in a large valley, the daily cycle of wind plays a huge role in creating the poor conditions.

Peak 2 Fire
(credit: CBS)

As the sun rises each day and heats the mountainsides and valley floor, air begins to rise, flowing up the slopes. This is called a valley breeze because it originates at the valley floor. It combines with a transport of heat energy through convection to help mix the air.

While air quality can be a concern during the day, especially near an active fire, things change drastically at night.

(credit: CBS)

This is because the process reverses, and cold air from the mountain tops flows down the slopes and to the valley floor. This is called a mountain breeze since it starts higher up in the mountains.

Because cold air is heavy and dense, it settles on the valley floor, helping to trap smoke and other pollutants.

Often you can see the dirty air sitting down low in a valley, which will look much like fog, if you have a higher vantage point just after sunrise.

Meteorologist Chris Spears travels weekly in the CBS4 Mobile Weather Lab reporting about Colorado's weather and climate. Check out his bio, connect with him on Facebook or follow him on Twitter @ChrisCBS4.

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