Temperature Inversion--What Causes it?

Fairbanks is surrounded on three sides by hills and has one of the lowest wind conditions in the world. The lack of wind allows the air over the city to remain relatively stagnant.

When the sky is clear, the ground and the air near it radiate heat energy to outer space. Clouds over the city prevent this radiation. That is the reason why, at the same temperature, it feels warmer outside under a cloudy sky than it does when the sky is clear. It is also the reason why you should shutter or curtain your windows on clear nights to prevent radiation to the cold sky.

When the sky is clear, the ground cools and cools the air near it. Thus an inversion forms, an inversion being the condition of higher temperature at altitude than at ground level.

The strongest inversions occur in winter; weaker ones occur in summer when the air is still. During winter nights and days there is an inversion more than 70% of the time.