Mountain and Valley Winds

CHAPTER TWO

AVIATION WEATHER

Figure 2-11 Land Breeze

Mountain and Valley Winds

In the daytime, mountain slopes are heated by the Sun's radiation, and in turn, they heat the

adjacent air through conduction. This air usually becomes warmer than air farther away from the

slope at the same altitude and, since warmer air is less dense, it begins to rise (Figure 2-10). It

cools while moving away from the warm ground, increasing its density. It then settles downward,

towards the valley floor, completing a pattern of circulation. This downward motion forces the

warmer air near the ground up the mountain and since it is then flowing from the valley, it is

called a valley wind.

Figure 2-12 Mountain and Valley Winds

2-12 Atmospheric Mechanics of Winds, Clouds and Moisture, and Atmospheric Stability