When warm, moist air sweeps in from the ocean and rises over a mountain range, it expands and cools. Explain how this cooling is related to the attractive forces between gas molecules. Why does this cause rain to form? When the air drops down the far side of the range, its pressure rises as it is compressed. Explain why this causes the air temperature to rise. How does the humidity of this air compare with the air that originally came in off the ocean? Now explain why the coast of California is lush farmland, whereas valleys (such as Death Valley) that lie to the east of the tall Sierra Nevada mountains are arid and dry.

Understand the intricacies of atmospheric movement starts with grasping the attractive forces between gas molecules. These forces are essentially weak bonds that draw the molecules toward each other. However, these are not the powerful covalent or ionic bonds you may know from chemistry; they're much more ephemeral and can be easily overcome by thermal energy.

When air, which is a mixture of gases, warms up, the kinetic energy of the gas molecules increases. This energy allows the molecules to resist attraction and move freely, causing the gas to expand. Conversely, as gas cools when it rises over a mountain range, the kinetic energy decreases, and the molecules come closer together due to the attractive forces, leading to cooling and sometimes causing rain to form.

Kinetic energy is directly related to temperature and defines the motion of gas molecules. An increase in kinetic energy, often as a result of heating, means the molecules move faster and more vigorously. This kinetic gusto enables molecules to overcome their mutual attractions and spread out, which is why warm air expands.

As air rises and expands in the atmosphere, it does the opposite; it loses kinetic energy, cools, and contracts. This decrease in kinetic energy, when moist air sweeps over a mountain, is partly responsible for the formation of clouds and precipitation, a phenomenon that profoundly affects weather patterns.

Clouds are an enchanting result of the cloud formation process, where moisture in the air condenses into droplets on tiny particles known as cloud condensation nuclei. The cooling of air when it ascends a mountain range is a classic setup for cloud creation. As the rising air expands and its temperature drops, it can hold less water vapor.

The excess vapor condenses into minuscule water droplets or ice crystals if the temperature is low enough. When millions of these droplets or crystals cluster together, they become visible as clouds. Eventually, the droplets may merge into larger drops, heavy enough to overcome air resistance and fall as rain, thereby shaping the local climate.

Thermal expansion and compression are behaviors exhibited by gases when they are heated or cooled. Upon heating, as mentioned, gas molecules move rapidly and tend to occupy more space due to increased kinetic energy, which results in expansion.

When ascending air cools and loses kinetic energy, it contracts. The opposite happens during compression, when descending air on the far side of a mountain range is squashed under higher pressure. The molecules are forced closer together, and their kinetic energy increases, causing the temperature to rise. This process is paramount in explaining why the air becomes warmer as it descends even though it has lost moisture during precipitation.

Humidity and temperature are inextricably linked in determining weather patterns. Temperature has a significant effect on the amount of moisture air can contain; warmer air can hold more moisture because higher temperatures impart more kinetic energy to water molecules, allowing them to remain in vapor form.

When saturated air rises and cools over a mountain, it can lead to orographic precipitation, which enriches the windward slopes with lush vegetation. However, as the air moves down the leeward side, it warms up and gains the capacity to hold moisture again, but this time, it's often devoid of its initial moisture load, leading to drier conditions. This interaction between humidity and temperature underlies the climatic difference between California's damp coast and its dry, inland valleys.