How Does Topography Influence Weather?

The topography of Earth's surface is one of the primary factors that causes our daily weather. Changes in elevation, especially around high mountain ranges, determine the distribution of precipitation on our planet. Bodies of water, especially Earth's oceans, shape our climates and create the high- and low-pressure systems that cause weather events.

Differential heating of surface materials helps to create weather systems. Water heats up and cools down much more slowly than land. As the sun shines, air masses over land become warmer than air masses over water. This creates "hot spots" and "cold spots," or areas of low and high pressure. These areas--the edges of which are referred to as warm and cold fronts--are moved around the planet by prevailing winds, creating such aspects of weather as level of precipitation, the speed and direction of winds, temperature and degree of cloud cover.

The topography of an area also helps determine the climate. This is because of ocean currents that carry masses of warm or cool air to coastal locations. Much of the U.S.' eastern coast, for instance, experiences warmer temperatures because of the Gulf Stream, a warm ocean current. In contrast, Maine experiences colder temperatures because the Gulf Stream doesn't reach that far north. Instead, Maine is affected by the Labrador current, which carries cold air masses from the north. Areas near oceans and large lakes have smaller temperature ranges than landlocked, or continental, areas.

Coastal areas are more likely to have more precipitation than continental areas because there's more water vapor in air masses above water. When these air masses move over land, they heat and rise. As the air rises, it cools and the water vapor condenses, forming clouds and precipitation. Daily weather such as a rain or snow often has a nearby body of water as its root cause. Similarly, desert environments receive little rainfall.

Rates of precipitation are also influenced by elevation. When an air mass hits a mountain range, it's forced to rise. As it rises, it cools and the water molecules within condense--a process known as adiabatic cooling. The condensing water vapor forms clouds and water droplets, resulting in precipitation. The side of a mountain range that receives wind and air masses, called the windward side, experiences large amounts of precipitation. An example in the United States is Seattle, Washington, which experiences high levels of precipitation because it's on the windward side of the Cascade Mountains.

Just as mountain ranges help create large amounts of precipitation on windward sides, there's usually little precipitation on the opposite, or leeward, sides because the air masses moving over the mountains have dropped moisture on the windward side of the range. Leeward sides of mountain ranges are said to be in a "rain shadow." Many areas to the east of the Rocky Mountains receive little precipitation because of the nearby topography.