Distinguish between weather and climate, name the basic elements of weather and climate, and list several important atmospheric hazards.

Weather influences our everyday activities, our jobs, and our health and comfort. Many of us pay attention to the weather only when it inconveniences us or when it adds to our enjoyment of outdoor activities. Nevertheless, few other aspects of our physical environment affect our lives more than the phenomena we collectively call the weather.

Weather in the United States

The United States occupies an area that stretches from the tropics to the Arctic Circle. It has thousands of miles of coastline and extensive regions far from the influence of the ocean. Some landscapes are mountainous, and others are dominated by plains. Pacific storms strike the west coast, while the eastern states are sometimes influenced by events in the Atlantic and the Gulf of Mexico. The states in the center of the country commonly experience weather events triggered when frigid southward-bound Canadian air masses clash with northward-moving tropical air masses from the Gulf of Mexico.

The United States likely has the greatest variety of weather of any country in the world. Severe weather events such as tornadoes, flash floods, and intense thunderstorms, as well as hurricanes and blizzards, are collectively more frequent and more damaging in the United States than in any other nation (Figure 1.1). Beyond its direct impact on the lives of individuals, weather strongly affects the U.S. economy through its influence on agriculture, energy use, water resources, and transportation.

Weather influences our lives a great deal. Yet it is also important to realize that people influence the atmosphere and its behavior as well. There are, and will continue to be, significant economic, political, and scientific decisions to make involving these human impacts. Dealing with the effects of and controlling air pollution is one example (Figure 1.2). Another is the ongoing effort to assess and address global climate change. There is clearly a need for increased awareness and understanding of our atmosphere and its behavior.

Meteorology, Weather, and Climate

The subtitle of this book includes the word meteorology. Meteorology is the scientific study of the atmosphere and the phenomena that we usually refer to as weather. Acted on by the combined effects of Earth’s motions and energy from the Sun, our planet’s formless and invisible envelope of air reacts by producing an infinite variety of weather, which in turn creates the basic pattern of global climates. Although not identical, weather and climate have much in common.

Weather refers to the state of the atmosphere at a given time and place. Weather is constantly changing, sometimes from hour to hour and at other times from day to day. Whereas changes in the weather are continuous and sometimes seemingly erratic, it is nevertheless possible to arrive at a generalization of these variations. Such a description of aggregate weather conditions is termed climate. It is based on observations that have been accumulated over many decades. Climate is often defined simply as “average weather,” but this definition is inadequate. An accurate portrayal of an area’s climate must also include variations and extremes, as well as the probabilities that such departures from the norm will take place. For example, farmers need to know the average temperature during their area’s growing season, but they must also know the date in the spring when the last freezing temperatures are most likely to occur.

Maps like the one in Figure 1.3 are familiar to everyone who checks the weather report from a website, a newspaper, or on television. In addition to showing predicted high temperatures for the day, this type of map shows other basic weather information about cloud cover, precipitation, and the location of fronts.

Suppose you were planning a vacation trip to an unfamiliar place. You would probably want to know what kind of weather to expect. Such information would help you select which clothes to pack and could influence what you decide to do during your stay. Unfortunately, weather forecasts that go beyond a few days are not very dependable. Thus, it may not be possible to get a reliable weather report about the conditions you are likely to encounter during your vacation.

Instead, you might ask someone who is familiar with the area about what kind of weather to expect. “Are thunderstorms common?” “Does it get cold at night?” “Are the afternoons sunny?” What you are seeking is information about the climate, the conditions that are typical for that place. Another useful source of such information is the great variety of climate tables, maps, and graphs that are available. For example, the graph in Figure 1.4 shows average daily high and low temperatures for each month, as well as extremes, for New York City.

Such information could, no doubt, help as you planned your trip. But it is important to realize that climate data cannot predict the weather. Although the place may usually (climatically) be warm, sunny, and dry during the time of your planned vacation, you may in fact experience cool, overcast, and rainy weather. A well-known saying summarizes the distinction between weather and climate: “Climate is what you expect, but weather is what you get.”

The nature of both weather and climate is expressed in terms of the same basic properties, or elements, that are measured regularly. The most important are (1) the temperature of the air, (2) the humidity of the air, (3) the type and amount of cloudiness, (4) the type and amount of precipitation, (5) the pressure exerted by the air, and (6) the speed and direction of the wind. These elements constitute the variables by which weather patterns and climate types are depicted, and many of these are shown as map symbols in Figure 1.3. Although you will study these elements separately at first, keep in mind that they are very much interrelated. A change in one of the elements often produces changes in the others.

Atmospheric Hazards

Natural hazards are a part of living on Earth. Every day they adversely affect millions of people worldwide and are responsible for staggering damages. Some, such as earthquakes and volcanic eruptions, are geologic in nature. Many others are related to the atmosphere.

For most people, severe weather events are far more fascinating than ordinary weather phenomena. A spectacular lightning display generated by a severe thunderstorm can elicit both awe and fear. Of course, hurricanes and tornadoes attract a great deal of much-deserved attention. A single tornado outbreak or hurricane can cause billions of dollars in property damage, much human suffering, and many deaths. The chapter-opening satellite image of Hurricane Sandy and the tornado damage depicted in Figure 1.5 are good examples of such severe weather. Severe storms are covered extensively in Chapters 10 and 11.

Other atmospheric hazards also adversely affect us. Some are storm related, such as blizzards, hail, and freezing rain. Others are not direct results of storms. Heat waves, cold waves, fog, wildfires, and drought are important examples. In some years, the loss of human life due to excessive heat or bitter cold exceeds that caused by all other weather events combined. Although severe storms and floods usually generate more attention, droughts can be just as devastating and carry an even bigger price tag, while extreme heat is the number-one killer worldwide.

Between 2004 and 2016, the United States experienced 102 weather-related disasters in which overall damages and costs reached or exceeded $1 billion (Figure 1.6). In addition to taking more than 4100 lives, these events exacted economic costs that exceeded $600 billion! Every day our planet experiences an incredible assault by the atmosphere, so it is important to develop an awareness and understanding of these significant weather events.

• climate: A description of aggregate weather conditions; the sum of all statistical weather information that helps describe a place or region.

• meteorology: The scientific study of the atmosphere and atmospheric phenomena; the study of weather and climate.

• weather: The state of the atmosphere at any given time.

• Meteorology is the scientific study of the atmosphere. Weather refers to the state of the atmosphere at a given time and place. It is constantly changing, sometimes from hour to hour. Climate refers to the average weather conditions and the sum of all statistical weather information that helps describe a place or region.

• The most important elements of weather and climate are (1) air temperature, (2) humidity, (3) type and amount of cloudiness, (4) type and amount of precipitation, (5) air pressure, and (6) the speed and direction of the wind.

• Some atmospheric hazards are storm related, such as lightning, blizzards, and hail. Others are not storm related, such as fog, heat waves, and drought.