Definition (Encyclopedia of Global Warming)
Weather forecasting is the branch of meteorology devoted to making short-term predictions about the weather. Early, nonscientific attempts at weather forecasting were based simply on people’s past experience and observations. Modern science is based on more detailed understandings of relevant mechanisms and much more precise observations. However, all weather forecasting, scientific or not, is an extrapolation of human knowledge and observations from the past and present into the future.
Advances in science and technology have endowed meteorologists with the ability to make more objective judgments and inferences than were previously possible. Modern weather forecasting includes three components: sophisticated and accurate instruments for making atmospheric observations and measurements, a mathematically precise forecast model, and a powerful computer. Forecasting based on these components is called “numerical weather prediction” (NWP).
Many advanced technologies are employed in modern-day atmospheric observation and measurement, including satellites, aircraft, radar, and lidar. These technologies have made possible more frequent and accurate descriptions of atmospheric conditions, providing a good starting point for predicting the evolution of the atmosphere in the future. The treatment of observed data and the procedure for using these data in a weather-forecasting model are collectively called “data...
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Significance for Climate Change (Encyclopedia of Global Warming)
Climate is an averaged state of long-term weather conditions. Therefore, climate can provide a general reference and guideline for weather forecasting. In fact, meteorologists use climate information in various weather forecasting methods, such as persistence forecasting, trend forecasting, and analog forecasting. On the other hand, weather forecasting may provide researchers with a snapshot of climate change. For example, global warming may manifest itself in alterations in the daily forecast of maximum and minimum temperatures. Although a particular day’s weather forecast may vary significantly, a persistent change in weather pattern over some period of time may indicate a change in the Earth’s climate system.
One of the issues raised by climate change is its consequences for future day-to-day weather patterns. The Intergovernmental Panel on Climate Change (IPCC) in its 2007 assessment report found that in a future warm climate, global weather would likely exhibit the following changes: higher maximum temperatures; more hot days and heat waves over nearly all land areas; higher minimum temperatures; fewer cold days, frost days, and cold waves over nearly all land areas; more intense precipitation events; increased summer drying over most midlatitude continental interiors and increased associated risks of drought; increases in tropical cyclone peak wind intensities, as well as mean and peak precipitation...
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Further Reading (Encyclopedia of Global Warming)
Ahrens, C. Donald. Essentials of Meteorology: An Invitation to the Atmosphere. 5th ed. Belmont, Calif.: Thomson Brooks/Cole, 2008. Widely used introductory textbook on atmospheric science; covers a wide range of topics on weather and climate.
Henson, Robert. The Rough Guide to Weather. 2d ed. New York: Rough Guides, 2007. This book gives quick references of various weather-related topics.
Intergovernmental Panel on Climate Change. Climate Change, 2007—Synthesis Report: Contribution of Working Groups I, II, and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Edited by the Core Writing Team, Rajendra K. Pachauri, and Andy Reisinger. Geneva, Switzerland: Author, 2008. Comprehensive overview of global climate change published by a network of the world’s leading climate change scientists under the auspices of the World Meteorological Organization and the United Nations Environment Programme.
Lutgens, Frederick K., and Edward J. Tarbuck. The Atmosphere. 10th ed. Upper Saddle River, N.J.: Pearson Prentice Hall, 2007. Introductory textbook that covers a wide range of atmospheric sciences.
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Weather Forecasting (Encyclopedia of Science)
Weather forecasting is the attempt by meteorologists to predict weather conditions that may be expected at some future time. Weather forecasting is the single most important practical reason for the existence of meteorology, the study of weather, as a science. Accurate weather forecasts help save money and lives.
Humans have been looking for ways to forecast the weather for centuries. Modern weather forecasting owes its existence to the invention of many weather recording instruments, such as the hygrometer, barometer, weather balloon, and radar. Three major technological developments have led weather forecasting to its current status: the development of instant communications with distant areas beginning in the late 1800s, remote sensing devices starting in the early 1900s, and computers in the late 1900s.
Weather recording instruments
In the fifteenth century, Italian artist and scientists Leonardo da Vinci (1452519) invented the hygrometer (pronounced hi-GROM-e-ter), an instrument that measures atmospheric humidity (moisture in the air). Around 1643, Italian physicist Evangelista Torricelli (1608647) created the barometer to measure air pressure differences. These instruments have been improved upon and refined many times since.
Weather information has long been displayed in map form. In 1686, English astronomer...
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Weather Forecasting (Science Experiments)
Weather forecasting before computers
Weather maps and computers
Air Pressure: How can air pressure be measured?
Weather forecasting,The scientific predictions of future weather patterns. the scientific prediction of weather patterns, may look simple when we watch a television weather forecast on the local news, but it's not. That forecast was based on data collected and analyzed from many sources.
About 12,000 weather stations throughout the world communicate weather observations and data to international weather centers every three hours where the information is analyzed by who study the weather and the atmosphere. The weather stations consist of outdoor shelters, known as Stevenson screens, that house instruments such as thermometers, which measure air temperature, and anemometers, which record wind speed. All instruments at these stations are of the same type and accuracy.
Weather stations also record many other weather elements, including types of clouds, humidity, air pressure, precipitation (rainfall...
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Weather Forecasting (World of Earth Science)
Weather forecasting is the attempt by meteorologists to predict the state of the atmosphere at some future time and the weather conditions that may be expected. Weather forecasting is the single most important practical reason for the existence of meteorology as a science. It is obvious that knowing the future of the weather can be important for individuals and organizations. Accurate weather forecasts can tell a farmer the best time to plant, an airport control tower what information to send to planes that are landing and taking off, and residents of a coastal region when a hurricane might strike.
Humans have been looking for ways to forecast the weather for centuries. The Greek natural philosopher Theophrastus wrote a Book of Signs, in about 300 B.C. listing more than 200 ways of knowing when to expect rain, wind, fair conditions, and other kinds of weather.
Scientifically-based weather forecasting was not possible until meteorologists were able to collect data about current weather conditions from a relatively widespread system of observing stations and organize that data in a timely fashion. By the 1930s, these conditions had been met. Vilhelm and Jacob Bjerknes developed a weather station network in the 1920s that allowed for the collection of regional weather data. The weather data collected by the network could be transmitted nearly instantaneously by use of the telegraph, invented in the 1830s by Samuel F. B. Morse. The age of scientific forecasting, also referred to as synoptic forecasting, was under way.
In the United States, weather forecasting is the responsibility of the National Weather Service (NWS), a division of the National Oceanic and Atmospheric Administration (NOAA) of the Department of Commerce. NWS maintains more than 400 field offices and observatories in all 50 states and overseas. The future modernized structure of the NWS will include 116 weather forecast offices (WFO) and 13 river forecast centers, all collocated with WFOs. WFOs also collect data from ships at sea all over the world and from meteorological satellites circling Earth. Each year the Service collects nearly four million pieces of information about atmospheric conditions from these sources.
The information collected by WFOs is used in the weather forecasting work of NWS. The data is processed by nine National Centers for Environmental Prediction (NCEP). Each center has a specific weather-related responsibility: seven of the centers focus on weather predictionhe Aviation Weather Center, the Climate Prediction Center, the Hydrometeorological Prediction Center, the Marine Prediction Center, the Space Environment Center, the Storm Prediction Center, and the Tropical Prediction Centerhile the other two centers develop and run complex computer models of the atmosphere and provide support to the other centershe Environmental Prediction Center and NCEP Central Operations. Severe weather systems such as thunderstorms, tornadoes, and hurricanes are monitored at the National Storm Prediction Center in Norman, Oklahoma, and the National Hurricane Center in Miami, Florida. Hurricane watches and warnings are issued by the National Hurricane Center's Tropical Prediction Center in Miami, Florida, (serving the Atlantic, Caribbean, Gulf of Mexico, and eastern Pacific Ocean) and by the Forecast Office in Honolulu, Hawaii, (serving the central Pacific). WFOs, other government agencies, and private meteorological services rely on NCEP's information, and many of the weather forecasts in the paper, and on radio and television, originate at NCEP.
Global weather data are collected at more than 1,000 observation points around the world and then sent to central stations maintained by the World Meteorological Organization, a division of the United Nations. Global data also are sent to NWS's NCEPs for analysis and publication.
The less one knows about the way the atmosphere works the simpler weather forecasting appears to be. For example, if clouds appear in the sky and a light rain begins to fall, one might predict that rain will continue throughout the day. This type of weather forecast is known as a persistent forecast. A persistent forecast assumes the weather over a particular geographic area simply will continue into the future. The validity of persistent forecasting lasts for a few hours, but not much longer because weather conditions result from a complex interaction of many factors that still are not well understood and that may change rapidly.
A somewhat more reliable approach to weather forecasting is known as the steady-state or trend method. This method is based on the knowledge that weather conditions are strongly influenced by the movement of air masses that often can be charted quite accurately. A weather map might show that a cold front is moving across the Great Plains of the United States from west to east with an average speed of 10 mph (16 kph). It might be reasonable to predict that the front would reach a place 100 mi (160 km) to the east in a matter of 10 hours. Since characteristic types of weather often are associated with cold fronts it then might be reasonable to predict the weather at locations east of the front with some degree of confidence.
A similar approach to forecasting is called the analogue method because it uses analogies between existing weather maps and similar maps from the past. For example, suppose a weather map for December 10, 2002, is found to be almost identical with a weather map for January 8, 1993. Because the weather for the earlier date is already known it might be reasonable to predict similar weather patterns for the later date.
Another form of weather forecasting makes use of statistical probability. In some locations on Earth's surface, one can safely predict the weather because a consistent pattern has already been established. In parts of Peru, it rains no more than a few inches per century. A weather forecaster in this region might feel confident that he or she could predict clear skies for tomorrow with a 99.9% chance of being correct.
The complexity of atmospheric conditions is reflected in the fact that none of the forecasting methods outlined above is dependable for more than a few days, at best. This reality does not prevent meteorologists from attempting to make long-term forecasts. These forecasts might predict the weather a few weeks, a few months, or even a year in advance. One of the best known (although not necessarily the most accurate) of long-term forecasts is found in the annual edition of the Farmer's Almanac.
The basis for long-range forecasting is a statistical analysis of weather conditions over an area in the past. For example, a forecaster might determine that the average snow fall in December in Grand Rapids, Michigan, over the past 30 years had been 15.8 in (40.1 cm). A reasonable way to try estimating next year's snowfall in Grand Rapids would be to assume that it might be close to 15.8 inches (40.1 cm).
Today this kind of statistical data is augmented by studies of global conditions such as winds in the upper atmosphere and ocean temperatures. If a forecaster knows that the jet stream over Canada has been diverted southward from its normal flow for a period of months, that change might alter precipitation patterns over Grand Rapids over the next few months.
The term "numerical" weather prediction is something of a misnomer because all forms of forecasting make use of numerical data such as temperature, atmospheric pressure, and humidity. More precisely, numerical weather prediction refers to forecasts that are obtained by using complex mathematical calculations carried out with high-speed computers.
Numerical weather prediction is based on mathematical models of the atmosphere. A mathematical model is a system of equations that attempt to describe the properties of the atmosphere and changes that may take place within it. These equations can be written because the gases that comprise the atmosphere obey the same physical and chemical laws that gases on Earth's surface follow. For example, Charles'Law says that when a gas is heated, it tends to expand. This law applies to gases in the atmosphere as it does to gases in a laboratory.
The technical problem that meteorologists face is that atmospheric gases are influenced by many different physical and chemical factors at the same time. A gas that expands according to Charles' Law may also be decomposing because of chemical forces acting on it. How can anyone make use of all the different chemical and physical laws operating in the atmosphere to come up with a forecast of future atmospheric conditions? The answer is mathematically complex. The task is not too much for computers, however. Computers can perform a series of calculations in a few hours that would take a meteorologist his or her whole lifetime to finish.
In numerical weather predicting, meteorologists select a group of equations that describe the conditions of the atmosphere as completely as possible for any one location at any one time. This set of equations can never be complete because even a computer is limited as to the number of calculations it can complete in a reasonable time. Thus, meteorologists pick out the factors they think are most important in influencing the development of atmospheric conditions. These equations are fed into the computer. After a certain period of time, the computer will print out the changes that might be expected if atmospheric gases behave according to the scientific laws to which they are subject. From this printout a meteorologist can make a forecast of the weather in an area in the future.
The accuracy of numerical weather predictions depend primarily on two factors. First, the more data that is available to a computer, the more accurate its results. Second, the faster the speed of the computer, the more calculations it can perform, and the more accurate its report will be. In the period from 1955 (when computers were first used in weather forecasting) to the current time, the percent skill of forecasts has improved from about 30% to more than 60%. The percent skill measure was invented to describe the likelihood that a weather forecast will be more accurate than pure chance.
Forecast accuracy also is difficult to judge because the average person's expectations probably have increased as the percent skill of forecasts also has increased. A hundred years ago, few people would have expected to have much idea as to what the weather would be like 24 hours in the future. Today,
an accurate next-day forecast often is possible. For periods of less than a day, a forecast covering an area of 100 mi2 (259 km2) is likely to be quite dependable.
See also Air masses and fronts; Atmospheric chemistry; Atmospheric circulation; Atmospheric composition and structure; Atmospheric inversion layers; Drought; El Niño and La Nina phenomena; Hydrologic cycle; Isobars; Land and sea breeze; Lightning; Ocean circulation and currents; Thunder; Tornado; Tropical cyclone; Weather forecasting methods; Weather radar; Weather satellite; Wind chill