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How Meteorologists
Forecast the weather

Weather Forecasting
01/06/99- Updated 06:10 PM ET -

"To the often-heard question, 'Why can't we make better weather forecasts?' I have been tempted to reply, 'Well, why should we be able to make any forecasts at all?' " - Edward N. Lorenz in The Essence of Chaos.

Lorenz is the MIT atmospheric science researcher whose work led to the development of the idea of chaos in physical systems. In meteorology, one of the important implications is that small differences in the initial conditions of the atmosphere can lead to big differences in the weather that results only a few days later. These differences can be too small to detect. This is why scientists say that day-to-day forecasts of the weather for more than about two weeks ahead will never be possible. Today, five days is about the limit of useful day-to-day forecasts. And, forecasts for five days ahead are, at best, little better than using "normal" climatic values.

All weather forecasts begin with observations of what the weather is doing all over the world. These observations are then fed into super computers that use mathematical models of the atmosphere to make predictions. In the United States, these computers are operated by the National Weather Service. The resulting forecasts are used by all weather forecasters, both those with the National Weather Service, those at television stations, and those at private forecasting companies, such as Weather Services Corp. in Lexington, Mass., which does all of USA TODAY's forecasts.

The links below will tell you more about how all of this is done.


Basics of forecasting

The University of Illinois' Online Meteorology section on weather forecasting is the best way to begin understanding the topic.

This site's projects and activities section gives teachers and students good ideas for learning more about weather and forecasting.

USA TODAY's understanding forecasts page has links to information that explain what forecasters mean and how to read weather maps.


Amateur forecasting

If you want to try your hand at doing some of your own weather forecasting, first check out the University of Illinois site listed above, then go to articles from a National Oceanic and Atmospheric Administration gopher server, which USA TODAY has posted on our site. First, don't count on most weather proverbs to tell you what's likely to happen. But the combination of readings from a barometer and wind direction can often give good clues what to expect.

Once you learn some of the basics of weather forecasting and how to read the different weather maps, you will want to visit the University of Michigan's WeatherNet weather maps page, which has both surface and upper-level weather maps


Understanding forecasts

The information that had been here on what forecasting terms mean and how to read weather maps is now part of our new understanding forecasts page.


Computer models

Many computer models have been developed the past three decades, which help meteorologists forecast weather. A USA TODAY Online text file gives a brief history of models and their role in forecasting.

Another USA TODAY text file briefly describes some of the models currently in use.

The National Weather Service Western Region has an introduction to Numerical Weather Prediction

A good way to access the images and text produced by these models is on the Ohio State University Forecast Weather Images page. Links from this page will take you not only to the U.S. models, but also some from other parts of the world.

The University of Michigan also has links to many of the different forecast models graphics. Click here to access the WeatherNet's computer model forecast page.


Improving forecasts

Forecasts have improved tremendously the past three decades with the explosion of computer technology. Whether or not this rapid improvement in weather forecasts continues depends on three main factors.

The ability to observe the atmosphere is crucial for improving forecasts. The National Centers for Environmental Predictions (NCEP) is improving observations of the atmosphere by modernizing observation techniques and using new technology.

The National Weather Service's Office of Meteorology has a Web site with more information on changes being made in forecasting.

The National Oceanic and Atmospheric Administration's Forecasting Systems Lab in Boulder, Colo., has several projects designed to improve forecasting. Click here to go to a web page with links to more information about these projects.


Ensemble forecasting

A big question for forecasters always is, "how reliable is this prediction?" A basic idea from chaos theory as it applies to weather forecasting is that small differences in the initial conditions of the atmosphere can lead to big differences in the weather that results only a few days later. But, some times small differences can make more difference that at other times. That is, sometimes the weather is more predictable than at other times. To find out whether the atmosphere is more or less predictable at a particular time, forecasters run their computer models several times to produce the same forecast. But, they change the initial conditions slightly for each run. If the results of the model runs with different conditions are close to each other, the forecasters know the atmosphere is behaving well and the forecasts have more chance of turning out well.

  • More about this is found in the second edition of the USA TODAY Weather Book, published in 1997


Hurricane forecast limits

A new hurricane model led to vast improvements in hurricane forecasting in the 1995 season. However, meteorologists say there are limitations on the accuracy and time range of hurricane forecasting.


Long-range forecasts

The National Weather Service issues long-range forecasts for weeks and months ahead. These forecasts are not detailed and can not tell you if it will rain on a particular day next month. A USA TODAY online file describes what long-range forecasts can and can not tell you. Another file contains some answers to commonly asked questions about long range forecasts.

Long range forecasts often depend on seasonal variations in the sea surface temperature of the oceans, such as those that are a part of El Nino.

A long-range forecast homepage has links to some long-range forecasts issued by NCEP and some more information about long range forecasts.

Often, climatic "normals" - or 30-year averages - are a more useful guide to planning than any kind of long-range forecast. USA TODAY's weather averages page has more information and links to averages for places around the world.



The USA and other nations support many research projects in atmospheric science in order to better understand some of laws and processes that govern the earth's atmosphere and oceans. One major project is the ongoing research into El Nino

The VORTEX Experiment was another major research project, which was designed to try to better understand tornadoes. A USA TODAY Online graphic gives more details about how the VORTEX Experiment was set up and some of the results.



The explosion in technology is one of the key factors that have improved forecasts. One of the new tools, which have enhanced observations of the atmosphere, is Doppler radar.

Hurricane hunter aircraft have been used the past several years to observe hurricanes and to aid forecasters in predicting hurricane landfall. A new high altitude jet craft is expected to be ready by August 1996. The new jet will likely lead to a major improvement in hurricane landfall forecasts.

A technology homepage describes some of the technology in use and being developed for weather forecasting.


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