Science Video

Perfect Weather Predictions
Meteorologists' Weather Forecasting Improving

May 1, 2008 — Meteorologists have markedly increased the accuracy of their forecasts in the last twenty years. Advances in radar and satellite technology have helped to improve daily forecasts, making a four-day forecast today better than a two-day forecast twenty years ago. They have also significantly improved forecasting for major winter storms and hurricanes.

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Every day, weather forecasters are put to the test for accurate daily predictions. It's a hard job that gets blamed for rained-out picnics, canceled barbecues and delayed planes; but today, our forecasts are more accurate than any other time in history.

We rely on our meteorologists to help plan our lives, but one wrong forecast and local meteorologists are the first to get blamed. Predicting the weather isn't easy, but despite a few missed temperatures, weather forecasting has actually made huge improvements in the last 20 years. "Our forecasts, on average for large storms, were about 90 percent accurate," Douglas Young, a meteorologist at the National Oceanic and Atmospheric Administration in Washington, D.C., told Ivanhoe.

Predicting where a hurricane is headed and where it will end up has improved. In 1985, forecasters predicted a hurricane's path 366 miles wide. Now, a hurricane's path can be predicted down to within a 111 mile-wide path. That's a 67 percent increase in accuracy! "This expected improvement will continue during the next decade or so as we fly aircraft inside the inner core of the storm to learn more information," Young said.

Technology advances in radar and satellites have also helped daily forecasts improve. A four-day forecast today is better than a two-day forecast was back in the mid 1980's. And it gets better ... "Our six-day forecasts are as good as our three-day forecasts used to be," Young said. And better … "Our three-day forecasts are accurate 75 percent of the time within five degrees," he said.

While meteorologists may not be perfect, forecasting continues to improve so the chances of a perfect forecast increase almost every day. A three-day forecast of one inch or more of precipitation -- like rain or snow -- is as accurate as a two-day forecast was ten years ago.

WHAT'S THE FORECAST: Weather forecasting is the application of science and technology to predict the state of the atmosphere for a future time and a given location. Humankind has attempted to predict the weather since ancient times. For millennia people have tried to forecast the weather. In 650 BC, the Babylonians predicted the weather from cloud patterns. In about 340 BC, Aristotle described weather patterns in Meteorologica.

Chinese weather prediction lore extends at least as far back as 300 BC. Ancient weather forecasting methods usually relied observed patterns of events. For example, it might be observed that if the sunset was particularly red, the following day often brought fair weather. This experience accumulated over the generations to produce weather lore. Today, weather forecasts are made by collecting data about the current state of the atmosphere and using computer models of the atmospheric processes to project how the atmosphere will evolve.

HOW STORMS DEVELOP: Storm clouds form as moisture evaporates from the earth into the atmosphere, where the droplets congregate and jostle against each other. The air cools off rapidly with altitude and the water vapor condenses into liquid drops, forming clouds. The process continues: more and more water vapor turns into liquid, and the moist air warms up even more and rises higher and higher. The severity of a storm will depend largely on the buoyancy of the rising air within the storm and the structure of the wind within the atmosphere.

WHAT IS DOPPLER RADAR: Doppler radar uses a well-known effect of light called the Doppler shift. Just as a train whistle will sound higher as it approaches a platform and then become lower in pitch as it moves away, light emitted by a moving object is perceived to increase in frequency (a blue shift) if it is moving toward the observer; if the object is moving away from us, it will be shifted toward the red end of the spectrum. Doppler radar sends out radio waves that bounce off objects in the air, such as raindrops or snow crystals, and then measures how much the frequency changes in returning radio waves to better determine wind direction and speed.

The American Meteorological Society contributed to the information contained in the video portion of this report.

Note: This story and accompanying video were originally produced for the American Institute of Physics series Discoveries and Breakthroughs in Science by Ivanhoe Broadcast News and are protected by copyright law. All rights reserved.