Mad About Science

How meteorologists predict the weather

By Ben Olson
Reader Staff

In this age of uncertainty, when the news often changes by the hour, how is it that meteorologists accurately predict the future with their weather forecasts? Are they mode soothsayers, scrying into crystal balls to tell us within a fair degree of accuracy how many inches of snow will fall next week? In a word, yes, that’s exactly what they are, but they don’t use tea leaves or crystal balls. Modern-day meteorologists use science and historical data stretching back generations to tell us what to expect for our daily and extended forecasts.

Today’s meteorologists have more tools available to them to predict the weather than those of the past. The ancient seafaring phrase, “red sky at night, sailor’s delight; red sky by morning, sailors take warning,” is probably one of the oldest weather prediction tools humankind has used. The phrase goes back at least to the Bible, where in Matthew XVI: 2-3 Jesus said, “When in evening, ye say, it will be fair weather: For the sky is red. And in the morning, it will be foul weather today; for the sky is red and lowering.”

There is some truth to that adage, as weather systems in the Northern Hemisphere generally move from west to east. That means a colorful sunrise indicates clouds to the west, which means rough weather could be on its way. If the clouds redden at night, it means they departed to the east giving a good indication that the weather will probably be calm tomorrow.

With the invention of basic weather instruments like thermometers and barometers in the 17th and 18th centuries, a new era of forecasting developed into a system of accurate record-keeping of the weather. 

When the electric telegraph came into existence in the 19th century, it allowed people from far-flung areas to quickly spread weather information, leading to the development of weather charts. This new, larger view of weather systems allowed people to see conditions and large-scale patterns across entire continents.

As with any science, the baseline of meteorological predictions was enhanced by the ability to spot these basic patterns and predict what would happen next. For example, rising air pressure is usually associated with calmer weather, so if the barometer trended upward, calms were probably on the way. Falling pressures, on the other hand, meant stormy weather ahead.

At the dawn of the 20th century, scientists began to rely on tools such as weather balloons to sample temperature, moisture and winds through the atmosphere. As specialists gathered and recorded more information, it became easier to predict how the weather worked, thus making forecasts more accurate further into the future.

When scientists and engineers developed radar in the World War II era, they employed the tool that the military used to locate enemy aircraft to see rain showers. In the 1950s, when computer weather models started to become a norm, radar became an indispensable tool for modern meteorologists to plot weather charts and accurately see not only rain clouds, but also, with Doppler radar, to measure the winds within the rain systems — that then helped them to map a course for the system to warn residents in the path of the storm to bring their umbrella to work the next morning.

Today, there are more than 150 radar towers across the United States, each monitored closely by meteorologists to give comprehensive coverage of the continent. Modern Doppler radar can detect all types of precipitation, the rotation of thunderstorm clouds, airborne tornado debris, and wind strength and direction.

In addition to ground-based radar stations, meteorologists now use weather satellites to monitor Earth from space, collecting observational data for scientists to analyze. Polar orbiting satellites orbit the Earth close to the surface, taking six or seven detailed images a day. Geostationary satellites stay over the same location on Earth high above the surface taking images of the entire Earth as frequently as twice a minute. Deep space satellites face the sun to monitor powerful solar storms and space weather, which affects us here on Earth.

Another lesser known data collection tool is the radiosonde, which is tied to weather balloons and launched in more than 90 locations across the U.S. every day. In their two-hour trip, radiosondes float to the upper stratosphere where they collect and transmit data every second about air pressure, temperature, relative humidity, wind speed and direction. 

To manage this mountain of data coming in every second of every day, the National Oceanic and Atmospheric Administration’s National Weather Service uses supercomputers that are capable of processing quadrillions of calculations per second. These beasts are about 6 million times more powerful than the iMac you use at home. As all the data is plugged into these supercomputers, they generate models, along with past and present weather data, to provide a forecast so meteorologists do less guessing and more predicting.

Next time you look online to the 10-day forecast to plan your outing, give a moment to thank all the scientists who came before us, providing everyone with the ability to look a little way into the future and know with a certain degree of accuracy what to expect from above.

Stay curious, 7B. Regular Mad About Science columnist Brenden Booby will be back next week.

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