Predicting a Tornado

A gentle wind blows from the south; then it dies away, and a hot and oppressive calm lies across the land. From the west comes a line of thunderheads. At first they are low on the horizon, but swiftly they rise and swell and dominate the sky. By this time, weather-wise Great Plains farmers, who know tornado signs, are sticking close to their cyclone cellars.

Such weather wisdom warns of tornado conditions only an hour ahead at best; usually much less. This is not time enough to broadcast an alarm to people who spend little time in the open and so cannot watch the sky. For such potential victims, the U.S. Weather Bureau, with a big assist from the Air Force, has developed a system that warns of tornadoes two to four hours ahead.

Peculiar Pattern. Tornado clouds are unpleasant subjects to study at close range, and so they are not completely understood. But practical information about them has accumulated. In 1948. Meteorologists Ernest J. Fawbush and Robert C. Miller were on duty at Tinker Air Force Base in Oklahoma, when a tornado swept across it. After the disaster they went over their data on conditions before the storm and found a "peculiar pattern." Five days later they came to their office, took a look at the day's charts and saw the same weather pattern. They did not dare use the dread word "tornado," but they told key men about their hunch that a tornado was coming. Tinker Field got a forecast of an 80-m.p.h. wind, which ensured all possible precautions. Less than seven hours after the warning, the "pattern" delivered the goods: a tornado that ripped right across Tinker Field. It was probably the first to be predicted with pinpoint accuracy.

Stimulated by this success, Fawbush and Miller dug through past records looking for weather patterns that had produced tornadoes. As their experience grew, their forecasts improved, and were extended to cover military installations all over the central U.S.

In general, they smelled a tornado when a layer of warm, moist air was covered by a layer of cool, dry air. The wind had to be strong and in the right direction, and the warm air at the surface had to be subject to a strong lifting action. When these conditions (and more subtle ones) coincided, a tornado was likely to lick out from the black center of a cloud.

Since the Air Force is not in the business of warning the general public, the Weather Bureau set up a "severe-weather warning center" in Washington in 1952 to develop the Tinker Field system. Moved to Kansas City in 1954, it now issues warnings two to four hours in advance, spotting about 70% of the tornadoes within 150 miles of the warning area.

This sort of warning, though useful, is still pretty general, affecting a large area that may be struck by only a single tornado. It cannot tell which thundercloud is a potential bad actor. Radar does not help much. It shows a squall line advancing, but tornado storms in the line look like ordinary thunderheads.

The Waves Know. A new electronic tool is much more promising than radar. As far back as 1947, Dr. Herbert L. Jones of Oklahoma Agricultural and Mining College discovered that lightning flashes from tornado clouds send out "sferics" (atmospheric radio waves) of unusually high frequency. Such waves can be detected a long way off, and distinguished from ordinary thunderstorm sferics.

This year two sferics-detecting networks are operating experimentally out of Tinker Field and Kansas City. They have radars that watch for squall lines, which average 150 miles long, each containing 15 to 20 thunderstorms. As the line advances, the sferics detectors sweep from storm to storm, measuring the frequency of its radio waves. In a violent squall line, two or three of the storms may be of the type that can produce tornadoes.

Dr. Jones hopes that his system will be ready next year for practical operation. Then the Weather Bureau can pinpoint an individual cloud and warn the people in its path to get under cover quick.

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