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The date 1939, however, has another significance: it was the start of World War II, during which meteorology suddenly came of age. It was quickly apparent that the war would be fought largely in the air. with weather often the controlling factor. Storms would put whole air forces out of action. For surface forces, clouds and fogs would be all-important shelter.
Rossby did a part-time hitch as head of research with the Weather Bureau, which had a new chief and was trying hard to bring itself up to date. But in 1941, with the war spreading fast, the University of Chicago asked him to head its new department of meteorology. He accepted partly because one of his basic beliefs is that after about ten years a group of associates have nothing new to tell each other. They should break it up. he thinks, and look for fresh stimulation.
To Chicago Rossby brought his old friend Horace Byers of California days, and made him executive assistant and backstop. This move was a lifesaver, for success had made Rossby increasingly individualistic. He was a wonderfully stimulating teacher, an inspiring leader, and he produced ideas at a fantastic rate, but he was also a poor manager. He hardly ever answered mail. Instead, he stacked unopened letters in a pile to ripen. When they were so old that their writers no longer hoped for an answer, he felt it would do no harm to throw them away. He cut classes, was usually stony broke, ignored university budget restrictions. Sometimes he would ring furiously for his secretary when he was already dictating to her.
Onrushing Crisis. These peculiarities might have got Rossby into serious trouble, in spite of his recognized genius, but the onrushing war was a crisis, and he thrived on crises. The U.S. was building the world's biggest air force, and soon it would need the world's biggest corps of meteorologists. There were only a few in the country, many of them hopelessly behind the times. The Government's solution was to put Rossby in charge of a monstrous, high-pressure training program. He crisscrossed the country, setting up branch units at New York University, U.C.L.A., Caltech and M.I.T. At the University of Chicago, Rossby lectured with a slight, but attractive, Swedish accent to classes of 400 students, force-feeding them with the Bjerknes doctrine.
The students got a crash-grounding in the sort of meteorology that would be most useful in war. They learned how to predict whether the sky over a German city would be clear enough at a certain hour for high-altitude, visual bombing. Similar methods predicted days when dirty weather would protect ground troops from enemy air.
Forecast on DDay. The biggest moment for military weathermen was critical Dday, when General Eisenhower's forces crossed the Channel to land on the Normandy coast. Everything depended on the weather, which could have broken up the invasion fleet as it had the Spanish Armada, sailing in the opposite direction, 356 years before. As June 1944 approached, the weather over the Channel remained impossibly bad. Each service demanded several different kinds of weather. The airborne infantry wanted cloud-cover to shelter it from enemy fighters; the bombers wanted clear skies. Ground forces wanted cloud-cover and fairly dry soil in Normandy to support their vehicles.