National Geographic : 1972 Apr
sky is red and lowring. O ye hypocrites, ye can discern the face of the sky; but can ye not discern the signs of the times?" Today's mariners-and farmers, and resort owners, and construction men, and all the rest of us who watch the weather each day-sel dom need depend on folklore. The National Weather Service (formerly the Weather Bu reau) provides detailed forecasts covering two and three days ahead. Since February 9, 1970 (the 100th birthday of the Weather Ser vice), less detailed five-day forecasts have been available daily. And for $3.50 a year the Weather Service will send you 30-day tem perature and precipitation outlooks by mail twice a month. Today's Forecasts: Bolder and Better How accurate are today's two- and three day predictions? Let the weathermen tell you. Allen D. Pearson, Director of the National Severe Storms Forecast Center in Kansas City, points out that "forecasts are now much more precise than they used to be. They are couched in less cautious language." Arthur Gustafson, who is in charge of San Francisco's forecast center, says, "Now we do better on two-day forecasts than we did for one day in the early '60's. And a decade ago, who would have dared tell you anything about Sunday's weather on Wednesday?" Dr. George Cressman, Director of the National Weather Service, puts it explicitly: "The national average verifications show that we can forecast today's or tonight's tempera ture to within about 31/2 degrees, and tomor row's to within about 41/2 degrees. If you count a forecast of over 50 percent chance of rain as meaning it will rain, and under 50 per cent as meaning no rain, our national aver ages show about 87 percent hits for today, and about 80 percent hits for tomorrow." To this Al Pearson adds a caution: "Weather forecasts are made for wide areas, not for pinpointed spots. Suppose the prediction is for 10 percent chance of rain, yet rain falls in one corner of that area. The man who is getting drenched screams, 'Ten percent! Don't those guys see what's up there?' He may not realize that most of the forecast area is as dry as can be. "Don't forget," says Pearson, "a prediction of only 10 percent chance of rain does not guarantee no rain. In fact, if we predict 10 percent chance of rain on 10 different days, by all the laws of probability it should rain on one of those days!" 522 So fast is weather science improving that Dr. Joseph Smagorinsky, one of today's most respected meteorologists, foresees that we can expect increased accuracy of forecasts over periods of up to several weeks, sufficient to be useful for economic planning and for weather hazard warning. Whether two- to three-week forecasts can ever be made with the same accuracy we now enjoy for two or three days is a matter of vigorous controversy. The answer depends on feverish research now going on with com puters, mathematics, techniques of observa tion, and satellites. And of these, perhaps most fascinating is the weather eye in space. Last summer as I worked on this article, a stubby object known as NOAA 1* was circling in earth orbit, passing northward over Cali fornia. It resembled an oblong packing crate with three purplish blue wings attached at one end (page 525). The wings, covered with solar cells to produce electricity for the satel lite, always faced the sun, and the spacecraft itself kept one side turned toward earth. Within the next hour and 55 minutes, NOAA 1 made a complete circuit of the globe, passing near the North Pole and then sweep ing south over Arabia and the Indian Ocean to Antarctica and back north again. Multiple eyes in the spacecraft scanned the swift-moving panorama 900 miles below. Two TV camera systems caught the glint of oceans and ice fields, the white expanse of clouds, the familiar outlines of continents and islands. More important, instruments known as radiometers detected heat and light radiation from earth, cloud, and sea. Unwinking Eye Scans the Entire Globe As Canada passed beneath, a radio com mand came up from an 85-foot antenna near Fairbanks, Alaska, operated by the National Environmental Satellite Service. "Give us your pictures," it signaled. Like an obedient child, NOAA 1 turned on magnetic tape recorders that had stored pictures from one of its TV cameras. Elec tronic impulses that encode patterns of light and dark went by radio from the spacecraft to the ground station, from which they were relayed to weather stations all over the United States. In hours, forecasters had the pictures on their desks, showing storm patterns that *NOAA takes its name from the new National Oceanic and Atmospheric Administration, which includes the National Weather Service, the National Environmental Satellite Service, and several other agencies of the Department of Commerce.