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The atmosphere is extremely thin relative to the rest of Earth. SEVERE WEATHER STATEMENT NATIONAL WEATHER SERVICE NORMAN OK 7:31 PM CDT MON MAY 3 1999 LARGE DAMAGING TORNADO MOVING THROUGH OKLAHOMA CITY METRO. A LARGE TORNADO HAS CAUSED EXTENSIVE DAMAGE IN SOUTHERN PORTIONS OF THE OKLAHOMA CITY METRO AREA. AT 7:31 PM THE TORNADO WAS ENTERING SOUTHERN OKLAHOMA COUNTY JUST EAST OF INTERSTATE 35 AND SOUTH OF CROSS ROADS MALL. PERSONS IN SOUTHEAST OKLAHOMA CITY AND MIDWEST CITY ARE IN DANGER! IF YOU LIVE NEAR THESE AREAS TAKE IMMEDIATE TORNADO PRECAUTIONS! THE TORNADO WAS MOVING NORTHEAST. THIS IS AN EXTREMELY DANGEROUS AND LIFE-THREATENING SITUATION. IF YOU ARE IN THE PATH OF THIS LARGE AND DESTRUCTIVE TORNADO . . . TAKE COVER IMMEDIATELY. BULLETIN - EAS ACTIVATION REQUESTED TORNADO WARNING NATIONAL WEATHER SERVICE NORMAN OK 10:17 PM CDT MON MAY 3 1999 THE NATIONAL WEATHER SERVICE IN NORMAN HAS ISSUED A * TORNADO WARNING FOR NOBLE COUNTY IN NORTHEAST OKLAHOMA UNTIL 10:45 PM CDT. * AT 10:17 PM CDT A ONE-MILE WIDE TORNADO WAS REPORTED NEAR MULHALL, MOVING NORTHEAST AT 30 MPH. THIS TORNADO WILL CROSS INTERSTATE 35 NEAR OR SOUTH OF PERRY. RESIDENTS IN NOBLE COUNTY NEED TO TAKE COVER NOW. PERRY IS IN THE PATH OF THIS STORM. THIS IS AN EXTREMELY DANGEROUS AND POTENTIALLY LIFE-THREATENING SITUATION. IF YOU ARE IN THE PATH OF THIS LARGE AND DESTRUCTIVE TORNADO, TAKE COVER IMMEDIATELY. TORNADOES ARE ESPECIALLY DANGEROUS AT NIGHT BECAUSE THEY ARE HARD TO SEE. TAKE COVER NOW. IF A BASEMENT IS NOT AVAILABLE, MOVE TO AN INTERIOR ROOM OR HALLWAY ON THE LOWEST FLOOR. LEAVE MOBILE HOMES AND VEHICLES FOR REINFORCED SHELTER. STAY AWAY FROM WINDOWS. During the afternoon and evening of May 3, 1999, dozens of emergency advisories like these two were issued to residents of the south central United States as one of the worst tornado outbreaks in decades punished the area. Worst hit was central Oklahoma, where at least 57 tornadoes killed 44 people and injured 748 others (Figure 1–1). In Kansas another five people were killed and 11,000 homes or businesses were damaged or destroyed. Over the next few days, the same storm that spawned the tornadoes slowly worked its way to neighboring states, killing five more people in Texas and Tennessee. The storm system contained eleven major storm elements, called supercells, that followed a southwest-to-northeast path. Each supercell produced at least one tornado, with the most destructive supercell yielding 22 in a 3-hour period while covering a distance of 61 kilometers (km), or 38 miles (mi). The largest of its tornadoes was about 2 km (1 mi) wide and stayed on the ground for nearly an hour and a half. As terrible as the outbreak was, things would have been very much worse had it not been for the extensive forecasting, tracking, and warning capabilities of the National Weather Service. One study based on long-term observations suggests that as many as 700 people might have perished had it not been for the recent modernization of the Weather Service. People such as Air Force Captain John Millhouse would readily agree with that notion. Having heard one of the tornado warnings, he and his family moved to the basement of their home. When they emerged unscathed, only two walls of the house were left standing; the rest was totally destroyed. Not all weather phenomena are as dramatic as tornadoes, but it is indisputable that the weather exerts a tremendous impact on our day-to-day lives: we revel in the beauty of a sunrise, marvel at the power of hurricanes, rely on the rain to nourish our gardens, and complain about the heat—and the cold. Despite its immediacy, most of us know relatively little about how and why the atmosphere behaves as it does. In the pages that follow, we hope to provide an account of both the how and the why, in ways that will lead you to an understanding of the underlying physical processes. This chapter introduces the most basic elements of meteorology, laying the foundation for much of what follows in the rest of the book.
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