WEATHER By Jack Williams FLORIDA HAS THE greatest amount of lightning activity in the United States; the central California coast has the least. SPRING TURNS PILOTS’ THOUGHTS TO THUNDERSTORMS SPRING’S FIRST WARM breezes signal an end to winter’s chill across the northern United States. These comfortable breezes should be a signal to pilots to begin thinking about thunderstorms. Winter’s reluctance to give way to warmth helps account for the fact that the greatest BIG PUSH ANY STORM OR CLOUD CLOSE TO BECOMING A THUNDERSTORM HAS STRONG UPDRAFTS AND DOWNDRAFTS THAT CREATE TURBULENCE. number of severe thunderstorms occurs during spring. The National Weather Service defines a “severe” thunderstorm as one “that produces a tornado, winds of at least 58 mph (50 knots), or hail at least three-quarter-inch in diameter.” Some severe thunderstorms meet all of these criteria. This definition applies to what people on the ground experience or could expect to experience if a severe thunderstorm is headed their way. As far as pilots are concerned, any thunderstorm should be considered severe. By definition, a cumulus cloud becomes a thunderstorm as soon as it produces a lightning stroke, since lightning is needed to produce the sound of thunder. Up-and-down air motions (updrafts and downdrafts) inside a cloud that contains both water drops and ice crystals create the positive and negative electrical charges within the cloud needed to cause lightning. This tells you that any storm or cloud close to becoming a thunderstorm has strong updrafts and downdrafts that create turbulence, which can be severe. Many water drops MIKE FIZER 40 / FLIGHTTRAINING.AOPA.ORGhttp://FLIGHTTRAINING.AOPA.ORG