In the cockpit of an airliner the pilot is quietly calculating the best course of action. The airplane is engulfed in a heavy cloud mass. The wing tips are not even visible, but periodically one can see a red glow caused by the blinking lights on the wing tips.
Thirty minutes ago the air had been smooth, but now the situation is rapidly becoming unpleasant. At frequent intervals the airplane bounces and shakes, indicating increasingly turbulent conditions. The seat belt sign is on. Every so often flashes of lightning light up the sky.
Some of the passengers who have flown a great deal are listening to the sounds of the engines and mentally flying the airplane. They reduce the air speed to minimize the effects of the air gusts and strain their eyes staring into the mist to see if they can spot the thunderstorms buried in the clouds. The cloud droplets and poor visibility are no cause for alarm. The danger is concentrated in the thunderstorms, where updrafts or downdrafts of several thousand feet per minute are waiting to lift or drop the