During a thunderstorm, clouds form at tens of thousands of feet into the atmosphere, where temperatures are as low as thirty-two degrees Fahrenheit-water's freezing point. Under these conditions, precipitation forms as ice crystals, hail, and rain. Driven by winds, ice particles of different sizes collide and become electrically charged, some with a positive charge, and others with a negative charge. The wind carries the positively charged ice crystals to the top of the clouds, while the heavier negatively charged hail collects at the bottom of the storm clouds. This process creates a positive electrical charge at the top of the clouds, while the bottom of the clouds develops a negative charge.

In negative-lightning strikes, invisible, n egatively charged streamers surge toward the ground from an extremely charged cloud base. As they approach the earth, invisible, positively charged streamers are attracted up- ward...