18. One region within the cloud builds up a positive charge and the other a negative charge. The bottom of the cloud usually ends up being negatively charged and the top positively charged. If the build up (separation) of charge becomes great enough, the negative charges may leap to the positive.
20. A lightning strike can heat the air in a fraction of a second. When air is heated that quickly, it expands violently and then contracts, like an explosion that happens in the blink of an eye. It's that explosion of air that creates sound waves, which we hear and call thunder .
29. Watch – event could occur, conditions are favorable. Warning– it is on its way to you! Be sure you know the difference between a watch and a warning!
30. Flash floods occur when water from a storm cannot run off quickly enough. Flash floods
31. Floods occur when water in a river overflows it banks because of heavy rain upstream.