What Are Thunderstorms? What Causes Them?
• The National Weather Service considers a thunderstorm severe if it produces hail at least 3/4-inch in diameter, winds of 58 mph or stronger, or a tornado. • Every Thunderstorm Needs: • Moisture: to form clouds and rain. • Unstable air: warm air that can rise rapidly. • Lift: cold or warm fronts, sea breezes, mountains, or the sun s heat are capable of lifting air to help form thunderstorms. Life Cycle of a Thunderstorm Developing Stage • Towering cumulus cloud indicates rising air. • Usually little if any rain during this stage. • Lasts about 10 minutes. • Occasional lightning. Mature Stage • Most likely time for hail, heavy rain, frequent lightning, strong winds, and tornadoes. • Storm occasionally has a black or dark green appearance. • Lasts an average of 10 to 20 minutes but may last much longer in some storms. Dissipating Stage • Rainfall decreases in intensity. • Can still produce a burst of strong winds. • Lightning remains a danger Tornadoes. . . Although tornadoes occur in m
