Almost all thunderstorm clouds grow to heights above 20,000 feet. With 35,000 feet being typical. The more intense ones continue upwards until they hit the top of the troposphere, called the tropopause. Since penetrating into the stratosphere takes a lot of energy, many cumulonimbus clouds flatten out on the tropopause into the classic anvil shape with the tip streaming off downwind. If the storm is unusually intense, the updraft may punch into the stratosphere in cauliflower-like turrets. These “trop busters” are usually severe storms, with internal updrafts perhaps exceeding 100 mph. At any given place and time the height of the tallest storms is thus controlled by the height of the troposphere. Over the U.S. the tops of the stronger storms range from 40,000 to 65,000 feet from spring through summer and from north to south, respectively. There are some radar reports of echoes exceeding 70,000 feet, but if these reports are correct, this would be a very rare event. In any case, most thunderstorms are high enough that commercial jet traffic does not fly over most storms but rather circumnavigates since there can be “surprises” inside thunderstorm tops including extreme turbulence, hail, lightning, and wind shears.
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