What is the highest cloud top ever recorded?

Dear Tom,
What is the highest cloud top ever recorded?
— Brian Gibson, Arden, N.C.
Dear Brian,
It’s not precisely known, but in general the higher the cloud top (in the middle latitudes), the more severe the weather associated with the cloud will be. The reference, of course, is to cumulonimbus clouds, the clouds that produce thunderstorms. In the Chicago area, typical summer thunderstorms develop to heights of 35,000 to 45,000 feet, but the tops of severe thunderstorms that produce large hail, damaging winds and even tornadoes can reach to 60,000 feet or more.
The devastating Plainfield tornado of Aug. 28, 1990, developed from a thunderstorm that towered to 65,000 feet. Earth’s tallest thunderstorms form in the tropics, where tops have been measured to about 75,000 feet — more than 14 miles into the atmosphere.