GOT A QUESTION FOR TOM? Ask him here!
Do forest fires add enough water vapor to the air to produce clouds above them? Three years ago I was vacationing in Arizona and a fire created a smoke column that was topped by a large cloud.
George Mellon, Bolingbrook
The cloud that you viewed was a pyrocumulus cloud (actually, a “flammagenitus” cloud— the name selected by the World Meteorological Organization in 2017). Pyrocumulus clouds are produced by strong heating of air above forest fires (also above volcanoes). The heated air rises and cools to the temperature necessary to cause condensation and cloud formation. Water vapor for condensation is already present in the air, not added to the air by the fire (although some moisture may also be added by the burning vegetation in forest fires).
Pyrocumulus clouds that produce lightning (especially above volcanoes) are a type of cumulonimbus clouds called cumulonimbus flammagenitus. They are the result of flammagenitus clouds that grow into thunderstorms.
Pyrocumulus clouds are often brownish in color because of forest fire smoke that is carried aloft withing the updraft column.