A cumulonimbus cloud with dry lightning. A firefighter (usually a wildland firefighter) calls this a cumulus overtimus in reference to the overtime that he / she will make if there are down strikes that start a fire.
While standing at the station looking at the clouds or when listening to the weather report that predicts dry lightening.
"It looks like there is a big build up of cumulus overtimus."
or
"Bring on the cumulus overtimus."
"It looks like there is a big build up of cumulus overtimus."
or
"Bring on the cumulus overtimus."
by AlistairMacIlherron September 21, 2009