Here is the moment when deep towering cumulus (containing cumulus congestus) turns to cumulonimbus: the ice-crystal development known as glaciation. Sometimes, as here, glaciation occurs when the towers penetrate into pileus clouds that have developed at what will become anvil level. Within minutes, the icy anvil was fully developed and spreading downshear, away from this vantage. Periodic flooding by mineral-laden waters in the Salt Plains National Wildlife Refuge killed the foreground trees, which long since have fallen, only to be replaced by growth begun since the last sustained inundation.
10 N Jet OK (9 Apr 94) Looking SE
36.8115, -98.1917