Stormy clouds ((Cumulonimbus, from the Latin cumulus (“heap”) and nimbus (“rainstorm”, “storm cloud”), is a dense towering vertical cloud associated with thunderstorms and atmospheric instability, forming from water vapor carried by powerful upward air currents. Cumulonimbus can form alone, in clusters, or along cold front squall lines. “Cumulonimbus cloud.” 7 January 2015.)) over Willamette Valley ((The Willamette Valley is the most populous region in the state of Oregon of the United States. Located in the state’s northwest, the valley is surrounded by mountain ranges to the east, west and south. “Willamette Valley.” Wikipedia. 9 November 2014.)), Ore.