Labels:cloud | text | sky | nature | fog | screenshot OCR: Cumulonimbus Clouds Also called thunderheads, cumulonimbus clouds indicate a sudden major change in the weather. Locally intense rain, hail and electrical storms are likely, and these clouds may also form in large numbers and cause a major storm event. This type of cloud and ston activity is common on the Snake River Plain where convection cells build readily as the Plain surface heats in daylight hours.