Towering anvil-topped cumulus. Mauna Kea, Hawaii NOAA Photo Collection 5. On a hot summer afternoon, in the distance you see a cumulus cloud that has grown to gigantic proportions. As you watch, the top of the cloud begins flattening out into a large anvil shape and you can hear distant thunder coming from it. This type of cloud is a: A. Nimbostratus B. Stratucumulus C. Cirrostratus D. Cumulonimbus Choose any one of the four answers above.