What is one sure sign that land is near? They form over land when the warm land air rises and cools.

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Convection from daytime heating over land drives warm air upward. As this rising air cools, moisture condenses and forms puffy clouds with flat bases—those are cumulus clouds. This vertical development from surface heating is a hallmark of land-based formation, making cumulus the best indicator among the options. Cirrus are high, wispy ice crystals; stratus are low, flat layers; and “nimbus” describes rain-bearing conditions, not a specific cloud type. So the described formation matches cumulus clouds.