Cumulus congestus clouds are a precursor to severe weather.
On warm sunny days heated air rises. As it rises, it absorbs water vapor. Warm air can hold more water vapor than cool air. As the warm air rises, it cools until it reaches its condensation point, or the point where water vapor begins condensing. Rain clouds are made up of condensed water and form when water molecules "clump together." Nimbus or rain clouds occur below 6,500 feet. These large gray clouds "look like rain."
Instructions
1. Look for flat, uniform gray clouds with a uniform base. Stratus clouds form a solid sheet or layer of cloud cover, often covering the entire sky. They often produce light precipitation or drizzle. Stratus clouds resemble low-hanging fog, and often form when early morning fog lifts.
2. Look for vertical clouds with flat bottoms and rounded tops. Cumulus clouds look puffy or cotton-like, and appear alone, in lines or in clusters. Small scattered cumulus clouds are called "fair weather" clouds and produce no precipitation. However, they can develop into tower-like cumulus congestus clouds capable of producing precipitation.
3. Look for rows of low, puffy gray clouds. Stratocumulus clouds are a cross between stratus and cumulus clouds, and look like layers of cloud clumps. They develop either ahead or behind a frontal system, and often signify worsening weather. They can produce light rain.
4. Look for dark gray clouds with a ragged base. Nimbostratus clouds are thick, dense stratus or stratocumulus clouds capable of producing steady moderate to heavy precipitation lasting several days. They develop along warm fronts where slowly rising warm air creates stratus and nimbostratus clouds.
5. Look for tall, dark, dense clouds. Cumulonimbus clouds form alone, in clusters or in a squall line. They form from cumulus congestus clouds, and can reach enormous heights. You will often see these before a thunderstorm and they are capable of forming super cells, capable of producing tornadoes. These clouds produce torrential downpours, often dumping as much as three feet of rain in an afternoon.
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