What indicates that immediate action should be taken due to flash flooding?

A warning indicates that immediate action should be taken due to flash flooding because it signifies a critical level of severity. In the context of weather events, a warning specifically alerts individuals and communities about imminent danger. It suggests that conditions are ripe for flash flooding, meaning that it is already occurring or will likely occur in a short period. Warnings are designed to prompt people to take action to protect life and property, such as moving to higher ground or leaving an affected area.

In contrast, alerts, advisories, and signals convey varying levels of urgency and are used to provide information about less imminent threats or general awareness. An alert may raise awareness but does not necessitate immediate action, while an advisory typically communicates less severe conditions and serves more as a precaution. A signal can relate to a broad range of alerts but does not specifically invoke the urgency that a warning does. Therefore, a warning directly communicates the need for prompt response due to the risk associated with the situation.