A rotating cloud is, broadly speaking, any cloud exhibiting rotational movement. However, when discussing severe weather, the term often refers to specific cloud formations associated with thunderstorms and the potential for tornadoes. One example is a rotating wall cloud.
Wall Clouds and Rotation
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A wall cloud is a lowered, often rain-free cloud base that forms beneath the main updraft of a supercell thunderstorm. The key characteristic of these clouds, in the context of this question, is that they can rotate.
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Rotation Matters: The presence of a rotating wall cloud is a significant indicator of potential severe weather. According to the provided reference, rotating wall clouds often develop before strong or violent tornadoes.
- This development can occur anywhere from a few minutes up to nearly an hour before a tornado touches down.
Monitoring for Tornado Formation
The rotation itself isn't enough to guarantee a tornado. It's crucial to watch for specific signs:
- Persistent, sustained rotation: Is the rotation consistent and lasting?
- Rapid vertical motion: Is the cloud base rising or falling quickly?
These factors, combined with the presence of a rotating wall cloud, increase the likelihood of tornado formation.
Example: Supercell Thunderstorm
A rotating cloud frequently forms beneath a supercell thunderstorm. Supercells are characterized by a rotating updraft called a mesocyclone. The wall cloud often develops within this mesocyclone, making it a visible sign of the storm's rotation.
Table: Characteristics of Rotating Wall Clouds
| Characteristic | Description |
|---|---|
| Location | Beneath the updraft of a supercell thunderstorm |
| Appearance | Lowered, often rain-free cloud base |
| Rotation | Exhibits persistent and sustained rotation |
| Tornado Indicator | Can develop before tornadoes |
| Monitoring Needed | Watch for rapid vertical motion |
