Is a low-hanging cloud in a thunderstorm a tornado?
Many low-hanging clouds are not tornadoes, but sometimes are wrongly reported as tornadoes anyway. The most important things to look for when you see a suspicious cloud feature are: (1) rapid cloud-base rotation, if you are close enough to make out cloud movement, and (2) a concentrated, whirling debris or dust cloud at ground level under the thunderstorm base. (Imagine this spinning rapidly.) It is common to have one without the other. Many thunderstorms produce dust plumes in their outflow; these tend to move in one direction and not rotate. In gustnadoes there is spinning motion at ground level but not at cloud base (therefore, not a tornado). If the ground is wet enough, or the circulation weak enough, there may not be any debris under a rotating cloud base. But persistent rotation in the cloud base is potentially very dangerous and should be reported. At night, also look for persistent cloud lowering to ground, especially if accompanied by a power flash.
