Gustnado, landspout, dust devil, waterspout
Not every spinning thing under a storm is a tornado, not every tornado comes from a mesocyclone, and the boundary between those two statements is genuinely disputed.
Four things that spin
- Gustnado
- NWS Fort Worth: "A surface-based circulation associated with thunderstorm outflow. Gustnadoes are not associated with updrafts and are not attached to cloud bases, so they are not considered true tornadoes." Short-lived, on the The leading edge of cool air rushing out of a storm, ahead of the rain. It is what makes the wind pick up sharply just before a storm arrives., and capable of real damage anyway.
- Landspout
- A tornado not associated with a rotating thunderstorm. It is counted as a tornado, and it is the land equivalent of a The over-water equivalent of a landspout. Usually weak, and a genuine hazard when one moves onshore.: the rotation starts near the ground and is stretched upward by a growing The column of rising air inside a storm. Everything a thunderstorm does, from hail to tornadoes, is downstream of how strong and how organised this is., rather than descending from a The rotating updraft inside a supercell, typically a few miles across. Radar can see it aloft; whether anything is rotating at the ground is a separate question..
- Dust devil
- A fair-weather vortex with no parent storm at all. If there is no thunderstorm overhead, this is what you are looking at.
- Cold-air funnel
- NWS glossary: "A A rotating condensation funnel hanging from a storm base with no ground contact and no debris beneath it. Reportable, and a different report from a tornado. or (rarely) a small, relatively weak tornado that can develop from a small shower or thunderstorm when the air aloft is unusually cold... They are much less violent than other types of tornadoes." NWS Louisville adds they "are usually harmless, but on rare occasions they can touch down and cause EF-0 level" damage.
The cue that does the work
Where the experts disagree
Here the course has to be honest with you rather than tidy. The AMS Glossary treats gustnadoes, landspouts and waterspouts all as tornadoes. Some NWS references, including the Fort Worth definition quoted above, state that a gustnado is not a tornado. Both are reputable. They do not agree.
This course does not resolve it, and you should be wary of any training that pretends to. What settles it operationally is your forecast office's reporting rules, which is module 7, and this lesson exists partly so that the disagreement does not ambush you there.
The practical consequence is smaller than it sounds. Describe what you saw rather than reaching for the label: a surface circulation lifting debris along the gust front, with nothing attached to the cloud base, is an unambiguous report whatever anybody calls it. A one-word classification that the office disagrees with is worse than a sentence they can act on.
- Do not report a dust devil as a tornado. No parent storm, no tornado, and this is the most common bad report of the four.
- Do not assume the spouts are harmless. Landspouts are tornadoes and are rated as such; waterspouts moving onshore are a genuine coastal hazard here.
- Do report a gustnado, as damaging wind on the gust front, with a description rather than a label.
Along the leading edge of an approaching storm, a tight swirl of dust is lifting off a field. Looking up, you can see no lowering, no funnel and no rotation in the cloud base above it. What is it most likely to be?
Two things matter: where you are relative to the storm, and whether anything connects the circulation to the cloud.On the gust front, with nothing attached above, this is a gustnado. The debris-cloud rule from lesson 7 applies to a circulation beneath a storm's updraft, not to any spinning dust anywhere near a storm. It is not a dust devil, because there is a parent storm right there. And note that the AMS Glossary would call it a tornado while NWS Fort Worth would not, which is exactly why you describe it rather than label it.