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.

In this lesson you will

  • Distinguish a gustnado, a surface circulation on the gust front not attached to the cloud base, from a tornado.
  • Define a landspout as a tornado not associated with a mesocyclone.
  • Identify a dust devil and a waterspout.
  • Define a cold-air funnel and state that it is usually harmless and rarely reaches the ground.

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 gust front, 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 waterspout: the rotation starts near the ground and is stretched upward by a growing updraft, rather than descending from a mesocyclone.
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 funnel cloud 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

Teaching point
Follow it upward. A tornado connects to a rotating storm above it. A gustnado is debris spinning at the surface along the gust front with nothing attached above. A dust devil has no storm over it in the first place. The question is never how impressive the spinning is, it is what the circulation is connected to.

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.

Check yourself

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?

  1. A gustnado. Describe the surface circulation and report it as a wind feature
  2. A tornado, because rotating debris at the surface always confirms one
  3. A dust devil, since there is no rotation in the cloud base
  4. A landspout, because the rotation started at the surface
Hint

Two things matter: where you are relative to the storm, and whether anything connects the circulation to the cloud.

Answer

A gustnado. Describe the surface circulation and report it as a wind feature

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.

Sources

  1. NWS Fort Worth, Spotter Handout 2022, and the Storm Spotter's Dictionary
  2. NWS online glossary (cold-air funnel)
  3. NWS Louisville, "Cold Air Funnel"
  4. AMS Glossary of Meteorology
  5. NSSL Severe Weather 101, tornado basics