The one definition every spotter is expected to know cold, and the three near-misses around it.
By the end of this lesson
M4.6.aState the NWS definitions of funnel cloud and tornado.
M4.6.bApply the debris-cloud rule: a debris or dust whirl confirms a tornado with no condensation funnel present.
M4.6.cExplain why a gustnado is not a tornado under NWS convention, and why local practice varies.
M4.6.dDefine landspout and cold-air funnel.
The criterion
That single paragraph contains the whole distinction, and clause b is the half people forget. The test is not "does the funnel reach the ground". It is "is the circulation reaching the ground", and a debris cloud proves that on its own.
What you can seeWhat to call it
Funnel aloft, nothing beneath itFunnel cloud
Funnel in contact with the groundTornado
Funnel aloft, debris or dust whirl beneath itTornado
No funnel at all, debris whirl beneath the stormTornado
Debris whirl 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., no storm-scale rotationA short-lived circulation at the surface along a gust front, lifting debris but not attached to the cloud base above. Some NWS references say it is not a true tornado; the AMS Glossary counts it as one., see below
Three of the five are tornadoes and only one of those has the picture everyone has in their head.
Gustnado
Read that definition carefully, because it argues with itself: it opens with "a small tornado" and then says the thing that makes a tornado a tornado, storm-scale rotation, is absent. In practice the NWS convention is that a gustnado is not a tornado and it is not warned or verified as one.
The practical tell is location, and it is the same tell as lesson 5: a whirl on the gust front, under or near a shelf cloud is a gustnado. A whirl under the The smooth, flat, dark cloud base on the rear flank of a storm, where warm air is flowing in and rising. It is named for the air going up, not for being dry: hail and large drops may still fall from it., near a wall cloud is a tornado until proven otherwise.
A tornado that forms without a mesocyclone, its rotation starting near the ground and being stretched upward by a growing updraft. It counts as a tornado. and A funnel, or rarely a weak tornado, dropping from a small shower when the air aloft is unusually cold. Much less violent than other tornadoes and it rarely reaches the ground.
Landspout
A non-supercell tornado, forming from the ground up along a boundary rather than 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. down. It is a tornado, and is reported as one. Typically narrow, tube-like, and often over open country.
Cold-air funnel
A small funnel under a shower or weak storm in a cold air mass, with no severe storm present. Rarely reaches the ground and rarely does damage. Report it, and expect it to be logged as a curiosity rather than a warning trigger.
Knowledge checkNot graded · the exam draws a fresh variant of this item
You can see a rotating column with a condensation funnel about halfway to the ground, and a clear whirl of dust lifting on the ground directly beneath it. What is it?
The definition has two clauses, a and b. Only one of them is about the funnel touching down.Clause b: a condensation funnel is a tornado if "a debris cloud or dust whirl is visible beneath it". The condensation funnel marks where the air is cold enough to condense, not where the circulation stops. Waiting for the funnel to reach the ground before reporting costs lead time on a tornado that is already there.
