A horizontal bar chart ranking variables by how far each one moves an outcome, widest bar at the top. The narrowing stack of bars is what gives the chart its name.
A tornado diagram presents the results of a sensitivity analysis as one bar per variable, drawn around a vertical baseline representing the outcome when every input sits at its expected value. Each bar runs from the outcome produced by that variable’s low value to the outcome produced by its high value, so bar length is the size of the range that one variable can open on its own. Sorting widest to narrowest puts the dominant driver on the top row, which is the whole point of the presentation. Bar width measures how far an outcome could move and never how likely that movement is, so a tornado prioritises attention rather than sizing a contingency.
Where this comes up
One bar per variable, the widest at the top, all of them measured against a baseline down the middle. A tornado diagram ranks what could move an outcome, and by how much.
A risk might happen. An issue already has. That single difference decides which artefact a line belongs in, what you record about it, and who you have to tell.
Contingency reserve sits inside the cost baseline, for risks already named and priced. Management reserve sits above it, for the ones nobody named. Level and authority, not size.
Most risk registers record one number per row. The number that actually justifies spending money is the distance between two of them.