Inflow features: bands, beaver tail, tail cloud

Inflow bandsA band of low cloud running along the low-level wind and moving toward a storm, marking the air being drawn in. Bands curved as though turning cyclonically may mean a mesocyclone.

The Field Guide describes inflow or feeder bands as "arranged parallel to the low-level winds and moving into or toward a thunderstorm". They are the visible signature of the storm drawing its fuel in.

And then it gives you something to act on: "Spotters should be especially wary of inflow bands that are curved in a manner suggesting cyclonic rotation; this pattern may indicate the presence of a mesocycloneThe 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.."

Two long features, one difference

Tail cloud

A horizontal cloud extending from the precipitation cascade region toward the wall cloudA localized, persistent lowering beneath the updraft base, on the rear inflow side of a storm, marking where air is being drawn up. Not all of them rotate, and a rotating one is what you report., with its base at about the same height as the wall cloud. Motion is toward the wall cloud, with rapid upward motion where the two meet.

Beaver tail

A broad, flat inflow band attached to the updraft baseThe 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., so its base is noticeably higher than a wall cloud, oriented roughly along the pseudo-warm front. Slang rather than a formally defined term, though the NWS glossary carries it.

Attachment point and base height separate them. A tail cloudA horizontal cloud reaching from the rain area toward the wall cloud, at about wall-cloud height, with its material moving toward the wall cloud. joins the wall cloud and sits at wall-cloud height. A beaver tailSpotter slang for a broad, flat inflow band attached to the updraft base, so it sits higher than a wall cloud. Frequently misreported as a funnel when seen end-on from a distance. joins the updraft base and sits higher. Once you have lesson 6, that difference is easy; before it, the two look like the same long ragged thing.

Neither is reportable on its own. Both are context: they tell you where the inflow is and therefore where the updraftThe 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. is, which is where you should be looking.

Why this lesson exists

NWS Northern Indiana published a page specifically about low hanging clouds being mistaken for funnel clouds and tornadoes, and beaver tails and scudRagged low cloud that forms in humid air near a storm and drifts about. It rises slowly and does not rotate, which is what separates it from a funnel, and it is the single most common thing mistaken for one. are what it is about. A long horizontal cloud viewed end-on, from several miles away, in poor light, looks very much like something descending from the base. Lesson 11 is the full treatment of that problem. The short version: a feature that is horizontal in reality can look vertical from the wrong angle.