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Module 04

Identifying rotation

Telling storm-scale rotation from everything that resembles it, and knowing which of the two is worth a report. Nine lessons that build from where rotation lives in a supercell to a documented real outbreak, and that spend as much time on the rotation you cannot see as on the rotation you can.

Start lesson 01

Lessons9

Reading timeabout 4 hrs

Objectives34

The lessons

Take them in order, or don't

01Storm-scale rotation and the supercell modelWhere rotation actually lives in a storm, what the word for it means, and why most of it never produces a tornado.Rotation detailStarts by taking a word away from you. "Mesocyclone" is a radar term, and a spotter who uses it about something they saw has already made the module's central mistake.25 min 02Reading the updraft baseStriations, inflow bands and the beaver tail: what an updraft looks like when it is turning, and how precipitation placement decides how much of it you get to see.Rotation detailThe cues that a storm is rotating before anything has lowered out of it, including the two inflow features that are constantly mistaken for each other.25 min 03The wall cloud, rotating and notThe feature spotters are most often looking for, its definition in full, and the three signals that decide whether it is worth a radio call.Rotation detailThe reportable lowering, with the qualifier that most training glosses over: a wall cloud on its own is not a rotation report.30 min 04The RFD and the clear slotThe dry downdraft that wraps around the circulation, the bright slot that gives it away, and why its arrival is the opposite of good news.Rotation detailThe cue most people read backwards. Clearing sky next to a wall cloud is not the storm falling apart, and treating it that way is how spotters get caught out.30 min 05Scud and the look-alikesRagged cloud fragments, rain shafts and outflow features generate most bad rotation reports. Here is what they are, and the checklist that stops you filing one.Rotation detailThe false-report lesson. Everything in it is something that has been called in as a tornado by somebody who meant well.30 min 06Funnel, tornado, debris cloud, gustnadoThe one definition every spotter is expected to know cold, and the three near-misses around it.Rotation detailThe ground-contact criterion in the exact words the NWS uses, and the vortices that are not tornadoes even though they reach the ground.30 min 07Proving rotationThe technique that separates rotation from drift, the minimum time it takes, and why a photograph can never be a rotation report.Rotation detailA method, not an instinct. This is the lesson that turns "it looked like it was turning" into something an office can act on.20 min 08Hard cases: QLCS, rain-wrapped and nocturnalRotation you cannot see, in a line, inside the rain, or in the dark, and how to be useful anyway.Rotation detailWhere the previous seven lessons stop working. This is most rotation east of the Plains, and Plains-shaped training treats it as a footnote.30 min 09Capstone: Hurricane Ivan, 15 to 16 September 2004Everything in this module, applied to one documented event where almost nothing was visible and the warnings went out anyway.Rotation detailA real outbreak in this platform's own forecast area, with the office's own verification numbers attached, including the ones that look bad.30 min

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