16 Reading Storm Signatures
This chapter ties the individual products together into the patterns you’ll actually look for during severe weather. The golden rule: never diagnose a storm from one product. Confidence comes from multiple products agreeing.
16.1 The three-product workflow
For any storm of interest, check, in order:
- Reflectivity: Where is it, how intense, what shape? (cores, gradients, hooks)
- Velocity (or azimuthal shear): Is it rotating? Where is the couplet?
- Dual-pol (CC especially): What’s in the air? Hail? Debris?
When all three point the same way, you have a confident read.
16.2 Supercells
A supercell is a storm with a persistent rotating updraft (mesocyclone). Look for:
- Reflectivity: a sculpted, isolated cell; a hook echo or pendant on the rear-right (relative to motion); a tight gradient on the inflow side; sometimes a BWER.
- Velocity / shear: a sustained couplet / shear maximum beneath the hook: the mesocyclone.
- Dual-pol: ZDR column in the updraft (intensifying); high-dBZ + low-CC hail core; possibly a TDS if tornadic.
16.3 The tornado checklist
Radar can strongly suggest a tornado, and increasingly it can confirm one:
| Signal | Product | What it means |
|---|---|---|
| Hook echo | Reflectivity | Classic mesocyclone shape |
| Tight, intense couplet (TVS) | Velocity | Strong, concentrated rotation |
| Strong shear maximum | Azimuthal shear | Rotation auto-flagged |
| Debris ball (very low CC) | Correlation coefficient | Debris lofted, so the tornado is on the ground (TDS) |
A Tornado Debris Signature (very low CC co-located with a strong velocity couplet and a reflectivity hook) is radar evidence that a tornado is actively lofting debris. It is one of the few ways radar can confirm a tornado. Debris must exist and be lofted into the beam, though, so a TDS can lag the tornado’s start and is harder to see at long range where the beam is high.
16.4 Squall lines and bow echoes
Linear storm systems bring their own signatures:
- Squall line: a continuous line of cells, often with a tight leading reflectivity gradient and a trailing region of stratiform rain.
- Bow echo: a segment of the line that bulges forward, the sign of a strong rear-inflow jet and damaging straight-line winds. In velocity, look for strong outbound speeds and a localized convergence/divergence signature behind the bow.
- Mesovortices: small couplets along the leading edge of a bow/QLCS (quasi-linear convective system) can spin up brief, fast-developing tornadoes. Watch velocity and shear along the whole line, including well away from the obvious bulge.
16.5 Hail
- Reflectivity: very high dBZ cores (55+); the three-body scatter spike (“flying eagle”), a spike of weak echo extending radially behind an intense core, is a strong large-hail indicator.
- Dual-pol: lowered CC and near-zero/negative ZDR within the high-dBZ core (tumbling hailstones).
16.6 Flash flooding
- Reflectivity & KDP: persistent high returns and high KDP (heavy liquid rain) training repeatedly over the same area. “Training” cells, storm after storm crossing the same ground, are the classic flash-flood setup. Use animation to spot it.
16.7 Putting it together
Reading radar well is pattern recognition built on the fundamentals from the previous chapters plus practice. Loop archived events of known outcome, predict what each product should show, and check yourself. Over time the colors stop being colors and start being a storm. Just remember the limits in the next chapter, because radar can fool you.