Radar signatures#radar
Reflectivity (dBZ) and dual-pol
At a glance
The main radar image — brighter colours mean more and bigger raindrops, hail, or whatever else is reflecting. Dual-pol adds shape and type information.
Deep dive
Reflectivity (Z) is measured in dBZ (decibels relative to reference return). Rough guide:
- 20–30 dBZ — light rain.
- 30–45 dBZ — moderate-to-heavy rain.
- 45–55 dBZ — heavy rain or small hail.
- 55+ dBZ — large hail signature in mid-levels.
- 70+ dBZ — giant hail, very rare.
Dual-pol products add:
- ZDR (Differential Reflectivity) — sign of particle shape (positive = oblate raindrops, near-zero = tumbling hail).
- CC (Correlation Coefficient) — uniformity; drops to 0.7–0.9 for mixed/non-meteorological returns.
- KDP (Specific Differential Phase) — rainfall rate estimator, useful for QPE.
Together these let radar discriminate rain vs hail vs debris — the latter produces the famous TDS (Tornado Debris Signature).