Reflectivity (dBZ) and dual-pol

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).