What is radar reflectivity and how is it interpreted?

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Radar reflectivity measures how much of the transmitted radar energy is returned by precipitation particles. The amount of energy that comes back depends on how many particles there are and how large they are, as well as their dielectric properties. When precipitation is stronger—more droplets or larger drops—the radar returns a larger signal, which meteorologists translate into higher reflectivity values, typically shown in dBZ. This reflectivity–to–rainfall relationship (the Z-R relationship) lets us estimate precipitation intensity from the observed reflectivity, though it’s influenced by drop size distribution and other factors like radar beam height. It is not a measure of how fast the particles are moving (that’s Doppler velocity), nor of wind direction aloft, nor of atmospheric temperature.