The scale of dBZ values can be seen along the bottom of the image.

dBZ stands for decibels of Z. It is a meteorological measure of equivalent reflectivity (Z) of a radar signal reflected off a remote object.¹ The reference level for Z is 1 mm⁶ m^-3, which is equal to 1 μm³. It is related to the number of drops per unit volume and the sixth power of drop diameter.

Reflectivity of a cloud is dependent on the number and type of hydrometeors, which includes rain, snow, and hail, and the hydrometeors' size. A large number of small hydrometeors will reflect the same as one large hydrometeor. The signal returned to the radar will be equivalent in both situations, so a group of small hydrometeors is virtually indistinguishable from one large hydrometeor on the resulting radar image.

A meteorologist can determine the difference between one large hydrometeor and a group of small hydrometeors as well as the type of hydrometeor through knowledge of local weather condition contexts.

One dBZ-scale of rain: > 40 heavy, 24-39 moderate and 8-23 light

References

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