How does radar reflectivity relate to precipitation type, and what data helps distinguish rain from hail?

• A. It indicates heavier precipitation and potential hail; polarization data helps distinguish type.
• B. It indicates lighter precipitation and no hail.
• C. It indicates wind shear.
• D. It has no relation to precipitation type.

Answer: (A)

Radar reflectivity is about how much energy is bounced back from precipitation particles. The more or larger the particles, the stronger the return, so higher reflectivity values usually mean heavier precipitation. In thunderstorms, very high reflectivity can indicate intense rain and can coincide with hail, but reflectivity alone doesn’t prove hail—we need additional information.

That additional information comes from dual-polarization data. Polarization provides clues about the shape and type of the hydrometeors. The differential reflectivity (ZDR) compares returns in the horizontal and vertical directions. Rain drops are typically flattened by aerodynamic forces, producing positive ZDR values, while hailstones are more spherical or irregular, often giving ZDR near zero or negative. The correlation coefficient (ρHV) measures how similar the signal is across the two polarizations; pure rain tends to yield very high correlation, whereas hail or mixed precipitation disrupts that harmony and lowers the correlation. By combining reflectivity with polarization indicators like ZDR and ρHV, you can better distinguish whether the heavy-looking echoes are rain or hail.