The radar's computers measure the frequency change of the reflected pulse of energy which then convert that change to a velocity of the object, either toward or from the radar. Information on the movement of objects either toward or away from the radar can be used to estimate the speed of the wind. The National Weather Service's Doppler radars can detect most precipitation within approximately 90 mi of the radar, and intense rain or snow within approximately 155 mi. However, light rain, light snow, or drizzle from shallow cloud weather systems are not necessarily detected. Echoes from objects like buildings and hills appear in almost all radar reflectivity images.
Radar returns from birds, insects, and aircraft are also rather common.
Echoes from migrating birds regularly appear during nighttime hours between late February and late May, and again from August through early November. Return from insects is sometimes apparent during July and August. However, during the peaks of the bird migration seasons, in April and early September, extensive areas of the south-central U.S. may be covered by such echoes. A portion of this help file was supplied courtesy of The National Weather Service.