Introduction
Doppler Weather Radar is your best defense against a hair-raising and wind-blown encounter with thunderstorms. The 155 stations in the National Weather Service’s (NWS) network provide overlapping, ground-based coverage of the nation’s inland and coastal boating areas. With an effective range of approximately 120 nautical miles, data from the NWS radar network is not accessible if you are well offshore. (Regardless of how you obtain your radar imagery, you are viewing NWS data as theirs is the only national radar network.)

Scanning The Atmosphere
Strong thunderstorms may be several miles high, and so the radar station must collect data from the Earth’s surface up into the upper reaches of the atmosphere in order to completely analyze the storm. Stations use a variety of scanning strategies, called Volume Coverage Patterns (VCP) to accomplish this goal. The antenna makes an initial, or base, scan by making one complete revolution at an elevation of 0.5° above the Earth’s surface, alternating between emitting and collecting backscattered energy pulses. When this base scan is complete, the antenna completes additional scans, repeatedly increasing the elevation by about one degree, until the highest elevation of the VCP is reached. The highest elevation scanned by NWS radar is 19.5°.
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