What a WSR-88D is
A 28-foot S-band dish (2.7–3.0 GHz) on a 30-metre tower, inside a fibreglass dome the size of a small house. 750 kW peak, 1 µs pulses. The S-band wavelength survives heavy rain without total attenuation — exactly what you need to see through a thunderstorm core.
Volume coverage patterns
The dish doesn't just spin — it climbs through elevation angles (0.5°, 1.5°, 2.4°...) building a 3D scan called a volume coverage pattern. A severe-weather VCP completes 14 elevations in 4 minutes; a clear-air pattern takes 10 minutes with greater sensitivity.
Dual-polarisation upgrade (2012)
Adding a vertical channel let NEXRAD tell rain from hail from debris. The 'tornado debris signature' on dual-pol — a sudden drop in correlation coefficient — is now the most reliable real-time confirmation of a tornado on the ground.
Why hobby radar fans love it
Every NEXRAD scan is public-domain Level II data, streamed by NOAA in real time. RadarScope, GRLevel, College of DuPage and dozens of open-source viewers all consume it. Your weather app gets its 'live radar' tile from the same feed.