What mobile radar system measured record winds in the 1999 Bridge Creek-Moore tornado?

The mobile radar system that measured record winds in the 1999 Bridge Creek–Moore tornado was Doppler on Wheels. The University of Oklahoma mobile radar recorded winds of about 301 mph initially and a peak estimate near 321 mph, the highest tornado wind speed ever measured by Doppler radar.

Doppler on Wheels, usually abbreviated DOW, is a truck-mounted radar system designed to drive close to severe storms. Unlike fixed weather radars, it can be positioned near a tornado, producing much finer measurements of the wind field. On May 3, 1999, a DOW team tracked the violent F5 tornado as it moved through Bridge Creek and Moore, Oklahoma.

A common mix-up is confusing DOW with WSR-88D, the fixed NEXRAD radar network. RaXPol is also a mobile radar system used in tornado research, but it was not the system associated with the famous 1999 measurement. The 321-mph value is a radar-observed wind estimate, not a direct measurement from an instrument placed inside the tornado.