Sensitive Doppler radars can measure the Doppler spectrum of echoes from refractive index irregularities in the clear air. In this paper horizontal winds estimated from the mean Doppler shift measured by the Sunset VHF Radar, near Boulder, CO, are compared with rawinsonde winds from balloons that passed within 25 km of the radar. Below 6 km MSL some of the measurements do not agree, presumably because of orographic effects. Above 6 km MSL almost all of the measurements agree within the experimental errors with a correlation coefficient of 0.96 with 16 measurements.