An updated version of radar data QC package was developed recently at NSSL and delivered earlier this year to NCEP/EMC. This package contains a newly improved radar velocity dealiasing algorithm. This algorithm has been tested with many difficult cases including hurricane Isabel-2003 and Katrina-2005 high-wind cases. The key idea and algorithm elements will be presented with illustrative examples. The QC package was also applied to data collected from six radars (KINX, KLZK, KSGF, KSRX, KTLX, KVNX) in May 2005 to generate innovations for error covariance estimation, while the background wind fields were provided by NCEP NMM forecasts. The estimated (observation and background) error covariances and bias differences will be examined for both clear and rainy days.