Phased-array weather radars have a significant advantage over new-generation weather radars in terms of spatial and temporal resolution. With the improvement of detection capability, the amount of phased-array radars data grows sharply, thus raising data transmission and storage problems. Existing weather radar data compression algorithms may reduce the amount of data transmitted and stored, and yet common data compression algorithms fail to consider the characteristics of phased-array radars sufficiently. This paper proposes a space-time predictive phased-array radar data compression algorithm (PARDC) to compress the redundancy associated with phased-array radar data using radial prediction to achieve efficient lossless compression. The algorithm performance of PARDC is evaluated using CHARTOR radar data, with experimental results showing that PARDC improves the compression rate performance by approximately 24% over the common compression algorithm.