From the product page (emphasis added):
Weather Radar - included free as part of the SP1 update, the PMDG 737NGX features a working simulation of the Collins WXR-2100 weather radar. In conjunction with the Active Sky Next weather engine addon, the radar depicts actual precipitation returns (not clouds!) and gives you full control over tilt, gain and radar mode including turbulence and windshear detection.
ASN is the only weather addon that reports precipitation accurately enough for PMDG to build a realistic weather radar.