Predictive windshear requires precipitation to work. Thus, it cannot detect CAT.
"Windshear prediction is radar based and is available below 1500’ AGL. It looks out to 5 nm ahead of aircraft. A warning message reading WINDSHEAR AHEAD will appear on PFD and ND. Color of the warning will be red or amber depending on level of warning. Levels include Advisory (display only) and the Warning and Caution messages have an aural warning alert as well. Predictive warnings are inhibited during takeoff after 100 kts. until 50’ AGL and then again inhibited on landing once below 50’ AGL. Windshear prediction uses the normal weather radar and there is only one radar installed. If the normal radar is turned off the windshear prediction will still operate normally if set to Auto. Prediction means that a possible windshear is ahead of you. Predictive windshear will not warn for CAT (Clear Air Turbulence), system must have precipitation to work."
From:
http://www.chipsplace.com/helpful/Airbus/Instrument.htm
Traditional windshear detection (GPWS Mode 7) uses the ADC to compute presence of windshear. It depends on sink rate at the time vs rate of speed loss in knots/sec.