Numerous studies have clearly demonstrated that the monitoring of cable force can be regarded as a royal road to diagnose the possible damages of cable-stayed bridges. The feasibility of this approach, however, deeply depends on accurate identification and filtration of the environmental temperature effect because it also significantly alters the cable force. A recent study by the authors discovered that an effective temperature defined by combining all the contributions from stay cable, bridge girder, and pylon is most strongly correlated with the cable force. Based on the above study, this work further applies the ensemble empirical mode decomposition to process the time histories of cable force and effective temperature for an extradosed bridge located in central Taiwan. It is evidently observed that the cable force and effective temperature can both be categorized into daily variation, season variation, and high-frequency noise with the order of decreasing weight. Moreover, a time shift around 1 to 2 hours generally exists between the daily variation of both investigated quantities. The correlation analysis conducted for the data of all four seasons indicates that daily and season variations have to be distinguished for accurately evaluating the temperature effect on the variation of cable force.