Piezoelectric transducers have been extensively investigated for the development of non-destructive techniques in structural health monitoring systems. Among the various techniques that have been proposed, the electromechanical impedance technique stands out for its simplicity of installation, where a piezoelectric transducer operates simultaneously as a sensor and an actuator, establishing a relationship between the electrical impedance of the transducer and the integrity of the structure. Although many studies have reported the feasibility of this technique, some practical challenges have hampered its effective application in real structures, where one of the most critical problems has been the temperature variation. In order to mitigate the temperature effects, damage indices and compensation methods have been proposed in recent years and satisfactory results have been obtained. However, these compensation methods are typically tested in laboratories using small structures with uniform temperature variation. On the other hand, large structures in real applications may be subject to irregular temperature variation. Therefore, this study aims to investigate the effects of irregular temperature variation on the impedance signatures of piezoelectric transducers and, consequently, on the feasibility of detecting structural damage. Experimental tests were performed on an aluminum plate with multiple piezoelectric transducers installed under different temperature conditions and the impedance signatures were qualitatively and quantitatively analyzed using damage indices. The results indicate that the irregular temperature variation can make some damage indices and compensation techniques unfeasible in real applications with large structures.