The aim of this work is to study the damage detection capability by means of Lamb wave propagation in a CFRP omega-stringer stiffened panel in presence of changing environmental conditions. Temperature influence in Lamb wave propagation as well as damage detection methods for changing environmental conditions have already been studied on other stiffened structures, although for different materials and geometries. For the actuation and sensing a network of bonded piezoceramic transducer has been used and the temperature test has been performed introducing the structure in an oven with temperatures going from 40°C until 80°C. A total of 13 delaminations or debondings have been induced in three zones of the structure geometry with a mobile impactor. After the impact introduction the temperature test has been repeated in order to compare the data acquired before and after the impact in the same environmental conditions. The temperature test has been used to first identify by experimental means the variations in Lamb wave propagation through the given CFRP-stiffened panel caused by temperature. Afterwards, signal processing permits to determinate the adequate modes, frequencies and parameters in order to detect damage. Dispersion curves assisted by a scatter study prove that A0 mode is the most suited mode for SHM means since it is the most sensitive to alterations in the structure. The last part of the study is finds several parameters capable to detect damage in spite of temperature variations.