Situation assessment in complex systems is often achieved by expert operators taking into account evolution of signals and comparing it with previous experiences. The similarity criteria used by operators to compare actual situations with previous ones are not easily explainable and in fact they are part of the cognitive procedure. This paper proposes to use qualitative representations of signal trends as experienced cases. The work is centred in two main aspects. First, episodes based representation of signal trends proposed in the CHEM project is used as a description of cases. Then, a similarity criterion among signal representations is defined by a Dynamic Time Warping approach. The usefulness of the approach is shown in an illustrative example by representing and comparing signal dynamics with the goal of Situation Assessment.