The paper deals with the integration of the Uncertainty Scenario Flexibility Indexes (USFI) in an operation planning problem. For USFI application in this medium term planning process, it is necessary to define a procedure that allows selecting the network states for which flexibility has to be evaluated. The proposed network state selection procedure is based on the use of Network State Indicators (NSI), whose value defines the network states for flexibility assessment. In order to choose the right NSI, a correlation analysis has been performed with some Penalty Functions (PF), chosen as an “indirect” measure of the importance of evaluating flexibility in a given state of the network. The NSI selection procedure includes many steps that have been implemented in home-made software, named Ne.S.C.A. (Network State Correlation Analysis), written in MatLab7® workspace, with multiple tasks. The results of the application of the procedure to the IEEE-RTS point out that the best NSI for the flexibility evaluation has been represented by the global network load.