Selecting either or both of these options will replace the cligen and/or windgen station selection fields in the "Location Information" panel on the main WEPS screen. The user will be able to select the desired "alternative weather" files on there via a file chooser dialog which is accessible by clicking on the folder icon next to those fields.
The "Alternative weather files" option is primarily used when one wants to use measured wind and/or weather data in place of the "generated" wind and weather data in a WEPS simulation run.