When using the Scenario Designer there does not appear to be away to change the weather while creating the scenario. And it defaults to Spring Clear. There is away to set the weather before you play by going to the Timetable mode and setting the weather there. Then navigate back to the Scenario Designer and run any scenario you want and it will have the same weather as used in Timetable mode.
Indeed, this is the way to do it. I wish there was like a key you pressed, like "W" or something on the Scenario Planner screen, so you can select the weather there and have it apply to the scenario you will play. Oh well, at least it is technically is possible to change season/weather, even if the way is convoluted.
Agree that would be very useful. I’m assuming that changing the start time for the Scenario, eg to hours of darkness, is actually reflected in the game but must admit I haven’t strayed from the default 12:00 so far.