Well I think a quick look at some past winners and you will see that the weather is not always the default. I mean using a payware plane is pretty cut and dry. As for scenery, if you look at the Hall of Fame a lot of the winners look like they might have some questionable scenery and weather.
I am not hating and really am trying to play by the rules but it says nothing about "weather modifiers" in the rules. I think that having a stipulation that discounts pics with weather editing is taking away from the contest. You need to compose your shot, pick the right aircraft and setting to meet that months criteria. I think that weather effects should not be banned.