Ok, too much time to think again & I have come up with a new 'brain fart'. Would it be feasible to do summer & winter versions of the SceneDB folder in order to have 'winter'ised' & 'summer'ised' bmps in the airfield folders. This has already been done to allow texture swapping with the world folder, why not go on to the next plateau? IMHO, this would have a much improved visual effect in winter mode.