Screenshot and Video below:

http://www.larabie.net/ogre/AnimatedSky4.wmv
The idea I had was to render a series of skyboxes for a 24 hour period from Bryce 5.5 and then blend between them in Ogre.
Took some playing around in Bryce with sun Azimuths and Altitudes, colours, clouds and stars, but I've finally got something that looks decent. Still needs some work but it's going to be a game system plugin in GOOF for environmental effects. Eventually there'll be a directional light that matches the sun direction from the skybox, light colour that matches the skybox, and fog, and interpolates as the skyboxes change.
You can see the blending between skyboxes since it's moving so fast, but obviously in the game it will be moving much slower and the transitions won't be apparent. The key thing is that the player sees a beautiful sky any time they look at it, and the changes aren't jarringly apparent.
It will also be possible to move from clear to cloudy, cloudy to stormy, etc. because the skyboxes run a 24 hour period and just have to be rendered out for each type of sky, then based on the current time it'll be possible to blend laterally to a new set of skyboxes.
I also need to background load the skybox textures and only switch once loaded to minimize the frame stuttering. It isn't apparent here because I've already moved through the skyboxes one complete cycle before capturing the video so the textures have already been loaded from disk once and the second load is fast.