I've written about the HDR effect before. And I've written about timelapse several times...
Per Erik Sviland just published a video that combines the stuff. Timelapse and HDR. That high dynamic range effect usually just add an intense feeling of something kitschy. But because it really enhance the clouds it works well in a video like this.
Gruda/Ullandhaug HDR Timelapse in HD from Per Erik Sviland on Vimeo.
Per Erik has also been kind enough to include a nice how-to explaining how he made this video on his blog.