More on the Harry Potter World in Universal Studios
Screamscape.com had a previous posting, but has recently had to take it down due to 'technical' problems (lawyers) that was of some interest recently.
"The ride system inside Hogwarts Castle is installed and functional, however all of the scenery and special effects still need to be installed, programmed and tested extensively before we’ll see the ride open."
It continued to say that "The ride experience will begin & end with an interesting little effect that will transport you through the use of the Floo Network, a giant fireplace and green flames."
They go on to reveal that "your ride experience will begin and end with an interesting little effect that will transport you through the use of the Floo Network, a giant fireplace and green flames."
As was discovered through a Zigmont posting at their site previously (also now gone), this is probably to do with the snow effect/machine.

For plenty of images, there are two galleries to check out:
Orlando Park News, and Amusement Insider.