Britain's Queen Elizabeth II

The memory of last year's fallen champion "Barbaro" and the first appearance by horse racing fan Queen Elizabeth of England will highlight Saturday's 133rd running of the Kentucky Derby at Churchill Downs.

The first Triple Crown race of the year also faces the threat of thunderstorms as the Saturday evening post time approaches (6:04 PM EDT). 

The undefeated three-year-old "Curlin" is the favorite in the race, but that could change if wet weather turns the track into a muddy quagmire.  Only seven of the 20 horses scheduled to start have ever run in wet conditions.

"Curlin" is trying to become the first winner of the Derby not to have run as a two-year-old.  He has won all three of his starts, but many believe his lack of experience could work against him in front of a raucous crowd expected to reach 150,000.

Some information for this report was provided by AP.