The Kentucky Derby usually has tastemakers flexing their fashion muscles … and, this year it was all plastic cover chic — ’cause everyone needed ponchos to cover their ensembles.

People streaming into Churchill Downs in Louisville on Saturday had to brace the elements … throwing on plastic over their nice clothes with a cloudy sky hanging menacingly above them.

Several ladies in their Sunday best seemed to be laughing it up … even if their fancy dresses had a slightly opaque screen cast over them.

Men in derby suits — some an eclectic mix of colors — looked like they were getting off Splash Mountain on Grad Night … hopefully those fedoras will keep their heads dry!

Some even went full Bubble Boy with their deployment of the rain gear … with this woman not willing to chance the plumes of her hat getting soaked.

The main event kicks off at 3:57 PM PT … and, as of right now, the Derby is expected to continue — though bettors may be changing the odds given the inclement weather.

Of course, big celebs also flew in for the event … with Anna Nicole Smith‘s daughter Dannielynn Birkhead wearing a vintage dress her mom donned at the racecourse many years ago.