Keith Urban, Ronnie Dunn, Alan Jackson and many more of country music's biggest stars headed to the Grand Ole Opry in Nashville a little early to rehearse for tonight's Music Builds: CMT Disaster Relief Concert telethon. Though they came casual -- you can see them here wearing baseball caps and T-shirts -- they came for a cause: to help the victims of the recent tornadoes and floods in the south.

Alabama, Gretchen Wilson, Tim McGraw, the Blind Boys of Alabama, and Little Big Town also warmed up their vocals during the rehearsals. Tonight, the big live fundraiser will kick off with performances from those mentioned, as well as Hank Williams Jr., Lady Antebellum, Sara Evans and Trace Adkins. Taylor Swift, Shania Twain and Carrie Underwood will make guest-appearances via video messages, and President Obama, Courtney Cox, Ellen DeGeneres and Nicole Kidman will also share their well-wishes and press a call-to-action.

The 'Music Builds: CMT Disaster Relief Concert' airs live on CMT at 9PM ET, and also will stream on CMT.com. All donations will go straight to the Red Cross relief efforts, so country music fans are encouraged to do their part -- and can do so by clicking here.