One plus of The Jayhawks playing the mid-Atlantic is that their former bandmate, guitarist Stephen McCarthy, often drives up from Richmond, Va., to rejoin the Minneapolis band, adding some extra country twang and bringing added authenticity to the classic albums the Long Ryders member made with them, 2006’s “Rainy Day Music.”  

His appearance with the band at the Hamilton in Washington DC Friday was not such a casual reunion — his addition was vital to fill out the band after Karen Grotberg begged off of dates in DC and Philly over the weekend due to a short medical leave.

Grotberg adds a lot to the band, and has ever since she joined in 1992 with thoughtful keyboards and sweet harmonies with frontman Gary Louris. On the band’s latest album “XOXO,” meant to showcase songs and vocals from each band member (and not rely so much on Louris), she was standout on a couple of songs.

This time it was drummer Tim O’Regan doing most of the harmonies with Louris as well as a couple of songs where he took lead, “Tampa to Tulsa” and a newer one, “Dogtown Days.” (O’Regan’s family was in the crowd, we were told, and there was a singalong to note his recent birthday).