Michigan Academy of Folk Music jam (Prospect Park / MAFM)

Thursdays. Runs seasonally.

Michigan Academy of Folk Music's own events page confirms 'Jam at the Park' at Prospect Park, describing 'weekly jams this summer on Thursday evenings' with simultaneous Slow Jams and Bluegrass Jams, free and open to the public [s1]. The page is current, and this is an ongoing annual summer series, currently in season as of August.