Grateful Dead’s Phil Lesh — Impromptu Jam Session in Central Park

Founding Grateful Dead member Phil Lesh whipped out his boomstick in Central Park today … but don”t worry he wasn”t arrested … he was just laying down some sick grooves.

Lesh pulled off the surprise gig during the NYC Jazz & Colors event in the Park … when he randomly started performing with some friends in front of around 30 people.

The 73-year old bassist played for about 30 minutes and even jammed out on the Beatles classic “Get Back” in between impromptu jazz sessions.

Far out.