Welsh was found dead in a Chicago hotel room. Investigators say Welsh was supposed to check out of the Raffaello Hotel at 1 p.m. Saturday. When he did not, hotel staff went to his room and found him unconscious and not breathing.
An autopsy was performed Sunday. Police say they do not suspect foul play in his death.
Welsh, 40, of Burlington, Vt., performed with Weezer from 1998 to 2001, leaving after suffering a nervous breakdown, according to the band's website. He eventually established himself in a second career as a painter.
"I'm taking a break from music," he told MetroWest Daily News in 2002. "I really feel the need to reinvent myself and move on, and I couldn't be happier painting. Music is still an important part of my life, but I really have no desire to actually play it."
Welsh was in town to meet up with his former band mates for their show Sunday night at the Congress Theatre. That concert, part of Riot Fest Chicago, will go on as planned. The band said in a statement that Welsh would have wanted the band to play on.
Weezer posted a message on its website saying that Welsh's time with the band was "vital, essential, wild, and amazing."
"A unique talent, a deeply loving friend and father, and a great artist is gone, but we will never forget him," the band said.
(The Associated Press contributed to this report.)