The shower began before the scheduled 7:05 p.m. starting time. After a wait of nearly two hours, the game was called.
This is the Dodgers' only visit to Camden Yards this season, so the teams will play a split-doubleheader on Saturday. The first game will start at 1:05 p.m. and the second at 7:05 p.m.
Los Angeles hasn't visited Camden Yards since 2002. The teams also met in California in 2004.
Hyun-Jin Ryu, who was scheduled to start for the Dodgers on Friday night, will start Saturday afternoon against Baltimore's Jason Hammel. Josh Beckett will start for the Los Angeles in the nightcap against left-hander Wei-Yin Chen.
The Dodgers entered the game mired in a four-game losing streak. Los Angeles scored only seven runs during the skid, which included a three-game sweep by the visiting San Diego Padres.
Baltimore is in the midst of a nine-game homestand that began with a series win over Tampa Bay. After facing AL East foes Boston, the New York Yankees and Tampa Bay in succession, getting ready for the Dodgers and interleague play was quite a change for the Orioles.
"It's a real challenge for your time," manager Buck Showalter. "We were here until well after midnight (Thursday) and today spent the whole day trying to gather the information our players need to know. It was one of those days where you close your door from noon to 3 trying to get everything done."