According to a release sent by BART, they’ll be running longer trains to manage crowds expected for events this weekend, but will be operating on an abbreviated schedule on Memorial Day Monday.
If you’re going to Carnaval on Saturday or Sunday, you can take BART to 24th St./Mission or 16th St./Mission stations, and walk to the festival area on Harrison. Sunday’s parade (which starts at 9:30) is “even easier” they say, as “as soon as you exit the stations you are on the parade route.”
On Memorial Day itself, they say BART will operate on a Sunday schedule, with service starting at 8 and running until midnight.