Run for the Valley … or be patient, make alternate travel plans and/or join the celebration. In addition to a Westside snarled by President Obama’s mid-day visit today, downtown L.A. will be a traffic mess this afternoon and evening when former President Bill Clinton and other celebs drop by Grand Park to attend Celebrate LA — last party in a series of heritage celebrations and also a farewell bash for outgoing Mayor Villaraigosa. (Anna Chen’s Go Metro Weekends has details.) The point here is that Spring Street, which runs north/south in front of City Hall, is closed. So just assume that any bus you might take through downtown L.A. will be detoured around the Grand Park/City Hall venue. The party runs 5 p.m. to 10 p.m. but the detours will be around until early tomorrow.