National Mall in March

Cherry blossom season in late March and early April brings beautiful blooms and absolute chaos. Hotel prices double and crowds triple, but the pink petals framing the monuments are legitimately spectacular. Fall hits the sweet spot - September through November offers perfect walking weather and manageable crowds. Summer is brutal. July and August bring swampy DC heat that makes outdoor exploration miserable by noon. Winter can be magical if you don't mind the cold - the museums are less crowded and holiday decorations add charm. Avoid the week between Christmas and New Year's unless you enjoy elbow-to-elbow tourism. Weekdays are always better than weekends, especially Tuesday through Thursday when school groups are fewer.