An extra wet and cool Memorial Day weekend wasn’t entirely unwelcome southwest of Salem at the Flat Nasty off-road park. Although a Saturday morning downpour caused a rain delay, this was met with a stoic shrug by the hundreds who filled the park’s steep hollows for its 20th anniversary celebration. After all, rolling with whatever happens is part of what’s kept Flat Nasty operating for two decades, whether that means adverse weather or automotive mishaps.