at Royal Troon at The Open in 2016.  The weather was gorgeous down in London, so I just packed a jacket and thought I'd be okay.  It never got above 52 degrees the entire day, IN JULY.  

A separate time, we spent ten gloriously beautiful warm Sep/Oct days around Scotland; you just can't count on it.  Must be why they have so many sweater stores everywhere for suckers who can never properly plan for a trip there.