1988 was one that turned cold really quickly. The summer, particularly from June to the first half/two-thirds of August, was then a warmest on record. Then at the end of August, it just turned cold, and never really looked back. October 1988 was one of the coldest on record, and in some spots, beat out the cold standard of October 1976:
Come to think of it, the warm west makes this look like the October version of February (or JFM) 2015.