Yeah this was the first day that really felt like an autumn air mass in the sense that despite full sunshine, it could not warm above the mid/upper 50s this afternoon.
We've had a few cooler afternoons but all of them so far have included clouds/low ceilings or rain. This was that first time where it was like, "yep, that sun isn't going to get it done" today. 55F and full sun and decent mixing is definitely a cool air mass.