Northern Ontario, Canada here.
At this time of year, mornings can be +2C (36F) climbing to a daytime high of +20C (68F). I still don't need to wear a coat or hoodie yet.
Several years ago, I attended Front Sight Firearms Training Center in Nevada for their 4 day defensive handgun course. I went in March to avoid the heat. It was nice and cool in the mornings, about 50F. There was a couple from Alaska in our pod of shooters. We were the only people in T -shirts in the mornings. Everyone else wore a jacket. Some wore parkas.
Instructors and staff were always checking us Northerners for adequate hydration and signs of heat exhaustion. They were awesome.
I agree, its all about what you are used to. I was in Auckland two weeks ago, the temperature was 62F by midday and around 45 at 8:00, people were going to work in heavy wool coats and even fur coats, I was just wearing a suit and thinking, as Lou says, its a perfect day.