Why is it easier to get sunburned when it hot outside?

The question is not as dumb as it sounds at first. I have spent a lot of time working in the yard since I was laid off a month ago. I live outside of Boston so the weather is usually still a bit chilly this time of year although it can be quite variable. For the past 2 weeks, the weather has been in the low 50’s - low 60’s during the day and mostly clear and sunny. I have worked outside for several of those days with just a short sleeve shirt on. My pasty-white Anglo skin didn’t even flinch. However, yesterday, the temperature rose to the mid to upper 70’s. I worked outside for about 2.5 hours and got burned to a crisp on the back of my neck and my face got mildly burned as well.

My question is:

Why did the air temperature matter? April sun is April sun right? The temperature is determined by warm and cold fronts moving through the area. Tomorrow, it is supposed to be in the mid-eighties. I know that I will have to wear sun screen or I will get fried. Why is this different than if tomorrow were 62 degrees and clear?

I’m not sure if there is anything to burning easier in warm weather but I know from personal experience that you can get dandy burns in colder weather (just try skiing on a sunny day without protection). I also remember my wife getting a doozy of a sunburn on a day that was in the low 60s. She was wearing shorts but the cool weather gave her no indication of heat from the sun so it never occurred to her that sitting in bleachers all day would be/was a problem. She got the severest sunburn of her life that day. She’d cry just walking or trying to sit down as it caused the skin on her knees to stretch.

In short, don’t discount the sun in cold weather as harmless. Warm weather may aid burning (I don’t know) but you can certainly get fried from any exposure to the sun in any temperature.

Probably because you’re more likely to expose more skin (shirt off, short pants) when its how out?

I’ve gotten doozy tans bordering on burns in the middle of winter up here in the Great White North.

Maybe there’s less water in the atmosphere to diffuse the UV light.

Close - the Earth’s on a tilt so at different times of the year thery’re different amounts of atmosphere for the UV rays to go through, so in summer when ‘your’ part of the Earth is tilted towards the sun there is less atmosphere fot the rays to go through so you burn easier.
Hope that makes sense.

I considered that but it doesn’t answer the question in the OP. Shagnasty was saying that (s)he would burn more easily on a warm day than a cold day even if it was the same day (or rather separated by only one day where the weather changed but the earth didn’t move appreciably far enough in its orbit to significantly affect the tilt issue).