How is it that the first 35 degree day after summer can cause me to feel like I'm freezing to death, but 35 degrees after well-below freezing weather makes me feel like putting on my shorts and a t-shirt and going to the lake?

It’s been up to -20 degrees here over a period of a couple of days. Today it’s 33 and it feels down right tropical. Didn’t even need to wear a coat, whereas if it had hit 33 after summer, I’d be bundled up. Is there a scientific explanation for this, or is it all simply a matter of perception?