But it isn't 10C , factor in the wind chill because even with no wind you are creating an air flow. Plenty of cyclists like to copy the pros with their equipment and clothing, yet don't follow them when it comes to wearing longs, weird.
I used to go to the Costa Blanca in March with a friend and we'd often have temperatures of 18-22 degrees C. We would be enjoying riding in our summer kit but we would see Spanish pros out training in full winter gear - arm warmers, leg warmers, long-fingered gloves, hats, and even scarves!
We'd also see old Spanish men in the mountaintop villages wearing thick jumpers and jackets, flat caps and so on.
I suppose if you are used to mid to high 30s in the summer then 18-22 degrees feels chilly!
I thought about going out on the bike today but there was a chilly wind blowing when I put my rubbish out. If it felt cold in my back yard, then it would feel really nippy 1,000 ft higher up! My lungs still don't like cold air ...I'll get on the gym bike later.