It's not so much temperature as sun. If it's sunny May to Sep then there are
very few days that aren't too hot.

Don't get me wrong, I can lounge by a swimming pool or sea in temps of 30C,
and provided I can have a dip thats fine. Most of my spare time is spent
walking or gardening though, and the summer sun is uncomfortable for me to
work in.

One of my best days this year was skiing from Geiterrygen to Fine at 1400M
in Norway in early March in clear blue skies. When I stopped, it was
difficult to move off, it was so pleasant lounging around in the sun. The
temperature was minus 5C.

(http://weather.4dinternet.co.uk/weat...ryggen2005.htm)

I suppose my perfect summer day would be sub 546 dm air with a NW wind,
pressure 1020 and rising and breezy with low humidity. However, even then
out walking it would be very hot in the sun traps in valleys or near woods.