The hi vis windbreaker jersey would be too hot (I've got a couple of those too) but there are non-windbreaker jerseys there which I've worn up to the high 20s, and even into 30-ish. You probably wouldn't want to wear them in temps much hotter than that, but for hotter days I either do the arm-cooler thing mentioned above, or I wear the long-sleeved jersey and bring a sleeveless. Then when it get really hot, I switch to the sleeveless and sunscreen.

I hadn't realized that much clothing lets significant amount of UV through: http://www.rei.com/learn/expert-advi...rotection.html for instance a cotton t-shirt might let 20% through which isn't huge but probably adds up in super-sunny conditions. Also I learn that Australia has pioneered UBF clothing ratings. My area is not on avg super-sunny but in spring we can get some very clear sunny days where everyone wants to go out & enjoy wearing light clothing but the strong sun combined w/little base tan can easily lead to burning after a day outside.

I use Pearl Izumi sun sleeves and any old jersey I want to wear. The new model is called inercooler or something like that. Living in Florida I have found them to actually be cooler than just a jersey even in the peak of summer heat and humidity.

http://t1.gstatic.com/images?q=tbn:A...lMbPGv8agQNKJ9

White or tan linen button up shirts,nice and cool on hot days.......couple bucks from Salvation Army or Goodwill....not so cheap new.....Soak it with water and it's great when it's hot out......Throw on a bow tie and your good for some fine dining........:)

http://www.performancebike.com/bikes...75_-1___400061

I have an older version of this jersey. I find it very comfortable of a 90F sunny day. It only has back pockets. The reflective white color makes a lot of difference, but it also gets noticeably dirt real easy. I just decided not to care about the grease stains.