I'm looking for an online map of the U.S. that's color-coded to show
the highest temperatures you'd expect to get in each area each summer.

NOT a daily map where you could look up the weather on some particular
date, but a map showing the maxiumum yearly highs.

It's easy to find maps that show the opposite -- the lowest winter
temperatures -- since gardeners use those maps to find their hardiness
zone, but I can't find any U.S. maps showing highest summer
temperatures. Any help would be appreciated.

Jim