It depends on the type of T&F athlete. Basically, the longer the distance the colder you want it to be. 40 degrees F is ideal marathoning weather. The 1500m runners would prefer 60-70F. And the sprinters like it hot. I am not a sprinter, but I have been told that 90 degrees is great weather for sprinting. Below 70F, they feel that their performances start to suffer.
Similarly, altitude can be a detriment to performance in many sports, but is great for sprinters, high jumpers, and long jumpers. Since they are working anaerobically, less oxygen in the air isn’t an issue for them. And apparently the thin air assists their performance with less air resistance.