I understand how the relationship between ET and air quality go hand in hand. What factors am I looking for. Humidity? barometic pressure?

What do you guys look at weather wise between runs?

 

Cool/Dry air is better for making power
But if it's too cool, it;s sometimes hard to get any grip.

Best run's I've ever had have been in Fall, when it's dry and getting hot, but it's not scortching.. Track is warm and grippy, air is dry and not too hot..