We joke about hot weather, but I heard on the news today that some airlines were not flying with a full load, leaving some passengers at the terminal. It's simple physics. Hot air is less dense, therefore, airplane wings don't produce as much lift. A longer take-off roll is needed for the extra speed required to take off in low-density air. The problem is even worse if there is bright sun on a black runway.

Airports located at higher elevations also require a longer roll because air is generally less dense a few thousand feet above sea level. Fortunately, high elevations often have cooler air which may make up some of the differrence, but if I heard it correctly, Denver was in for a high of 104 degrees F today.

So fly early in the day before it gets so hot.
Howard