Temperature

Since hot air balloons fly by changing the temperature inside the balloon with heat, it stands to reason that outside air temperature is going to affect balloon flights, and it does! When the air in the balloon is heated, it becomes hotter and thus less dense than the surrounding outside air. This hotter air is lighter and the balloon will float upward. The more heat, the higher up you go. A balloon will fly when its temperature is around 140 degrees above the outside air temperature (generally). So, the colder it is outside, the less heat it takes to fly and conversely, the hotter it is outside, the more heat it will take to fly.