Hot Air Balloons are subject to a number of FAA rules and regulations and are only able to fly in ideal weather conditions and times of the day.
Ideal weather conditions for hot air balloons include winds of less than 7 miles per hour and a cloud ceiling of at least 1000 feet.
Hot air balloons do not inflate during the day because when surface winds are calm, hot air balloon pilots can control the altitude of the balloon very finely by heating or venting the air inside. During the day these light surface winds are broken up by “thermals.” These are rising columns of warm air that spiral skywards, caused by the heating effect of the sun on the ground. Birds and glider pilots love them but for a hot air balloon; thermals make it very difficult to control the balloon. So the warmer the day the greater the possibility of thermals. This is the reason that dusk and dawn are the most optimal times to inflate.
Below is a video from our Head Balloon Pilot, Tommy Rachel, from the 2019 festival discussing weather and safety regulations.