Hot and high

In aviation, hot and high is a condition of low air density due to high ambient temperature and high airport elevation. Air density decreases with increasing temperature and altitude. At any given true airspeed, lower air density reduces the amount of lift generated by the wings or the rotors of an aircraft, which may hamper an aircraft's performance and hence its ability to operate safely. The reduced density also reduces the performance of the aircraft's engine, compounding the effect. Aviators gauge air density by calculating the density altitude.