Helicopters and Heat

I was recently reminded of a law of thermodynamics when I read this Washington Post article, As extreme heat bakes the West, emergency helicopters struggle to fly

As we continue to see summer temperatures soaring over 100 degrees, understand that those temperatures will impact the ability of helicopters to lift what would be normal loads, or not fly at all. Just another factor for us to take into consideration during wildland fire operations, search and rescue ops and also medical evacuation. Remember too, elevation also has an impact on the lift capacity of helicopters, even when it is not super hot.