I did my initial training in a high altitude area, where it got pretty hot in the summer, so I'm not at all surprised when I hear an ASOS announce:
Caution: Density Altitude (a few thousand above field elev.)
But recently, I was flying in SE. Kansas when it was extremely cold outside. The ASOS announced:
Caution: Density Altitude minus 1800 ft
I understand that cold winter air can make the air extremely dense, leading to a negative density altitude. But I don't understand the caution part of it.
As far as I'm aware, low density altitudes mean your engine generates more power, and your wings generate more lift. Everything is better with low density altitudes, right?
What is the caution for? What should I be looking out for?