Very high, thin, feathery clouds formed from ice crystals​

Cirrus clouds

Explanation:

Cirrus clouds are referred to as the thin, wispy, and feathery clouds which is made up of ice crystals. Cirrus clouds are also called mare's tails due to the fact that their shape resemble a horse's tail.

When a jet streak is approaching, they are the first sign thst will be noticed. They're found at heights which are above 20,000 feet.