Definition
A category of clouds whose bases form at altitudes generally above 20,000 feet AGL in the middle latitudes. Because they form in the cold upper troposphere, they are composed almost entirely of ice crystals rather than water droplets. This group includes cirrus, cirrostratus, and cirrocumulus.
Plain English
Clouds that sit very high up in the sky — above about 20,000 feet — and are made of ice crystals rather than water. They are the thin, wispy or sheet-like clouds you often see far overhead on clear days.
Context Anchor
You will see this term in weather study, cloud descriptions, forecasts, and preflight weather planning.
Why Pilots Care
Their presence often signals an approaching weather system that may affect visibility or turbulence later in the flight.
Grounding Statement
Picture thin, wispy clouds far overhead while the air near the airport is still clear.
Intuition Check
Do not read high clouds as just any clouds that look high from where you stand. In this FAA context, high clouds are a specific cloud-height group found in the upper part of the atmosphere.
Example Sentence 1
The briefer noted only scattered high clouds along the route, so visibility at cruise altitude would be excellent.
Example Sentence 2
High clouds moving in from the west often mean a change in conditions by the time the flight reaches its destination.