Planes usually fly in the troposphere, but may go up to the edge of the stratosphere. Little moisture enters the stratosphere, so clouds are rare. Even though the stratosphere has complex wind systems, violent storms don’t occur there. Because the air temperature in the stratosphere slowly increases with altitude, it does not cause convection and has a stabilizing effect on atmospheric conditions in the region. Stability generally limits vertical extensions of cloud and leads to the lateral spreading of high cumulonimbus cloud with characteristic anvil heads. This means that weather (in the form of clouds) is almost entirely confined to the troposphere below. That’s why airline pilots prefer to fly in the stratosphere.
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