Jet Stream Turbulence

What is Jet Stream Turbulence?

Jet stream turbulence is a type of clear air turbulence (CAT) associated with the intense windshear found near the core of jet streams—fast-moving, narrow bands of wind in the upper troposphere and lower stratosphere. Jet streams have a defined minimum speed of 60 knots and can extend for thousands of kilometers, with a typical vertical thickness of about 6000 ft.

Where and Why Does It Occur?

The strongest turbulence is usually found just beneath or at the level of the jet stream core, on the cold-air side of the jet. This is where the windspeed changes most rapidly with height and distance (maximum windshear), particularly across the thermal gradient of the frontal zone. In curved jet streams, turbulence is enhanced on the inside of the bend, where isotachs (lines of equal wind speed) are tightly packed.

Visual and Operational Clues

Although jet stream turbulence is often invisible, long streaks of cirrus clouds can sometimes mark its presence. However, CAT can occur in completely clear air, making it difficult to detect visually. Modern aircraft systems can help identify jet streams by monitoring wind and temperature changes. For flight planning, routes should avoid the core windshear zone by flying above or below the jet stream when possible.

Types of Jet Streams and Seasonal Effects

Jet streams include the polar front, subtropical, and occasionally tropical (easterly) jets. Their positions, speeds, and intensity vary seasonally and geographically, with the polar front jet stream being especially relevant for transcontinental flights. The risk of turbulence increases during winter when jet streams are typically stronger.