Definition
A narrow band of strong winds, typically found near the tropopause between roughly 30,000 and 40,000 feet, where wind speeds are commonly 50 knots or greater and can exceed 200 knots. Jet streams generally flow from west to east in meandering patterns and are caused by sharp temperature contrasts between large air masses.
Plain English
A fast river of wind high in the atmosphere that flows mostly west to east. Aircraft flying inside it get a big push if they're going the same direction, or a hard slowdown if going against it.
Context Anchor
Pilots encounter jet stream information in weather briefings, route planning, and forecasts for higher-altitude flights.
Derivation
The name comes from the word 'jet' meaning a fast, narrow stream of fluid (like water from a hose). Discovered by high-altitude pilots in WWII who found unexpected strong winds aloft, the name describes exactly what it is: a stream of air moving like a jet.
Why Pilots Care
Riding a jet stream tailwind can cut flight time and fuel use on eastbound legs, while headwinds increase both on westbound legs; the edges often produce clear air turbulence.
Analogy
A jet stream is like a fast river within the air. If an aircraft flies with the flow, it can move faster over the ground; if it flies against the flow, it can be slowed down.
Grounding Statement
Picture a long, fast-moving ribbon of wind high above the ground, with aircraft either riding with it, pushing against it, or crossing through it.
Intuition Check
Jet stream does not mean exhaust from jet engines. It means a natural, high-altitude current of fast-moving air.
Example Sentence 1
Eastbound flights often climb to higher altitudes to ride the jet stream and save fuel.
Example Sentence 2
Turbulence was forecast along the southern edge of the jet stream at flight level 380.