Jet Stream
The jet stream is a fast-moving, narrow band of air flowing in the upper troposphere and lower stratosphere, typically at altitudes of FL250–FL450. Jet streams are driven by temperature gradients between air masses and can exceed 200 knots. They have a profound effect on aircraft performance and weather patterns.
Jet Streams in Canada
Canada is regularly affected by two major jet streams: the Polar Jet (the main westerly jet stream at roughly 50–60°N, typically FL300–FL400) and the Subtropical Jet (further south and higher, less commonly affecting Canadian operations). The Polar Jet’s position determines much of Canadian weather — cold fronts, storm systems, and severe weather are all organized by the jet.
Effect on Flight Operations
- Eastbound: A strong jet stream can add 50–150 knots to groundspeed — significant fuel savings on transatlantic or transcontinental routes
- Westbound: The same jet stream creates severe headwinds, increasing flight time and fuel burn
- Clear Air Turbulence (CAT): The jet stream’s wind shear zone is the primary source of CAT
- Organized weather: Fronts, lows, and storm tracks follow the jet
On the TC Written Exam
Jet streams appear in the meteorology section. Know: they form due to temperature contrast between air masses; they produce CAT on the cyclonic (poleward) side; they affect eastbound and westbound flight times significantly.
Related Terms
See also: Clear Air Turbulence, Cold Front, Low-Level Jet.