How can we expect encountering Jet stream from reading charts?

[Ref AC 00-45H, weather.gov]

How can we expect encountering Jet stream from reading charts?

We have various method to check the location of Jet stream:

  1. Mid-Level SIGWX Chart
  2. Constant Pressure Charts (Isotach chart) : both 300 mb and 200 mb

Note: Isotach – a line connecting points of equal wind speed.

For Mid-Level SIGWX Chart, a bold (green) line represents a jet stream axis with a wind speed of more than 80 kts. An arrowhead is used to indicate wind direction. Wind change bars (double-hatched, light green lines) positioned along a jet stream axis identifies 20-knot wind speed changes. When Jet stream’s maximum speed is 120 kts or more, “Jet stream vertical depth forecasts” are included  – Jet depth is defined as the vertical depths to the 80-knot wind field above and below the jet stream axis using flight levels.

For the Isotach chart of 300 mb and 200 mb are primarily used to located the jet stream. The jet stream is identified where the wind speed is 70 kt (81 mph / 130 km/h) or greater (colored shading). Rule of thumb, contours of equal wind speed (isotachs, drawn at 20 KT intervals) with parallel direction of the wind is likely the location of Jet stream.

 

How can we expect encountering CAT?

Since, CAT is likely appearing at upwind of the base of the trough on the polar side of a jet stream, we can try to locate the location of jet stream instead!

What’s CAT (Clear Air Turbulence)?

 

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