FAA Airline Transport Pilot (ATM)Meteorology and Weather ServicesHard
A flight planner examining a 500-millibar constant pressure chart for an upcoming transcontinental flight is primarily using it to determine which of the following?
- AFreezing levels over oceanic areas below 5,000 feet
- BSurface frontal boundaries and sea-level pressure centers
- CWind and temperature patterns at approximately 18,000 feet MSL
- DPrecipitation type and intensity at the surface
Show answer & explanationAnswer & explanation
Correct answer: C. Wind and temperature patterns at approximately 18,000 feet MSL
Constant pressure charts depict conditions at a specific pressure level rather than a fixed altitude. The 500 mb chart corresponds to approximately 18,000 feet MSL and is used to identify mid-level wind flow, troughs, ridges, and temperature patterns relevant to upper-level flight planning, including jet stream location.
Why the other options are wrong
- A. Low-altitude freezing levels are better derived from soundings or the 850 mb chart, not 500 mb.
- B. Surface fronts and sea-level pressure are shown on surface analysis charts, not the 500 mb chart.
- D. Precipitation type/intensity is better shown on radar summary or surface charts.
Constant Pressure Chart (500 mb)
An upper-air chart depicting height, wind, and temperature data at a constant pressure surface (500 mb ≈ 18,000 ft), used to analyze mid-level flow, troughs, and ridges.
- 500 mb level ≈ 18,000 feet MSL
- Used to locate troughs, ridges, and the jet stream
- Height contours on the chart function like isobars, indicating wind flow
Memory trick: '500 for Five-hundred-hPa halfway up' — think 18,000 ft mid-level flow