FAA Instrument Flight Instructor (FII)WeatherHard
A pilot reviewing a 500-millibar constant pressure chart before a high-altitude flight notices height contour lines that are very closely spaced over the route. What should the pilot conclude about conditions at that altitude?
- AWeak winds are expected due to a shallow pressure gradient
- BStrong winds are expected due to a steep height (pressure) gradient
- CThe chart indicates a temperature inversion at that level
- DPrecipitation is certain along the route regardless of wind
Show answer & explanationAnswer & explanation
Correct answer: B. Strong winds are expected due to a steep height (pressure) gradient
On a constant pressure chart, height contours are analogous to isobars on a surface chart. Closely spaced contours indicate a steep height gradient, which corresponds to a strong pressure gradient and therefore strong winds, similar to tightly packed isobars on a surface analysis.
Why the other options are wrong
- A. Widely spaced contours, not closely spaced ones, indicate weak winds.
- C. Contour spacing relates to wind speed, not directly to temperature inversions.
- D. Contour spacing alone does not determine precipitation; moisture and lift are also required.
Constant Pressure Chart Contour Spacing
On upper-air constant pressure charts, height contours represent lines of equal geopotential height; their spacing indicates wind speed similar to isobars on surface charts.
- Closely spaced contours = steep gradient = strong winds
- Widely spaced contours = weak gradient = light winds
- Commonly analyzed at 500mb, 700mb, 850mb, and other standard levels
Memory trick: Tight lines on the chart mean tight winds in the sky.