Meteorology: Stability, Winds and Balloon-Specific Hazards
Core concepts
Meteorology for balloon pilots concentrates on the lowest few thousand feet. You must understand how surface heating produces thermals and convective turbulence, why stable air gives smooth flight and haze while unstable air gives gusty surface winds and cumulus build-up, and how the diurnal cycle drives the best flying windows near sunrise and sunset. Learn the difference between the surface wind, the gradient wind aloft, and the boundary-layer effect that turns wind clockwise with height in the northern hemisphere. Know how to read a METAR and a TAF, decode QNH and QFE, and interpret a significant weather chart and a low-level forecast.
Balloon-specific hazards
Balloons are slow and cannot penetrate strong wind shear, so shear between the surface and 500 ft is a launch stopper. Learn the signs of an inversion (mist layers, smoke flattening, temperature increasing with height) and how it can cap convection but also trap haze. Understand valley drainage winds, sea breezes, and the rotor and lee effects downwind of hills. Know that thunderstorms, icing, and fog are absolute no-go conditions, and that a balloon cannot climb through a low cloud layer to reach clear air above.
Traps and a rule of thumb
Questions often ask for the most likely cause of a given observation, or for the forecast trend. Traps include confusing QFE with QNH, assuming a calm surface wind means calm at 1,000 ft, and forgetting that a forecast is valid for a period and an area, not a point. Rule of thumb: if the surface wind exceeds 10 kt, or the surface-to-500-ft shear exceeds 5 kt, treat the launch as marginal and seek a second observation.
Worked example
A METAR reads surface wind 180/08 kt, QNH 1018, few clouds at 3,000 ft, temperature 12 °C, dew point 9 °C. The spread is 3 °C, so fog is unlikely but mist is possible in valleys; the light southerly and few cloud suggest a stable, flyable morning. The pilot should still check the low-level wind forecast for shear before committing.