Weather and Meteorology
Reading weather like a balloon pilot
This domain asks whether the air is stable, whether the surface wind will stay light, whether fog will form, and whether density altitude will steal lift. The answers come from the METAR, TAF, winds aloft forecast and the temperature-dewpoint relationship.
Stability and moisture
- Stable air: smooth, poor visibility, stratus, steady precipitation - comfortable but often low ceilings.
- Unstable air: cumulus build-ups, gusty surface wind, thermals, showers and thunderstorms - a rough ride and a questionable launch.
- Temperature/dewpoint spread: a small spread means the air is near saturation. Cooling to the dewpoint produces fog or a low ceiling; a spread of 2-3 degrees C overnight with clear skies and light wind is a classic radiation-fog setup.
- Inversions: a clear, calm morning surface inversion gives the light winds balloonists want, but it traps smoke and creates wind shear at the inversion top as you climb into the stronger gradient wind.
Winds, fronts and hazards
Winds aloft forecasts (FD) give direction in degrees true and speed in knots at 3,000, 6,000, 9,000 and 12,000 ft; METAR wind is also true, while ATIS and tower winds are magnetic. A cold front brings a sharp wind shift, gusts and squall lines; a warm front brings drizzle, fog and low ceilings. Stay at least 20 NM from thunderstorms - a balloon cannot outrun one. High density altitude (hot, high, humid) reduces the lift available at any given envelope temperature.
Worked example
METAR KABC 121153Z 00000KT 1/8SM FG VV001 13/13 A3008: calm wind, one-eighth statute mile visibility, fog, vertical visibility 100 ft, temperature and dewpoint both 13 C. The air is saturated, so there is no launch and no altitude at which VFR cloud clearance could be maintained. Compare a TAF for the same field showing 18008KT P6SM SCT050 22/12 - 10 degrees of spread, good visibility, a flyable morning with a light southerly surface wind.
Traps
Reading the spread in Fahrenheit when the report is Celsius; assuming a light surface wind means light wind at 2,000 ft; and ignoring that high humidity raises density altitude even at low elevation.