Meteorology for Low-Level RPAS Operations
Low-level flying sits in the most disturbed part of the atmosphere. The exam tests whether you can read a METAR or TAF, then translate surface conditions into what happens at 100 m.
Wind and turbulence
Surface friction slows wind near the ground, so wind speed increases with height - the wind gradient. Expect 100 m winds noticeably stronger and veered compared with the reported surface wind. Buildings, treelines and ridges generate mechanical turbulence and rotor zones downwind. Gust spread matters more than mean wind for a light airframe.
Air mass and local effects
In the Philippines, the amihan (northeast monsoon) and habagat (southwest monsoon) set the seasonal wind, and the ITCZ brings convective cloud and thunderstorms. Sea breezes reverse coastal winds in the afternoon. Thunderstorm outflow produces sudden strong gusts and microbursts that no small RPAS can counter.
Density and performance
High temperature, high humidity and high field elevation all reduce air density, cutting propeller thrust and lift while raising motor temperatures. Battery capacity and usable power fall in extreme heat as well as in cold.
Worked example
METAR: surface wind 240 at 8 kt, visibility 10 km, few cloud at 1800 ft, temperature 33 °C, dew point 26 °C, QNH 1009 hPa. Reasoning: at 100 m expect roughly 250° at 12 to 15 kt and less obstruction; the 7 °C dew-point spread means mist is unlikely but watch evening cooling; 33 °C plus high humidity means a density-altitude performance penalty, so reduce payload or flight time. Thunderstorm cells in the TAF cancel the sortie.
Traps
Planning on the surface wind only; ignoring dew-point spread when fog is forecast; launching with a thunderstorm approaching.