Meteorology for Low-Level Application
Weather that matters at spray height
Agricultural flying happens in the boundary layer, where wind, temperature and stability decide whether the product reaches the target. Candidates must understand surface wind, gusts, turbulence, and the diurnal cycle. Stability matters: a stable layer suppresses vertical mixing and can hold a spray cloud; an unstable layer promotes convection and drift.
Concepts to command
Know how to read a METAR and TAF, including wind direction and speed, visibility, cloud, temperature and dew point, and QNH. Understand the difference between QNH, QFE and QNE. Know the formation of fog and dew, and the risk of morning inversions. Understand wind shear and mechanical turbulence near trees and buildings, which is critical at spray height. Know the sea breeze, valley winds and slope winds. Understand the meaning of the wet-bulb temperature and the risk of evaporation affecting droplet size. Know the rules on flight in icing, thunderstorms and reduced visibility.
Traps
Questions often test the difference between QNH and QFE, or ask for the wind at the spray site when only an aerodrome METAR is available. Another trap: assuming calm surface wind means no drift; a light wind at height can still carry product. Watch for inversion questions: an inversion traps drift and inversions are common at dawn.
Rule of thumb
For spraying, the ideal window is a light, steady wind (enough to indicate direction) with a stable-to-neutral boundary layer and no inversion. If the wind is calm and the sky is clear at dawn, suspect an inversion and wait.
Worked example: A METAR reports 08005KT, 10 km, 18/16, QNH 1018. The wind is from 080° at 5 kt, visibility 10 km, temperature 18 °C, dew point 16 °C, QNH 1018 hPa. The 2 °C spread warns of fog risk if the temperature falls; the light wind warns of drift and possible inversion.