Meteorology
Observations versus forecasts
A METAR is an observation, issued routinely; a SPECI is a special observation for significant change; a TAF is a forecast for a specified period. Decode in order: wind, visibility, cloud, temperature/dewpoint, pressure. SIGMET warns of significant en-route weather; area forecasts cover lower-level operations.
The details that matter to a remote pilot
Wind is named by the direction it blows from. METAR wind is reported in degrees true; broadcast (ATIS-style) wind is magnetic. Height references differ: cloud and operating limits are usually AGL, altimetry is AMSL - mixing them changes your ceiling. A gust spread of 10 kt or more makes low-level hovering unstable. A small temperature/dewpoint spread signals fog or low cloud. Thunderstorms bring gust fronts, microbursts and wind shear, and are a hard stop. Sea breezes build in the afternoon; terrain accelerates and curls wind. Cold reduces battery capacity even when the air is dense.
Worked example / rule of thumb
25012G22KT 9999 SCT025 22/14 Q1015 reads: wind from 250° true at 12 kt gusting 22 kt, visibility over 10 km, scattered cloud at 2500 ft, temperature 22 °C, dewpoint 14 °C, QNH 1015 hPa. The 10 kt gust factor and the 8 °C spread warrant caution near the surface.
Traps
Reading 25012KT as "wind toward 250"; treating a TAF as observed fact; ignoring the difference between surface wind and wind at 120 m; underestimating downdraughts near buildings on a hot day.