Meteorology and Hazardous Weather for Instrument Flight
Weather that matters to IFR
Instrument pilots must interpret METAR, TAF, SIGMET, AIRMET, and PIREP products, and understand the formation of icing, turbulence, thunderstorms, and low stratus. Know the conditions for structural icing (visible moisture and temperatures near or below freezing), the types of icing (rime, clear, mixed), and the hazards of freezing rain. Understand wind shear, microbursts, and the conditions that favor them, plus the meaning of ceiling and visibility in approach minima.
Traps
Questions often confuse an AIRMET with a SIGMET: SIGMETs address severe or hazardous phenomena, AIRMETs address moderate hazards over larger areas. Another trap is assuming that a forecast of "no significant weather" means no hazard. Watch for questions on the temperature/dewpoint spread as a fog predictor and on the difference between reported and forecast conditions.
Worked example
A TAF shows "BKN008 OVC015 2SM BR". The ceiling is 800 ft broken, visibility 2 statute miles in mist. If the approach requires a 600 ft ceiling and 1 NM visibility, the forecast is below minima, so an alternate is required.
Rule of thumb
Icing needs visible moisture and a freezing level; the most dangerous icing is often just above the freezing level in large supercooled droplets.