Weather Hazards: Thunderstorms, Icing, Turbulence, Visibility
Thunderstorms
Requirements: moisture, instability, lifting. Life cycle: cumulus → mature → dissipating. Hazards: lightning, hail, severe turbulence, microbursts, icing, downbursts. Avoid by ≥20 NM laterally and fly above the anvil. Do not attempt to fly beneath a cumulonimbus.
Icing
- Rime: rough, opaque, from supercooled droplets in stratiform cloud.
- Clear (glaze): smooth, transparent, heavy, from large supercooled drops in cumuliform cloud - most dangerous.
- Mixed: combination. Icing is worst at 0 to −15 °C, especially around −2 to −10 °C. Freezing rain is the most severe.
Turbulence
- Mechanical: near terrain/obstacles.
- Thermal: convection.
- Clear-air turbulence (CAT): near jet streams, no visual cue.
- Wake turbulence: behind heavy aircraft; avoid by spacing and staying above the flight path.
Visibility
Fog forms by cooling (radiation, advection) or mixing. Radiation fog: clear night, light wind, high RH, forms near dawn. Advection fog: warm moist air over cold surface. Haze = suspended particles.
Worked example
On approach in +2 °C air with rain, expect freezing rain aloft at colder levels; if the freezing level is near the surface, anticipate severe clear icing. Plan a diversion or alternate.
Traps
Clear ice is more dangerous than rime. CAT has no radar return. Radiation fog needs clear skies and light wind, not strong wind.