Thunderstorms and Other Hazardous Weather Phenomena
What the exam tests
This domain tests thunderstorm formation, structure, hazards and avoidance.
Core rules
- Thunderstorms require moisture, instability and a lifting trigger. Lifecycle: cumulus (updrafts), mature (updrafts and downdrafts, lightning, hail, rain), dissipating (downdrafts dominate).
- Hazards include severe turbulence, hail, lightning, microbursts, tornadoes, icing and heavy rain. Hail and downbursts can occur outside the visible rain shaft.
- Squall lines are lines of storms, often along or ahead of a cold front; supercells are long-lived rotating storms with the greatest severe-weather risk.
- Avoid the cell by a wide margin and avoid the anvil downwind; do not attempt to fly between closely spaced cells.
Worked example
Surface temperature 32°C, dew point 23°C, hot humid afternoon and cumulus building. The spread is 9°C, so cloud base is roughly 9 × 400 = 3,600 ft AGL. Deep vertical growth and a dark base suggest a storm is developing. The reasoning is moisture plus a low cloud base plus strong heating: expect convective hazards and avoid the area.
Traps
Thinking lightning only occurs in the mature stage; underestimating hail outside the rain core; flying under an anvil; treating a single cumulus as harmless in a very unstable air mass.