Thunderstorm hazards
Hazard list (TC AIM AIR 2.7.1; AWH 22.7):
- Severe turbulence
- Hail
- Lightning
- Structural icing
- Low-level wind shear
- Tornadoes
- Precipitation static (also called static electricity)
- Heavy precipitation
- Low ceiling and visibility
- Rapid altimeter error
- Engine water ingestion
Combinations (PHAK ch.12):
- Every thunderstorm carries some, in numerous combinations.
- Cannot tell which by looking.
Ceiling and visibility (PHAK ch.12):
- Inside cloud: can fall to near zero.
- Between cloud base and ground: stay restricted by rain or dust.
Microburst (downburst): deadly on approach or departure.
Lightning: every thunderstorm produces it by definition (AWH 22.7.2).
- A strike can: puncture aircraft skin, damage communications and navigation equipment, cause engine failure, momentarily blind pilot, disrupt low- and medium-frequency radio, even from a distant strike (TC AIM AIR 2.7.1, PHAK ch.12).
- Nearby lightning can induce permanent magnetic compass error. Unlike dip-induced turning/acceleration errors, which come and go with heading or speed change.
- Strike probability greatest between -5C and 5C. Strikes also occur in clear air near a storm (TC AIM AIR 2.7.1).
- Vivid or frequent lightning means severe activity; severe storms flash more often (PHAK ch.12; TC AIM AIR 2.7.2).
Static discharge (AWH 22.7.8):
- Cause: flying through cloud, precipitation, or particles (ice, sand, dust) builds static electricity, discharging as corona off sharp points and edges.
- Sign: steady, high level of radio noise.
- At night: weak glow, St. Elmo's Fire. Harmless.
Hail formation (AWH 14.4.5):
- Supercooled droplets above freezing level freeze onto a nucleus.
- Drafts carry it up and down; more droplets freeze on.
- Grows in layers.
Favoured by:
- Strong updrafts
- High supercooled liquid water content
- Large cloud drops
- Great vertical height
Hail hazards (PHAK ch.12):
- Can fall in clear air several miles from the storm.
- Surface rain does not mean no hail aloft. Expect it especially under the anvil of a large cumulonimbus.
- Can significantly damage an aircraft in a few seconds.
Trap: judging hazards by a storm's look or by surface rain; any thunderstorm can carry any, and rain below does not rule out hail aloft.
References
- FAA Aviation Weather Handbook (FAA-H-8083-28)
- FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25), ch.12
- TC AIM AIR 2.7.1
- TC AIM AIR 2.7.2 (vivid lightning means severe activity)
- TC AIM AIR 2.8 (low-level wind shear / microburst)
- FAA-H-8083-25_PHAK ch.12 (Lightning)
- FAA-H-8083-25_PHAK ch.12 (Hail)
- FAA-H-8083-28_aviation-weather-handbook.md 14.4.5 (Hail)
- FAA-H-8083-28_aviation-weather-handbook.md 22.7.2 (Lightning)
- FAA-H-8083-28_aviation-weather-handbook.md 22.7.8 (Static Electricity)