Under what conditions does clear structural icing typically form on an aircraft?

1. Temperatures between 0°C and -10°C, in clouds with high supercooled liquid water content and large droplet sizes.
2. Temperatures between -15°C and -40°C, in clouds with low liquid water content and small droplet sizes.
3. Temperatures above freezing (0°C to +5°C) in high relative humidity during high-speed cruise.
4. Temperatures below -40°C in clear, dry air near high-altitude jet streams.