MVFR and LIFR
- VFR (Visual Flight Rules, 目视飞行规则) conditions: Visibility 5 miles or more, ceiling 3,000 feet or higher
- MVFR (Marginal VFR, 临界VFR) conditions: Visibility 3-5 miles, ceiling 1,000-3,000 feet
- IFR (Instrument Flight Rules, 仪表飞行规则) conditions: Visibility less than 3 miles, ceiling 1,000 feet or lower
- LIFR (Low IFR): Visibility 1 mile or less, ceiling 500 feet or lower