AIM Text
- Categorical terms, describing either reported or forecast general ceiling and visibility conditions, are defined as follows:
- LIFR (Low IFR). Ceiling less than 500 feet and/or visibility less than 1 mile.
- IFR. Ceiling 500 to less than 1,000 feet and/or visibility 1 to less than 3 miles.
- MVFR (Marginal VFR). Ceiling 1,000 to 3,000 feet and/or visibility 3 to 5 miles inclusive.
- VFR. Ceiling greater than 3,000 feet and visibility greater than 5 miles; includes sky clear.
- The cause of LIFR, IFR, or MVFR is indicated by either ceiling or visibility restrictions or both. The contraction “CIG” and/or weather and obstruction to vision symbols are used. If winds or gusts of 25 knots or greater are forecast for the outlook period, the word “WIND” is also included for all categories including VFR.
Source: FAA Aeronautical Information Manual · current edition · paragraph 7-1-7.
The short answer
This AIM section is FAA advisory guidance defining the four categorical terms used to describe reported or forecast ceiling and visibility: LIFR, IFR, MVFR, and VFR. It explains how each category is keyed to specific ceiling heights and visibility ranges, and how “CIG,” weather symbols, and “WIND” flag the cause, supporting flight planning under 14 CFR 91.103.
Research Notes
Common Questions
What ceiling and visibility define MVFR versus IFR?
Per this advisory section, MVFR (Marginal VFR) is a ceiling of 1,000 to 3,000 feet and/or visibility 3 to 5 miles inclusive. IFR is a ceiling 500 to less than 1,000 feet and/or visibility 1 to less than 3 miles. LIFR is below those IFR values; VFR is a ceiling greater than 3,000 feet and visibility greater than 5 miles, including sky clear.
What does “CIG” or “WIND” mean in a categorical outlook?
The AIM states the cause of LIFR, IFR, or MVFR is shown by ceiling or visibility restrictions or both, using the contraction “CIG” and/or weather and obstruction-to-vision symbols. If winds or gusts of 25 knots or greater are forecast for the outlook period, the word “WIND” is added to all categories, including VFR — e.g., “IFR CIG RA WIND.”
What is LIFR and how low are its limits?
LIFR (Low IFR) is defined in this section as a ceiling less than 500 feet and/or visibility less than 1 mile. The example “LIFR CIG” denotes low IFR caused by a low ceiling, while “IFR FG” denotes IFR caused by visibility restricted by fog.