LIFR
Also called: Low Instrument Flight Rules, Low IFR
LIFR, Low Instrument Flight Rules, is the lowest of the four aviation weather flight categories. It means a ceiling below 500 feet and/or visibility of less than 1 statute mile. Whichever of the two is lower sets the category. The categories above it, in order, are IFR, MVFR, and VFR.
Aviation Flight Categories
| Category | Ceiling | Visibility |
|---|---|---|
| VFR | Greater than 3,000 feet | Greater than 5 statute miles |
| MVFR | 1,000 to 3,000 feet | 3 to 5 statute miles |
| IFR | 500 to below 1,000 feet | 1 to less than 3 statute miles |
| LIFR | Below 500 feet | Less than 1 statute mile |
The category is set by whichever is lower, the ceiling or the visibility. These are weather categories, not the legal minimums for a flight, which depend on airspace, regulations, equipment, and pilot qualifications.
Related Terms
IFR
Instrument Flight Rules govern flights conducted under instrument procedures and can be used in clear weather too. Separately, the IFR weather category means a ceiling from 500 to less than 1,000 feet and/or visibility from 1 to less than 3 statute miles, with lower values classified as LIFR. Legal operating requirements depend on airspace, regulations, equipment, and pilot qualifications.
MVFR
Marginal Visual Flight Rules, conditions between VFR and IFR with ceiling 1000-3000 feet and/or visibility 3-5 miles. MVFR indicates reduced but still visual conditions requiring extra caution.
VFR
Visual Flight Rules allow flight using visual references when the applicable visibility and cloud-clearance minimums are met. Those minimums vary by airspace class, altitude, and day or night under 14 CFR 91.155. Separately, the VFR weather category means a ceiling above 3,000 feet and visibility greater than 5 statute miles.
Ceiling
The height above ground of the lowest broken or overcast cloud layer, or vertical visibility into an obscuration. Scattered clouds do not form a ceiling. A ceiling below 1,000 feet falls in the IFR or LIFR weather category; legal flight and approach requirements depend on airspace, visibility, regulations, equipment, and pilot qualifications.
Visibility
The horizontal distance at which objects can be seen and identified. U.S. aviation reports express prevailing visibility in statute miles. Below 3 statute miles falls in the IFR or LIFR weather category, but legal visual-flight minimums vary with airspace, altitude, and day or night under 14 CFR 91.155.
METAR
Meteorological Aerodrome Report, a standardized format for reporting current weather conditions at airports. METARs are issued hourly (or more frequently during significant changes) and include wind, visibility, clouds, temperature, and pressure.
TAF
Terminal Aerodrome Forecast, a weather forecast for the area within 5 miles of an airport. TAFs are issued every 6 hours and cover a 24-30 hour period, providing expected winds, visibility, clouds, and precipitation.
LIFR: Guides and Explainers
These explainers connect this definition to real-world forecasting and decision-making.
Guides
METAR Codes Decoded: A Pilot's Guide to Reading Aviation Weather
Learn how to read and decode METAR weather reports. Understand aviation weather codes, visibility, cloud layers, and all the abbreviations pilots need to know.
Weather Education
GFS vs HRRR vs NAM: Which Weather Model Should You Trust?
Learn the differences between GFS, HRRR, NAM, and the Euro model. Understand which forecast model to trust for different situations and how weather enthusiasts can interpret model data.
Helpful Tools and Hubs
Use these pages to apply the concept, compare conditions, or follow related weather workflows.
Tool
Flight Rule Calculator
A free tool for working this out with your own numbers.
Feature
Aviation Weather
Track METARs, TAFs, and airport conditions in a pilot-friendly layout.
Use Case
Weather App for Pilots
Follow the aviation workflow for METARs, TAFs, ceilings, and crosswinds.
Tool
Cloud Base Calculator
Estimate cloud base height from temperature and dew point spread.
Sources
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Browse by Category
In the WeatherAI App
WeatherAI's free METAR view says whether the ceiling or the visibility sets a station's flight category, and TAF detail opens with a flight-category strip across the forecast period. WeatherAI is not an FAA-approved flight-planning product.
Availability, coverage, update frequency, and alert delivery vary by data source, region, subscription plan, device permissions, and service conditions.