VFR, MVFR, IFR, LIFR: What the Flight Categories Mean

A flight category is a one-word summary of exactly two numbers: the ceiling and the surface visibility at a single reporting station. VFR means a ceiling above 3,000 ft AGL and visibility better than 5 statute miles. MVFR means a ceiling of 1,000 to 3,000 ft and/or visibility of 3 to 5 SM. IFR means 500 to below 1,000 ft and/or 1 to below 3 SM. LIFR is anything worse. Whichever of the two numbers is uglier sets the category, and that is what the “and/or” in the published definitions is doing.

Now the part that matters more than the numbers. The four terms appear nowhere in 14 CFR. They are defined in AIM 7-1-7, Categorical Ceiling and Visibility Conditions as “categorical terms, describing either reported or forecast general ceiling and visibility conditions,” and the AIM is guidance rather than regulation. The Aviation Weather Center publishes the same bands and colors its maps with them. No rule requires you to hold a category, and the boundaries do not line up with 14 CFR 91.155, the section that sets the actual VFR weather minimums. A field showing IFR can be legal to depart VFR. A field showing VFR can have its lowest cloud at 400 ft. The category is a convention; the FAR is the law. For the legal numbers class by class, our guide to VFR weather minimums by airspace class has the whole table.

The four categories, by the numbers

Category	Ceiling (AGL)	Visibility	Map color
VFR	Above 3,000 ft, or no ceiling	Above 5 SM	Green
MVFR	1,000 to 3,000 ft	3 to 5 SM	Blue
IFR	500 to below 1,000 ft	1 to below 3 SM	Red
LIFR	Below 500 ft	Below 1 SM	Purple

Read both columns together and let the worse one win. A 900 ft ceiling with 10 SM underneath it is IFR. A 5,000 ft ceiling with 3/4 SM in fog is LIFR. The Aviation Weather Center publishes this table on its GFA help page and describes it as a set of rules “commonly used throughout the aviation industry,” which is an honest way of saying convention rather than requirement.

One consequence of the worse-one-wins logic is that the category alone never tells you which number caused it. Red could mean a solid 700 ft overcast on a clear-air day, or unlimited sky with 2 SM in smoke. Those are different flights. The AIM makes the same point by pairing the category with a cause in its own examples: IFR FG for IFR due to fog, MVFR CIG HZ FU for marginal conditions caused by both a ceiling and visibility restricted by haze and smoke.

A ceiling is only BKN, OVC, or a vertical visibility

This is where the categories surprise people, so get it exact. 14 CFR 1.1 defines a ceiling as “the height above the earth’s surface of the lowest layer of clouds or obscuring phenomena that is reported as ‘broken’, ‘overcast’, or ‘obscuration’, and not classified as ‘thin’ or ‘partial’.”

In METAR terms that is BKN, OVC, or a vertical visibility group. FEW and SCT are never a ceiling, no matter how low they sit. A scattered layer at 400 ft does not make the field IFR, and the map will happily show green over an airport where the first cloud is at pattern altitude. The AWC’s GFA carries a separate flag for exactly this case, VFR*, which it defines as “VFR with non-ceiling clouds below 3,000 ft AGL.” Most consumer displays do not carry that flag, so a low scattered deck vanishes into the same green dot as a cloudless day.

Take a report like this one, read the way we would say it out loud. Portland, Maine, observed 1153Z: wind from 140 at 8 knots, visibility 4 statute miles in mist, a few clouds at 400 ft, broken at 1,200 ft, overcast at 3,000 ft, temperature 14°C, dew point 13°C, altimeter 29.87. The raw line behind that reading:

METAR KPWM 121153Z 14008KT 4SM BR FEW004 BKN012 OVC030 14/13 A2987

The ceiling is 1,200 ft, not 400, because FEW004 does not qualify. That puts the ceiling in the MVFR band, and 4 SM is MVFR too, so the field is MVFR. Drop the visibility to 2 SM and nothing about the clouds changes, but the field is now IFR on the strength of the visibility alone. If a group in a raw report stops you, paste the line into our METAR decoder, and the glossary has the individual sky-cover and obscuration codes.

Where the categories and the FARs part company

The clearest mismatch is Class G in daylight. Below 1,200 ft AGL an airplane needs 1 statute mile of flight visibility and clear of clouds under 91.155, so a field reporting 2 SM is legal to work out of and is colored IFR on every map in the country. Nothing is wrong with either fact. They answer different questions.

The categories also measure a different visibility than the rule does. What a METAR reports is ground visibility, which 14 CFR 1.1 defines as “prevailing horizontal visibility near the earth’s surface as reported by the United States National Weather Service or an accredited observer.” The 91.155 table regulates flight visibility, “the average forward horizontal distance, from the cockpit of an aircraft in flight.” Those two diverge often and predictably. Four miles in haze at the surface, with tops at 1,500 ft, can be thirty miles of forward visibility once you are on top.

The two systems do meet in one place. Inside a surface area, both halves of the MVFR/IFR boundary are also regulatory numbers. Paragraph 91.155(c) prohibits operating beneath the ceiling under VFR within the lateral boundaries of controlled airspace designated to the surface for an airport when that ceiling is less than 1,000 ft, the same 1,000 ft that separates MVFR from IFR. Paragraph 91.155(d) requires 3 statute miles of ground visibility, or flight visibility where the field reports none, to take off, land, or enter the pattern in a Class B, C, D, or E surface area. That is the same 3 SM again. So at a field with a surface area, blue going to red really does mark the moment basic VFR closes, and the legal way out is a Special VFR clearance, whose own 1 statute mile under 91.157 is one more category line: the one between IFR and LIFR.

What the categories say nothing about is everything else. Wind, gusts, crosswind component, icing, turbulence, convection, runway condition, and density altitude all sit outside the scheme. A green dot is compatible with a 30-knot direct crosswind and a thunderstorm eight miles out.

What MVFR feels like from the left seat

The MVFR band is wide, and its two ends fly nothing alike. A 3,000 ft ceiling with 5 SM is an ordinary overcast day where you can hold pattern altitude, see the next town, and navigate visually without much thought. A 1,100 ft ceiling with 3 SM is a different airplane ride. You are down at 700 or 800 ft to keep 500 ft below the cloud, the horizon is a suggestion, terrain and towers are closer than you would like, and you are navigating head-down more than head-up.

In that band the trend matters more than the value. Pull the last two or three hourly observations and see which way the numbers are stepping. A field that has gone 3,000 to 2,200 to 1,400 in three hours is not an MVFR field. It is an IFR field that has not finished arriving. This is also where the difference between an observation and a forecast starts to bite: the categories on a forecast map are the forecaster’s expectation rather than a measurement, a distinction our post on METARs versus TAFs works through.

The category is a machine’s answer

Most of the categories you read came off an automated station, and both inputs have known limits worth carrying around.

The ASOS ceilometer is a vertically pointed laser, sited near the touchdown zone of the primary instrument runway at most airports, with a reporting range of 12,000 ft. It sees only what drifts directly over that one point. Per the NWS ASOS User’s Guide, the system processes the most recent 30 minutes of 30-second samples every minute, with the last 10 minutes counted twice so the report stays responsive to change. The ceiling in a METAR is therefore a time-average of one column of air standing in for a sky that may be ragged, and a broken deck two miles off the departure end contributes nothing to it.

Visibility comes from a forward-scatter sensor that samples about 0.75 cubic feet of air and reports a running 10-minute harmonic mean. A human observer judges prevailing visibility around a full 360-degree circle. The guide is blunt that the two are “based on different concepts.” Reported visibility also stops counting at 10 miles, so 10SM in a METAR means ten miles or better and nothing more precise than that.

None of this makes the category wrong. It makes it a measurement with a footprint, and the footprint is one point on one airport at one moment.

A green dot is not a go decision

The categories earn their place as a scanning tool. Twelve fields along a route, four colors, and in three seconds you know where the weather lives and which METARs deserve a full read. That is a good use of a convention, and it is the use the Aviation Weather Center built it for.

What it cannot do is decide anything. It does not know your airspace, your rating, your currency, the wind, or the ice. It does not know that the scattered layer under a green dot is at 600 ft. Use the color to find the airports worth reading, read the observation, check the number against the rule for the airspace you will be in, then check it against the limits you set for yourself in a personal go/no-go framework. The dot is where that work starts.

Common questions

Is it legal to fly VFR when a field is reporting IFR conditions?

Sometimes, and it depends entirely on the airspace. In Class G below 1,200 ft AGL during the day, an airplane needs 1 statute mile and clear of clouds, so a 2 SM report that colors the map red is still legal. Inside a surface area it usually is not: 14 CFR 91.155(c) bars VFR beneath a ceiling under 1,000 ft there, and 91.155(d) demands 3 statute miles to take off, land, or fly the pattern. The category never answers this. The airspace does.

Does MVFR mean I need an instrument rating?

No. MVFR is not a rule and confers no requirement. A 2,000 ft ceiling with 4 SM visibility is legal for a VFR pilot in Class E or Class G airspace, and 4 SM meets the 3 SM requirement in Class B through D. What MVFR does tell you is that the field is one step from conditions that would stop you, which is why many pilots set a personal ceiling above the MVFR boundary rather than at it.

What is the difference between IFR conditions and flying under IFR?

IFR conditions describe the weather: a ceiling of 500 to below 1,000 ft and/or 1 to below 3 SM visibility at a reporting station. Flying under IFR describes how you are operating, on an instrument flight plan with a clearance, and you can do that in clear air on a cloudless day. The categories are meteorological. The flight rules are yours to choose, within what the airspace allows.