Learn how to read aviation ceiling and visibility charts, decode VFR-to-LIFR categories, check valid times and apply the data to a flight route.
For Aviation & Real-World Flying, read a ceiling and visibility chart by checking its valid time and legend, then compare the plotted or shaded ceiling and visibility with the chart’s thresholds. The worse of the two sets the displayed flight category. Assess the entire route, then verify it against airport observations and forecasts.
Treat the category as a screening tool, not an automatic go or no-go decision. VFR weather minima, terrain clearance, aircraft equipment, pilot qualifications and operating rules still apply.
What counts as an aviation ceiling?
An aviation ceiling is the height above ground level of the lowest layer reported as broken, overcast or an indefinite ceiling caused by vertical visibility. Few and scattered layers are not ceilings, even when they are low.
BKN020means a broken layer and a 2,000-foot ceiling.SCT008 BKN025means scattered cloud at 800 feet but a ceiling of 2,500 feet.VV003means vertical visibility of 300 feet into an obscuration, which is treated as the ceiling.
Ceiling heights in airport reports are normally expressed in hundreds of feet above the reporting location. Visibility is measured separately and usually represents prevailing horizontal visibility. US products commonly use statute miles, while products elsewhere may use metres or kilometres. Runway visual range is a different, runway-specific measurement. Our examples of decoding METAR cloud layers and visibility show how the underlying reports produce these values.
What do the chart colours mean?
On many US flight-category displays, green means VFR, blue means MVFR, red means IFR and magenta means LIFR. These colours are common rather than universal, so the product’s own legend always takes precedence.
| Category | Ceiling | Visibility | Common colour |
|---|---|---|---|
| VFR | Above 3,000 ft AGL | Above 5 SM | Green |
| MVFR | 1,000–3,000 ft AGL | 3–5 SM | Blue |
| IFR | 500 to below 1,000 ft AGL | 1 to below 3 SM | Red |
| LIFR | Below 500 ft AGL | Below 1 SM | Magenta |
The displayed category is whichever condition is more restrictive. A 4,000-foot ceiling with two miles visibility is IFR; a 700-foot ceiling with ten miles visibility is also IFR. Do not average the two values. MVFR is planning shorthand, not a separate set of airspace rules.
A combined flight-category chart performs that comparison for you. Separate ceiling and visibility charts instead show cloud-base heights and visibility ranges, so you must identify the worse result yourself. Some plots express ceiling in hundreds of feet or use a different colour scale; check the label, units and legend rather than relying on colour memory. Our guide to FAA weather-chart symbols and legends explains the common plotting conventions.
How should you use ceiling and visibility charts for flight planning?
Use the chart to find restrictive areas at the time your aircraft will reach them, not merely at departure time.
- Identify the product type. An observation or analysis depicts conditions around its stated time. A forecast chart depicts a future valid time, while model guidance may not represent an official airport forecast.
- Check issue and valid times. They are not interchangeable. Convert UTC carefully and select the panel closest to your estimated arrival time at each part of the route.
- Read the legend and units. Confirm whether the product shows combined categories, ceiling height, visibility distance or probability. Check whether heights are AGL or use another stated datum.
- Trace the complete route. Examine departure, climb-out, en-route terrain, destination and alternate areas. A good category at both airports does not prove that the weather between them is suitable.
- Compare ceiling and visibility separately. Apply the worse category at every point. Pay special attention to valleys, coasts and rising terrain, where local cloud or fog can differ sharply from a smoothed chart.
- Examine the trend. Compare consecutive forecast periods rather than one frame. Conditions deteriorating towards your ETA deserve more margin than the same values in an improving trend.
- Corroborate the picture. Check nearby observations, terminal forecasts and other relevant hazards. Our route-based method for applying weather charts covers timing, terrain and alternate planning without treating one chart as the whole briefing.
For VFR planning, choose a different altitude, route or departure time when the forecast leaves inadequate clearance from terrain and cloud, even if the chart remains nominally VFR or MVFR. For IFR planning, the category indicates likely operating conditions but says nothing by itself about icing, thunderstorms, turbulence, wind or aircraft capability.
Why might the chart disagree with a METAR or simulator?
Chart boundaries are broad summaries, while a METAR is a point observation at a particular place and time. A coloured boundary should not be interpreted as a sharp wall of weather.
- Time mismatch: the chart, METAR and forecast may have different observation or valid times. Match each one to its timestamp.
- Spatial interpolation: conditions between reporting stations may be estimated or modelled. Check nearby stations on both sides of the route rather than trusting one shaded area.
- Local weather: fog, showers, sea breezes and terrain obscuration can affect one airport without appearing clearly in a broad regional display.
- Datum or unit confusion: mistaking hundreds of feet for feet, statute miles for kilometres, or AGL for MSL can change the planning decision completely.
- Simulator weather synthesis: live or preset weather engines may blend, delay or reinterpret source data. Plan from one consistent set of reports, then accept that the simulated cloud base may not reproduce it exactly.
Can the chart tell you whether an approach is legal?
No. A ceiling and visibility chart does not replace the approach chart, reported runway visibility or the operating rules that apply to the flight.
Compare the destination report with the procedure’s decision altitude or minimum descent altitude and its required visibility or runway visual range. Ceiling can affect whether visual references are likely to appear, but approach legality and continuation rules vary by jurisdiction and type of operation. Our explanation of using approach visibility and altitude minimums covers that separate decision.