What Cloud Ceiling Selection represents
This worksheet treats five through seven oktas as broken and eight as overcast, then selects the lowest qualifying base. It does not infer obscuration or vertical visibility.
Cloud Ceiling Selection begins with layer 1 base, layer 1 cover, layer 2 base, layer 2 cover, layer 3 base, layer 3 cover. Mark each value as observed, remotely sensed, modeled, assumed, or derived, and preserve its valid time and spatial support.
Checked numerical example
Layers at 500 m/3 oktas, 1,200 m/6 oktas, and 2,500 m/8 oktas select 1,200 m AGL.
Reset restores this Cloud Ceiling Selection example. Repeat it independently with the stated constants and rounding before replacing demonstration values with observations or scenarios.
Continue the Cloud Ceiling Selection workflow with the related Random-Overlap Total Cloud Cover Calculator, keeping the same observation support and conventions.
Continue the Cloud Ceiling Selection workflow with the related Extinction Coefficient from Visibility Calculator, keeping the same observation support and conventions.
Collecting compatible inputs
Enter observed or scenario layer bases above ground with total cover in integer oktas. Keep all three layers tied to the same site, time, observation method, and ceiling definition.
Record site, coordinates, elevation, timestamp, time zone, path direction, wavelength or sensor band, target definition, cloud-layer method, solar-time convention, averaging period, and quality flags when relevant to Cloud Ceiling Selection.
Continue the Cloud Ceiling Selection workflow with the related Sunshine Duration Percentage Calculator, keeping the same observation support and conventions.
Interpreting Selected cloud ceiling
The selected layer is a rule-based ceiling candidate. A lower scattered layer does not qualify, while a higher broken layer does if no lower qualifying layer exists.
Compare Cloud Ceiling Selection outputs only after aligning reference height, sky footprint, path, illumination, contrast convention, and temporal average. Similar numbers can describe different optical or geometric quantities.
Boundary and monotonic checks
Layer bases must increase upward so the record represents a physically ordered profile.
For Cloud Ceiling Selection, change one input at a time and predict whether the answer should rise, fall, or remain fixed. Unexpected behavior can expose percent-fraction, degree-radian, metre-kilometre, or layer-order mistakes.
Where the model stops
Official ceiling observations can include vertical visibility into an obscuration and use reporting conventions beyond this compact three-layer selection. It has no aviation operational authority.
Cloud Ceiling Selection is transparent educational arithmetic, not a cloud observation, weather forecast, solar-resource assessment, flight rule, runway visual range report, instrument calibration, or operational safety authority.
Spatial and temporal representativeness
Cloud and visibility can change across seconds, kilometres, viewing directions, and vertical layers. One Cloud Ceiling Selection input set represents only its declared path, footprint, and interval.
When combining several Cloud Ceiling Selection samples, document weights and retain individual values so variability is not hidden by a single mean or total.
Uncertainty and sensitivity
Vary the least certain Cloud Ceiling Selection input over a credible range and retain the resulting spread in selected cloud ceiling. Display precision cannot overcome observer classification, retrieval uncertainty, spatial variability, or an empirical coefficient.
A Cloud Ceiling Selection sensitivity range is not automatically a probability interval. It omits correlations, model-form error, sampling mismatch, sub-grid cloud structure, nonuniform visibility paths, and uncertainty outside the entered variables.
Cloud amount, overlap, and layers
Cloud fraction is an area or sky-dome proportion, while a ceiling is a height classification and optical depth is attenuation. Cloud Ceiling Selection should not substitute one quantity for another merely because each relates to cloud.
When layers enter Cloud Ceiling Selection, state whether overlap is random, maximum, observed, or ignored. Adding layer percentages directly can exceed 100% and double-count vertically aligned cloud.
Visibility and contrast conventions
Visibility from Cloud Ceiling Selection depends on the target contrast threshold and extinction units. Meteorological optical range fixes a two-percent contrast convention; a general contrast range or runway screening estimate may use another threshold.
Do not equate Cloud Ceiling Selection optical distance with prevailing visibility, slant range, night visual range, or official RVR without the required observation and processing conventions.
Solar geometry and radiation conventions
Solar elevation is measured above the geometric horizon, while azimuth here is clockwise from true north. Cloud Ceiling Selection must retain whether radiation is normal to the rays or incident on a horizontal surface.
Civil time is not solar hour angle. Longitude, time zone, equation of time, atmospheric refraction, shading horizon, and surface tilt belong in Cloud Ceiling Selection only when the displayed model explicitly includes them.
Formula and convention
The working relationship is Ceiling = lowest layer with cover ≥ 5 oktas. Cloud Ceiling Selection uses only the displayed entries and does not retrieve imagery, station observations, ephemerides, forecasts, or runway systems.
Keep percentages as percentages at entry and convert them to fractions only where the formula shows it. For Cloud Ceiling Selection, retain angle direction, optical threshold, height reference, and distance unit with the answer.
Frequent clouds and visibility errors
Typical Cloud Ceiling Selection errors include mixing oktas and tenths, confusing AGL with MSL, adding overlapping layers, treating degrees as radians, using sea-level-reduced visibility, or applying a two-percent constant to a five-percent threshold.
Reject impossible Cloud Ceiling Selection combinations rather than forcing an answer. Keep a clear zero distinct from missing or obscured sky, preserve signs on hour angle, and verify every inverse distance and logarithm denominator before downstream use.
Checking this optical result
How should the result be rounded?
Keep full precision inside Cloud Ceiling Selection, then round no more finely than the least certain measurement or model assumption supports.
When should I recalculate?
Recalculate Cloud Ceiling Selection when its site, time, path, layer, sky footprint, illumination, source observation, or model assumption changes.
What does Cloud Ceiling Selection report?
Cloud Ceiling Selection reports selected cloud ceiling from the displayed inputs and formula.
Can forecast or scenario inputs be used?
Yes. Label the Cloud Ceiling Selection output as a scenario; the page does not fetch or validate a forecast.
How can I verify Cloud Ceiling Selection?
Repeat Ceiling = lowest layer with cover ≥ 5 oktas with the recorded conversions, then test the checked example and a physical boundary.
Why could another source disagree?
Another source may use different cloud overlap, optical threshold, solar convention, coefficient, sensor path, height reference, or rounding than Cloud Ceiling Selection uses.