The one calculation behind every number in the tool — turning a cloud height reported at a nearby station into an estimate of that same deck's height above your facility.
Cloud bases in a METAR or TAF are given as height above ground level (AGL) at the reporting station. If your facility sits higher than that station, the same cloud deck is effectively lower above your facility — and vice-versa. The adjustment applied to every layer is:
For example, facility 8OH9 sits at 937 ft. Its nearest METAR and TAF both happen to be KLUK at 472 ft — 465 ft lower. A reported BKN010 (broken at 1,000 ft) becomes an estimated broken at 535 ft over 8OH9.
This is an estimate, not a measurement
The math assumes the cloud base sits at a single, constant altitude above sea level (MSL) and extends flat and level from the station all the way to your facility. Real cloud bases are not perfectly flat, level decks: they slope, vary, and break up over distance and terrain. The adjusted figure tells you roughly where that layer would be over your facility if the deck held level — a planning aid for sites without their own weather reporting, not a true on-site ceiling. Only an actual observation at your facility can give you that.
Try it
Drag the slider (or the cloud) to set the ceiling as reported at KLUK. The same cloud deck sits at a fixed altitude — but because 8OH9 is 465 ft higher, its height above your facility is lower. The alert reflects the estimated height at 8OH9. The flat, level deck shown here is a simplification — real cloud bases vary over distance, so this is an estimate, not an on-site measurement.
Cloud altitude (MSL)1472 ft
Reported at KLUK (472 ft)1000 ft AGL
Adjusted for 8OH9 (937 ft)535 ft AGL
Ceiling — adjusted height below 1000 ft
Which layers matter
A ceiling in aviation is the lowest broken (BKN) or overcast (OVC) layer — these are tagged accordingly.
We also adjust and display the lowest few (FEW) and scattered (SCT) layers, even though they aren't ceilings.
Once you understand the adjustment, the next thing to weigh is how far away the reporting station is — see Station distance. The height flags applied to each adjusted layer are covered in Cloud / ceiling flags.
