User Guide›Missing observation data

Missing observation data

When a weather station’s sensor isn’t reporting, its report simply omits that group. The tool tells you the data is missing rather than drawing the gap as clear sky.

Here is a real report from KHAO:

METAR KHAO 240153Z AUTO A3016 RMK A02 SUPNO PWINO $

There is no cloud group and no visibility group in it. Not “clear” — absent. The station is reporting an altimeter setting and little else.

Why this matters A missing group and a clear sky produce the same thing on a naive display: nothing. Left alone, a facility whose ceilometer had failed would show no cloud layers, no flag color, and a neutral outline — identical to a facility genuinely in the clear. Scanning a grid, you would read it as benign. The tool now says, explicitly, that it doesn’t know.

What you’ll see

Depending on which sensor is silent, the facility shows one of three messages:

Cloud data missing
Visibility data missing
Visibility and Cloud data missing

Each carries a short note explaining how confident the tool is about why:

“Station reports sensor not operating” — the report explicitly named the failed sensor (SKYNO, CLDNO, VISNO) or carried the maintenance indicator $. The station is telling you the equipment is down.
“Not reported by this station” — the group is simply absent, with nothing in the report explaining it. It may be an outage, or the station may not report that element at all.

Clear sky is not missing data

This is the distinction most worth getting right. CLR, SKC, NCD, NSC, and CAVOK are positive observations: the sensor looked and found nothing below its reporting threshold. Those still read “No cloud layers.”, exactly as before, and carry no missing-data message.

The tool distinguishes the two by reading the raw report text, not by counting how many layers came back — because a dead ceilometer and a genuinely clear sky both return zero layers. If you ever want to check its reasoning, the raw report is always on the page.

Where the cues appear

List view and the expanded facility card — the message appears in place of the cloud and visibility rows.
Grid view — the same message, plus the box is outlined with a dashed neutral border. It’s deliberately not a flag color: this is a data-integrity warning, not a weather severity, and coloring it blue, red, or pink would corrupt what those colors mean. The dashed outline takes precedence over the Custom Alert split border.
Map view — a white ! to the right of the facility identifier on its pill. Click the pill to open the facility and read which sensor is out.

Why it goes quiet past 15 nm

If the reporting station is more than 15 nm away, the grid box already replaces its conditions with the WX >15NM AWAY banner and the map pill shows no missing-data mark. There are no cloud or visibility rows on display at that range, so flagging them as missing would be marking the absence of something that was never going to be shown. Open the facility and the message is there with the rest of the estimate. See Station distance.

Forecasts are not flagged

This applies to METARs only. A TAF that omits a cloud group is a forecaster’s judgement about what’s worth stating, not a broken sensor, so TAF periods are never marked as missing data.

The point of all this A tool that quietly renders missing data as good weather is worse than one that shows nothing at all, because it invites a decision. When helisiapp lite doesn’t know, it says so — and an unflagged facility here has never meant “conditions are fine.” It means nothing crossed a threshold. Check the raw report, and get an approved briefing.