Visibility is not the distance to every hazard
A model’s visibility value is a broad estimate for a point and time. It does not show whether a particular buoy, headland or vessel is visible from your deck. Conditions may differ along the route or change while afloat. A good value at departure does not establish a clear entrance on return.
The RNLI’s sea-fog guidance discusses the difficulty of predicting local banks and the need to monitor conditions. Use local marine information and actual observations alongside the weather forecast. An apparently clear shore is not proof that the whole passage is clear.
Do not replace navigation decisions with a colour
The model does not know your passage plan, navigation equipment or the visibility needed to identify the route. A GO means only that its listed inputs avoid the stronger penalties. It cannot determine a suitable speed or whether a skipper can comply with the relevant rules.
The explorer demonstrates the visibility cap using otherwise benign complete inputs. It is deliberately not an instruction to continue at 1,001 m or to treat the first metre above a boundary as meaningful protection. Missing visibility produces insufficient data rather than an optimistic assumption.
Worked examples from the existing scorer
These complete hypothetical hours run through the same scoring functions used by the live tool. They are not observations or forecasts. The displayed effective score includes any cap.
| Example | Effective score | Verdict | Model reasons |
|---|---|---|---|
| Visibility 3,000 m | 100/100 | GO | No model penalties |
| Visibility 2,999 m | 64/100 | MAYBE | poor visibility · MAYBE cap |
| Visibility 999 m | 40/100 | NO-GO | fog — dangerous on water · NOGO cap |
Exact example inputs and units
temp and feels: °C; wind and gust: km/h; precipitation: mm/h; visibility: m; rain probability, cloud and humidity: %. Weather code is WMO; UV is an index. Pressure, where shown, is context in hPa and does not affect this scorer.
[
{
"example": "Visibility 3,000 m",
"inputs": {
"temp": 15,
"feels": 15,
"precip": 0,
"pop": 0,
"wind": 10,
"gust": 20,
"vis": 3000,
"code": 0,
"cloud": 10,
"humidity": 60,
"uv": 0,
"pressure": 1010
}
},
{
"example": "Visibility 2,999 m",
"inputs": {
"temp": 15,
"feels": 15,
"precip": 0,
"pop": 0,
"wind": 10,
"gust": 20,
"vis": 2999,
"code": 0,
"cloud": 10,
"humidity": 60,
"uv": 0,
"pressure": 1010
}
},
{
"example": "Visibility 999 m",
"inputs": {
"temp": 15,
"feels": 15,
"precip": 0,
"pop": 0,
"wind": 10,
"gust": 20,
"vis": 999,
"code": 0,
"cloud": 10,
"humidity": 60,
"uv": 0,
"pressure": 1010
}
}
]Planning bands and the limits of the number
The existing model starts at 100, subtracts its condition penalties and applies critical caps. GO is 70–100, MAYBE 45–69 and NO-GO 0–44. A MAYBE cap limits the effective score to 64, and a NO-GO cap to 40. These are application suitability bands, not certified safe operating limits.
Rain branches are alternatives: matching probability, intensity and weather-code triggers do not mean adding the same rain penalty repeatedly. Separate factors can combine. A cap prevents benign temperature or dry weather from cancelling a critical flagged condition. Use the reasons beside the result to understand what changed.
The model requires complete numeric weather inputs. Missing visibility, rain probability or another required value returns Insufficient data; it is never filled with an invented favourable value. Local warnings, closures, equipment instructions and actual observations can change your decision even when the model returns GO.
Read the full sailing methodology and thresholds. The model and these examples were cross-checked on 18 October 2026. No physical field-test or safety certification is claimed.
Equipment and an alternative plan
Choose a passage and return that remain within the crew’s competence and the vessel’s capabilities. Check marine visibility forecasts and local information. Delay or stay ashore when visibility makes the plan unsuitable; carrying equipment is not the same as being able to use it effectively.
Questions about Sailing in fog: visibility, a return route and model limits
Does 1,000 m establish legal visibility?
No. The threshold is an app setting, not a statement of navigation law.
Can the forecast see every fog bank?
No. Local visibility can differ from a model point.
What happens if visibility is missing?
The shared input guard returns insufficient data.
Sources and limits
The numeric application bands come from the existing GoNoGo scorer and methodology. External guidance is linked for its stated context; it is not presented as endorsement of this model.
Live forecast data is supplied by Open-Meteo. An illustrative model output is different from a live forecast, and a forecast is different from a local observation.