How our mountain forecasts work.

Source data.

Scheduled server jobs retrieve numerical forecast data through Open-Meteo. The service uses deterministic forecast grids for the central outlook, multi-model spread and ensemble information to describe uncertainty, and longer-range ensemble guidance for weather-window planning.

The website reads already-generated forecast files from the Mountain Weather API. Loading a public forecast page does not trigger a new weather-provider request, so every visitor sees the same dated run and the source service is not used as live page-rendering compute.

From a forecast grid to a summit.

Every peak forecast uses the summit’s coordinates and elevation. Wind is adjusted for terrain exposure and then expressed at the approximate near-ground level occupied by a walker. Where credible lying-snow evidence indicates a smoother surface, the wind conversion can account for that change.

Regional forecasts use a representative high-ground elevation suited to the terrain. That is why Dartmoor and the Peak District use 500 m guidance while higher mountain regions use 700, 800 or 900 m. Individual peaks always retain their own summit height.

What the forecast fields mean.

Summit wind and gusts

Expected sustained wind and stronger gusts at the named summit or regional reference height. Local acceleration on a ridge or through a gap can still be greater.

Cloud-free summit

The modelled share of daylight hours in which cloud is expected to sit clear of the summit. It is a modelled clear-hour share, not a calibrated probability promise.

Cloud base

The expected lower boundary of hill cloud. It can vary across a range and change quickly between slopes, corries and plateaux.

Feels like

An estimate of how cold it may feel when wind is combined with the forecast air temperature at height.

Freezing level

The approximate elevation where air temperature reaches 0°C. Surface ice and snow can persist below it, especially after colder weather.

Thunder and spate

Potential high-consequence hazards shown with cautious timing. Scottish spate guidance may be supported by recent SEPA rainfall-gauge evidence; a rainfall gauge is not a live river-level reading.

Inversions

A possible cloud-sea signal shown only when the modelled moist layer and cloud top sit sufficiently below a summit. Timing remains broad and older evidence loses confidence.

Confidence and forecast updates.

Confidence reflects how well the available models and ensemble members agree, particularly on wind, cloud height and timing. Low confidence does not mean that poor weather is expected; it means the range of plausible outcomes is wider and the forecast deserves another check nearer the time.

A full multi-day outlook is normally generated in the evening, followed by an early-morning check of the current day. Each page displays its forecast run or generation time. Material overnight changes are retained by the API rather than being hidden by small numerical fluctuations.

Limits, observations and safety.

Mountain forecasts cannot resolve every shower, cloud streamer, turbulent gust or local temperature pocket. Accuracy generally decreases with lead time, and exposed terrain can produce conditions more severe than a gridded model indicates.

Before setting out, check relevant official weather warnings. In winter, consult the regional reports from the Scottish Avalanche Information Service where applicable. Continue to observe wind, visibility, burns, snow and ground conditions during the day, and be prepared to change the route or turn back.

Mountain Weather is an independent planning service, not an official warning or avalanche-forecast authority.