MeteoSwiss ICON CH
Open data weather forecasts from MeteoSwiss
Data Sources
This API uses MeteoSwiss high-resolution ICON Central Europe forecasts. Information about MeteoSwiss weather models is available here.
| Weather Model | Region | Spatial Resolution | Temporal Resolution | Forecast Length | Update frequency |
|---|---|---|---|---|---|
| ICON CH1 |  | 0.01° (~1 km) | Hourly | 33 hours | Every 3 hours |
| ICON CH2 | | 0.02° (~2 km) | Hourly | 120 hours | Every 6 hours |
Native Model Variables
ICON-CH directly predicts the fields listed below. Open-Meteo retains these fields or uses them to calculate more convenient API variables. In particular, ICON-CH provides both direct and diffuse solar radiation and a native sunshine duration.
| Native ICON-CH field | Level | Use in the Open-Meteo API |
|---|---|---|
| Temperature | 2 m, surface | temperature_2m, surface_temperature |
| Dew point | 2 m | Relative humidity and dew point |
| U and V wind components | 10 m | Wind speed and direction |
| Wind gusts | 10 m | wind_gusts_10m |
| Mean sea-level pressure | Mean sea level | pressure_msl and derived surface pressure |
| Total precipitation | Surface | precipitation, rain, snowfall |
| Direct and diffuse solar radiation | Surface | Global, direct, diffuse radiation, DNI and GTI |
| Cloud cover total, low, mid and high | Surface | cloud_cover and the individual layers |
| Sunshine duration | Surface | sunshine_duration |
| CAPE, convective inhibition, cloud base, freezing level, snow depth | Surface | Corresponding API variables and weather-code inputs |
Precipitation probability is calculated from the matching ICON-CH1 or ICON-CH2 ensemble. Pressure-level and height-level data is not yet integrated.
Derived Variables
ICON-CH publishes cloud cover, both direct and diffuse solar radiation and sunshine duration natively. Several convenient API variables are not direct model output — Open-Meteo derives them from the native fields for every forecast step.
| Derived Variable | How it is derived? |
|---|---|
| Weather code | Computed from cloud cover, precipitation, snowfall, wind gusts, CAPE and convective inhibition. MeteoSwiss does not publish a WMO weather symbol. |
| Snowfall and rain | Precipitation counts as snow where the native snow line is below the location elevation, converted with 0.7 cm per mm. Rain is total precipitation minus the snowfall water equivalent. |
| Wind speed and direction | Calculated from the native U and V wind components at 10 m. |
| Precipitation probability | Share of the ICON-CH1 or ICON-CH2 ensemble members with more than 0.1 mm/h of precipitation. |
| Dew point | Calculated from 2 m temperature and relative humidity. MeteoSwiss publishes dew point, from which relative humidity is stored, then dew point is recomputed on request. |
| Surface pressure | Calculated from mean sea-level pressure, 2 m temperature and terrain elevation. |
| Diffuse radiation, DNI and GTI | Diffuse radiation is global minus native direct radiation. Direct normal irradiance, global tilted irradiance and instant values follow from solar geometry. No radiation separation model is required. |
| Apparent temperature, ET₀, vapour pressure deficit and wet bulb temperature | Standard formulas combining 2 m temperature, humidity, wind speed and solar radiation. ET₀ follows the FAO-56 Penman-Monteith equation. |
Sunrise, sunset, daylight duration and the day-or-night flag are astronomical calculations. Daily values are aggregated from hourly data.
API Documentation
For a detailed list of all available weather variables please refer to the general Weather Forecast API. Only notable remarks are listed below
- Grid and Projection: MeteoSwiss data is originally provided on an unstructured icosahedral grid. To enable fast access and map rendering, Open-Meteo reprojects the data onto a rotated lat/lon grid with similar resolution. The domain area is cropped by 20 km along the borders to eliminate edge artifacts.
- Precipitation: With the high spatial resolution of 1–2 km, the model captures intense, convective showers. However, due to the highly localised nature of these events, actual precipitation at a specific location may be over- or underestimated. Precipitation probability is derived from all ensemble members to indicate the likelihood of precipitation occurring.
- Direct Solar Radiation: The ICON models from MeteoSwiss include direct solar radiation as a native output. In contrast, many other weather models only supply global radiation, requiring users to estimate direct radiation via separation models.
- Wind, Temperature, and Cloud Forecasts at Heights of 100m and Above: Forecasts at elevated height levels are not yet integrated. If this data is of interest to you, please reach out to discuss possible integration.
- Sunshine Duration is natively computed by the ICON model. For other weather models, Open-Meteo derives sunshine duration using direct normal irradiance (DNI).
- Snowfall and Freezing Level Height may show invalid values if the computed level lies below ground. To address this, Open-Meteo adjusts these levels to extend below ground level when necessary—similar to the handling in models like GFS.
- CAPE and Convective Inhibition are calculated using mean-layer values, consistent with other ICON domains. Convective inhibition may be -1 indicating that the model could not calculate convective inhibition.