Ensemble Weather Forecast API

Hundreds Of Weather Forecasts, Every time, Everywhere All at Once

Tl;dr: The Open-Meteo Ensemble API lets you easily access hundreds of ensemble weather forecasts. With many different forecasts available, you can get an idea of how likely a particular weather prediction is.

What are Ensemble Models?

Ensemble weather forecasts are a special type of forecasting method that takes into account the uncertainties in predicting the weather. They do this by running multiple simulations or models with slight differences in the starting conditions or settings.

Each simulation, known as an ensemble member, represents a possible outcome of the weather. By running many ensemble members, the forecasts can show a range of possibilities rather than just one prediction. This range reflects the uncertainty in the forecast.

For example, let's consider a 14-day temperature forecast for Paris using ensemble forecasting. In the beginning, the ensemble members may predict temperatures between 25-28°C consistently. But as the days go by, the forecasts start to differ more. This means that beyond a certain point, it becomes harder to say exactly what the temperature will be, as different ensemble members suggest different outcomes.

Ensemble forecasts provide not only the most likely forecast but also information about the likelihood of different scenarios occurring. This helps forecasters and decision-makers understand the range of possibilities and make more informed choices based on the level of uncertainty in the weather forecast.

Temperature Ensemble Forecast for Paris, France

Weather forecasts can be more or less reliable depending on where you are and the big weather patterns happening at the time. For example, in Paris, there is a stable high-pressure system over England, which makes the forecasts more dependable for the next few days. This stable weather pattern helps forecasters predict the weather more accurately in the near future.

But in Budapest, Hungary, the weather is currently more unpredictable. The ensemble forecasts for Budapest show greater variations, especially when it comes to rainfall. Even after just the first day of the forecast, the different ensemble members have a wide range of temperature predictions, from 17-27°C. This means there is more uncertainty and less agreement among the forecasts for Budapest compared to Paris.

Temperature Ensemble Forecast for Budapest, Hungary

By using enough ensemble weather forecasts, we can figure out how likely it is to have a maximum temperature of at least 25°C in a day. This is just one example of what the API can do. Besides temperature, the API also gives access to other weather information like wind speed, rainfall, snowfall, clouds, and solar radiation. With all these different variables available, the API can be used for many different purposes in various industries and fields.

Ensemble API

Open-Meteo seamlessly combines ensemble models from well-known organizations like NOAA (American weather service), DWD (German), CMCC (Canadian), and ECMWF (European).

These models have some limitations because of the computer power needed to run them, so they are typically done at a lower level of detail (about 25 kilometers). However, they make up for this by providing forecasts for a longer period of time, up to 35 days in advance.

Each weather model in the ensemble has its own unique characteristics. They differ in the level of detail, the types of weather variables they provide, the number of members they run, how far into the future they can forecast, and how often they are updated. Some models start by giving forecasts every 3 hours, and then switch to every 6 or 12 hours. Managing these diverse models from different weather services presents challenges due to their inherent differences and variations.

Available Ensemble Models at Open-Meteo

To make things easier, the Ensemble API brings all the models together in one place, so you don't have to download each model separately. You can directly compare them using the API's interface. The API makes sure that the data is consistent by converting everything to hourly values, even though some models might only provide data every 3 hours. This makes it simpler to access and analyze the ensemble forecasts for different applications.

The interactive documentation and URL generator of the API are designed to be user-friendly. They automatically hide weather variables that are not available, so you can easily find and use the ones you need. This feature helps you navigate the API and make the most of its capabilities.

Ensemble API Documentation and URL configurator

The Ensemble API provides direct access to individual member forecasts, but future versions may integrate probabilistic forecasts to get the likelyhood of a given weather condition. This work is tracked on GitHub in ticket #349.

Bringing together ensemble model forecasts is a big step towards making medium-term weather forecasts beyond 7 days easier to access and understand. The Ensemble API serves as a strong base by providing blazingly fast access to data from hundreds of weather models. Every time, Everywhere, All at Once (Leave a “Like” if you get the reference 😉).

If you would like to contribute join us at GitHub discussions or comment below.

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