Type of site
| Norwegian (Bokmål and Nynorsk),
|Norwegian Broadcasting Corporation and the Norwegian Meteorological Institute
|September 19, 2007
yr.no is a website and a mobile app for weather forecasting and dissemination of other types of meteorological information hosted by the Norwegian Broadcasting Corporation in collaboration with the Norwegian Meteorological Institute. The website was launched in September 2007.
The word yr means drizzle in Norwegian.
Yr.no generates weather forecasts for millions of places around the world. Its 3-day forecast uses two different weather models with a 2.5 km resolution in Scandinavia and the Norwegian islands, and for other places, the ECMWF's IFS model in high-resolution configuration (HRES), with a 9 km resolution.
For the 10 day forecast, yr.no employs the ECMWF-ENS model with a 18 km resolution for Norwegian territories, and for the rest of the world, IFS-HRES with a 9 km resolution.
Outside of Scandinavia, the 3-day forecasts are updated every six hours, and the 10-day forecasts every 12 hours.
In addition to data from the Norwegian Meteorological Institute, yr.no uses open data from various collaborators such as
It also collects information from different types of private weather stations.
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HIRLAM, the High Resolution Limited Area Model, is a Numerical Weather Prediction (NWP) forecast system developed by the international HIRLAM programme.
Numerical weather prediction (NWP) uses mathematical models of the atmosphere and oceans to predict the weather based on current weather conditions. Though first attempted in the 1920s, it was not until the advent of computer simulation in the 1950s that numerical weather predictions produced realistic results. A number of global and regional forecast models are run in different countries worldwide, using current weather observations relayed from radiosondes, weather satellites and other observing systems as inputs.
The ECMWF reanalysis project is a meteorological reanalysis project carried out by the European Centre for Medium-Range Weather Forecasts (ECMWF). The first reanalysis product, ERA-15, generated reanalyses for approximately 15 years, from December 1978 to February 1994. The second product, ERA-40 begins in 1957 and covers 45 years to 2002. As a precursor to a revised extended reanalysis product to replace ERA-40, ECMWF released ERA-Interim, which covers the period from 1979 to 2019. A new reanalysis product ERA5 has recently been released by ECMWF as part of Copernicus Climate Change Services. This product has higher spatial resolution and covers the period from 1979 to present. Extension up to 1940 became available in 2023.
Ensemble forecasting is a method used in or within numerical weather prediction. Instead of making a single forecast of the most likely weather, a set of forecasts is produced. This set of forecasts aims to give an indication of the range of possible future states of the atmosphere. Ensemble forecasting is a form of Monte Carlo analysis. The multiple simulations are conducted to account for the two usual sources of uncertainty in forecast models: (1) the errors introduced by the use of imperfect initial conditions, amplified by the chaotic nature of the evolution equations of the atmosphere, which is often referred to as sensitive dependence on initial conditions; and (2) errors introduced because of imperfections in the model formulation, such as the approximate mathematical methods to solve the equations. Ideally, the verified future atmospheric state should fall within the predicted ensemble spread, and the amount of spread should be related to the uncertainty (error) of the forecast. In general, this approach can be used to make probabilistic forecasts of any dynamical system, and not just for weather prediction.
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