Have you ever wondered how weather forecasts are made? It is quite a complicated process, but we are going to do our best to explain it in this article!
On Yr you will find weather forecasts for 13 million places around the world - 10 days ahead.
How the forecasts are made and how often they are updated is location dependent. The common feature is that all forecasts are created by a weather model and are post-processed before you see them on Yr.
In short, this is how forecasts are made:
- The world is divided into a grid
- Analysis/observations tell us about the current weather conditions
- Laws of physics are used to calculate the weather in the future
What is a weather forecasting model?
A numerical weather forecasting model is a computer model which describes the atmosphere at a given time and its further development. Weather observations from all over the world are used to give a (as good as possible) description of the atmosphere’s condition at a given time.
Then, laws of physics, empirical relationships and mathematical modeling are used to calculate the weather’s development forward in time.
A world of squares
The calculation of the weather’s development is made in a 3D grid. The squares in this grid are 2.5 kilometers wide for the Scandinavian region and around 9 kilometers for the rest of the world.
This means that a weather forecast is created for every ninth kilometer on Earth.
Millions of calculations are made before a weather forecast is ready.
GRID: The models are based on a grid. All the weather variables, such as temperature and clouds, are calculated at different locations in the world. ILLUSTRATION: ERIK BOLSTAD
Weather forecast models on Yr
A lot of computing power is therefore needed to be able to produce reliable weather forecasts, something supercomputers can provide. Increased computing power and long term development has given us the weather forecast system MetCoOp EPS (MEPS) which is an operational collaboration between Norway, Sweden and Finland.
The area covered by the model is shown to the left in the figure below. The model development is made possible by the European ALADIN-HARMONIE-collaboration.
Additionally, we use several advanced statistical methods to correct known errors and weaknesses in the models. This makes us capable of producing even more local forecasts than what the grid itself would give us. Such corrections are made mainly in the Scandinavian region.
The various forecasts
Short term forecasts (the forecast for the next 2-3 days)
- Weather forecast system MetCoOp EPS (MEPS) is used for Norway and nearby regions (red frame in the figure above) and has a distance of 2.5 km between the calculation points.
- For the Arctic regions (blue frame in the figure), the model Arome-Arctic is used with a resolution of 2.5 km.
- The weather model HRES from ECMWF is used for the rest of the world. The calculations are made at the European Centre for Medium Range Weather Forecasts (ECMWF) - a collaboration of several European countries. The HRES model has a distance of 9 km between the calculation points.
Long term forecast (forecast for the next 3-10 days)
- For mainland Norway and other Norwegian areas the ensemble system ECMWF-ENS with a resolution of 18 km is used.
- The weather model HRES from ECMWF is used for the rest of the world with a resolution of 9km
Precipitation forecast - forecast in real time
On Yr you will find our live precipitation forecast for the Nordic area. It shows the expected precipitation amount for the next 90 minutes. The live precipitation forecast on Yr is using radar data to calculate where precipitation is expected.
The live forecast is updated every 5 minutes and is therefore the latest and most accurate forecast on Yr.
The precipitation forecast is made for a smaller area at 1 kilometer x 1 kilometer and because of that, local showers are better represented. This is why it is important that you use “Location based forecast” to get a forecast as accurate as possible for your current location!
Precipitation forecast is shown only if precipitation is expected for the chosen location.
The temperature forecasts on Yr are updated every hour in the Nordic area. In this area, Yr is using data from private weather stations in order to get as good a temperature forecast as possible. Temperature forecasts will then become more accurate, especially during winter, as long as there are enough observations in the area.