Complex, chaotic atmosphere
The atmosphere is essentially a chaotic structure! as the processes taking place in it are very numerous and complex. The most important processes! can be describ with a handful of physical laws. However! these are very complex to solve, which is why they are represent! in a very simplifi way in a weather model.
Due to the simplifications and in particular due to the – to put it bluntly – too inaccurate initial state in a weather model, the forecast error usually increases with the advancing forecast horizon.
What is an “initial state”?
A weather model must be f an initial state before it can calculate the forecast. It basically has to know what the state of the atmosphere is at the start of the calculation for every location. However, measurements are not available at every location, which is why the initial state is always an approximation of the actual state of the atmosphere.
However, there are weather conditions where the forecast uncertainty does not increase steadily, but fluctuates from day to day. This is the case for next Sunday. The forecast for this day is significantly less certain than for the following days.
In the current case, this is relat to a developing countercurrent situation. The weather models are currently having difficulty calculating the correct position and intensity of the pressure centers:
Forecast of the geopotential at 500 hPa (approx. 5500 m above panama phone number library sea level) on the left and the air pressure at sea level on the right for Sunday afternoon, 30.4.23, according to the European weather model IFS-HRES. T = low pressure area, H = high pressure area. The blue arrows show the wind direction at the corresponding height (left at 500 hPa, right at the ground).
Forecast of the geopotential at 500 hPa (approx. 5500 m above sea level) on the left and the air pressure at sea level on the right for Sunday afternoon, 30.4.23, according to the European weather model IFS-HRES. T = low pressure area, H = high pressure area. The blue arrows show the wind direction at the corresponding height (left at 500 hPa, right at ground level). (Source: ECMWF/MeteoSwiss)
Next Sunday, westerly winds will be blowing at altitude, while easterly/northeasterly winds will be blowing at ground level (countercurrent situation). The pressure and wind conditions at altitude are particularly uncertain (not shown in the graphic above). This will ultimately have a strong influence on how pronounc the countercurrent situation will be over Switzerland.
Rain showers near Riehen BS
Rain showers near Riehen BS (Photo: Meteomeldungen/App)
ensemble forecasts
Nowadays, ensemble forecasting is very well establish in leave a website exit intent technology tracks weather forecasting. The model is not only allow to calculate the forecast once, but dozens of times, each time with a alb directory slightly different initial state. The different calculations allow probabilities and uncertainties to be calculat. The more different the model solutions are, the more uncertain the forecast is. For next Sunday, our model COSMO-2E (with a total of 21 different calculations) calculates the following, sometimes very different, forecasts.
