The seasonal outlook is a forecast of temperature trends for the next three months. Current and past seasonal forecasts for Switzerland give an idea of the possibilities and limitations of this type of forecasting. In spite of the undisputed advances that have been made over recent years, the quality and applicability of long-range forecasting for Switzerland is still limited.
The seasonal outlook is generated monthly for the following three consecutive months for each of the three regions of Switzerland: the north-east, west and south. The charts for past forecasts contain the additional information on actual observed seasonal temperature averages. This allows the climatologists to assess the quality of past forecasts.
In contrast to weather forecasts, long-range prognoses on climate evolution are naturally beset by a high degree of uncertainty. Although significant advances have been made over recent years with the introduction of high performance computers and model simulations, the quality of long-range forecasting for central Europe and also for Switzerland still has its limitations.
Seasonal temperature outlook
The height of the coloured columns indicates the probability of the coming three months being cool (blue), moderate (green) or warm (red) based on a comparison of the same season over many years. There is a probability of around 55% of the weather being warm in north-eastern Switzerland during the months of March to May 2014. In this case, the average temperature over three months will be over 9.9 °C. There is a probability of around 25% of the average temperature being between 8.8 °C and 9.9 °C. Lower temperatures, i.e. below 8.8 °C, are somewhat less likely, with a probability of 20 percent. The additional error bars shown on each coloured bar show the variability range (uncertainty) for the forecast.
The values for three categories are determined on the basis of recorded temperatures since 1981, and are calculated individually for each forecast period. For the months of March to May, the long-range average temperature is set at between 8.8 °C and 9.9 °C. These values are determined so as to ensure that each of the three categories occurs with equal frequency (shown by the grey horizontal line at 33.3 percent).
It can happen that a forecast does not show any clear trend. For instance, in the seasonal outlook for March to May 2013, the columns for cool, moderate and warm spring temperatures are of similar heights. The uncertainty bars on the individual columns are overlapping, and a trend prediction is not possible. It is often the case that clear trends are not available in seasonal outlooks for Switzerland.