Newspaper headlines tell us that the upcoming autumn will be exceptionally warm or that we are in for an unusually harsh winter. But, just what are long-range forecasts and can they be trusted?
Kuva: Raimo Rosholm
Long ago, a majority of the people in society made a living directly from agriculture. So, it was natural that a farmer would use whatever method available to find out what the coming summer weather would be. The folklore surrounding weather is rich indeed. In the old days, people knew that "If there be no freeze on St. Paul's Day, no cold candlelight, then frost there will be come July" or "A starry sky on New Year's Eve night, all the more berries that year, with no end in sight."
Finland's variable weather had--and still has--a major impact on, above all, farmers, but also others working in occupations that are heavily affected by weather conditions.
Before diving headlong into the scientific basis for long-range forecasts, we have do away with commonly held misconceptions and false expectations related to them. When talking about long-range forecasts, it should be kept in mind that they are not intended for predicting specific, daily weather conditions, but rather indicate the average type of weather expected during the forecast period. "Weather data for a very specific time and place can be, ideally, predicted approximately ten days in advance. So, it isn't possible to make a weather forecast for midsummer when it's still the first of May," explains Jussi Kaurola, Director of Weather and Safety at the Finnish Meteorological Institute.
Because there is some degree of uncertainty in long-range forecasts, they cannot be used to determine whether, for example, next summer will be cool. Instead, long-range forecasts state the likelihood of the summer being cool. In other words: "There is a 40% chance of next summer being cool, a 40% chance of it being normal and only a 20% chance of it being warm. In addition, there is a 70% chance of July having the heaviest rainfall of all the summer months."
Long-range forecasts are made using nearly the same approach as short-range forecasts. When making a short-range forecast, attention is usually only paid to atmospheric changes. Conversely, when making a long-range forecast, consideration must be given to not only the atmosphere, but also changes in the sea surface temperature, which affects the prevailing weather conditions. Making a successful long-range forecast depends a great deal on familiarity with the interaction of the atmosphere and sea as well as how specifically weather models are able to take a wide range of contributing factors into consideration. In Finland, making forecasts is complicated by the fact that the weather is extremely variable and the sea surface temperature does not have as much impact on the prevailing weather conditions as in, for example, the tropics.
It is difficult to make forecasts because the chaotic nature of the atmosphere is hard to describe. Just to provide an idea of this, picture the total number of molecules in the atmosphere as a 1 followed by 44 zeros. In order to make a perfect weather forecast, one would need to take each and every molecule into consideration and calculate every single interaction between them. As opposed to making a normal forecast, preparing a long-range forecast requires more time and a lot of computational power.
"The Finnish Meteorological Institute doesn't have its own long-range forecasting model. Instead, we are a member of the European Centre for Medium-Range Weather Forecasts (ECMWF), where long-range forecasts are developed through international co-operation. This allows us to use, for example, Long-range forecasts from the ECMWF and develop custom-tailored products designed specifically for Finnish conditions and needs," explains Head of Unit (Climate Service Centre) Hilppa Gregow.
The aim is to use long-range forecasting in fields, whose operations are significantly affected by changes in the weather conditions. However, there is clearly a growing need for long-range forecasting. Many criticise long-range forecasting as being mere entertainment and no more reliable than a roll of the dice. "There's no need to simply reject this out of hand, but we do still want to investigate the reliability of long-range forecasting more, so that we can confidently assure our customers of its forecasting ability," says Kaurola.
This is why the Finnish Meteorological Institute has decided to invest in the development of long-range forecasting by launching a project, whose aim is to make more reliable seasonal forecasts in Finland and our neighbouring regions. New, customised long-range forecasts are expected to be ready for use, perhaps, in the next few years. Forecasts can be customised for use in such fields as energy production, transportation, tourism and even agriculture." For example, long-range forecasts for the electricity market can provide information to support decision-making, because making as long-range a forecast as possible for renewable forms of energy, such as wind and solar power, would benefit them immensely in terms of stabilising the market.