Probability Forecasting in Sweden: Some Results of Experimental and Operational Programs at the Swedish Meteorological and Hydrological Institute

Abstract

This paper describes new operational and experimental forecasting programs at the Swedish Meteorological and Hydrological Institute (SMHI) designed to provide users with more detailed and more useful weather forecasts. User groups currently served by these programs include construction contractors, farmers, electric power companies, street and highway departments, and ski resorts. The programs represent a major component of a SMHI-wide effort to develop products to meet the needs of the public and private sectors in Sweden for meteorological and hydrological information. An important feature of these programs is that many of the forecasts are expressed in probabilistic terms, and some results of the probability forecasting components of four programs are presented here. These subjective forecasts specify the likelihood of occurrence of various precipitation, wind speed, temperature, and cloud amount events, and they generally involve relatively short lead times and/or valid periods. The probabilistic forecasts of measurable precipitation are found to be reasonably reliable and definitely skillful. Some forecasts of larger precipitation amounts and the wind speed forecasts for shorter lead times also demonstrate positive skill, and the probabilistic temperature forecasts appear to be quite reliable. On the other hand, most of the experimental and operational probability forecasts reveal some degree of overforecasting, which tends to increase as lead time increases and as the climatological probability of the event decreases. As a result, the wind speed forecasts for longer lead times, some forecasts of precipitation amount, and the cloud amount forecasts exhibit negative skill. Some factors that may have contributed to the deficiencies in the forecasters' performance are identified. The need to refine various components of the forecasting system is emphasized, and current efforts to implement such refinements at SMHI are outlined.