Circulation weather types and their influence on temperature and precipitation in Estonia

An existing objective classification scheme of the atmospheric circulation, where daily circulation is determined through the strength, direction and vorticity of the geostrophic flow has been applied over the Baltic Sea region for the time period of 1968–1997. The results at sea level and the higher isobaric levels of 500 hPa, 700 hPa and 850 hPa are presented here. The analysis revealed that the most common circulation types are anticyclonic and cyclonic. The mean-square-error skill scores are used to investigate classification's suitability for describing the variability of the local (Pärnu) daily weather elements. The skill scores of the objective classification are essentially higher than those for the German Weather Service's \Grosswetterlagen\ scheme, but the scores are still low due to the high variability of daily temperature and precipitation within the weather types. Temperature is best described by the classifications at higher levels of pressure (500 hPa and 700 hPa), but precipitation is best described by those at the lower levels (sea level and 850 hPa). Developing one good classification for both variables is non-trivial.