1Institute of Geonics, AS CR - Czech republic
2Czech Hydrometeorological Institute - Czech republic
Thunderstorms are in the territories of the Czech Republic and neighbouring countries almost exclusively the phenomena occurring in the warm season. In the cold half of the year, from October to March, an average incidence of thunderstorms is only 2% with the least occurrence being recorded in January. Yet, winter thunderstorms are dangerous particularly for air traffic because during them the cloud base is rapidly falling down and visibility is suddenly worsening due to heavy snowfall. Notwithstanding these facts, the issue of their occurrence in the central European space has been paid little attention so far.
Long years of study into historical weather extremes in the territory of the Czech Republic revealed over ten chronicle entries on the occurrence of winter thunderstorms in the period between November and February from the 16th to the beginning of the 20th centuries. The irregular phenomenon was even devoted three occasional prints in central Europe in the 2nd half of the 16th century, two of which were issued in Germany. Fires caused by winter thunderstorms were no sporadic cases.
The occurrence of thunderstorms in winter was apparently associated with the passage of pronounced cold fronts. This can be documented on cases from the end of December 1555 when heavy thunderstorms and consequent fires were recorded within a short period of time in Holland, Germany and in Czech lands. It is assumed that the situation in 1627 was similar when a winter thunderstorm was recorded in Prague and in Holešov, south-eastern Moravia on 28 December. In February 1581, a thunderstorm in Prague became one of three unusual events publicized by the local occasional newspaper.
The beginning of modern studies into winter thunderstorms dates back to the 1960s with the use of lightning flash counters and later also with the use of systems for large-scale lightning flash detection and localization. However, more comprehensive meteorological and climatological assessments of their occurrence are still missing. The authors of the paper aim at outlining possibilities of the incidence of winter thunderstorms in the present and at contributing with some answers to the question of the long-term fluctuation of their frequency.