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ABSTRACT
A tornado climatology for Finland is constructed from 1796 to 2007. The climatology consists of two datasets. A historical dataset (1796-1996) is largely constructed from newspaper archives and other historical archives and datasets, and a recent dataset (1997-2007) is largely constructed from eyewitness accounts sent to the Finnish Meteorological Institute and news reports. This article describes the process of collecting and evaluating possible tornado reports. Altogether, 298 Finnish tornado cases compose the climatology: 129 from the historical dataset and 169 from the recent dataset. An annual average of 14 tornado cases occur in Finland (1997-2007). A case with a significant tornado (F2 or stronger) occurs in our database on average every other year, composing 14% of all tornado cases. All documented tornadoes in Finland have occurred between April and November. As in the neighboring countries in northern Europe, July and August are the months with the maximum frequency of tornado cases, coincident with the highest lightning occurrence both over land and sea. Waterspouts tend to be favored later in the summer, peaking in August. The peak month for significant tornadoes is August. The diurnal peak for tornado cases is 1700-1859 local time.
1. Introduction
As late as the mid-1990s, Finnish meteorologists generally assumed that severe convective storms or tornadoes did not occur in Finland and, if they occurred, they were rare. Tornado reports were not collected, and no research on severe convective storms was published fromthe 1960s until recently.However, since 1997, severe thunderstorms, and especially tornadoes, have received a lot of media attention in Finland. Thus, Finnish meteorologists have started to appreciate the occurrence and threat of severe weather. This appreciation has led to several studies on severe weather in Finland: a climatology of mesoscale convective systems (Punkka and Bister 2005), a case study of a severe thunderstorm outbreak (Punkka et al. 2006), micrometeorological measurements of a microburst (Järvi et al. 2007), a severe hail climatology (Tuovinen et al. 2009), and several case studies of tornadoes (e.g., Teittinen et al. 2006; Teittinen and Mäkelä2008;Outinen and Teittinen 2008; Rauhala and Punkka 2008). Yet, no climatology of tornadoes exists for Finland.
Historically, in Italy and France, scientific papers on tornado cases were published by the seventeenth century (Peterson 1982). The first research covering all of...