Synoptic Climatology of Tornado Environments in Finland

Although severe-storm forecasting parameters have been widely used in forecasting, they have many weaknesses. A better approach to forecasting deep moist convection and its associated severe weather is through the ingredients-based approach. To best prepare forecasters for 1–3-day forecasts of severe-weather potential, forecasters will want to know the most common ways that these ingredients are brought together for a given region. The purpose of this paper is to determine what weather patterns bring together the ingredients for tornadogenesis in Finland.

To construct a synoptic climatology of the environments during which tornadoes form in Finland, we used a climatology containing 253 tornadoes in Finland and 184 tornado days (1948–2007). The environment of each tornado day was characterized by data from the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalyses plotted from the Web page at the Physical Sciences Division (PSD) of the NOAA/Earth System Research Laboratory. For each tornado day, the reanalysis data of the time preceding the first tornado observation was used. For each tornado day, 300-hPa, 500-hPa, 850-hPa and surface maps were produced, and they were clustered manually into 8 distinct classes of tornado environments. The most common environment was jet-exit region with 49 events. To produce composite synoptic maps, the PSD Web page was used to create composites from the NCEP–NCAR reanalyses. The tornado environments in Finland from in this study are compared to the previously published tornado environments of the United States.