Environments of major convective wind events in Finland

In this study, the environmental characteristics of derecho and other major convective wind events in Finland during the period 1961–2022 were analyzed. We found 10 derechos, with at least 400 km long damage track, and 17 other major convective wind events that caused a damage track longer than 100 km. Representative soundings from nearby sounding stations were searched for the events. Proximity soundings were found for 8 derecho and 9 other major convective wind events. The soundings were compared to a set of 108 non-severe thunderstorm day soundings. The ThundeR rawinsonde package was used to retrieve data, draw vertical profiles, and calculate convective parameters.  

Proximity soundings show that the derechos occurred in environments with diverse values of mixed layer convective available potential energy, or CAPE, (the interquartile range was 530–1590 J/Kg). These CAPE values are generally high for Finland, but low in comparison to the derecho environments in the United States and in Central Europe. The other major convective wind events have occurred in environments with a wide range but on average smaller CAPE values compared to derechos. Expectedly, the non-severe thunderstorm days show distinctly lower CAPE than the derecho environments. 

Contrary to CAPE, the range of 0–6 km bulk vertical wind shear in the derecho environments in Finland (interquartile range of 15–19 m/s) is generally more similar to those in other countries. In the 0–3 km layer, however, mean bulk wind shear is somewhat higher (interquartile range of 12–18 m/s) than what is observed elsewhere. In the environments of other major convective wind events, the average wind shear is close to that of derechos, but the variability is larger and the highest vertical wind shear values are observed in this category. 

This work has enhanced the climatological understanding of derecho and other major convective wind event occurrence and gave insight of the ranges of convective parameters in their environments in Finland. These can be utilized by meteorologists as a guidance in severe convective storm forecasting in Finland.