High-energy radiation originating from thunderclouds can be registered by detectors on satellites and on the ground surface. Intense bursts of photons with energy 10 keV-100 MeV lasting 0.1-5 ms are called terrestrial gamma ray flashes (TGFs) and are usually observed from satellites (Fishman et al., 1994;Mailyan et al., 2016;Østgaard et al., 2019). Thunderstorm ground enhancements (TGEs) and gamma ray glows can be observed under thunderclouds and have a duration of up to several hours (Chilingarian, 2011;A. Gurevich et al., 2016;Torii et al., 2009). The gamma-radiation of thunderclouds is caused by bremsstrahlung of runaway electrons, which accelerate and multiply in the electric field, forming relativistic runaway electron avalanches (RREAs) (

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The connection between thunderstorms and relativistic runaway electron avalanches is an important topic that has attracted the attention of many researchers. Among other things, there are a lot of various simulations of the dynamics of electron avalanches. This article was written mostly in response to the article The critical avalanche of runaway electrons by Evgeny Oreshkin (EPL, 124 (2018) 15001) which shows rather large numbers for an estimate of the number of runaway electrons. The results of our own simulation and comparison with other papers are presented.