The comparative analysis of three thunderstorms on Aragats in May 2021 demonstrates that relativistic runaway electron avalanches (RREAs) are developing in large areas of the thunderous atmosphere. In the active storm zone, RREAs last tens of seconds to a few minutes, until lightning flashes terminate electron acceleration. Thus, RREAs development is paired with lightning activity, creating huge electron fluxes preceding the development of lightning leaders. If the lightning activity is far from the detector site, measured particle fluxes (thunderstorm ground enhancements - TGEs) are smoothly enhanced and decayed when the atmospheric conditions cannot anymore sustain the electron runaway process. The TGE has a symmetrical shape and can last up to 10 minutes and more. The differential energy spectra of electrons and gamma rays recovered by particle spectrometers are used to estimate the heigh of a strong accelerating electric field region, which can extend down to tens meters above the earth’s surface.