The knowledge of the radioactive 14C yield under atmosphere thunderstorm flash conditions (the additional discovered channel of 14C production relative to the main - cosmogenic one) is important for radiocarbon analysis. It is proposed the gross model for evaluation of the thunderstorm 14C yield simulated for the altitudes up to 15 km. It was obtained that yield from the thunderstorm mechanisms of 14C creation cannot compete with cosmogenic production which is six orders of value larger. The obtained result allows to take off the problematic issue on thunderstorm radiocarbon generation in the atmosphere as the additional significant source.