The GRAPES-3 experiment contains a large area (560 sq.m) muon telescope that detects over 4 billion muon of energy ≥1 GeV every day. The constant intensity of cosmic rays gets affected by the changes occurring in the pressure and the temperature of our atmosphere as well as due to the variations in the interplanetary magnetic field which in turn get reflected into variations in the muon intensity. These high precision muon data allow corrections to be made for each of these phenomenon. However, even after all these corrections are the muon data display short term (~15-30 minutes) intensity decreases which invariably occurred during major thunderstorms. A detailed investigation of such events revealed that thunderstorm act as giant capacitors capable of accelerating muon. In fact the measurements of muon intensity variations and thunderstorm electric field can be used to estimate not just the average electric potential (1.3 GV) across the thunderstorm but also its speed (60 km/h), area (>400 sq.km), altitude (11.4 km above sea level), as well as the charge stored (>1100 C), energy stored (720 GJ) and the power (>2 GW) needed to sustain its electric potential. Each of these measured parameters is about an order of magnitude larger than previously reported values.