This paper presents a methodology that employs the electrostatic field variations caused by thundercloud formation or displacement to generate lightning warnings over a region of interest in Southeastern Brazil. It was shown that the better critical field threshold is 0.9 kV/m for a encircle area with 10 km radius around the sensor installation. Values found for the POD (34%) and for the FAR (69%), using the critical field threshold of 0.9 kV/m and area with a radius of 10 km are consistent with studies found in literature