Electric field instruments were used to measure the electric fields on the ground from June to October 2008 in Tianjin. The variations of the electric fields under such weather conditions as clear sky, stable rainfall, squall line, and heavy rainfall are discussed and analyzed. Combining with Doppler radar and lightning positioning data, the squall line process on 4 September 2008 and the rainstorm process on 14 July 2008 are analyzed. It is found that the atmospheric electric field data, which exhibit a jitter 15 to 45 minutes before the occurring of a thunderstorm, are highly indicative in strong convective weather monitoring and early warning; the combined use of radar and lightning positioning data can effectively improve the accuracy of thunder and lightning warning and forecasts; the multipoint atmospheric electric field detection can expand the monitoring range, and the electric field data can be used to determine the path of thunderstorms.